Mol Neurobiol DOI 10.1007/s12035-015-9379-8

Mahogunin Ring Finger-1 (MGRN1), a Multifaceted : Recent Unraveling of Neurobiological Mechanisms

Arun Upadhyay1 & Ayeman Amanullah1 & Deepak Chhangani1 & Ribhav Mishra1 & Amit Prasad2 & Amit Mishra1

Received: 6 March 2015 /Accepted: 27 July 2015 # Springer Science+Business Media New York 2015

Abstract In healthy cell, inappropriate accumulation of poor Introduction or damaged proteins is prevented by cellular quality control system. Autophagy and ubiquitin proteasome system (UPS) Human cell normally contain billions of proteins, and normal provides regular cytoprotection against proteotoxicity induced integral function of a protein is dependent on its shape, size, by abnormal or disruptive proteins. E3 ubiquitin are and proper localization in appropriate cellular compartments crucial components in this defense mechanism. Mahogunin [1]. Proteins continuously perform all major work of cells, in Ring Finger-1 (MGRN1), an E3 of the order to maintain cellular homeostasis. Millions of ribosomes Really Interesting New (RING) finger family, plays a synthesize nascent polypeptide chains with an approximate pivotal role in many biological and cellular mechanisms. rate of six amino acids per second in cells [2, 3](Fig.1a). Previous findings indicate that lack of functions of MGRN1 Disruption in the confirmations of three-dimensional structure can cause spongiform neurodegeneration, congenital heart de- of a polypeptide chains tends to misfold them, which may fects, abnormal left-right patterning, and mitochondrial dys- result in abnormal toxic aggregation due to the failure of cor- functions in mice brains. However, the detailed molecular rect assembly or loss of protein control mechanism in cells [4]. pathomechanism of MGRN1 in cellular functions and dis- Integrity of a newly synthesized protein is continually at risk eases is not well known. This article comprehensively repre- of abnormal folding and aggregation due to transcriptional sents the molecular nature, characterization, and functions of and/or translational failures or exposure of distinct stress con- MGRN1; we also summarize possible beneficiary aspects of ditions at both intracellular and extracellular levels Fig. 1b.To this novel E3 ubiquitin ligase. Here, we review recent litera- survive under such non-tolerable stress conditions, cells ture on the role of MGRN1 in the neuro-pathobiological evolved a very efficient interconnected central surveillance mechanisms, with precise focus on the processes of neurode- protein quality control mechanism that can either refold, de- generation, and thereby propose new lines of potential targets grade, and/or separate misfolded proteins with the help of for therapeutic intervention. chaperones and two proteolytic systems [5]. Chaperones target hydrophobic stretches of unfolded pro- teins and also recognize misfolded proteins for their further Keywords MGRN1 . Ubiquitin ligase . Cellular quality folding or degradation. Regular actions of chaperones are to control mechanism . Neurodegenerative diseases . Aging promote folding of newly synthesized proteins and to facilitate their translocation across membranes to reduce the unwanted load of aggregation [6]. Autophagy pathway is involved in the * Amit Mishra degradation of major random cytoplasmic bulk of cell; recent [email protected] studies have elaborated the selective mechanism of autophagy pathway with the help of chaperones and E3 ubiquitin ligases 1 Cellular and Molecular Neurobiology Unit, Indian Institute of in the clearance of non-native or poorly folded proteins [7] Technology Jodhpur, Jodhpur, Rajasthan 342011, India Fig. 1c–e. Chaperone-assisted selective autophagy (CASA) is 2 School of Basic Sciences, Indian Institute of Technology Mandi, an important mechanism, which helps in the muscle mainte- Mandi, Himachal Pradesh 175005, India nance via degradation of damaged filamin [8]. Loss of CASA Mol Neurobiol

Fig. 1 Illustrative representation of cellular protein quality control healthy cells limit accumulation of non-native proteins aggregation with mechanism. a In cells ribosomes translate mRNA into newly the help of cellular protein quality control mechanism (molecular synthesized chain of amino acids and molecular chaperones try to fold chaperones, various type of selective autophagy processes, ubiquitin them into a perfectly folded protein. b Exposure of different internal and proteasome system, and lysosome system) and alleviate proteotoxic external cellular stress conditions contributes to influence misfolding and insults in cells aggregation in the crowded cellular milieu. c–e During stress conditions,

functions leads to muscles weakness and declination of cyto- may increase cytoprotective potential of cells against toxic skeleton architecture [9]. In living cells, isolation of misfolded proteins [11]. proteins, removal of unwanted aggregated proteins, and repair Here, we are representing a comprehensive overview of of partially folded or non-native proteins improve intercon- this review article (see box). Our current review summarizes nected networks of cellular cytoprotective mechanisms. In the main framework for protein quality control mechanism the process of elimination of damaged proteins, chaperone- (QC) and then discusses various steps and components of mediated autophagy (CMA) is another very crucial and selec- QC process. In next upcoming section, we narrow down our tive approach that takes help of lysosomes in the removal of focus on the linkage of less explored crucial E3 ubiquitin specific proteins [10]. To counter the challenges of protein ligase MGRN1 with ubiquitin system. We deliver well- aggregation and solve the problem of misfolded proteins linked information on molecular nature, gene structure, iso- clearance, cells evolved another alternative mechanism, i.e., forms, mutations, and interacting proteins or crucial substrates chaperone-assisted proteasomal degradation (CAP) which of MGRN1 E3 ubiquitin ligase with its roles in Mol Neurobiol pathobiological mechanisms. The next half of article compre- MGRN1 Gene Structure and Isoforms hensively represents molecular functions of MGRN1 in neu- rodegeneration and then discusses the cellular defense role of In mice, MGRN1 is encoded by mahogunin gene lying on MGRN1 against protein misfolding and aggregation. After 16. Alternative splicing of exons (12 and 17) QC functions of MGRN1, we provided additional information generates four MGRN1 isoforms. MGRN1 null mutant de- on diverse cellular and physiological functions of MGRN1 in velops dark black color, but all four isoforms do not display the context of diseases and developmental abnormalities. In significant role in pigment-type switching. Isoforms I, II, and last future prospective and key questions section of this review III were well expressed in the brain, kidney, and heart, and elaborates hidden and versatile potential of MGRN1, which almost equal expression of all isoforms were observed in liver may generate new interesting questions and also propose im- tissue [18]. Expression profile of MGRN1 in brain tissue is portant implications of MGRN1 in the therapeutic interven- also high in both mouse and human and retains more than tion of neurodegeneration and aging. 90 % sequence similarity in its homologues, perhaps RING Box 1 domain region is also conserved in invertebrates and verte- brates genomes [16]. Human MGRN1 gene contains 17 MGRN1: one protein, multiple functions; implications in diseases exons, and alternative usage of exons (12, 16, and 17) pro- ▪ MGRN1, an E3 ubiquitin ligase, found to be involved in protein quality duces different isoforms as shown in Fig. 2a, b. Melanoma control mechanism, providing cytoprotection against proteotoxic cells were shown to express four MGRN1 isoforms [19]. It insults has also been shown in various cellular localization studies ▪ Overview of MGRN1 gene, protein, its isoforms, and evolutionarily that MGRN1 expresses in different cellular compartments conserved domains such as cytoplasm, plasma membrane, early endosome, and ▪ Interactions of MGRN1 with numerous proteins and its aberrant nucleus [19, 20]. Recently, it has been shown that RNF157 is a functions/mutations linked with various diseases homologue of the mahogunin ring finger-1 E3 ligase involved ▪ MGRN1 alleviates proteotoxicity generated by different cellular stress in the maintenance as well as regulation of dendritic growth in conditions cultured neurons and is also crucial for neuronal survival [21]. ▪ E3 ubiquitin ligase MGRN1 facilitates the elimination of misfolded/ non-native proteins from cells MGRN1 acts as an E3 ubiquitin ligase. Domain associated ▪ Cellular and physiological functions of MGRN1: pigment synthesis, with RING 2 (DAR2) is another evolutionary conserved do- endosomal lysosomal trafficking, mitochondrial functioning, and main, localized adjacent to RING finger domain. In embryonic development Arabidopsis,RINGE3ubiquitinligaseAtAIRP3/LOG2 ▪ Exploring future perspectives and therapeutic interventions of MGRN1 (LOSS OF GDU 2) associates and ubiquitylates RD21 in cytoprotection, neurodegeneration and aging (Responsive to Dehydration 21) [22]. Arabidopsis thaliana LOG2 and MGRN1 are functionally conserved, and mammali- an MGRN1 interacts with plant membrane protein GLUTAMINE DUMPER1 (GDU1) and further induces its Molecular Nature and Journey of MGRN1: a Link ubiquitylation [23]. As shown in Fig. 2c, d,variousspecies to the Ubiquitin System retain MGRN1 protein containing DAR2 and RING finger do- main that exhibits a similar or conserved region. We know that Mouse mahoganoid mutation related to darkening of coat col- MGRN1 in various species do not represent an exact level of or is associated with mahogunin gene lying on chromosome similarity in RING finger and DAR2 domain region, still previ- 16; mutations in this gene change the phenotypic effects of ous studies and current observation provides a clue that they agouti protein [12, 13]. Human MGRN1 full-length homo- may have a potential to restore their cellular functions. logue identified is KIAA0544, and the precise cytogenetic Recently, it has been shown that MGRN1 comprises a PSAP location is 16p13.3 [14]. Mahogunin encodes a C3HC4 motif, which is also conserved in different species. Interestingly, Really Interesting New Gene (RING) domain protein and PSAP motif of mouse MGRN1 binds with ubiquitin E2 variant supposed that it could retain E3 ubiquitin ligase activity on (UEV) domain of tumor susceptibility gene 101 (TSG101), a the basis of sequence similarity [15]. In another study, it was component of the endosomal sorting complex required for trans- clearly shown that recombinant mahogunin exhibits E3 ubiq- port I (ESCRT-I); site directed mutagenesis mutant of MGRN1, uitin ligase activity with UBC5 (Ubiquitin-conjugating en- i.e., MGRN1 (ASAA) did not bind with TSG101. PSAP motif zyme E2 5). This study also suggests that lack of function of is absent in both the vertebrate family member MGRN2 mahogunin can lead to substrate accumulation [16]. MGRN1 (RNF157) and invertebrate MGRN homologues [24]. Cys residues deleted forms (Δ278–281 and Δ292–293) do Earlier, it has been demonstrated that RING finger domain not retain auto-ubiquitination activity and UBC3 (ubiquitin- is dedicated to numerous cellular functions, e.g., signal trans- conjugating E2 3), E2 protein also not demonstrates duction, transcription, and protein ubiquitination [25–27]. auto-ubiquitination with MGRN1 E3 ubiquitin ligase [16, 17]. Recently, it has also been observed that MGRN1 regulated Mol Neurobiol

Fig. 2 Schematic diagram representing MGRN1: location, gene of DAR2 and Ring finger domain (Zebrafish (NP_956173.1), Pigeon structure, isoforms, organization, and sequence alignment. a, b (XP_005508472.1), Xenopus (NP_001083558.1), Mouse (NP_ Location of MGRN1 gene on human chromosome 16 and genomic 001239366.1), Human (NP_001135761.2), and Arabidopsis structure of MGRN1 showing exons 1–17 (a); the linear structure of (Q9S752.1)). Sequences were aligned using Clustal Omega and different isoforms of MGRN1 generated by alternative splicing of 12 visualized using Jalview [108, 109]. Default coloring scheme for and 17 exons; details are explained in section (MGRN1 Gene Structure Clustal Omega in the Jalview program was used. Absolute conservation and Isoforms) (b)[19, 24, 37]. c MGRN1 proteins from various species of amino acids is depicted by asterisk (*). Score 0–9 followed by plus showing the conservation of DAR2-RING region and PSAP motif [23, sign represents conservation levels 107]. d Sequence alignment of MGRN1 proteins showing conservation

Mc1r functional coupling to the cAMP cascade is independent it is needful to obtain the crystal structure of MGRN1, which of ubiquitylation [19]. To gain insight into the RING finger is still not known. Since various sequence analysis reveal that domain organization of MGRN1 and to better understand the MGRN1 contains a RING finger domain [16, 17, 23], there- elementary steps for the regulation of MGRN1 ligase activity, fore, most likely in near future additional critical substrates Mol Neurobiol and hidden cellular functions of MGRN1 may be identified. Knockdown of MGRN1 deregulates endosome-to-lysosome Compelling evidences indicate roles and functional implica- trafficking of epidermal growth factor receptor [37]. Most like- tions of MGRN1 in neurodegenerative diseases. In the next ly, under lack of MGRN1 functions,otherE3ubiquitinligase section, we elucidate and provide insight of MGRN1 into may take over the ubiquitination of TSG101 and inhibit the disease-related proteins, which may also open new perspec- formation of insoluble aggregates. TAL (also known as tives of critical substrates identification. LRSAM1) and are two different E3 ubiquitin ligases, which are involved in the ubiquitinylation of TSG101 protein [38–40]. MGRN1 null mutants exhibit problems in pigment- Molecular Functions of MGRN1 type switching, induce oxidative stress, and show mitochondri- in Neurodegenerative Diseases al dysfunction preceding neurodegeneration [41, 42]. Proteinaceous infectious particles prions (PrPSC)aregener- Recently published draft map of human proteome explores the ated from normal cellular isoform PrPC via post-translational identification of proteins encoded by more than 17,000 process and cause Creutzfeldt-Jakob and Gerstmann- (near about 84 % of human protein coding genes) [28]. In Straussler-Scheinker diseases [43–45]. Previously, it has been densely packed cellular environment, high protein concentra- shown that MGRN1 interacts with both transmembrane iso- tion intensely fold up the fatal chances of their unwanted inter- form linked with prion disease (CtmPrP) and toxic cytosolic actions with other native and non-native proteins which may form (cyPrP). Depletion of MGRN1 leads to altered lysosomal further lead to high probability of misfolding and aggregation morphology and contributes in neurodegeneration due to its of existing and newly synthesized polypeptide chains [29, 30]. improper sequestration [46]. It is known that pathogenic forms In previous few years, numerous studies have established a fact of prion protein originate from the conversion of its own nor- that neuronal cells are more susceptible and vulnerable towards mal form. But, it still remains central to research on prions to misfolded proteins associated toxicity [31, 32]. Chaperones and know how these infective proteins lead to neuronal dysfunction E3 ubiquitin ligases are the key players in cellular quality con- and death. An interesting observation detects that MGRN1 lack trol system for the clearance of abnormal proteins while their of function or overexpression both do not induce prion proteins lack of function may cause various neurodegenerative diseases like pathological symptoms on intracerebral inoculation of [20, 33, 34]. MGRN1 is a putative RING finger domain con- Rocky Mountain Laboratory (RML) prion protein. Increase taining E3 ubiquitin ligase and is widely expressed in different or decrease in MGRN1 levels do not influence the progression tissues including brain [18]. of transmissible spongiform encephalopathy in mice inoculated Presence of vacuoles throughout the central nervous system with proteinaceous infectious prions particles (PrPSC)[47]. and further degenerative changesarethepivotalcharacteristics Nevertheless, mounting evidences suggest cellular quality of neurodegeneration [35, 36]. ESCRT-I component TSG 101 control components target prions for their clearance, and fail- Ubiquitin E2 variant (UEV) domain binds with MGRN1 ure of such efforts generates severely toxic insults and mito- through its PSAP motif. Interaction of MGRN1 with TSG101 chondrial dysfunction. Furthermore, this affects cellular pro- promotes its multimonoubiquitylation in a proteasome inde- cesses such as post-Golgi vesicular trafficking of membrane pendent manner. MGRN1 null mouse suggests that neuronal proteins [48–52]. One potential interpretation of these studies cells are specifically under higher risk as compared to other cell is that loss of MGRN1 function plays a significant role in types because of the disruptive endosomal–lysosomal system. neurodegenerative diseases, somewhere linked with

Table 1 Enlisted representation of MGRN1 interacting proteins and molecular functions and aberrant function of MGRN1 linked with various diseases

Interacting proteins of MGRN1 References Molecular functions of MGRN1 References MGRN1 mutations detrimental effects References

TSG101 [37] Energy and insulin homeostasis [15] Abnormal left-right axis patterning [95] cyPrP/(Ctm)PrP [46] Embryonic patterning [95] MC1R/MC2R [19, 110] Mitochondrial function [41] Congenital heart defects [95] Molecular chaperone [61] Endosomal trafficking [37] NEDD4 [111] Melanocortin signaling [19, 110] Spongiform neurodegeneration [16] Cellular protein quality control [61, 112] α-tubulin [113] Microtubule stability and mitotic [113] spindle orientation Expanded Polyglutamine Proteins [112] Spermatogenesis [114] Male infertility [114] Mol Neurobiol mitochondrial dysfunction, vacuoles formation and oxidative pattern. Expansions of polyglutamine proteins generates in- stress via interaction with the components of cellular quality soluble ubiquitin positive aggregates and serve as chief factor control mechanism as summarized in Table 1. Perhaps these in nine known expanded trinucleotide (CAG) repeat expan- speculations need further detailed study in near future. sion disorders [68]. Ataxin-3 causes spinocerebellar ataxia type-3, a neurodegenerative disease; it sequesters p62/ SQSTM1 in to expanded polyglutamine ataxin-3 aggregates MGRN1 Interaction with Cellular Protein Quality [69]. Similarly, expanded polyglutamine proteins sequester Control Components Against Misfolded Aggregates: various transcription factors including TATA box binding pro- Internal Competition or Defined Cooperation in QC tein (TBP) and CREB binding protein (CBP) [70–72]. Pathway? However, the precise molecular mechanism of neuronal loss in Huntington disease (HD) is not known. Few studies elabo- Each cell retains an ability to cope up against proteotoxic rate that Htt aggregates repress p53-mediated transcription insults and to sustain the proteostasis after broad cellular dys- and sequestration of NF-Y transcriptional factor and decrease functions [53, 54]. However, much information is still un- Hsp70 expression level [73–75]. known such as why various components of cellular quality To further explore the cellular QC function of MGRN1 in control pathways deposit [55, 56] or get sequestered [57, 58] cells, we performed colocalization studies with expanded with abnormal protein aggregates? Whether such unwanted polyglutamine proteins. Surprisingly, we observed recruit- interactions are healthier cooperative attempts to solve the ment of MGRN1 with ubiquitin and p62 positive inclusions problem or these are misregulated detrimental competitive of polyglutamine-expanded proteins both in in vitro and trials to target misfolded proteins? Eukaryotic cells perform in vivo models as represented diagrammatically in Fig. 3d. cotranslational folding with the help of few molecular chaper- Overexpression of MGRN1 provides cytoprotection against ones (Hsp40 and Hsp70). Cellular stress conditions induce a toxicity linked with expanded polyglutamine proteins [34]. major shift in intracellular distribution of chaperones such as Previously, it has been studied that few E3 ubiquitin ligases Hsp70; overexpression of Hsp70 provides cytoprotection (E6-AP, CHIP, Gp78, and Hrd1) promote the degradation of against various cellular insults and inhibits apoptosis [59, polyglutamine aggregation and suppress the toxicity mediated 60]. We observed in our previous study [61] that under distinct by expanded polyglutamine proteins [76–79]. Above de- cellular stress conditions, MGRN1 follows the similar profile scribed studies support our recent finding that MGRN1 is a of Hsp70; both proteins colocalize and pivotally are recruited putative E3 ubiquitin ligase that can target pathogenic expand- with heat-denatured misfolded luciferase protein inclusions as ed polyglutamine proteins for their elimination and able to depicted in Fig. 3a, b. protect cells against poly (Q)-induced toxic events. Our earlier finding suggests the possible molecular pathomechanism implication of MGRN1 in neurodegenerative diseases; we extended our findings and observed that under Distinct Molecular Functions of MGRN1: Multiple stress conditions, MGRN1 interacts with various cellular QC Cellular Possibilities and Challenges components. Earlier, it has been observed that p62/SQSTM1 polyubiquitin-binding protein andlightchain3(LC3)colocal- Previous detailed studies of MGRN1 gene and its encoded izes with mutant huntingtin aggregates [62–64]. p62 generates product in E3 ubiquitin ligase have led to tremendous impli- a stress response triggered by oxidative stress [65, 66]. Our cations in neurodegenerative diseases and open new overlap previous study also provides a clear insight that MGRN1 E3 between the known interacting partners and genes. In the cur- ubiquitin ligase could also be recruited to p62 positive rent review, we summarize and illustratively depict the major polyubiquitinated perinuclear protein aggregates during the au- cellular functions of MGRN1 as represented in Fig. 4: (a) role tophagy dysfunction as shown illustratively in Fig. 3c [20]. in pigment switching, (b) MGRN1 involvement in endosomal Proteasome inhibition leads to a strong colocalization of p62 lysosomal trafficking, (c) MGRN1 depletion induced mito- with Hsp70 chaperone in perinuclear aggregates [67]. chondrial dysfunction, (d) irregular left-right axis patterning Altogether, these observations raise a convincing possibility in MGRN1 mutant mice. Substantial evidences from various that MGRN1, p62, Hsp70, and probably a few components studies indicate that more imperative MGRN1 functions re- of ubiquitin proteasome system (UPS) and autophagy some- main to be discovered. where crosstalk or interact to each other for the sorting and MGRN1 mutant mice brains develop completely black effective clearance of misfolded proteins in dense cellular pool. coat color linked with agouti signaling protein (ASIP); four More recent work indicates that, probably, MGRN1 acts as different MGRN1 isoforms usually do not represent signifi- a crucial player in cellular QC pathway. The emerging func- cant functional difference in pigment-type switching [15, 16, tions of MGRN1 prompted us to further validate its QC capa- 18]. Aberrant function of Mc1r and Agouti influence pigmen- bility against other misfolded proteins in a more defined tation in mice [18, 80]. Interaction of MGRN1 with Mc1r Mol Neurobiol

Fig. 3 Recruitment of MGRN1 with misfolded protein aggregates and and aggregation of MGRN1 colocalizes with ubiquitin, p62, and Hsp70 molecular function in cellular quality control mechanism. a, b Numerous inclusions in cells (c); furthermore, MGRN1 also recruits with ubiquitin diseases have been identified linked with abnormal aggregation of and p62 positive expanded polyglutamine proteins inclusions (Huntingtin misfolded proteins with chaperones and components of cellular QC and Ataxin-3) in cells; similarly disruptive profile of MGRN1 was pathway. MGRN1 is recruited towards abnormal aggregates and observed in R6/2 transgenic mice model of Huntington disease (d)[34]. colocalizes with Hsp70 chaperone under unusual subsets of stress This unique feature of MGRN1 provides significant recognition of being inducing conditions (a); MGRN1 associates with heat stress conditions categorized as quality control E3 ubiquitin ligase most likely involved in induced luciferase protein inclusions in cells (b)[20]. c, d Accumulation protein conformational disorders generates pheomelanin via agouti signaling protein pathway. Lysosomes are membrane bound acidic vacuoles, majorly But in the absence of MGRN1, Mc1r activation takes place responsible for the recycling of damaged or poor organelles, via alpha melanocyte stimulating hormone (α-MSH). macromolecules, and proteins by endocytosis and autophagy. Exchange of GDP-GTP induces cAMP production that leads Defects in lysosomal functions due to genetic mutations lead to eumelanin (black/brown pigment) synthesis through to lysosomal storage disorders (LSDs) and also cause aging adenylyl cyclase [81–83]. and neurodegenerative diseases [84–86]. siRNA-mediated Mol Neurobiol

Fig. 4 A schematic diagram to represent MGRN1 loss of function proteasomal independent manner [16, 24, 37]. c Depletion of MGRN1 causing multifactorial disturbances or problems in various critical induces mitochondrial dysfunction in cells and mice; this may act as a cellular activities. a MGRN1 associates with Mc1r and produces causative factor in neurodegenerative diseases [41]. d Mutations in pheomelanin through agouti signaling pathway and lack of MGRN1 MGRN1 produce complex congenital heart defects (CHD) and function or null mutants in mice generates dark coat color [15, 17, 18]. abnormal LR patterning in mice embryos [95]. Overall, these studies b MGRN1 null mutants demonstrate disturbed endolysosomal trafficking suggest that MGRN1 occupies a wide range of diverse cellular and early enlarged endosomes. RING finger E3 ubiquitin ligase activity functions and, therefore, needs an in-depth observation linked with of MGRN1 targets TSG101 for multiple mono-ubiquitination in diseases

down regulation of endogenous MGRN1 modulates the stabilizes lysosomal membrane via binding with endolysosomal structures; cells appear with enlarged early endolysosomal anionic phospholipid bis (monoacylglycero) endosomes and disarrays endolysosomal trafficking of epider- phosphate (BMP) [87]. mal growth factor receptor (EGFR) [37]. MGRN1 null mutant Ribosomes are also active in mitochondria and synthesize a mice brains have altered profile of multimonoubiquitinated number of proteins. Oxidative stress results in the aggregation TSG101 and may have insoluble TSG101 aggregates. of misfolded or damaged proteins in crowded cellular milieu Probably, in MGRN1 null mice, aberrant function of normal and overall potentially affects the numerous cellular functions TSG101 contribute in the molecular pathomechanism of neu- [88, 89]. Proteomic analysis of MGRN1 null mutant mice rodegeneration associated with endolysosomal trafficking brain reveal that mitochondrial proteins were significantly re- [24]. In our previous study, we also observed that after au- duced with elevated oxidative stress. Complex IV (cyto- tophagy inhibition, p62, ubiquitin, and Hsp70 chaperone co- chrome c oxidase) level was dramatically reduced in localize with MGRN1 near to the nuclear periphery region. MGRN1 null mutant mice [41]. We also observed that Interestingly, it has earlier been shown that lysosomal Hsp70 siRNA-mediated depletion of MGRN1 in cells make them Mol Neurobiol more susceptible for mild oxidative stress and overexpression and autophagy pathway. Chaperones promote the folding of MGRN1 provide cytoprotection against oxidative stress of non-native proteins and increase their further chances induced cell death [20]. of survival in dense crowded milieu. It is very important Our existing knowledge about the mechanism of left-right to search inducers of molecular chaperones, which can (LR) body axis determination during development period is prevent or suppress misfolding of proteins and this strat- still limited. The accumulated evidences established a strong egy may be useful as therapeutic intervention in neurode- role of few genes such as Nodal, EGF–CFC family of extra- generation and aging [100–102]. Cooperative functions of cellular factors, Lefty1, Lefty2, and transforming-β-related autophagy and ubiquitin proteasome system can serve as signaling molecules in LR axis determination [90–94]. an integral part of clearance mechanism and may heal the Recently, interesting finding has also come to insight detrimental cellular loss induced by proteotoxic insults concerning the important role of MGRN1 in left-right (LR) [103–105]. One of the key tactics is to find out novel signaling cascade and embryonic patterning determination. chemical inducers which can specifically promote protein This study elaborates that MGRN1 mutant embryos exhibit degradation, and this strategy can be also useful to keep complex congenital heart defects (CHD) and abnormal LR low basal levels of over accumulated abnormal proteins patterning [95]. However, more refined new crucial substrates [106]. Understanding the detailed physiological functions finding studies targeting the ubiquitin ligase activity of of protein quality control mechanism and its hidden pos- MGRN1 implicated in normal left-right (LR) axis embryo sible mechanisms in the causation can help in the preven- developments are imperatively needful. It is also important tion of neurotoxic load caused by protein misfolding to recognize the proteins that significantly crosstalk to aggregation. MGRN1 and also to know how their aberrant forms directly An increasing body of evidence opens few first order or indirectly generate moderate risk of diseases by affecting questions about the cellular and molecular nature of MGRN1 diverse cellular functions. MGRN1 and about its function as an E3 ubiquitin ligase. But how does the aberrant function of MGRN1 interplay significant role in neurodegeneration still remain ob- Future Prospective and Key Questions scures? How does the E3 ubiquitin ligase activity of MGRN1 influence the endogenous levels of crucial sub- Different neurodegenerative diseases share common cellu- strates, mitochondrial dysfunction, and misfolded protein lar and molecular problem of misfolded proteins aggrega- aggregate formation needs further detailed analyses and tion and inclusion bodies formation. In previous studies, it careful interpretation? In principle, detailed molecular has been shown that ubiquitin, proteasome, autophagy characterization of MGRN1 can exert new significant pathway components, molecular chaperones, nascent poly- findings to influence the cellular PQC pathway and most peptide chains, and transcription factors are chiefly present likely opens new hidden potential of this novel gene in with aggregates or inclusion bodies [29]. Few interesting aging and neurodegeneration. However, it remains less reports indicate that overwhelmed aggregation of abnormal clear how the MGRN1 is activated for the misfolded proteins compromises the proteolytic functions of both protein recruitment cascade along with other components ubiquitin proteasome system and autophagy pathway [96, of UPS and autophagy pathway? The lessons learned 97]. Perturbations in the function of proteolytic machinery from previous findings already reveal that MGRN1 could generate a major challenge to resolve or find a possible serve as a wide range of essential cellular functions. But cure against the problem of protein aggregation in neuro- what are the key coplayers of MGRN1; which other E3 degenerative diseases. The blood–brain barrier (BBB) is a ubiquitin ligases can execute similar functions in the highly selective permeability barrier, which restricts the macromolecular crowding need detailed study and passage of numerous drugs and major molecules and es- implementation. sentially, this is another fundamental challenge to deliver Over the past few years, incredible progress has been made drugs across the blood–brain barrier [98, 99]. Still, the in interpreting the role of E3 ubiquitin ligases in neurodegen- pivotal reason why neuronal cells are not capable to elim- erative diseases. Now, it is important to design new drugs, inate visible abnormal protein aggregates and how their based on the defective processing caused by the aberrant func- formation contributes in proteotoxicity generation and tions of these E3 ubiquitin ligases. MGRN1 loss of function neuropathogenesis is not well known. could disturb the endolysosomal trafficking; however, the de- Now, another important aspect is needed to be ad- tailed molecular pathomechanism is unknown. In near future, dressed to the neuroprotective agents or molecular tactics identification of MGRN1 crystal structure may reveal more that could be used for the suppression of neurotoxic load about the role of its E3 ubiquitin ligase activity, substrate caused by protein misfolding aggregation? Normally, pro- binding capacity, and improve our understanding about how teins are routinely cleared by ubiquitin proteasome system MGRN1 mutations generate a wide variety of functional Mol Neurobiol tribulations in cells. The mechanistic basis of these analyses of 11. Kettern N, Dreiseidler M, Tawo R, Hohfeld J (2010) Chaperone- MGRN1 most likely opens the hidden high versatile potential assisted degradation: multiple paths to destruction. Biol Chem 391(5):481–489. doi:10.1515/BC.2010.058 of this novel protein to further improve our understanding to 12. Green M (1989) Genetic variants and strains of the laboratory protect cells from proteotoxic old or damaged proteins. mouse., vol 12–403. Catalog of mutant genes and polymorphic loci. Oxford University Press, New York 13. Lane PW, Green MC (1960) Mahogany, a recessive color muta- Acknowledgments This work was supported by the Department of tion in linkage group v of the mouse. J Hered 51(5):228–230 Biotechnology, Government ofIndia.AMwassupportedby 14. Nagase T, Ishikawa K, Miyajima N, Tanaka A, Kotani H, Nomura Ramalinganswami Fellowship (BT/RLF/Reentry/11/2010) and Innova- N, Ohara O (1998) Prediction of the coding sequences of uniden- tive Young Biotechnologist Award (IYBA) scheme (BT/06/IYBA/ tified human genes. IX. The complete sequences of 100 new 2012) from the Department of Biotechnology, Government of India. cDNA clones from brain which can code for large proteins AU was supported by a research fellowship from the Council of Scientific in vitro. DNA Res 5(1):31–39 and Industrial Research-University Grants Commission (CSIR-UGC), 15. Phan LK, Lin F, LeDuc CA, Chung WK, Leibel RL (2002) The Government of India. The authors would like to thank Mr. Bharat Pareek mouse mahoganoid coat color mutation disrupts a novel C3HC4 for his technical assistance and the entire lab management during the RING domain protein. J Clin Invest 110(10):1449–1459. doi:10. manuscript preparation. We apologize to various authors whose work 1172/JCI16131 could not be included due to space limitations. 16. He L, Lu XY, Jolly AF, Eldridge AG, Watson SJ, Jackson PK, Barsh GS, Gunn TM (2003) Spongiform degeneration in – Compliance with Ethical Requirements mahoganoid mutant mice. Science 299(5607):710 712. doi:10. 1126/science.1079694 17. He L, Eldridge AG, Jackson PK, Gunn TM, Barsh GS (2003) Conflict of Interest The authors declare that they have no competing Accessory proteins for melanocortin signaling: attractin and interests. mahogunin. Ann N Y Acad Sci 994:288–298 18. Bagher P, Jiao J, Owen Smith C, Cota CD, Gunn TM (2006) Characterization of mahogunin ring finger-1 expression in mice. Pigment Cell Res 19(6):635–643. doi:10.1111/j.1600-0749.2006. References 00340.x 19. Perez-Oliva AB, Olivares C, Jimenez-Cervantes C, Garcia-Borron 1. Dobson CM (2003) and misfolding. Nature JC (2009) Mahogunin ring finger-1 (MGRN1) E3 ubiquitin ligase 426(6968):884–890. doi:10.1038/nature02261 inhibits signaling from melanocortin receptor by competition with 2. Duncan R, Hershey JW (1983) Identification and quantitation of Galphas. J Biol Chem 284(46):31714–31725. doi:10.1074/jbc. levels of protein synthesis initiation factors in crude HeLa cell M109.028100 lysates by two-dimensional polyacrylamide gel electrophoresis. J 20. Chhangani D, Jana NR, Mishra A (2013) Misfolded proteins rec- Biol Chem 258(11):7228–7235 ognition strategies of E3 ubiquitin ligases and neurodegenerative – 3. Ingolia NT, Lareau LF, Weissman JS (2011) Ribosome profiling diseases. Mol Neurobiol 47(1):302 312. doi:10.1007/s12035- of mouse embryonic stem cells reveals the complexity and dynam- 012-8351-0 ics of mammalian proteomes. Cell 147(4):789–802. doi:10.1016/j. 21. Matz A, Lee SJ, Schwedhelm-Domeyer N, Zanini D, Holubowska cell.2011.10.002 A, Kannan M, Farnworth M, Jahn O et al (2015) Regulation of 4. Bucciantini M, Giannoni E, Chiti F, Baroni F, Formigli L, Zurdo J, neuronal survival and morphology by the E3 ubiquitin ligase RNF157. Cell Death Differ 22(4):626–642. doi:10.1038/cdd. Taddei N, Ramponi G et al (2002) Inherent toxicity of aggregates 2014.163 implies a common mechanism for protein misfolding diseases. Nature 416(6880):507–511. doi:10.1038/416507a 22. Kim JH, Kim WT (2013) The Arabidopsis RING E3 ubiquitin ligase AtAIRP3/LOG2 participates in positive regulation of 5. Chen B, Retzlaff M, Roos T, Frydman J (2011) Cellular strategies high-salt and drought stress responses. Plant Physiol 162(3): of protein quality control. Cold Spring Harb Perspect Biol 3(8): 1733–1749. doi:10.1104/pp.113.220103 a004374. doi:10.1101/cshperspect.a004374 23. Guerra DD, Pratelli R, Kraft E, Callis J, Pilot G (2013) Functional 6. Kim YE, Hipp MS, Bracher A, Hayer-Hartl M, Hartl FU (2013) conservation between mammalian MGRN1 and plant LOG2 ubiq- Molecular chaperone functions in protein folding and proteostasis. uitin ligases. FEBS Lett 587(21):3400–3405. doi:10.1016/j. – Annu Rev Biochem 82:323 355. doi:10.1146/annurev-biochem- febslet.2013.08.045 060208-092442 24. Jiao J, Sun K, Walker WP, Bagher P, Cota CD, Gunn TM (2009) 7. Fimia GM, Kroemer G, Piacentini M (2013) Molecular mecha- Abnormal regulation of TSG101 in mice with spongiform neuro- – nisms of selective autophagy. Cell Death Differ 20(1):1 2. doi:10. degeneration. Biochim Biophys Acta 1792(10):1027–1035. doi: 1038/cdd.2012.97 10.1016/j.bbadis.2009.08.009 8. Arndt V, Dick N, Tawo R, Dreiseidler M, Wenzel D, Hesse M, 25. Borden KL (2000) RING domains: master builders of molecular Furst DO, Saftig P et al (2010) Chaperone-assisted selective au- scaffolds? J Mol Biol 295(5):1103–1112. doi:10.1006/jmbi.1999. tophagy is essential for muscle maintenance. Curr Biol 20(2):143– 3429 148. doi:10.1016/j.cub.2009.11.022 26. Lorick KL, Jensen JP, Fang S, Ong AM, Hatakeyama S, 9. Ulbricht A, Eppler FJ, Tapia VE, van der Ven PF, Hampe N, Weissman AM (1999) RING fingers mediate ubiquitin- Hersch N, Vakeel P, Stadel D et al (2013) Cellular conjugating enzyme (E2)-dependent ubiquitination. Proc Natl mechanotransduction relies on tension-induced and chaperone- Acad Sci U S A 96(20):11364–11369 assisted autophagy. Curr Biol 23(5):430–435. doi:10.1016/j.cub. 27. Borden KL, Freemont PS (1996) The RING finger domain: a 2013.01.064 recent example of a sequence-structure family. Curr Opin Struct 10. Kaushik S, Cuervo AM (2012) Chaperone-mediated autophagy: a Biol 6(3):395–401 unique way to enter the lysosome world. Trends Cell Biol 22(8): 28. Kim MS, Pinto SM, Getnet D, Nirujogi RS, Manda SS, 407–417. doi:10.1016/j.tcb.2012.05.006 Chaerkady R, Madugundu AK, Kelkar DS et al (2014) A draft Mol Neurobiol

map of the human proteome. Nature 509(7502):575–581. doi:10. 47. Silvius D, Pitstick R, Ahn M, Meishery D, Oehler A, Barsh GS, 1038/nature13302 DeArmond SJ, Carlson GA et al (2013) Levels of the Mahogunin 29. Olzscha H, Schermann SM, Woerner AC, Pinkert S, Hecht MH, Ring Finger 1 E3 ubiquitin ligase do not influence prion disease. Tartaglia GG, Vendruscolo M, Hayer-Hartl M et al (2011) PLoS One 8(1), e55575. doi:10.1371/journal.pone.0055575 Amyloid-like aggregates sequester numerous metastable proteins 48. Uchiyama K, Muramatsu N, Yano M, Usui T, Miyata H, with essential cellular functions. Cell 144(1):67–78. doi:10.1016/ Sakaguchi S (2013) Prions disturb post-Golgi trafficking of mem- j.cell.2010.11.050 brane proteins. Nat Commun 4:1846. doi:10.1038/ncomms2873 30. Dobson CM (2004) Principles of protein folding, misfolding and 49. Yuan F, Yang L, Zhang Z, Wu W, Zhou X, Yin X, Zhao D (2013) aggregation. Semin Cell Dev Biol 15(1):3–16. doi:10.1016/j. Cellular prion protein (PrPC) of the neuron cell transformed to a semcdb.2003.12.008 PK-resistant protein under oxidative stress, comprising main mi- 31. Muchowski PJ, Wacker JL (2005) Modulation of neurodegenera- tochondrial damage in prion diseases. J Mol Neurosci : MN 51(1): tion by molecular chaperones. Nat Rev Neurosci 6(1):11–22. doi: 219–224. doi:10.1007/s12031-013-0008-6 10.1038/nrn1587 50. Winkler J, Tyedmers J, Bukau B, Mogk A (2012) Hsp70 targets 32. Walker LC, Diamond MI, Duff KE, Hyman BT (2013) Hsp100 chaperones to substrates for protein disaggregation and Mechanisms of protein seeding in neurodegenerative diseases. prion fragmentation. J Cell Biol 198(3):387–404. doi:10.1083/jcb. JAMA Neurol 70(3):304–310. doi:10.1001/jamaneurol.2013.1453 201201074 33. Demand J, Alberti S, Patterson C, Hohfeld J (2001) Cooperation 51. Lin Z, Zhao D, Yang L (2013) Interaction between misfolded PrP of a ubiquitin domain protein and an E3 ubiquitin ligase during and the ubiquitin-proteasome system in prion-mediated neurode- chaperone/proteasome coupling. Curr Biol 11(20):1569–1577 generation. Acta Biochim Biophys Sin (Shanghai) 45(6):477– 34. Chhangani D, Nukina N, Kurosawa M, Amanullah A, Joshi V, 484. doi:10.1093/abbs/gmt020 Upadhyay A, Mishra A (2014) Mahogunin ring finger 1 sup- 52. Liberski PP, Brown DR, Sikorska B, Caughey B, Brown P (2008) presses misfolded polyglutamine aggregation and cytotoxicity. Cell death and autophagy in prion diseases (transmissible Biochim Biophys Acta. doi:10.1016/j.bbadis.2014.04.014 spongiform encephalopathies). Folia Neuropathol 46(1):1–25 35. Jacomy H, Talbot PJ (2003) Vacuolating encephalitis in mice in- 53. Du Toit A (2014) Post-translational modification: sweetening pro- fected by human coronavirus OC43. Virology 315(1):20–33 tein quality control. Nat Rev Mol Cell Biol 15(5):295. doi:10. 36. Fraser JR (2002) What is the basis of transmissible spongiform 1038/nrm3787 encephalopathy induced neurodegeneration and can it be 54. van Oosten-Hawle P, Morimoto RI (2014) Transcellular chaper- repaired? Neuropathol Appl Neurobiol 28(1):1–11 one signaling: an organismal strategy for integrated cell stress 37. Kim BY, Olzmann JA, Barsh GS, Chin LS, Li L (2007) responses. J Exp Biol 217(Pt 1):129–136. doi:10.1242/jeb.091249 Spongiform neurodegeneration-associated E3 ligase Mahogunin 55. Scotter EL, Vance C, Nishimura AL, Lee YB, Chen HJ, Urwin H, ubiquitylates TSG101 and regulates endosomal trafficking. Mol Sardone V, Mitchell JC et al (2014) Differential roles of the ubiq- Biol Cell 18(4):1129–1142. doi:10.1091/mbc.E06-09-0787 uitin proteasome system and autophagy in the clearance of soluble 38. Amit I, Yakir L, Katz M, Zwang Y, Marmor MD, Citri A, and aggregated TDP-43 species. J Cell Sci 127(Pt 6):1263–1278. Shtiegman K, Alroy I et al (2004) Tal, a Tsg101-specific E3 ubiq- doi:10.1242/jcs.140087 uitin ligase, regulates receptor endocytosis and retrovirus budding. 56. Sontag EM, Vonk WI, Frydman J (2014) Sorting out the trash: the Genes Dev 18(14):1737–1752. doi:10.1101/gad.294904 spatial nature of eukaryotic protein quality control. Curr Opin Cell 39. Li L, Liao J, Ruland J, Mak TW, Cohen SN (2001) A TSG101/ Biol 26:139–146. doi:10.1016/j.ceb.2013.12.006 MDM2 regulatory loop modulates MDM2 degradation and 57. Wolff S, Weissman JS, Dillin A (2014) Differential scales of pro- MDM2/p53 feedback control. Proc Natl Acad Sci U S A 98(4): tein quality control. Cell 157(1):52–64. doi:10.1016/j.cell.2014. 1619–1624. doi:10.1073/pnas.98.4.1619 03.007 40. Cheng TH, Cohen SN (2007) Human MDM2 isoforms translated 58. Polling S, Mok YF, Ramdzan YM, Turner BJ, Yerbury JJ, Hill AF, differentially on constitutive versus p53-regulated transcripts have Hatters DM (2014) Misfolded polyglutamine, polyalanine, and distinct functions in the p53/MDM2 and TSG101/MDM2 feed- superoxide dismutase 1 aggregate via distinct pathways in the cell. back control loops. Mol Cell Biol 27(1):111–119. doi:10.1128/ J Biol Chem 289(10):6669–6680. doi:10.1074/jbc.M113.520189 MCB.00235-06 59. Mosser DD, Caron AW, Bourget L, Denis-Larose C, Massie B 41. Sun K, Johnson BS, Gunn TM (2007) Mitochondrial dysfunction (1997) Role of the human heat shock protein hsp70 in protection precedes neurodegeneration in mahogunin (Mgrn1) mutant mice. against stress-induced apoptosis. Mol Cell Biol 17(9):5317–5327 Neurobiol Aging 28(12):1840–1852. doi:10.1016/j. 60. Kakkar V, Meister-Broekema M, Minoia M, Carra S, Kampinga neurobiolaging.2007.07.012 HH (2014) Barcoding heat shock proteins to human diseases: 42. Miller KA, Gunn TM, Carrasquillo MM, Lamoreux ML, looking beyond the heat shock response. Dis Model Mech 7(4): Galbraith DB, Barsh GS (1997) Genetic studies of the mouse 421–434. doi:10.1242/dmm.014563 mutations mahogany and mahoganoid. Genetics 146(4):1407– 61. Chhangani D, Mishra A (2013) Mahogunin ring finger-1 1415 (MGRN1) suppresses chaperone-associated misfolded protein ag- 43. Prusiner SB (1991) of prion diseases. Science gregation and toxicity. Sci Rep 3:1972. doi:10.1038/srep01972 252(5012):1515–1522 62. Bjorkoy G, Lamark T, Brech A, Outzen H, Perander M, Overvatn 44. Pan KM, Baldwin M, Nguyen J, Gasset M, Serban A, Groth D, A, Stenmark H, Johansen T (2005) p62/SQSTM1 forms protein Mehlhorn I, Huang Z et al (1993) Conversion of alpha-helices into aggregates degraded by autophagy and has a protective effect on beta-sheets features in the formation of the scrapie prion proteins. huntingtin-induced cell death. J Cell Biol 171(4):603–614. doi:10. Proc Natl Acad Sci U S A 90(23):10962–10966 1083/jcb.200507002 45. Miesbauer M, Rambold AS, Winklhofer KF, Tatzelt J (2010) 63. Pankiv S, Clausen TH, Lamark T, Brech A, Bruun JA, Outzen H, Targeting of the prion protein to the cytosol: mechanisms and Overvatn A, Bjorkoy G et al (2007) p62/SQSTM1 binds directly consequences. Curr Issues Mol Biol 12(2):109–118 to Atg8/LC3 to facilitate degradation of ubiquitinated protein ag- 46. Chakrabarti O, Hegde RS (2009) Functional depletion of gregates by autophagy. J Biol Chem 282(33):24131–24145. doi: mahogunin by cytosolically exposed prion protein contributes to 10.1074/jbc.M702824200 neurodegeneration. Cell 137(6):1136–1147. doi:10.1016/j.cell. 64. Zatloukal K, Stumptner C, Fuchsbichler A, Heid H, Schnoelzer 2009.03.042 M, Kenner L, Kleinert R, Prinz M et al (2002) p62 Is a common Mol Neurobiol

component of cytoplasmic inclusions in protein aggregation dis- 80. Barsh G, Gunn T, He L, Schlossman S, Duke-Cohan J (2000) eases. Am J Pathol 160(1):255–263. doi:10.1016/S0002-9440(10) Biochemical and genetic studies of pigment-type switching. 64369-6 Pigment Cell Res 13(Suppl 8):48–53 65. Ishii T, Itoh K, Takahashi S, Sato H, Yanagawa T, Katoh Y,Bannai 81. Hida T, Wakamatsu K, Sviderskaya EV, Donkin AJ, Montoliu L, S, Yamamoto M (2000) Transcription factor Nrf2 coordinately Lynn Lamoreux M, Yu B, Millhauser GL et al (2009) Agouti regulates a group of oxidative stress-inducible genes in macro- protein, mahogunin, and attractin in pheomelanogenesis and phages. J Biol Chem 275(21):16023–16029 melanoblast-like alteration of melanocytes: a cAMP-independent 66. Ishii T, Yanagawa T, Yuki K, Kawane T, Yoshida H, Bannai S pathway. Pigment Cell Melanoma Res 22(5):623–634. doi:10. (1997) Low micromolar levels of hydrogen peroxide and protea- 1111/j.1755-148X.2009.00582.x some inhibitors induce the 60-kDa A170 stress protein in murine 82. Barsh GS (2007) Regulation of pigment type switching by agouti, peritoneal macrophages. Biochem Biophys Res Commun 232(1): melanocortin signaling, attractin, and mahoganoid. In: The 33–37. doi:10.1006/bbrc.1997.6221 Pigmentary System: Physiology and Pathophysiology: Second 67. Viiri J, Hyttinen JM, Ryhanen T, Rilla K, Paimela T, Kuusisto E, Edition. pp 395–409. doi:10.1002/9780470987100.ch19 Siitonen A, Urtti A et al (2010) p62/sequestosome 1 as a regulator 83. Walker WP, Gunn TM (2009) Piecing together the pigment-type of proteasome inhibitor-induced autophagy in human retinal pig- switching puzzle. Pigment Cell Melanoma Res 23(1):4–6. doi:10. ment epithelial cells. Mol Vis 16:1399–1414 1111/j.1755-148X.2009.00654.x 68. Robitaille Y, Lopes-Cendes I, Becher M, Rouleau G, Clark AW 84. Bahr BA, Bendiske J (2002) The neuropathogenic contributions (1997) The neuropathology of CAG repeat diseases: review and of lysosomal dysfunction. J Neurochem 83(3):481–489 update of genetic and molecular features. Brain Pathol 7(3):901– 85. Kurz T, Terman A, Gustafsson B, Brunk UT (2008) Lysosomes in 926 iron metabolism, ageing and apoptosis. Histochem Cell Biol 69. Donaldson KM, Li W, Ching KA, Batalov S, Tsai CC, Joazeiro 129(4):389–406. doi:10.1007/s00418-008-0394-y CA (2003) Ubiquitin-mediated sequestration of normal cellular 86. Boland B, Kumar A, Lee S, Platt FM, Wegiel J, Yu WH, Nixon proteins into polyglutamine aggregates. Proc Natl Acad Sci U S RA (2008) Autophagy induction and autophagosome clearance in A 100(15):8892–8897. doi:10.1073/pnas.1530212100 neurons: relationship to autophagic pathology in Alzheimer's dis- 70. McCampbell A, Taylor JP, Taye AA, Robitschek J, Li M, Walcott ease. J Neurosci : Off J Soc Neurosci 28(27):6926–6937. doi:10. J, Merry D, Chai Y et al (2000) CREB-binding protein sequestra- 1523/JNEUROSCI.0800-08.2008 tion by expanded polyglutamine. Hum Mol Genet 9(14):2197– 87. Kirkegaard T, Roth AG, Petersen NH, Mahalka AK, Olsen OD, 2202 Moilanen I, Zylicz A, Knudsen J et al (2010) Hsp70 stabilizes 71. Perez MK, Paulson HL, Pendse SJ, Saionz SJ, Bonini NM, lysosomes and reverts Niemann-Pick disease-associated lysosom- Pittman RN (1998) Recruitment and the role of nuclear localiza- al pathology. Nature 463(7280):549–553. doi:10.1038/ tion in polyglutamine-mediated aggregation. J Cell Biol 143(6): nature08710 1457–1470 88. Harbauer AB, Zahedi RP, Sickmann A, Pfanner N, Meisinger C 72. Yamanaka T, Nukina N (2010) Transcription factor sequestration (2014) The protein import machinery of mitochondria-a regulato- by polyglutamine proteins. Methods Mol Biol 648:215–229. doi: ry hub in metabolism, stress, and disease. Cell Metab 19(3):357– 10.1007/978-1-60761-756-3_14 372. doi:10.1016/j.cmet.2014.01.010 73. Sugars KL, Rubinsztein DC (2003) Transcriptional abnormalities 89. Beal MF (2005) Mitochondria take center stage in aging and neu- in Huntington disease. Trends Genet 19(5):233–238. doi:10.1016/ rodegeneration. Ann Neurol 58(4):495–505. doi:10.1002/ana. S0168-9525(03)00074-X 20624 74. Steffan JS, Kazantsev A, Spasic-Boskovic O, Greenwald M, Zhu 90. Collignon J, Varlet I, Robertson EJ (1996) Relationship between YZ, Gohler H, Wanker EE, Bates GP et al (2000) The asymmetric nodal expression and the direction of embryonic turn- Huntington's disease protein interacts with p53 and CREB- ing. Nature 381(6578):155–158. doi:10.1038/381155a0 binding protein and represses transcription. Proc Natl Acad Sci 91. Lowe LA, Supp DM, Sampath K, Yokoyama T, Wright CV,Potter U S A 97(12):6763–6768. doi:10.1073/pnas.100110097 SS, Overbeek P, Kuehn MR (1996) Conserved left-right asymme- 75. Yamanaka T, Miyazaki H, Oyama F, Kurosawa M, Washizu C, try of nodal expression and alterations in murine situs inversus. Doi H, Nukina N (2008) Mutant Huntingtin reduces HSP70 ex- Nature 381(6578):158–161. doi:10.1038/381158a0 pression through the sequestration of NF-Y transcription factor. 92. Meno C, Saijoh Y, Fujii H, Ikeda M, Yokoyama T, Yokoyama M, EMBO J 27(6):827–839. doi:10.1038/emboj.2008.23 Toyoda Y, Hamada H (1996) Left-right asymmetric expression of 76. Miller VM, Nelson RF, Gouvion CM, Williams A, Rodriguez- the TGF beta-family member lefty in mouse embryos. Nature Lebron E, Harper SQ, Davidson BL, Rebagliati MR et al (2005) 381(6578):151–155. doi:10.1038/381151a0 CHIP suppresses polyglutamine aggregation and toxicity in vitro 93. Shiratori H, Hamada H (2006) The left-right axis in the mouse: and in vivo. J Neurosci : Off J Soc Neurosci 25(40):9152–9161. from origin to morphology. Development 133(11):2095–2104. doi:10.1523/JNEUROSCI.3001-05.2005 doi:10.1242/dev.02384 77. Ying Z, Wang H, Fan H, Zhu X, Zhou J, Fei E, Wang G (2009) 94. Yan YT, Gritsman K, Ding J, Burdine RD, Corrales JD, Price SM, Gp78, an ER associated E3, promotes SOD1 and ataxin-3 degra- Talbot WS, Schier AF et al (1999) Conserved requirement for dation. Hum Mol Genet 18(22):4268–4281. doi:10.1093/hmg/ EGF-CFC genes in vertebrate left-right axis formation. Genes ddp380 Dev 13(19):2527–2537 78. Yang H, Zhong X, Ballar P, Luo S, Shen Y, Rubinsztein DC, 95. Cota CD, Bagher P, Pelc P, Smith CO, Bodner CR, Gunn TM Monteiro MJ, Fang S (2007) Ubiquitin ligase Hrd1 enhances the (2006) Mice with mutations in Mahogunin ring finger-1 degradation and suppresses the toxicity of polyglutamine- (Mgrn1) exhibit abnormal patterning of the left-right axis. Dev expanded huntingtin. Exp Cell Res 313(3):538–550. doi:10. Dyn 235(12):3438–3447. doi:10.1002/dvdy.20992 1016/j.yexcr.2006.10.031 96. Menzies FM, Fleming A, Rubinsztein DC (2015) Compromised 79. Mishra A, Dikshit P, Purkayastha S, Sharma J, Nukina N, Jana NR autophagy and neurodegenerative diseases. Nat Rev Neurosci (2008) E6-AP promotes misfolded polyglutamine proteins for 16(6):345–357. doi:10.1038/nrn3961 proteasomal degradation and suppresses polyglutamine protein 97. Bence NF, Sampat RM, Kopito RR (2001) Impairment of the aggregation and toxicity. J Biol Chem 283(12):7648–7656. doi: ubiquitin-proteasome system by protein aggregation. Science 10.1074/jbc.M706620200 292(5521):1552–1555. doi:10.1126/science.292.5521.1552 Mol Neurobiol

98. Nau R, Sorgel F, Eiffert H (2010) Penetration of drugs through the family of Arabidopsis. Plant Physiol 137(1):13–30. doi:10.1104/ blood-cerebrospinal fluid/blood–brain barrier for treatment of cen- pp.104.052423 tral nervous system infections. Clin Microbiol Rev 23(4):858– 108. Sievers F, Wilm A, Dineen D, Gibson TJ, Karplus K, Li W, Lopez 883. doi:10.1128/CMR.00007-10 R, McWilliam H et al (2011) Fast, scalable generation of high- 99. Pardridge WM (2011) Drug transport in brain via the cerebrospi- quality protein multiple sequence alignments using Clustal nal fluid. Fluids and barriers of the CNS 8(1):7. doi:10.1186/2045- Omega. Mol Syst Biol 7:539. doi:10.1038/msb.2011.75 8118-8-7 109. Clamp M, Cuff J, Searle SM, Barton GJ (2004) The Jalview Java 100. Ohtsuka K, Kawashima D, Gu Y, Saito K (2005) Inducers and co- alignment editor. Bioinformatics 20(3):426–427. doi:10.1093/ inducers of molecular chaperones. Int J Hyperth 21(8):703–711. bioinformatics/btg430 doi:10.1080/02656730500384248 110. Cooray SN, Guasti L, Clark AJ (2011) The E3 ubiquitin li- 101. Nagai Y, Fujikake N, Popiel HA, Wada K (2010) Induction of gase Mahogunin ubiquitinates the melanocortin 2 receptor. – molecular chaperones as a therapeutic strategy for the Endocrinology 152(11):4224 4231. doi:10.1210/en.2011- polyglutamine diseases. Curr Pharm Biotechnol 11(2):188–197 0147 102. Rokutan K (2003) Molecular chaperone inducers in medicine and 111. Gunn TM, Silvius D, Bagher P, Sun K, Walker KK (2013) diseases. Nihon Yakurigaku Zasshi 121(1):15–20 MGRN1-dependent pigment-type switching requires its ubiquitination activity but not its interaction with TSG101 or 103. Lilienbaum A (2013) Relationship between the proteasomal sys- NEDD4. Pigment Cell Melanoma Res 26(2):263–268. doi:10. tem and autophagy. Int J Biochem Mol Biol 4(1):1–26 1111/pcmr.12059 104. Ding WX, Ni HM, Gao W, Yoshimori T, Stolz DB, Ron D, Yin 112. Chhangani D, Nukina N, Kurosawa M, Amanullah A, Joshi V, XM (2007) Linking of autophagy to ubiquitin-proteasome system Upadhyay A, Mishra A (2014) Mahogunin ring finger 1 sup- is important for the regulation of endoplasmic reticulum stress and – presses misfolded polyglutamine aggregation and cytotoxicity. cell viability. Am J Pathol 171(2):513 524. doi:10.2353/ajpath. Biochim Biophys Acta 1842(9):1472–1484. doi:10.1016/j. 2007.070188 bbadis.2014.04.014 105. Chhangani D, Chinchwadkar S, Mishra A (2014) Autophagy cou- 113. Srivastava D, Chakrabarti O (2014) Mahogunin-mediated alpha- pling interplay: can improve cellular repair and aging? Mol tubulin ubiquitination via noncanonical K6 linkage regulates mi- – Neurobiol 49(3):1270 1281. doi:10.1007/s12035-013-8599-z crotubule stability and mitotic spindle orientation. Cell Death Dis 106. Raina K, Crews CM (2010) Chemical inducers of targeted protein 5, e1064. doi:10.1038/cddis.2014.1 degradation. J Biol Chem 285(15):11057–11060. doi:10.1074/jbc. 114. Cheng D, Xiong C, Li J, Sui C, Wang S, Li H, Jiang X (2014) The R109.078105 effect of mahogunin gene mutant on reproduction in male mice: a 107. Stone S, Hauksdóttir H, Troy A, Herschleb J, Kraft E, Callis J new sight for infertility? Andrologia 46(2):98–105. doi:10.1111/ (2005) Functional analysis of the RING-type ubiquitin ligase and.12050