| 1. |
- Billing, Ola, 1981-, et al.
(författare)
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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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Ingår i: PLOS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:4, s. e34507-
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Tidskriftsartikel (refereegranskat)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-
(författare)
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Insulin secretion and ASNA-1-dependent function of the endoplasmic reticulum in C. elegans
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)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.
(författare)
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Mitochondrial function is required for secretion of DAF-28/insulin in C. elegans.
- 2011
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 6:1, s. e14507-
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Tidskriftsartikel (refereegranskat)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.
(författare)
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ASNA-1 activity modulates sensitivity to cisplatin
- 2010
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Ingår i: Cancer Research. - : American Association for Cancer Research. - 0008-5472 .- 1538-7445. ; 70:24, s. 10321-10328
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Tidskriftsartikel (refereegranskat)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.
(författare)
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Increased sensitivity to platinating agents and arsenite in human ovarian cancer by downregulation of ASNA1
- 2009
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Ingår i: Oncology Reports. - : Spandidos Publications. - 1021-335X .- 1791-2431. ; 22:4, s. 869-875
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Tidskriftsartikel (refereegranskat)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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| 9. |
- Kao, Gautam, et al.
(författare)
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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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Ingår i: Development. - Cambridge : Company of Biologists Limited. - 0950-1991 .- 1477-9129. ; 131:4, s. 755-765
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Tidskriftsartikel (refereegranskat)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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