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Disruption in Iron Homeostasis and Impaired Activity Jain et al. Cell Biosci (2020) 10:105 https://doi.org/10.1186/s13578-020-00468-2 Cell & Bioscience RESEARCH Open Access Disruption in iron homeostasis and impaired activity of iron-sulfur cluster containing proteins in the yeast model of Shwachman-Diamond syndrome Ayushi Jain1, Phubed Nilatawong1,2, Narinrat Mamak3, Laran T. Jensen4 and Amornrat Naranuntarat Jensen1,5,6* Abstract Background: Shwachman-Diamond syndrome (SDS) is a congenital disease that afects the bone marrow, skeletal system, and pancreas. The majority of patients with SDS have mutations in the SBDS gene, involved in ribosome bio- genesis as well as other processes. A Saccharomyces cerevisiae model of SDS, lacking Sdo1p the yeast orthologue of SBDS, was utilized to better understand the molecular pathogenesis in the development of this disease. Results: Deletion of SDO1 resulted in a three-fold over-accumulation of intracellular iron. Phenotypes associated with impaired iron-sulfur (ISC) assembly, up-regulation of the high afnity iron uptake pathway, and reduced activi- ties of ISC containing enzymes aconitase and succinate dehydrogenase, were observed in sdo1∆ yeast. In cells lacking Sdo1p, elevated levels of reactive oxygen species (ROS) and protein oxidation were reduced with iron chelation, using a cell impermeable iron chelator. In addition, the low activity of manganese superoxide dismutase (Sod2p) seen in sdo1∆ cells was improved with iron chelation, consistent with the presence of reactive iron from the ISC assembly pathway. In yeast lacking Sdo1p, the mitochondrial voltage-dependent anion channel (VDAC) Por1p is over- expressed and its deletion limits iron accumulation and increases activity of aconitase and succinate dehydrogenase. Conclusions: We propose that oxidative stress from POR1 over-expression, resulting in impaired activity of ISC con- taining proteins and disruptions in iron homeostasis, may play a role in disease pathogenesis in SDS patients. Keywords: Shwachman-diamond syndrome, Iron overload, Yeast, Iron sulfur cluster, POR1 overexpression Background dysfunction, skeletal abnormalities, and have a high risk Shwachman-Diamond syndrome (SDS) is an autoso- of malignant transformation [6–11]. Even though SDS is mal recessive disorder characterized as a ribosomopathy a rare genetic disorder, it is a common cause of inherited [1–4]. Defects in ribosome biogenesis, due to mutations exocrine pancreatic dysfunction and bone marrow failure in ribosomal proteins and assembly factors, can lead to a [12–15]. wide range of clinical phenotypes [5]. Patients with SDS Te majority of SDS patients have loss of function sufer from bone marrow failure, exocrine pancreatic mutations in SBDS (SDS1, OMIM #260400) [16]. Te best characterized function of SBDS is its role in the release *Correspondence: [email protected] and recycling of eIF6 from pre-60S ribosomes, a process 1 Department of Pathobiology, Faculty of Science, Mahidol University, 272 that also involves the GTPase activity of Elongation Fac- Rama 6 Road, Bangkok 10400, Thailand tor-Like 1 (EFL1) (SDS2, OMIM # 617941) [17–20]. Te Full list of author information is available at the end of the article © The Author(s) 2020. This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creat iveco mmons .org/licen ses/by/4.0/. The Creative Commons Public Domain Dedication waiver (http://creat iveco mmons .org/publi cdoma in/ zero/1.0/) applies to the data made available in this article, unless otherwise stated in a credit line to the data. Jain et al. Cell Biosci (2020) 10:105 Page 2 of 12 release of eIF6 is a required step in the maturation of the rescuing low activity of Sod2p. However, impaired activ- 60S ribosomal subunit [1, 3, 21, 22]. Reduced formation ity of ISC enzymes in sdo1∆ cells was not restored with of mature 60S ribosome subunits results in impaired pro- iron chelation. Deletion of POR1 is known to alleviate tein translation in cells with SDS defciency [3, 23, 24]. stress sensitivity in sdo1∆ cells [32] and we report that SBDS physically interacts with EFL1 and mutations in iron accumulation is also reduced in por1∆ sdo1∆ yeast. EFL1 are also associated with SDS [17–20]. Interestingly, In addition, activity of ISC enzymes in sdo1∆ cells was several SBDS missense mutations reduce binding afn- improved by prior deletion of POR1. Our results indicate ity with EFL1 [18]. In addition, clinical features similar that loss of Sdo1p is linked to disruptions in ISC biogen- to SDS have been reported for mutations in DnaJ Heat esis, mediated by over-expression POR1, that potentially Shock Protein Family (Hsp40) Member C21 (DNAJC21, promotes subsequent iron over-accumulation. OMIM # 617052), a protein that may act as a co-chaper- one for HSP70 [25, 26] and the Signal Recognition Parti- Results cle 54 (SRP54, OMIM # 618752), that binds to the signal Cells defcient for Sdo1p display elevated iron content sequence of presecretory proteins when they emerge Our previous studies reported elevated oxidative stress from the ribosomes and directs them to the translocon as well as reduced levels and activity of manganese- on the endoplasmic reticulum membrane [27, 28]. containing superoxide dismutase 2 (Sod2p) in yeast SBDS is a multi-functional protein and SBDS muta- cells lacking Sdo1p [32, 39]. Iron released from the ISC tions impact processes beyond ribosome biogenesis. biogenesis pathway is highly reactive and can inactivate Additional proposed functions for SBDS include rRNA Sod2p through competition with manganese binding to processing [22, 29, 30], cellular stress responses [31, 32], this enzyme [40, 41]. We therefore investigated whether and lysosome function [33]. Cells depleted for SBDS also iron homeostasis is altered in sdo1∆ yeast. Cells lacking appear to be under a chronic state of stress [34–36] and Sdo1p accumulated three-fold higher levels of iron com- are sensitized to agents that impair endoplasmic reticu- pared to wild-type yeast (Fig. 1a), similar to that seen for lum (ER) function and conditions that promote DNA several yeast mutants with defects in ISC biogenesis [42– damage [31]. Mammalian cells defcient for SBDS and 47]. Te elevated iron content of sdo1∆ cells does not yeast cells lacking Sdo1p, the orthologue of SBDS, also appear to be associated with loss of mitochondrial DNA display sensitivity to oxidative and osmotic stress [32, (mtDNA), as iron content in a rho0 strain lacking mtDNA 37]. Yeast deleted for SDO1 exhibit mitochondrial dys- was similar to WT yeast (Fig. 1a). function, instability of mtDNA, and decreased activity of Reduced translational efciency observed in sdo1∆ mitochondrial manganese superoxide dismutase (Sod2p) cells [1, 2], was not associated with iron over-accumula- [32, 38, 39]. Stress sensitivity and mitochondrial dysfunc- tion. Yeast mutants that exhibit reduced polysome num- tion in cells defcient for SBDS/Sdo1p appears to be sepa- bers: dbp3∆, dbp7∆, dom34∆ and yar1∆ [48–51] did not rate from attenuated protein translation [31, 32, 39]. exhibited increased iron content relative to WT cells Even with better understanding of the functions of (Fig. 1b). Similarly, limiting protein synthesis in WT cells SBDS/Sdo1p, the molecular mechanisms of how muta- using cycloheximide did not result in elevated iron accu- tions in SBDS impact disease progression remains mulation (Fig. 1c). Tese results indicate that iron over- unclear. Current treatments for SDS patients do not tar- accumulation in cells lacking Sdo1p is not directly linked get the underlying cause of the disease and instead are to the reduced translational efciency. aimed at alleviating symptoms of this disorder. Elucida- tion of the key steps in the cellular pathogenesis of SDS Depletion of iron improves the activity should enable the development of therapies capable of of manganese‑superoxide dismutase Sod2p and reduces targeting defciencies leading to the disease state. oxidative stress in cells lacking Sdo1p Using a Saccharomyces cerevisiae model of SDS, We speculated that iron over-accumulation may con- we examined potential causes of cellular stress from tribute to the lowered levels of Sod2p activity in sdo1∆ impaired Sdo1p function. Oxidative damage and inacti- cells. Treatment with the cell impermeable iron che- vation of Sod2p in sdo1∆ cells previously described [39] lator, bathophenanthroline disulfonic acid (BPS), sig- were similar to efects seen in yeast mutants that over- nifcantly reduced iron content of sdo1∆ cells (Fig. 2a), accumulate intracellular iron due to defects in iron sulfur without altering growth rates (Fig. 2b). As seen in Fig. 2c, cluster (ISC) biogenesis [40, 41]. Examination of cellular d, Sod2p activity was increased in iron depleted sdo1∆ iron content demonstrated that sdo1∆ cells accumulate cells, suggesting that the excess iron in sdo1∆ can bind three-fold more iron compared to wild-type yeast. Lim- and inactivate Sod2p. However, following iron depletion iting iron accumulation in sdo1∆ cells reduced oxidative the abundance of Sod2p protein in sdo1∆ yeast remained damage and environmental stress sensitivity as well as low compared to WT cells (Fig. 2c and e). Tis indicates Jain et al. Cell Biosci (2020) 10:105 Page 3 of 12 content was limited by growth with BPS; however, ROS production remained elevated compared to cells with intact Sdo1p (Fig. 3a). Protein oxidation from H2O2 exposure was also signifcantly decreased in cells lack- ing Sdo1p when intracellular iron was depleted (Fig.
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