187

REVIEW

IGF2 mRNA-binding protein 2: biological function and putative role in type 2 diabetes

Jan Christiansen1, Astrid M Kolte2, Thomas v O Hansen2 and Finn C Nielsen2 Departments of 1Biology and 2Clinical Biochemistry, Rigshospitalet, University of Copenhagen, Blegdamsvej 9, 2100 Copenhagen, Denmark

(Correspondence should be addressed to F C Nielsen; Email: [email protected])

Abstract

Recent genome-wide association (GWA) studies of type 2 diabetes (T2D) have implicated IGF2 mRNA-binding protein 2 (IMP2/IGF2BP2) as one of the several factors in the etiology of late onset diabetes. IMP2 belongs to a family of oncofetal mRNA-binding proteins implicated in RNA localization, stability, and translation that are essential for normal embryonic growth and development. This review provides a background to the IMP protein family with an emphasis on human IMP2, followed by a closer look at the GWA studies to evaluate the significance, if any, of the proposed correlation between IMP2 and T2D. Journal of Molecular Endocrinology (2009) 43, 187–195

Introduction dwarf phenotype of the knock-out mouse (IMP noun: small devil or demon). To add to the general confusion, Insulin-like growth factor 2 (IGF2) mRNA-binding the public databases unfortunately annotate these protein 2 (IMP2/IGF2BP2) belongs to a family of RNA-binding proteins as IGF2BP. Figure 1A provides a mRNA-binding proteins (IMP1, IMP2, and IMP3) phylogenetic overview of experimentally described involved in RNA localization, stability, and translation. members of this RNA-binding protein family, including IMPs are mainly expressed during development and are their original abbreviation. essential for normal embryonic growth and develop- ment. Based on a series of genome-wide association (GWA) studies, IMP2 was recently implicated in type 2 diabetes (T2D). Here, we review the molecular proper- Evolutionary history of IMPs ties of the IMP family and IMP2, as well as the possible connection between IMP2 and T2D. Genes encoding paralogous factors within an individual species is a typical vertebrate feature, originating from two gene duplications allowing subsequent non-, sub- or neo-functionalization. Inspection of the exon–intron Nomenclature architecture of the mammalian members reveals a considerable level of conservation, since IMP1 and The nomenclature of the IMP family is not straight- IMP3 are encoded by 15 exons, whereas the slightly forward, mainly because the members of the family larger IMP2 protein is encoded by 16 exons (Fig. 1B). were identified and ascribed different functions in In addition, the human IMP2 gene encodes a splice different biological systems. Attempts to reach a variant where exon 10 is skipped, generating an IMP2 unifying acronym (VICKZ; Yisraeli 2005), based on isoform originally named p62 (Zhang et al. 1999a). the first letter of the initially described members have Among the mammalian species, intron 2 is by far the not caught on, so until a clearer picture in terms of largest intron, and the single nucleotide polymorphism molecular mechanism has emerged, the awkward (SNP) reported to be associated with T2D in the GWA nomenclature is likely to persist. The human members studies described below is situated within the 125 kbp received their acronym IMP from the original obser- intron 2 in the IMP2 gene at chromosome 3 q27.2 vation of a high-affinity binding site in one of the IGF2 position 186994381 (Fig. 1B). An intriguing feature mRNAs (Nielsen et al. 1999) and from the anticipated of the chromosomal locations of the IMP genes is

Journal of Molecular Endocrinology (2009) 43, 187–195 DOI: 10.1677/JME-09-0016 0952–5041/09/043–187 q 2009 Society for Endocrinology Printed in Great Britain Online version via http://www.endocrinology-journals.org

Downloaded from Bioscientifica.com at 09/29/2021 10:57:14AM via free access 188 J CHRISTIANSEN and others . IMP2 and type 2 diabetes

seems clear that the four KH domains constitute a functional entity in terms of high-affinity RNA-binding, granular RNP assembly, and RNA localization (Nielsen et al. 2002), although invertebrate homologs may exhibit rudimentary features of the two RRMs. We are lacking high-resolution structural infor- mation for both the IMPs alone and, more urgently, their complexes with target RNAs. So the present picture is based on biochemical experiments and inference from structural data derived from RRMs and KH domains in other RNA-binding proteins. Whereas ample biochemical evidence has accumulated regarding the RNA-binding potential of KH domains in IMPs, the significance of the two RRMs is far more Figure 1 (A) Phylogeny of the IMP family of RNA-binding proteins elusive, since there are no data pointing to a direct role represented by an unrooted dendogram of IMPs and their in RNA-binding (Git & Standart 2002, Nielsen et al. orthologs. IMP1 is almost identical to mouse coding region 2002, 2004). Inspection of the characteristic RNP2 and determinant-binding protein (CRD-BP) and closely related to RNP1 consensus sequences in the two RRMs in IMP2 chicken zip-code binding protein 1 (ZBP1), and IMP3 is reveals that RRM1 exhibits the characteristic consen- orthologous to Xenopus Vg1RBP/Vera and mouse K-homology overexpressed in cancer (KOC). IMP2 has no experimentally suses, whereas RRM2 does not. Nevertheless, a described orthologs and represents the most distant member of comparison of vertebrate IMP2 orthologs shows that the IMP family. Drosophila IMP (dIMP) is composed of only four the conservation pressure on both RRMs is similar to KH domains. (B) Schematic representation of the IMP2 gene and the conservation of the KH domains, so whatever the protein structure. Exons are shown as boxes and 50 and 30untranslated regions are indicated by red color. IMP2 is function of the two RRMs, it must be advantageous in composed of 16 exons. The human IMP2 gene encodes a splice chordates (the sea squirt Ciona intestinalis exhibits one variant where exon 10 is skipped, generating an IMP2 isoform member with the modular 2C4 architecture). originally named p62. Among the mammalian species, intron 2 is There is no evidence that the different human IMP by far the largest intron, and the SNP rs4402960 reported to be associated with T2D in the GWA studies is situated within the isoforms should target different RNA molecules. The 125-kbp intron 2 in the IMP2 gene at q27.2 on chromosome 3 contribution of each KH domain to the RNA-binding position 186994381. platform is unclear, but if comparisons with structural studies of Nova KH domains (Jensen et al. 2000) are the synteny with, e.g., HOX clusters, DLX, and IGFBP carried out, the probable scenario is that each KH (not to be confused with IMP) genes in what has been domain binds to a 4-nucleotide motif, and that high termed as paralogons (Sundstrom et al. 2008), probably affinity and specificity are provided by the multiple KH reflecting an ancestral chromosome. domains. The multiplicity of putative contacts is further enhanced by the dimerization of IMPs via a sequential mechanism on its RNA target, and both homo- and Protein structure heterodimerization among the paralogs seem feasible (Nielsen et al. 2004). KH3 and KH4 domains, at least The human IMP1–3 family members, with expected from IMP1, encompass an ability to dimerize both in a molecular masses of 63, 66, and 64 kDa and an overall homo- and heteromeric manner, and it is also the same sequence identity of 59%, exhibit six characteristic part of the protein that is able to associate with HuD RNA-binding modules, namely two N-terminal RNA (Atlas et al. 2004) and PABP (Patel & Bag 2006). A direct recognition motifs (RRM1 and 2) and four C-terminal interaction with fragile X mental retardation protein hnRNP K-homology (KH1–4) domains (Fig. 1B; Niel- (FMRP) in an RNA-independent manner has also been sen et al. 1999). Whereas two RRMs or four KH domains reported to be mediated via KH3 and KH4 (Rackham & can be found in other RNA-binding proteins such as Brown 2004), but the latter interaction is more hnRNP A1 and KSRP respectively, the 2C4 modular controversial, since FMRP and IMP1 do not seem to architecture seen in IMPs is unique. A similarity of colocalize in the same RNP granules (Jønson et al. sequence and spacing in regions between the two RRMs 2007). Both IMP2, the splice variant p62 (that lacks 43 and between KH domains 1 and 2 and domains 3 and 4, amino acids between KH2 and KH3), and IMP3 are also combined with the considerable divergence of regions able to form homodimers (Nielsen et al.2004). between RRM2 and KH1 and between KH2 and KH3, Moreover, IMP2 was previously found to interact with has led to the notion that the RNA-binding modules the AU-rich element-binding factor AUF1 (Moraes et al. cooperate pairwise (Git & Standart 2002). From both 2003) indicating that IMP2 could be involved in the a phylogenetic and experimental standpoint, it also regulation of mRNA stability.

Journal of Molecular Endocrinology (2009) 43, 187–195 www.endocrinology-journals.org

Downloaded from Bioscientifica.com at 09/29/2021 10:57:14AM via free access IMP2 and type 2 diabetes . J CHRISTIANSEN and others 189

Cellular functions

Different RNA-binding proteins are attached to eukary- otic mRNAs during their life cycle. Major transitions include the exchange of nuclear RNA-binding proteins with cytoplasmic factors. Moreover, the exon-junction complex that is deposited during splicing is removed during the pioneering round of translation (for review see Maquat 2004, Moore 2005). The composition of RNA-binding proteins specify cytoplasmic events such as RNA localization, translation, and stability (for review see Hieronymus & Silver 2004). IMPs are mainly cytoplasmic, but the presence of two nuclear export signals imply that they attach to their target mRNAs in the nucleus and facilitate nuclear export of the transcripts (Nielsen et al. 2003, Oleynikov & Singer 2003). In the cytoplasm, they form large RNP granules dispersed around the nucleus and in cellular protrusions (Fig. 2A). Granules travel at a speed of 0.2 mm/s, and during migration cells are able to switch from a delocalized to a localized pattern (Nielsen et al. 2002). In neuronal cells, granules localize to dendrites and growth cones (Zhang et al. 2001, Tiruchinapalli et al. 2003), and in Xenopus oocytes the IMP3 ortholog Vg1RBP/Vera anchors at the vegetal pole (Deshler et al. 1998, Havin et al. 1998). IMP1 granules represent a unique RNP entity, distinct from neuronal hStaufen and/or FMRP gran- ules, P-bodies and stress-granules (Jønson et al. 2007). Granules are 100–300 nm in diameter and consist of Figure 2 (A) Cellular distribution of IMP2 in human HT1080 IMPs, 40S ribosomal subunits, shuttling hnRNPs, mammary cancer cells. Note the typical granular appearance poly(A)-binding proteins, and mRNAs. Moreover, (insert) and localization of the protein in cellular extensions granules contain CBP80 and factors belonging to the (arrows) and around the nucleus. (B) Whole mount in situ hybridization of IMP2 mRNA in a developing mouse embryo at exon-junction complex. They lack eIF4E, eIF4G and E12.5. Note that IMP2 mRNA is mainly expressed in the fore- and 60S ribosomal subunits, indicating that constituent hindbrain and the limb buds. mRNAs have never been translated. Embodied mRNAs correspond to about 3% of the transcriptome, so the individual granules are likely to be heterogeneous. motile fibroblasts (Farina et al. 2003). In the same vein, Messenger RNAs encoding proteins participating in the neuronal ZBP1 is required for the localization of b-actin secretory pathway and ER-associated quality control, as mRNA to dendrites and growth cones (Zhang et al. well as ubiquitin-dependent metabolism, are enriched 2001, Tiruchinapalli et al. 2003). Finally, IMPs also play in IMP1 granules (Jønson et al. 2007), providing a role in H19 and Tau-mRNA transport (Runge et al. support to the concept of RNP granules as post- 2000, Atlas et al. 2004). RNA localization is important in transcriptional operons (Keene & Tenenbaum 2002). the establishment of cellular asymmetries – for instance Target mRNAs for IMPs frequently exhibit multiple during migration. The salient feature behind the binding sites that are located in either the 50untranslated mechanism is the ability to transport mRNAs in a region (UTR), the 30UTR or even in the coding region. repressed form, and at a given signal, unload the RNA Therefore, it could be anticipated that the proteins enabling protein synthesis at the final destination. affect several different post-transcriptional events. Although not necessarily mutually exclusive with regard Based on studies of Xenopus Vg1RBP/Vera (IMP3 to RNA localization, IMPs also control both the ortholog), it was recognized early that this RNA- translatability and stability of particular mRNAs. IMPs binding protein was important for RNA localization impair translation of leader 3 IGF2 mRNA that exhibits (Deshler et al. 1998, Havin et al. 1998). This view gained at least six binding elements in the 50UTR (Nielsen et al. support from other early studies indicating that the 1999), and the mouse IMP1 ortholog CRD-BP was at chicken IMP1 ortholog ZBP1 was implicated in an early stage found to stabilize the c-myc transcript by localization of b-actin mRNA to the leading edge of preventing the access of an endonuclease to the coding www.endocrinology-journals.org Journal of Molecular Endocrinology (2009) 43, 187–195

Downloaded from Bioscientifica.com at 09/29/2021 10:57:14AM via free access 190 J CHRISTIANSEN and others . IMP2 and type 2 diabetes

region (Doyle et al. 1998). Moreover, IMPs prolong the with the previously described IMP1 and IMP3 half-life of CD44 mRNA and stimulate invadopodia expression during development (Mueller-Pillasch et al. formation (Vikesaa et al. 2006). 1999, Mori et al. 2001, Hansen et al. 2004). However, in contrast to its paralogs – IMP2 is also found in a variety of adult organs. Physiological roles The physiological role of IMPs has been addressed by reverse genetics in different loss- and gain-of-function models. In Drosophila, aberrant expression of neuronal The IMP proteins have previously been regarded as dIMP is followed by compromised synaptogenesis oncofetal, since they originally were discovered in both centrally and peripherally, indicating that dIMP developing embryos and in transformed cells (Nielsen is required for proper axon guidance (Boylan et al. et al. 1999). Clearly, the fetal expression is most 2008). In Xenopus, knockdown of Vg1RBP/Vera (the prominent, but data demonstrating postnatal IMP3 ortholog) showed that it was necessary for expression of IMPs are accumulating (Mori et al. 2001, migration of cells from the roof plate of the neural Wang et al. 2003, Hansen et al. 2004). Mammalian IMPs tube and for neural crest migration (Yaniv et al. 2003). are expressed in a biphasic fashion – with an early Consistent with a possible role of Vg1RBP/Vera in cell expression in the oocyte and in the zygote (for review movement, the cells were correctly determined but see Nielsen et al. 2001, Yaniv & Yisraeli 2002), followed simply remained at their site of origin. IMP1 deficient by an increase in the expression of all three IMPs from mice are on average 40% smaller than normal sex- mouse embryonic day 10.5–12.5(Nielsen et al. 1999, matched littermates and exhibit a significant perinatal Runge et al. 2000). mortality and imperfect development of the gut. Global At midgestation IMPs are expressed in most devel- expression profiling of the postnatal intestine showed a oping cells, and particularly high concentrations are reduced expression of transcripts encoding extracellu- found in neuronal and epithelial cells. Imp1 and Imp3 lar matrix components (Hansen et al. 2004). Mice mRNAs are mainly expressed in fore- and hindbrain, in overexpressing IMP1 in mammary epithelial cells the snout, the branchial arches, the gut, the tail, the develop mammary tumors (Tessier et al. 2004), showing vertebrae, and in skin (Mueller-Pillasch et al. 1999, Mori that IMPs may play a causal role in cancer. Of interest to et al. 2001, Hansen et al. 2004). A similar pattern is the putative role of IMP2 in diabetes, overexpression of also observed in Xenopus, zebrafish, and Drosophila IMP3/K homology domain containing protein over- (Mueller-Pillasch et al. 1999, Zhang et al. 1999b, Nielsen expressed in cancer (KOC) using the metallothionin et al. 2000, Adolph et al. 2009). Towards the end of promoter was found to induce acinar-ductal metaplasia embryogenesis, Imp3 mRNA expression has essentially (Wagner et al. 2003). Moreover, loss-of-function analysis disappeared, whereas sustained IMP1 expression is indicatesthatVg1RBP/Veraisrequiredforthe observed in small and large intestine, kidney, and liver. establishment of pancreatic fate within the endoderm During embryogenesis, the expression of IMP2 (Spagnoli & Brivanlou 2006). resembles that of IMP1 and IMP3 (Hansen, Hammer, Christiansen & Nielsen, 2005, unpublished; Fig. 2B). At E17.5, IMP2 staining remains significant in the brain – including the neopallial cortex, ventricular zone, and IMP2 in T2D the striatum – in the nasal cavity, lung, liver, intestine, and in the kidney. Moreover, IMP2 mRNA has been An association between IMP2 and T2D was recently detected in several organs during the perinatal period inferred from a series of GWA studies (Saxena et al. and in adult tissues, such as brain, gut, bone marrow, 2007, Scott et al. 2007, The Welcome Trust Control kidney, lung, muscle, liver, testis, and pancreas, in Consortium 2007; Table 1), demonstrating that SNPs mouse or human (Gu et al. 2004, Hammer et al. 2005, mainly located in the second intron of IMP2 provided Hansen et al. unpublished). Taken together, it may be a moderately increased risk of developing T2D. concluded that IMP2 expression is largely overlapping Subsequent replication studies in different populations

Table 1 Primary type 2 diabetes genome-wide associations (GWAs) where an association to insulin-like growth factor 2 mRNA-binding protein 2 (IMP2) was found

Cases (n) Controls (n) Population

Genome-wide association studies with association to IMP2 Welcome Trust Case Control Consortium (2007) 1924 2938 UK Saxena et al. (2007) 1464 1467 Scandinavian Scott et al. (2007) 1161 1174 Finland (FUSION)

Journal of Molecular Endocrinology (2009) 43, 187–195 www.endocrinology-journals.org

Downloaded from Bioscientifica.com at 09/29/2021 10:57:14AM via free access IMP2 and type 2 diabetes . J CHRISTIANSEN and others 191 and meta-analyses have further supported the finding IMP2 plays in T2D. Intron 2 harboring the majority of (Grarup et al. 2007, Scott et al. 2007, Zeggini et al. 2007, the significant SNPs spans about 125 kb, and it is not Groenewoud et al. 2008, Herder et al. 2008, Hertel et al. obvious how the variants should affect splicing or 2008, van Hoek et al. 2008, Horikawa et al. 2008, otherwise regulate expression. Fine mapping and Kirchhoff et al. 2008, Lyssenko et al. 2008, Ng et al. 2008, re-sequencing are necessary to uncover additional Omori et al. 2008, Palmer et al. 2008, Sanghera et al. causal IMP2 variants. SNPs could also directly affect or 2008, Tabara et al. 2008, Wu et al. 2008; Table 2). The be linked to nearby variants affecting microRNAs, reported association with the IMP2 locus based on all larger non-coding transcripts, or even antisense studies (OR 1.14 (95% CI 1.10–1.17)), represents a 3% mRNAs transcribed in the large intron 2. Moreover, as difference in allele frequency between the case and it has been pointed out, other genes such as the protein control groups in over 34 000 subjects (Duesing et al. phosphatase 1 regulatory subunit 2 (PPP1R2), mitogen- 2008). It should be recalled that all 10 GWA-identified activated protein kinase (MAP3K13), lipase H (LIPH), risk genes only explain 5% of the inherited risk of T2D diacylglycerol kinase g-1 (DGKG), a-2-HS-glycoprotein (Altshuler et al. 2008). GWA studies mainly identify (AHSG), and the insulin-sensitizing adipokine adipo- common variants and are likely to overlook rare causal nectin (ADIPOQ), which have been implicated in variants (Donnelly 2008), so if the genetic backbone of metabolism and regulation of insulin activity, are T2D, as previously suggested, consists of a few rare and located in proximity to IMP2 (Doria et al. 2008). penetrant variants (for review see Doria et al. 2008), Replication studies have indicated that IMP2 variants these may be overlooked in GWA studies. Finally, it are more likely associated with reduced b-cell function should be mentioned that a number of studies failed to (Grarup et al. 2007, Horikoshi et al. 2007, Groenewoud demonstrate any association to IMP2 (Table 3 with et al. 2008, Lyssenko et al. 2008, Palmer et al. 2008) references), but in some cases this may simply reflect than with reduced insulin sensitivity or fasting glucose their limited power. levels (Ruchat et al. 2008), but we are still awaiting a We also need to consider if the reported SNP detailed analysis of the expression of IMP2 protein in association is causally related to IMP2 and which role adult human pancreas. Microarray data from the

Table 2 Replication studies of type 2 diabetes (T2D) where an association to insulin-like growth factor 2 mRNA-binding protein 2 (IMP2) is found

Cases (n) Controls (n) Population

Replication studies with association to IMP2 Scott et al. (2007) 1215 1258 Finland Zeggini et al. (2007) 14 586 17 968 WTCC, DGI, FUSION, UKT2DGC, EFSOCH Grarup et al. (2007) 4089 5043 Danish Kirchhoff et al. (2008) 1065 Germanya Omori et al. (2008) 1630 1064 Japan Palmer et al. (2008) 1268C581 HispanicCAfrican–Americanb Groenewoud et al. (2008) 126c 146d The NetherlandsCGermany Wu et al. (2008) 424e 1908g Chinese Han 878f Sanghera et al. (2008) 532 386 Khatri Sikh van Hoek et al. (2008) 6544h The Netherlands Horikawa et al. (2008) 1921 1622 Japan Ng et al. (2008) 3041 3678 Asian Herder et al. (2008)i 433 1438 Germany Tabara et al. (2008) 506 402 Japan Lyssenko et al. (2008) 2201 16 630 SwedenCFinland Hertel et al. (2008)j 1638 1858 Norway aPersons with increased T2D risk. brs4402960 is only associated to decreased disposition index in Hispanics. cImpaired glucose tolerance. dNormal glucose tolerance. eT2D. fIncreased fasting glucose. gNormal fasting glucose. hPopulation-based study. iNon-signifcant after Bonferroni correction. jBorderline significant. www.endocrinology-journals.org Journal of Molecular Endocrinology (2009) 43, 187–195

Downloaded from Bioscientifica.com at 09/29/2021 10:57:14AM via free access 192 J CHRISTIANSEN and others . IMP2 and type 2 diabetes

Table 3 Genome-wide associations (GWAs) and replication studies of type 2 diabetes (T2D) where no association to insulin-like growth factor 2 mRNA-binding protein 2 (IMP2) is found

Study type Cases (n) Controls (n) Population

Studies with no association to IMP2 Horikoshi et al. (2007) Replication 864 864 Japan Sladek et al. (2007) GWAs 661 614 France Sladek et al. (2007) Replication 2617 2894 France Steinthorsdottir et al. (2007) GWAs 1399 5275 Iceland Replication 3826 12 562 Europe Steinthorsdottir et al. (2007) Replication 1457 986 Hong Kong Replication 865 1106 West Africa Pascoe et al. (2007) Replication 1276a Europe Takeuchi et al. (2008) Replication 658 474 Japan Moore et al. (2008) Replication 3819b Caucasian, African– American, Hispanic, Asian, American–Indian Duesing et al. (2008) Replication 1455 1638 France Horikoshi et al. (2007) Replication 864 864 Japan Bronstein et al. (2008) Replication 1131 1147 Ashkenazi Jewish Lee et al. (2008) Replication 908 502 Korea Rong et al. (2008) Replication 1561 1940 Pima Indians Lewis et al. (2008) Replication 993 1054 African–American

aHealthy individuals from the RISC cohort. bIndividuals at high risk for T2D.

Diabetes Genome Anatomy Project (DGAP; http:// the intrauterine environment, are believed to play a www.diabetesgenome.org), recently presented by Doria role for the development of T2D. There is presently no et al. showed that IMP2 mRNA is expressed in islets, evidence of major differences in RNA-binding ability and islet IMP2 mRNA expression was not significantly among the IMPs and the functional significance of different among diabetics and normal subjects, so particular protein interactions needs further character- additional studies are needed to define the role ization. However, in contrast to IMP1 and IMP3, IMP2 is of IMP2 in islet function and T2D. Support for a role widely expressed in many adult tissues including the of IMP2 in pancreatic function, as a whole, mainly gut, muscle, and the brain. In these organs, small comes from mouse studies of fetal and adult pancreas quantitative differences in IMP2 expression could have (Mueller-Pillasch et al. 1999, Gu et al. 2004, Hansen et al. a subtle impact on, e.g., food uptake, metabolism, unpublished), and the function of IMP2 in b-cell feeding behavior, or even more complex behavioral function has not been directly addressed. Several of features, which could affect physical activity or the risk the T2D association studies mention that the IMP3 of obesity and thus life-time risk of developing T2D. orthologs Vg1RBP/Vera and IMP3/KOC have been implicated in Xenopus pancreatic development and mouse pancreatic metaplasia respectively (Wagner Concluding remarks et al. 2003, Spagnoli & Brivanlou 2006), but it should be noted that all IMPs are expressed in the developing Although there is compelling evidence for the associ- pancreas, and none of the GWAs provide evidence for ation between SNPs in IMP2 and T2D, we have presently an association with either IMP1 or IMP3. Perhaps, this no molecular mechanism that explains the involvement simply reflects that IMP1 and IMP3 do not contain in T2D. Future studies defining the expression, RNA similar causal variants as IMP2, but further studies are targets and protein interactions of IMP2 in relevant needed to confirm this. tissues, as well as a characterization of the metabolism in T2D is frequently described as a complex disease the IMP2 knock-out mouse may provide additional clues. characterized by reduced insulin sensitivity in muscle, Moreover, resequencing may be necessary to identify fat, and liver, combined with a perturbed pancreatic causal variants in IMP2 and support the direct involve- glucose response and insulin secretion. Both processes ment of IMP2 in T2D. If these analyses are accomplished are influenced by a series of different pathways under with a positive outcome, they may force us to change our control of both environmental and genetic factors (for general picture of T2D and further emphasize the review see Kahn 1994). Among these, physical inactivity, enormous potential of GWA studies in providing new obesity, the gut microbiome and food uptake, and even and fundamental understanding of common diseases.

Journal of Molecular Endocrinology (2009) 43, 187–195 www.endocrinology-journals.org

Downloaded from Bioscientifica.com at 09/29/2021 10:57:14AM via free access IMP2 and type 2 diabetes . J CHRISTIANSEN and others 193

Declaration of interest Groenewoud MJ, Dekker JM, Fritsche A, Reiling E, Nijpels G, Heine RJ, Maassen JA, Machicao F, Schafer SA, Haring HU et al. 2008 Variants The authors declare that there is no conflict of interest that could be of CDKAL1 and IGF2BP2 affect first-phase insulin secretion during perceived as prejudicing the impartiality of the research reported. hyperglycaemic clamps. Diabetologia 51 1659–1663. Gu L, Shigemasa K & Ohama K 2004 Increased expression of IGF II mRNA-binding protein 1 mRNA is associated with an advanced clinical stage and poor prognosis in patients with ovarian cancer. Funding International Journal of Oncology 24 671–678. Hammer NA, Hansen TO, Byskov AG, Rajpert-De Meyts E, Grondahl ML, This research did not receive any specific grant from any funding Bredkjaer HE, Wewer UM, Christiansen J & Nielsen FC 2005 agency in the public, commercial or not-for-profit sector. Expression of IGF-II mRNA-binding proteins (IMPs) in gonads and testicular cancer. Reproduction 130 203–212. Hansen TV, Hammer NA, Nielsen J, Madsen M, Dalbaeck C, Wewer UM, Christiansen J & Nielsen FC 2004 Dwarfism and impaired gut Acknowledgements development in insulin-like growth factor II mRNA-binding protein 1-deficient mice. Molecular and Cellular Biology 24 4448–4464. We would like to thank the Danish Natural Science and Medical Havin L, Git A, Elisha Z, Oberman F, Yaniv K, Schwartz SP, Standart N Research Councils, the Danish Cancer Society and the Lundbeck, & Yisraeli JK 1998 RNA-binding protein conserved in both Toyota and Novo Nordisk Foundations that have supported the microtubule- and microfilament-based RNA localization. Genes and research. Development 12 1593–1598. Herder C, Rathmann W, Strassburger K, Finner H, Grallert H, Huth C, Meisinger C, Gieger C, Martin S, Giani G et al. 2008 Variants of the PPARG, IGF2BP2, CDKAL1, HHEX, and TCF7L2 genes confer risk References of type 2 diabetes independently of BMI in the German KORA studies. Hormone and Metabolic Research 40 722–726. Hertel JK, Johansson S, Raeder H, Midthjell K, Lyssenko V, Groop L, Adolph SK, Delotto R, Nielsen FC & Christiansen J 2009 Embryonic Molven A & Njolstad PR 2008 Genetic analysis of recently identified expression of Drosophila IMP in the developing CNS and PNS. Gene type 2 diabetes loci in 1,638 unselected patients with type 2 diabetes Expression Patterns 9 138–143. and 1,858 control participants from a Norwegian population-based Altshuler D, Daly MJ & Lander ES 2008 Genetic mapping in human cohort (the HUNT study). Diabetologia 51 971–977. disease. Science 322 881–888. Hieronymus H & Silver PA 2004 A systems view of mRNP biology. Genes Atlas R, Behar L, Elliott E & Ginzburg I 2004 The insulin-like growth and Development 18 2845–2860. factor mRNA binding-protein IMP-1 and the Ras-regulatory protein van Hoek M, Dehghan A, Witteman JC, van Duijn CM, Uitterlinden AG, G3BP associate with tau mRNA and HuD protein in differentiated Oostra BA, Hofman A, Sijbrands EJ & Janssens AC 2008 Predicting P19 neuronal cells. Journal of Neurochemistry 89 613–626. type 2 diabetes based on polymorphisms from genome-wide Boylan KL, Mische S, Li M, Marques G, Morin X, Chia W & Hays TS association studies: a population-based study. Diabetes 57 2008 Motility screen identifies Drosophila IGF-II mRNA-binding 3122–3128. protein–zipcode-binding protein acting in oogenesis and synapto- genesis. PLoS Genetics 4 e36. Horikawa Y, Miyake K, Yasuda K, Enya M, Hirota Y, Yamagata K, Bronstein M, Pisante A, Yakir B & Darvasi A 2008 Type 2 diabetes Hinokio Y, Oka Y, Iwasaki N, Iwamoto Y et al. 2008 Replication susceptibility loci in the Ashkenazi Jewish population. Human of genome-wide association studies of type 2 diabetes susceptibility Genetics 124 101–104. in Japan. Journal of Clinical Endocrinology and Metabolism 93 Deshler JO, Highett MI, Abramson T & Schnapp BJ 1998 A highly 3136–3141. conserved RNA-binding protein for cytoplasmic mRNA localization Horikoshi M, Hara K, Ito C, Shojima N, Nagai R, Ueki K, Froguel P & in vertebrates. Current Biology 8 489–496. Kadowaki T 2007 Variations in the HHEX gene are associated with Donnelly P 2008 Progress and challenges in genome-wide association increased risk of type 2 diabetes in the Japanese population. studies in humans. Nature 456 728–731. Diabetologia 50 2461–2466. Doria A, Patti ME & Kahn CR 2008 The emerging genetic architecture Jensen KB, Musunuru K, Lewis HA, Burley SK & Darnell RB 2000 of type 2 diabetes. Cell Metabolism 8 186–200. The tetranucleotide UCAY directs the specific recognition of RNA Doyle GA, Betz NA, Leeds PF, Fleisig AJ, Prokipcak RD & Ross J 1998 by the Nova K-homology 3 domain. PNAS 97 5740–5745. The c-myc coding region determinant-binding protein: a member Jønson L, Vikesaa J, Krogh A, Nielsen LK, Hansen T, Borup R, of a family of KH domain RNA-binding proteins. Nucleic Acids Johnsen AH, Christiansen J & Nielsen FC 2007 Molecular Research 26 5036–5044. composition of IMP1 ribonucleoprotein granules. Molecular and Duesing K, Fatemifar G, Charpentier G, Marre M, Tichet J, Hercberg S, Cellular Proteomics 6 798–811. Balkau B, Froguel P & Gibson F 2008 Evaluation of the association of Kahn CR 1994 Banting Lecture. Insulin action, diabetogenes, and the IGF2BP2 variants with type 2 diabetes in French Caucasians. Diabetes cause of type II diabetes. Diabetes 43 1066–1084. 57 1992–1996. Keene JD & Tenenbaum SA 2002 Eukaryotic mRNPs may represent Farina KL, Huttelmaier S, Musunuru K, Darnell R & Singer RH 2003 posttranscriptional operons. Molecular Cell 9 1161–1167. Two ZBP1 KH domains facilitate beta-actin mRNA localization, Kirchhoff K, Machicao F, Haupt A, Schafer SA, Tschritter O, Staiger H, granule formation, and cytoskeletal attachment. Journal of Cell Stefan N, Haring HU & Fritsche A 2008 Polymorphisms in the Biology 160 77–87. TCF7L2, CDKAL1 and SLC30A8 genes are associated with impaired Git A & Standart N 2002 The KH domains of Xenopus Vg1RBP mediate proinsulin conversion. Diabetologia 51 597–601. RNA binding and self-association. RNA 8 1319–1333. Lee YH, Kang ES, Kim SH, Han SJ, Kim CH, Kim HJ, Ahn CW, Cha BS, Grarup N, Rose CS, Andersson EA, Andersen G, Nielsen AL, Nam M, Nam CM et al. 2008 Association between polymorphisms in Albrechtsen A, Clausen JO, Rasmussen SS, Jorgensen T, Sandbaek A SLC30A8, HHEX, CDKN2A/B, IGF2BP2, FTO, WFS1, CDKAL1, et al. 2007 Studies of association of variants near the HHEX, KCNQ1 and type 2 diabetes in the Korean population. Journal of CDKN2A/B, and IGF2BP2 genes with type 2 diabetes and impaired Human Genetics 53 991–998. insulin release in 10,705 Danish subjects: validation and extension Lewis JP, Palmer ND, Hicks PJ, Sale MM, Langefeld CD, Freedman BI, of genome-wide association studies. Diabetes 56 3105–3111. Divers J & Bowden DW 2008 Association analysis in african www.endocrinology-journals.org Journal of Molecular Endocrinology (2009) 43, 187–195

Downloaded from Bioscientifica.com at 09/29/2021 10:57:14AM via free access 194 J CHRISTIANSEN and others . IMP2 and type 2 diabetes

americans of European-derived type 2 diabetes single nucleotide Common variants of the novel type 2 diabetes genes CDKAL1 and polymorphisms from whole-genome association studies. Diabetes 57 HHEX/IDE are associated with decreased pancreatic beta-cell 2220–2225. function. Diabetes 56 3101–3104. Lyssenko V, Jonsson A, Almgren P, Pulizzi N, Isomaa B, Tuomi T, Patel GP & Bag J 2006 IMP1 interacts with poly(A)-binding protein Berglund G, Altshuler D, Nilsson P & Groop L 2008 Clinical risk (PABP) and the autoregulatory translational control element of factors, DNA variants, and the development of type 2 diabetes. PABP-mRNA through the KH III–IV domain. FEBS Journal 273 New England Journal of Medicine 359 2220–2232. 5678–5690. Maquat LE 2004 Nonsense-mediated mRNA decay: splicing, Rackham O & Brown CM 2004 Visualization of RNA–protein translation and mRNP dynamics. Nature Reviews. Molecular Cell interactions in living cells: FMRP and IMP1 interact on mRNAs. Biology 5 89–99. EMBO Journal 23 3346–3355. Moore M 2005 From birth to death: the complex lives of eukaryotic Rong R, Hanson RL, Ortiz D, Wiedrich C, Kobes S, Knowler WC, mRNAs. Science 309 1514–1518. Bogardus C & Baier LJ 2008 Association analysis of variation Moore AF, Jablonski KA, McAteer JB, Saxena R, Pollin TI, Franks PW, in/near FTO, CDKAL1, SLC30A8, HHEX, EXT2, IGF2BP2, Hanson RL, Shuldiner AR, Knowler WC, Altshuler D et al. 2008 LOC387761 and CDKN2B with type 2 diabetes and related Extension of type 2 diabetes genome-wide association scan results in quantitative traits in Pima Indians. Diabetes 58 478–488. the diabetes prevention program. Diabetes 57 2503–2510. Ruchat SM, Elks CE, Loos RJ, Vohl MC, Weisnagel SJ, Rankinen T, Moraes KC, Quaresma AJ, Maehnss K & Kobarg J 2003 Identification Bouchard C & Perusse L 2008 Association between insulin and characterization of proteins that selectively interact with secretion, insulin sensitivity and type 2 diabetes susceptibility isoforms of the mRNA binding protein AUF1 (hnRNP D). Biological variants identified in genome-wide association studies. Acta Chemistry 384 25–37. Diabetologia 46 217–226. Mori H, Sakakibara S, Imai T, Nakamura Y, Iijima T, Suzuki A, Yuasa Y, Runge S, Nielsen FC, Nielsen J, Lykke-Andersen J, Wewer UM & Takeda M & Okano H 2001 Expression of mouse igf2 mRNA- Christiansen J 2000 H19 RNA binds four molecules of insulin-like binding protein 3 and its implications for the developing central growth factor II mRNA-binding protein. Journal of Biological nervous system. Journal of Neuroscience Research 64 132–143. Chemistry 275 29562–29569. Mueller-Pillasch F, Pohl B, Wilda M, Lacher U, Beil M, Wallrapp C, Sanghera DK, Ortega L, Han S, Singh J, Ralhan SK, Wander GS, Hameister H, Knochel W, Adler G & Gress TM 1999 Expression of Mehra NK, Mulvihill JJ, Ferrell RE, Nath SK et al. 2008 Impact of the highly conserved RNA binding protein KOC in embryogenesis. nine common type 2 diabetes risk polymorphisms in Asian Indian Mechanisms of Development 88 95–99. Sikhs: PPARG2 (Pro12Ala), IGF2BP2, TCF7L2 and FTO variants Ng MC, Park KS, Oh B, Tam CH, Cho YM, Shin HD, Lam VK, Ma RC, So confer a significant risk. BMC Medical Genetics 9 59. WY, Cho YS et al. 2008 Implication of genetic variants near TCF7L2, Saxena R, Voight BF, Lyssenko V, Burtt NP, de Bakker PI, Chen H, SLC30A8, HHEX, CDKAL1, CDKN2A/B, IGF2BP2, and FTO in type Roix JJ, Kathiresan S, Hirschhorn JN, Daly MJ et al. 2007 Genome- 2 diabetes and obesity in 6,719 Asians. Diabetes 57 2226–2233. wide association analysis identifies loci for type 2 diabetes and Nielsen J, Christiansen J, Lykke-Andersen J, Johnsen AH, Wewer UM & triglyceride levels. Science 316 1331–1336. Nielsen FC 1999 A family of insulin-like growth factor II mRNA- Scott LJ, Mohlke KL, Bonnycastle LL, Willer CJ, Li Y, Duren WL, binding proteins represses translation in late development. Erdos MR, Stringham HM, Chines PS, Jackson AU et al. 2007 Molecular and Cellular Biology 19 1262–1270. A genome-wide association study of type 2 diabetes in Finns detects Nielsen J, Cilius Nielsen FC, Kragh Jakobsen R & Christiansen J 2000 multiple susceptibility variants. Science 316 1341–1345. The biphasic expression of IMP/Vg1-RBP is conserved between Sladek R, Rocheleau G, Rung J, Dina C, Shen L, Serre D, Boutin P, vertebrates and Drosophila. Mechanisms of Development 96 129–132. Vincent D, Belisle A, Hadjadj S et al. 2007 A genome-wide Nielsen FC, Nielsen J & Christiansen J 2001 A family of IGF-II mRNA association study identifies novel risk loci for type 2 diabetes. Nature binding proteins (IMP) involved in RNA trafficking. Scandinavian 445 881–885. Journal of Clinical and Laboratory Investigation 234 93–99. Spagnoli FM & Brivanlou AH 2006 The RNA-binding protein, Vg1RBP, Nielsen FC, Nielsen J, Kristensen MA, Koch G & Christiansen J 2002 is required for pancreatic fate specification. Developmental Biology Cytoplasmic trafficking of IGF-II mRNA-binding protein by 292 442–456. conserved KH domains. Journal of Cell Science 115 2087–2097. Steinthorsdottir V, Thorleifsson G, Reynisdottir I, Benediktsson R, Nielsen J, Adolph SK, Rajpert-De Meyts E, Lykke-Andersen J, Koch G, Jonsdottir T, Walters GB, Styrkarsdottir U, Gretarsdottir S, Christiansen J & Nielsen FC 2003 Nuclear transit of human zipcode- Emilsson V, Ghosh S et al. 2007 A variant in CDKAL1 influences binding protein IMP1. Biochemical Journal 376 383–391. insulin response and risk of type 2 diabetes. Nature Genetics 39 Nielsen J, Kristensen MA, Willemoes M, Nielsen FC & Christiansen J 770–775. 2004 Sequential dimerization of human zipcode-binding protein Sundstrom G, Larsson TA & Larhammar D 2008 Phylogenetic and IMP1 on RNA: a cooperative mechanism providing RNP stability. chromosomal analyses of multiple gene families syntenic with Nucleic Acids Research 32 4368–4376. vertebrate Hox clusters. BMC Evolutionary Biology 8 254. Oleynikov Y & Singer RH 2003 Real-time visualization of ZBP1 Tabara Y, Osawa H, Kawamoto R, Onuma H, Shimizu I, Miki T, Kohara K association with beta-actin mRNA during transcription and & Makino H 2008 Replication study of candidate genes associated localization. Current Biology 13 199–207. with type 2 diabetes based on genome-wide screening. Diabetes 58 Omori S, Tanaka Y, Takahashi A, Hirose H, Kashiwagi A, Kaku K, 493–498. Kawamori R, Nakamura Y & Maeda S 2008 Association of CDKAL1, Takeuchi F, Ochiai Y, Serizawa M, Yanai K, Kuzuya N, Kajio H, Honjo S, IGF2BP2, CDKN2A/B, HHEX, SLC30A8, and KCNJ11 with Takeda N, Kaburagi Y, Yasuda K et al. 2008 Search for type 2 diabetes susceptibility to type 2 diabetes in a Japanese population. Diabetes 57 susceptibility genes on chromosomes 1q, 3q and 12q. Journal of 791–795. Human Genetics 53 314–324. Palmer ND, Goodarzi MO, Langefeld CD, Ziegler J, Norris JM, Tessier CR, Doyle GA, Clark BA, Pitot HC & Ross J 2004 Mammary Haffner SM, Bryer-Ash M, Bergman RN, Wagenknecht LE, Taylor tumor induction in transgenic mice expressing an RNA-binding KD et al. 2008 Quantitative trait analysis of type 2 diabetes protein. Cancer Research 64 209–214. susceptibility loci identified from whole genome association studies Tiruchinapalli DM, Oleynikov Y, Kelic S, Shenoy SM, Hartley A, in the Insulin Resistance Atherosclerosis Family Study. Diabetes 57 Stanton PK, Singer RH & Bassell GJ 2003 Activity-dependent 1093–1100. trafficking and dynamic localization of zipcode binding protein Pascoe L, Tura A, Patel SK, Ibrahim IM, Ferrannini E, Zeggini E, 1 and beta-actin mRNA in dendrites and spines of hippocampal Weedon MN, Mari A, Hattersley AT, McCarthy MI et al. 2007 neurons. Journal of Neuroscience 23 3251–3261.

Journal of Molecular Endocrinology (2009) 43, 187–195 www.endocrinology-journals.org

Downloaded from Bioscientifica.com at 09/29/2021 10:57:14AM via free access IMP2 and type 2 diabetes . J CHRISTIANSEN and others 195

Vikesaa J, Hansen TV, Jonson L, Borup R, Wewer UM, Christiansen J Yisraeli JK 2005 VICKZ proteins: a multi-talented family of regulatory & Nielsen FC 2006 RNA-binding IMPs promote cell adhesion and RNA-binding proteins. Biologie Cellulaire 97 87–96. invadopodia formation. EMBO Journal 25 1456–1468. Zeggini E, Weedon MN, Lindgren CM, Frayling TM, Elliott KS, Wagner M, Kunsch S, Duerschmied D, Beil M, Adler G, Mueller F Lango H, Timpson NJ, Perry JR, Rayner NW, Freathy RM et al. & Gress TM 2003 Transgenic overexpression of the oncofetal 2007 Replication of genome-wide association signals in UK RNA binding protein KOC leads to remodeling of the exocrine samples reveals risk loci for type 2 diabetes. Science 316 pancreas. Gastroenterology 124 1901–1914. 1336–1341. Wang T, Fan L, Watanabe Y, McNeill PD, Moulton GG, Bangur C, Zhang JY, Chan EK, Peng XX & Tan EM 1999a A novel cytoplasmic Fanger GR, Okada M, Inoue Y, Persing DH et al. 2003 L523S, an protein with RNA-binding motifs is an autoantigen in human RNA-binding protein as a potential therapeutic target for lung hepatocellular carcinoma. Journal of Experimental Medicine 189 cancer. British Journal of Cancer 88 887–894. 1101–1110. Welcome Trust Case Control Consortium 2007 Genome-wide associ- Zhang Q, Yaniv K, Oberman F, Wolke U, Git A, Fromer M, Taylor WL, ation study of 14,000 cases of seven common diseases and 3,000 Meyer D, Standart N, Raz E et al. 1999b Vg1 RBP intracellular shared controls. Nature 447 661–678. distribution and evolutionarily conserved expression at multiple Wu Y, Li H, Loos RJ, Yu Z, Ye X, Chen L, Pan A, Hu FB & Lin X 2008 stages during development. Mechanisms of Development 88 Common variants in CDKAL1, CDKN2A/B, IGF2BP2, SLC30A8, 101–106. and HHEX/IDE genes are associated with type 2 diabetes and Zhang HL, Eom T, Oleynikov Y, Shenoy SM, Liebelt DA, Dictenberg JB, impaired fasting glucose in a Chinese Han population. Diabetes 57 Singer RH & Bassell GJ 2001 Neurotrophin-induced transport of a 2834–2842. beta-actin mRNP complex increases beta-actin levels and stimulates Yaniv K & Yisraeli JK 2002 The involvement of a conserved family of growth cone motility. Neuron 31 261–275. RNA binding proteins in embryonic development and carcino- genesis. Gene 287 49–54. Yaniv K, Fainsod A, Kalcheim C & Yisraeli JK 2003 The RNA-binding Received in final form 4 May 2009 protein Vg1 RBP is required for cell migration during early neural Accepted 8 May 2009 development. Development 130 5649–5661. Made available online as an Accepted Preprint 8 May 2009

www.endocrinology-journals.org Journal of Molecular Endocrinology (2009) 43, 187–195

Downloaded from Bioscientifica.com at 09/29/2021 10:57:14AM via free access