| 1. |
- Billing, Ola, 1981-, et al.
(author)
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A directed RNAi screen based on larval growth arrest reveals new modifiers of C. elegans insulin signaling
- 2012
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In: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:4, s. e34507-
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Journal article (peer-reviewed)abstract
- Genes regulating Caenorhabditis elegans insulin/IGF signaling (IIS) have largely been identified on the basis of their involvement in dauer development or longevity. A third IIS phenotype is the first larval stage (L1) diapause, which is also influenced by asna-1, a regulator of DAF-28/insulin secretion. We reasoned that new regulators of IIS strength might be identified in screens based on the L1 diapause and the asna-1 phenotype. Eighty-six genes were selected for analysis by virtue of their predicted interaction with ASNA-1 and screened for asna-1-like larval arrest. ykt-6, mrps-2, mrps-10 and mrpl-43 were identified as genes which, when inactivated, caused larval arrest without any associated feeding defects. Several tests indicated that IIS strength was weaker and that insulin secretion was defective in these animals. This study highlights the role of the Golgi network and the mitochondria in insulin secretion and provides a new list of genes that modulate IIS in C. elegans.
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| 2. |
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| 3. |
- Billing, Ola, 1981-
(author)
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Insulin secretion and ASNA-1-dependent function of the endoplasmic reticulum in C. elegans
- 2014
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Doctoral thesis (other academic/artistic)abstract
- ASNA1 is a well-conserved ATPase involved in a wide range of functions, including cisplatin resistance, growth control, insulin secretion and targeting of tail-anchored (TA) proteins to membranes. It is a positive regulator of insulin secretion both in the roundworm Caenorhabditis elegans and in humans. Insulin secretion and downstream insulin/IGF signalling (IIS) stands at the heart of many human pathologies, such as diabetes, Alzheimer’s disease and cancer. A better understanding of IIS may therefore prove vital for treatment and cure of these diseases. This thesis aims to further investigate the function of asna-1, and to identify new regulators of IIS based on the asna-1 phenotype in C. elegans.Worms lacking ASNA-1 arrest growth in the first larval stage, L1, with reduced insulin secretion. The L1 arrest represents the strongest of the IIS phenotypes in worms. Most regulators of the insulin pathway have been identified in screens for other IIS phenotypes, influencing lifespan or the dauer diapause. Therefore, new regulators could be found by screening for genes which, when inactivated, cause an asna-1-like L1 arrest. Using bioinformatic approaches, a set of 143 putative asna-1 interactors were identified, based on their predicted or confirmed interaction with asna-1 in various organisms. Depletion of the Golgi SNARE homologue YKT-6 or the mitochondrial translocase homologue TOMM-40 caused asna-1-like larval arrests. Using several criteria, including genetic suppression by daf-16/Foxo, it was established that YKT-6 and TOMM-40 are positive regulators of IIS. Both proteins were also required for normal DAF-28/insulin secretion.Further investigation of TOMM-40 identified it as a ubiquitously expressed mitochondrial translocase in C. elegans: It localized to mitochondrial membranes and was required for importing a tagged mitochondrial reporter across mitochondrial membranes. Depletion of TOMM-40 caused a collapse of the proton gradient across the inner mitochondrial membrane and triggered the mitochondrial unfolded protein response (UPR). Worms with defective mitochondria failed to grow normally in presence of food, but this growth defect was suppressed by daf-16(mgDf50). In addition, tomm-40(RNAi) led to DAF-16/FOXO activation, an effect that was suppressed by over expression of DAF-28/insulin. Taken together, these findings support a model whereby signals of food availability are conveyed through respiring mitochondria to promote DAF-28/insulin secretion, which in turn promotes growth.Biochemical studies have identified ASNA-1 as a chaperone that targets a subset of newly synthesized TA proteins to a receptor at the endoplasmic reticulum (ER) membrane. However, these findings have not been tested in vivo in a metazoan model. A reporter-based system to analyse TA protein targeting into the ER in live animals using confocal microscopy was set up. A model asna-1-dependent TA protein, Y38F2AR.9/SEC-61β, required functional ASNA-1 for correct targeting to the ER. Conversely, a model asna-1-independent TA protein, CYTB5.1/cytochrome B5, did not. This phenotype was shared with the predicted asna-1 receptor homologue, wrb-1. Consistently, WRB-1 was found to localize to the ER. However, other wrb-1 mutant phenotypes only partially overlap with those of asna-1 mutants, suggesting that ASNA-1 is either partially independent of WRB-1 for TA protein targeting or that ASNA-1 has additional functions besides its role in TA protein targeting.Confocal microscopy also indicated that the ER morphology was aberrant in asna-1 and wrb-1 mutants. ER UPR was elevated in the asna-1 mutants, as indicated by the upregulation of an hsp-4/BiP reporter. Transmission and immuno-electron microscopy of these mutants revealed a swollen ER lumen, which is another hallmark of ER stress. High levels of autophagy in asna-1 animals and the presence of ER-containing autophagosomes in both asna-1 and wrb-1 mutants indicated a stress-induced remodelling of the ER membrane in these two mutants. In addition, both mutants had normal mitochondrial morphology, but showed severe effects on Golgi compartment morphology. Hypothetically, all these phenotypes could be due to defects in the signal recognition particle (SRP) pathway. This is because Y38F2AR.9/SEC-61β is both a TA protein and a component of the SEC-61 translocon. However, both Golgi and ER morphology was normal in Y38F2AR.9/sec-61β(tm1986) mutant animals, suggesting that the organellar defects seen in asna-1 and wrb-1 were due to a TA protein-dependent mechanism rather than an SRP-dependent mechanism. In addition, asna-1 mutants displayed numerous protein aggregates, consistent with a proposed role for ASNA-1 in shielding aggregation-prone TA protein membrane anchors from the hydrophilic environment of the cytosol.In conclusion, YKT-6 and TOMM-40 are positive regulators of IIS and DAF-28/insulin secretion, implicating roles for Golgi and mitochondria in IIS. DAF-28 is a metabolically regulated insulin in C. elegans, since its secretion depends on active mitochondria. Mutants for asna-1 and its predicted receptor wrb-1 show severe defects in ER and Golgi morphology. These defects may occur because TA protein targeting in asna-1 and wrb-1 mutants is defective, which is also demonstrated here in the first analysis of this process in live animals.
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| 4. |
- Billing, Ola, 1981-, et al.
(author)
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Mitochondrial function is required for secretion of DAF-28/insulin in C. elegans.
- 2011
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In: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 6:1, s. e14507-
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Journal article (peer-reviewed)abstract
- While insulin signaling has been extensively studied in Caenorhabditis elegans in the context of ageing and stress response, less is known about the factors underlying the secretion of insulin ligands upstream of the insulin receptor. Activation of the receptor governs the decision whether to progress through the reproductive lifecycle or to arrest growth and enter hibernation. We find that animals with reduced levels of the mitochondrial outer membrane translocase homologue TOMM-40 arrest growth as larvae and have decreased insulin signaling strength. TOMM-40 acts as a mitochondrial translocase in C. elegans and in its absence animals fail to import a mitochondrial protein reporter across the mitochondrial membrane(s). Inactivation of TOMM-40 evokes the mitochondrial unfolded protein response and causes a collapse of the proton gradient across the inner mitochondrial membrane. Consequently these broadly dysfunctional mitochondria render an inability to couple food abundance to secretion of DAF-28/insulin. The secretion defect is not general in nature since two other neuropeptides, ANF::GFP and INS-22::VENUS, are secreted normally. RNAi against two other putative members of the TOMM complex give similar phenotypes, implying that DAF-28 secretion is sensitive to mitochondrial dysfunction in general. We conclude that mitochondrial function is required for C. elegans to secrete DAF-28/insulin when food is abundant. This modulation of secretion likely represents an additional level of control over DAF-28/insulin function.
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| 5. |
- Hemmingsson, Oskar, 1975-, et al.
(author)
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ASNA-1 activity modulates sensitivity to cisplatin
- 2010
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In: Cancer Research. - : American Association for Cancer Research. - 0008-5472 .- 1538-7445. ; 70:24, s. 10321-10328
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Journal article (peer-reviewed)abstract
- Cancer can be cured by platinum based chemotherapy but resistance is a major cause of treatment failure. Here we present the nematode Caenorhabditis elegans as a model to study interactions between the platinum drug cisplatin and signaling pathways in vivo. Null mutations in a single gene, asna-1, makes worms hypersensitive to cisplatin. The metalloregulated ATPase ASNA-1 promotes insulin secretion and membrane insertion of tail-anchored proteins. Using structural data from ASNA-1 homologs, we identify specific ASNA-1 mutants that are sensitive to cisplatin while still able to promote insulin signaling. Mutational analysis reveals that hypersensitivity of ASNA-1 mutants to cisplatin remains in absence of CEP-1/p53 or apoptosis. Human ASNA1 can substitute for the worm gene, indicating a conserved function. Cisplatin sensitivity is not affected by decreased insulin signaling in wild type nematodes or restored insulin signaling in asna-1 mutants. These findings provide a functional insight into ASNA-1, demonstrate that C. elegans can be used to characterize cisplatin resistance mechanisms and propose that rationally designed drugs against ASNA-1 can sensitize cancer cells to cisplatin.
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| 6. |
- Hemmingsson, Oskar, 1975-, et al.
(author)
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Increased sensitivity to platinating agents and arsenite in human ovarian cancer by downregulation of ASNA1
- 2009
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In: Oncology Reports. - : Spandidos Publications. - 1021-335X .- 1791-2431. ; 22:4, s. 869-875
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Journal article (peer-reviewed)abstract
- Platinating agents constitute the first line treatment for ovarian cancer but treatment failure is common because of intrinsic and acquired resistance. Cancer cells develop the RASP-phenotype (cross resistance against arsenite, antimonite and platinum) associated with decreased accumulation of cisplatin and arsenite. ASNA1 is a possible subunit of a transport system for cisplatin and arsenite due to homology to arsA, an ATPase in the E. coli ars-complex responsible for efflux of arsenite and antimonite. Eukaryotic ASNA1 is a targeting factor for membrane insertion of tail-anchored proteins involved in the secretory pathway and cellular stress responses. The purpose with this study was to evaluate if ASNA1 expression influenced cisplatin, carboplatin, oxaliplatin or arsenite sensitivity in ovarian cancer. Human ovarian cancer cell line 2008 was transfected with a sense or an antisense ASNA1 construct. ASNA1 downregulated and overexpressing clones were identified by Western blots. Cell growth and chemosensitivity was determined by the MTT assay. Down-regulated ASNA1 expression was associated with retarded growth and increased sensitivity to cisplatin, carboplatin, oxaliplatin and arsenite whereas the cisplatin resistant 2008/A overexpresses ASNA1. These observations support the hypothesis that ASNA1 is a target to overcome platinum resistance in ovarian cancer.
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| 7. |
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| 8. |
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| 9. |
- Kao, Gautam, et al.
(author)
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C. elegans SUR-6/PR55 cooperates with LET-92/protein phosphatase 2A and promotes Raf activity independently of inhibitory Akt phosphorylation sites
- 2004
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In: Development. - Cambridge : Company of Biologists Limited. - 0950-1991 .- 1477-9129. ; 131:4, s. 755-765
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Journal article (peer-reviewed)abstract
- Protein phosphatase 2A (PP2A) can both positively and negatively influence the Ras/Raf/MEK/ERK signaling pathway, but its relevant substrates are largely unknown. In C. elegans, the PR55/B regulatory subunit of PP2A, which is encoded by sur-6, positively regulates Ras-mediated vulval induction and acts at a step between Ras and Raf. We show that the catalytic subunit (C) of PP2A, which is encoded by let-92, also positively regulates vulval induction. Therefore SUR-6/PR55 and LET-92/PP2A-C probably act together to dephosphorylate a Ras pathway substrate. PP2A has been proposed to activate the Raf kinase by removing inhibitory phosphates from Ser259 from Raf-1 or from equivalent Akt phosphorylation sites in other Raf family members. However, we find that mutant forms ofC. elegans LIN-45 RAF that lack these sites still require sur-6. Therefore, SUR-6 must influence Raf activity via a different mechanism. SUR-6 and KSR (kinase suppressor of Ras) function at a similar step in Raf activation but our genetic analysis suggests that KSR activity is intact in sur-6 mutants. We identify the kinase PAR-1 as a negative regulator of vulval induction and show that it acts in opposition to SUR-6 and KSR-1. In addition to their roles in Ras signaling, SUR-6/PR55 and LET-92/PP2A-C cooperate to control mitotic progression during early embryogenesis.
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| 10. |
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| 11. |
- Natarajan, Balasubramanian, 1981-, et al.
(author)
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Depletion of the ER chaperone ENPL-1 sensitizes C. elegans to the anticancer drug cisplatin
- 2013
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In: Worm. - : Landes Bioscience. - 2162-4046 .- 2162-4054. ; 2:1
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Journal article (peer-reviewed)abstract
- Cisplatin is an essential chemotherapeutic drug in the treatment of many cancers. Its use, however, is limited by the development of resistance in many tumors. The ability to re-sensitize resistant tumors could significantly strengthen cisplatin therapy in patients. Caenorhabditis elegans is a suitable model for studying the cytoplasmic role of cisplatin in tumor cells. We have previously shown that the ATPase ASNA-1 has similar roles as a factor governing cisplatin sensitivity in mammalian tumor cells and C. elegans. Here we study the endoplasmic reticulum (ER) resident chaperone ENPL-1/GRP94 and find that its depletion makes worms sensitive to cisplatin. Elevated ER stress levels in enpl-1 mutants is the likely cause of this sensitivity because a correlation can be made between cisplatin sensitivity and the high ER stress levels. We also find that asna-1 mutants have elevated unfolded protein response (UPR) activity and that the intrinsically cisplatin resistant wild-type worms become sensitive when ER stress is high. We conclude that enpl-1 is a cisplatin sensitizing factor and suggest that manipulation of its levels or of UPR activity will enhance the effects of cisplatin based cancer therapy.
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| 12. |
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| 13. |
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| 14. |
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| 15. |
- Podraza, Agnieszka, et al.
(author)
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ENPL-1, the Caenorhabditis elegans homolog of GRP94, promotes insulin secretion via regulation of proinsulin processing and maturation
- 2020
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In: Development. - Cambridge : The Company of Biologists. - 1477-9129 .- 0950-1991. ; 147:20
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Journal article (peer-reviewed)abstract
- © 2020. Published by The Company of Biologists Ltd. Insulin/IGF signaling in Caenorhabditis elegans is crucial for proper development of the dauer larva and growth control. Mutants disturbing insulin processing, secretion and downstream signaling perturb this process and have helped identify genes that affect progression of type 2 diabetes. Insulin maturation is required for its proper secretion by pancreatic β cells. The role of the endoplasmic reticulum (ER) chaperones in insulin processing and secretion needs further study. We show that the C. elegans ER chaperone ENPL-1/GRP94 (HSP90B1), acts in dauer development by promoting insulin secretion and signaling. Processing of a proinsulin likely involves binding between the two proteins via a specific domain. We show that, in enpl-1 mutants, an unprocessed insulin exits the ER lumen and is found in dense core vesicles, but is not secreted. The high ER stress in enpl-1 mutants does not cause the secretion defect. Importantly, increased ENPL-1 levels result in increased secretion. Taken together, our work indicates that ENPL-1 operates at the level of insulin availability and is an essential modulator of insulin processing and secretion.
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| 16. |
- Podraza-Farhanieh, Agnieszka, 1991, et al.
(author)
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A proinsulin-dependent interaction between ENPL-1 and ASNA-1 in neurons is required to maintain insulin secretion in C. elegans.
- 2023
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In: Development (Cambridge, England). - : The Company of Biologists. - 1477-9129 .- 0950-1991. ; 150:6
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Journal article (peer-reviewed)abstract
- Neuropeptides, including insulin, are important regulators of physiological functions of the organisms. Trafficking through the Golgi is crucial for the regulation of secretion of insulin-like peptides. ASNA-1 (TRC40) and ENPL-1 (GRP94) are conserved insulin secretion regulators in Caenorhabditis elegans (and mammals), and mouse Grp94 mutants display type 2 diabetes. ENPL-1/GRP94 binds proinsulin and regulates proinsulin levels in C. elegans and mammalian cells. Here, we have found that ASNA-1 and ENPL-1 cooperate to regulate insulin secretion in worms via a physical interaction that is independent of the insulin-binding site of ENPL-1. The interaction occurs in DAF-28/insulin-expressing neurons and is sensitive to changes in DAF-28 pro-peptide levels. Consistently, ASNA-1 acted in neurons to promote DAF-28/insulin secretion. The chaperone form of ASNA-1 was likely the interaction partner of ENPL-1. Loss of asna-1 disrupted Golgi trafficking pathways. ASNA-1 localization to the Golgi was affected in enpl-1 mutants and ENPL-1 overexpression partially bypassed the ASNA-1 requirement. Taken together, we find a functional interaction between ENPL-1 and ASNA-1 that is necessary to maintain proper insulin secretion in C. elegans and provides insights into how their loss might cause diabetes in mammals.
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| 17. |
- Raj, Dorota, et al.
(author)
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Alternative redox forms of ASNA-1 separate insulin signaling from tail-anchored protein targeting and cisplatin resistance in C. elegans
- 2021
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In: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 11:1
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Journal article (peer-reviewed)abstract
- Cisplatin is a frontlinecancer therapeutic, but intrinsic or acquired resistance is common. We previouslyshowed that cisplatin sensitivity can be achieved by inactivation ofASNA-1/TRC40in mammalian cancer cells and inCaenorhabditiselegans. ASNA-1 has two more conservedfunctions: in promoting tail-anchored protein (TAP) targeting to theendoplasmicreticulum membrane and in promoting insulin secretion. However, the relationbetween its different functions has remained unknown. Here, we show that ASNA-1exists in two redox states that promote TAP-targeting and insulin secretion separately.The reduced state is the one required for cisplatin resistance: an ASNA-1 point mutant, in which the protein preferentially was found in the oxidized state, was sensitive to cisplatin and defective for TAP targeting but had no insulin secretion defect. The same was true for mutants inwrb-1,which we identifyas theC. eleganshomolog of WRB, the ASNA1/TRC40 receptor. Finally,we uncover a previously unknown action of cisplatin induced reactive oxygen species: cisplatin inducedROSdrives ASNA-1 into the oxidized form, andselectively prevents an ASNA-1-dependent TAP substrate from reaching the endoplasmicreticulum. Our work suggests that ASNA-1 acts as aredox-sensitive target forcisplatin cytotoxicity and that cisplatin resistance is likely mediated by ASNA-1-dependent TAP substrates. Treatments that promote an oxidizing tumor environmentshould be explored as possible means to combatcisplatin resistance. © 2021, The Author(s).
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| 18. |
- Raj, Dorota, et al.
(author)
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Cisplatin toxicity is counteracted by the activation of the p38/ATF-7 signaling pathway in post-mitotic C. elegans
- 2023
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In: Nature Communications. - 2041-1723. ; 14:1
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Journal article (peer-reviewed)abstract
- Cisplatin kills proliferating cells via DNA damage but also has profound effects on post-mitotic cells in tumors, kidneys, and neurons. However, the effects of cisplatin on post-mitotic cells are still poorly understood. Among model systems, C. elegans adults are unique in having completely post-mitotic somatic tissues. The p38 MAPK pathway controls ROS detoxification via SKN-1/NRF and immune responses via ATF-7/ATF2. Here, we show that p38 MAPK pathway mutants are sensitive to cisplatin, but while cisplatin exposure increases ROS levels, skn-1 mutants are resistant. Cisplatin exposure leads to phosphorylation of PMK-1/MAPK and ATF-7 and the IRE-1/TRF-1 signaling module functions upstream of the p38 MAPK pathway to activate signaling. We identify the response proteins whose increased abundance depends on IRE-1/p38 MAPK activity as well as cisplatin exposure. Four of these proteins are necessary for protection from cisplatin toxicity, which is characterized by necrotic death. We conclude that the p38 MAPK pathway-driven proteins are crucial for adult cisplatin resilience. In contrast to mammalian cells, C. elegans models can be useful because of cells being post-mitotic in adults. Here the authors show activation of the p38 pathway in cisplatin resistant adult animals and characterise the proteins upstream and downstream of the p38 MAPK signalling pathway that are involved in the cisplatin response.
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| 19. |
- Raj, Dorota, et al.
(author)
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Identification of C. elegans ASNA-1 domains and tissue requirements that differentially influence platinum sensitivity and growth control.
- 2022
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In: PLoS genetics. - : Public Library of Science (PLoS). - 1553-7404. ; 18:12
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Journal article (peer-reviewed)abstract
- ASNA1 plays an essential role in cisplatin chemotherapy response, type 2 diabetes, and heart disease. It is also an important biomarker in the treatment response of many diseases. Biochemically, ASNA1 has two mutually exclusive redox-modulated roles: a tail-anchored protein (TAP) targeting function in the reduced state and a holdase/chaperone function in the oxidized state. Assigning biochemical roles of mammalian ASNA1 to biomedical functions is crucial for successful therapy development. Our previous work showed the relevance of the C. elegans ASNA-1 homolog in modeling cisplatin response and insulin secretion. Here we analyzed two-point mutants in highly conserved residues in C. elegans ASNA-1 and determined their importance in separating the cisplatin response function from its roles in insulin secretion. asna-1(ΔHis164) and asna-1(A63V) point mutants, which both preferentially exist in the oxidized state, displayed cisplatin sensitivity phenotype as well as TAP insertion defect but not an insulin secretion defect. Further, using targeted depletion we analyzed the tissue requirements of asna-1 for C. elegans growth and development. Somatic depletion of ASNA-1 as well as simultaneous depletion of ASNA-1 in neurons and intestines resulted in an L1 arrest. We concluded that, targeting single residues in ASNA-1 affecting Switch I/Switch II domain function, in comparison to complete knockdown counteracted cisplatin resistance without jeopardizing other important biological functions. Taken together, our study shows that effects on health caused by ASNA1 mutations can have different biochemical bases.
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