Loss of HSPA9 induces peroxisomal degradation by increasing pexophagy.
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ABSTRACT:
SUBMITTER: Jo DS
PROVIDER: S-EPMC7595578 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Peroxisome biogenesis disorders (PBDs) are metabolic disorders caused by the loss of peroxisomes. The majority of PBDs result from mutation in one of 3 genes that encode for the peroxisomal AAA ATPase complex (AAA-complex) required for cycling PEX5 for peroxisomal matrix protein import. Mutations in these genes are thought to result in a defect in peroxisome assembly by preventing the import of matrix proteins. However, we show here that loss of the AAA-complex does not prevent matrix protein import, but instead causes an upregulation of peroxisome degradation by macroautophagy, or pexophagy. The loss of AAA-complex function in cells results in the accumulation of ubiquitinated PEX5 on the peroxisomal membrane that signals pexophagy. Inhibiting autophagy by genetic or pharmacological approaches rescues peroxisome number, protein import and function. Our findings suggest that the peroxisomal AAA-complex is required for peroxisome quality control, whereas its absence results in the selective degradation of the peroxisome. Thus the loss of peroxisomes in PBD patients with mutations in their peroxisomal AAA-complex is a result of increased pexophagy. Our study also provides a framework for the development of novel therapeutic treatments for PBDs.
| S-EPMC5446072 | biostudies-literature
Project description:Autophagy is a membrane trafficking pathway that sequesters proteins and organelles into autophagosomes. The selectivity of this pathway is determined by autophagy receptors, such as the Pichia pastoris autophagy-related protein 30 (Atg30), which controls the selective autophagy of peroxisomes (pexophagy) through the assembly of a receptor protein complex (RPC). However, how the pexophagic RPC is regulated for efficient formation of the phagophore, an isolation membrane that sequesters the peroxisome from the cytosol, is unknown. Here we describe a new, conserved acyl-CoA-binding protein, Atg37, that is an integral peroxisomal membrane protein required specifically for pexophagy at the stage of phagophore formation. Atg30 recruits Atg37 to the pexophagic RPC, where Atg37 regulates the recruitment of the scaffold protein, Atg11. Palmitoyl-CoA competes with Atg30 for Atg37 binding. The human orthologue of Atg37, acyl-CoA-binding domain containing protein 5 (ACBD5), is also peroxisomal and is required specifically for pexophagy. We suggest that Atg37/ACBD5 is a new component and positive regulator of the pexophagic RPC.
| S-EPMC3926955 | biostudies-literature
Project description:Pexophagy is a process that selectively degrades peroxisomes by autophagy. The Pichia pastoris pexophagy receptor Atg30 is recruited to peroxisomes under peroxisome proliferation conditions. During pexophagy, Atg30 undergoes phosphorylation, a prerequisite for its interactions with the autophagy scaffold protein Atg11 and the ubiquitin-like protein Atg8. Atg30 is subsequently shuttled to the vacuole along with the targeted peroxisome for degradation. Here, we defined the binding site for Atg30 on the peroxisomal membrane protein Pex3 and uncovered a role for Pex3 in the activation of Atg30 via phosphorylation and in the recruitment of Atg11 to the receptor protein complex. Pex3 is classically a docking protein for other proteins that affect peroxisome biogenesis, division, and segregation. We conclude that Pex3 has a role beyond simple docking of Atg30 and that its interaction with Atg30 regulates pexophagy in the yeast P. pastoris.
| S-EPMC4375511 | biostudies-literature
Project description:AimsWe examined that (a) how the endotoxic stress affects peroxisomal function and autophagic degradation of peroxisomes-pexophagy, (b) how a superimposed dysfunction of lysosomes and pexophagy modifies responses to lipopolysaccharide (LPS), and (c) the mechanisms of peroxisomal contribution to renal injury. To accomplish this, we used lysosome-defective Lyst-mice in vivo and primary endothelial cells in vitro, and compared the responses with wild-type (WT) littermates.ResultsLPS induced pexophagic degradation, followed by proliferation of peroxisomes in WT mice, which was abolished in Lyst-mice. Lyst-mice exhibited impaired activation of catalase, which together with preserved hydrogen peroxide-generating β-oxidation resulted in redox disequilibrium. LPS treatment induced a heightened inflammatory response, increased oxidative damage, and aggravated renal injury in Lyst-mice. Similarly, as in vivo, LPS-activated lysosomal (LYS) pexophagy and transiently repressed peroxisomes in vitro, supported by reduced peroxisomal density in the vicinity of lysosomes. Peroxisomal dynamics was also abolished in lysosome-defective cells, which accumulated peroxisomes with compromised functions and intraorganellar redox imbalance.InnovationWe demonstrated that pexophagy is a default response to endotoxic injury. However, when LYS dysfunction (a frequent companion of chronic diseases) is superimposed, recycling and functioning of peroxisomes are impaired, and an imbalance between hydrogen peroxide-generating β-oxidation and hydrogen peroxide-detoxifying catalase ensues, which ultimately results in peroxisomal burnout.ConclusionOur data strongly suggest that pexophagy, a cellular mechanism per se, is essential in functional maintenance of peroxisomes during LPS exposure. Inhibition of pexophagy results in accumulation of impaired peroxisomes, redox disequilibrium, and aggravated renal damage.
| S-EPMC3691927 | biostudies-literature
Project description:Peroxisomes are highly dynamic organelles that have multiple functions in cellular metabolism. To adapt the intracellular conditions to the changing extracellular environment, peroxisomes undergo constitutive segregation and degradation. The segregation of peroxisomes is mediated by 2 dynamin-related GTPases, Dnm1 and Vps1, whereas, the degradation of peroxisomes is accomplished through pexophagy, a selective type of autophagy. During pexophagy, the size of the organelle is always a challenging factor for the efficiency of engulfment by the sequestering compartment, the phagophore, which implies a potential role for peroxisomal fission in the degradation process, similar to the situation with selective mitochondria degradation. In this study, we report that peroxisomal fission is indeed critical for the efficient elimination of the organelle. When pexophagy is induced, both Dnm1 and Vps1 are recruited to the degrading peroxisomes through interactions with Atg11 and Atg36. In addition, we found that specific peroxisomal fission, which is only needed for pexophagy, occurs at mitochondria-peroxisome contact sites.
| S-EPMC4091152 | biostudies-literature
Project description:The important physiologic role of peroxisomes is shown by the occurrence of peroxisomal biogenesis disorders (PBDs) in humans. This spectrum of autosomal recessive metabolic disorders is characterized by defective peroxisome assembly and impaired peroxisomal functions. PBDs are caused by mutations in the peroxisomal biogenesis factors, which are required for the correct compartmentalization of peroxisomal matrix enzymes. Recent work from patient cells that contain the Pex1(G843D) point mutant suggested that the inhibition of the lysosome, and therefore the block of pexophagy, was beneficial for peroxisomal function. The resulting working model proposed that Pex1 may not be essential for matrix protein import at all, but rather for the prevention of pexophagy. Thus, the observed matrix protein import defect would not be caused by a lack of Pex1 activity, but rather by enhanced removal of peroxisomal membranes via pexophagy. In the present study, we can show that the specific block of PEX1 deletion-induced pexophagy does not restore peroxisomal matrix protein import or the peroxisomal function in beta-oxidation in yeast. Therefore, we conclude that Pex1 is directly and essentially involved in peroxisomal matrix protein import, and that the PEX1 deletion-induced pexophagy is not responsible for the defect in peroxisomal function. In order to point out the conserved mechanism, we discuss our findings in the context of the working models of peroxisomal biogenesis and pexophagy in yeasts and mammals.
| S-EPMC7037794 | biostudies-literature
Project description:Peroxisomes are degraded by a selective type of autophagy known as pexophagy. Several different types of pexophagy have been reported in mammalian cells. However, the mechanisms underlying how peroxisomes are recognized by autophagy-related machinery remain elusive. PEX3 is a peroxisomal membrane protein (PMP) that functions in the import of PMPs into the peroxisomal membrane and has been shown to interact with pexophagic receptor proteins during pexophagy in yeast. Thus, PEX3 is important not only for peroxisome biogenesis, but also for peroxisome degradation. However, whether PEX3 is involved in the degradation of peroxisomes in mammalian cells is unclear. Here, we report that high levels of PEX3 expression induce pexophagy. In PEX3-loaded cells, peroxisomes are ubiquitinated, clustered, and degraded in lysosomes. Peroxisome targeting of PEX3 is essential for the initial step of this degradation pathway. The degradation of peroxisomes is inhibited by treatment with autophagy inhibitors or siRNA against NBR1, which encodes an autophagic receptor protein. These results indicate that ubiquitin- and NBR1-mediated pexophagy is induced by increased expression of PEX3 in mammalian cells. In addition, another autophagic receptor protein, SQSTM1/p62, is required only for the clustering of peroxisomes. Expression of a PEX3 mutant with substitution of all lysine and cysteine residues by arginine and alanine, respectively, also induces peroxisome ubiquitination and degradation, hence suggesting that ubiquitination of PEX3 is dispensable for pexophagy and an endogenous, unidentified peroxisomal protein is ubiquitinated on the peroxisomal membrane.
| S-EPMC4206534 | biostudies-literature
Project description:Myelodysplastic syndromes (MDS) are the most common adult myeloid blood cancers in the US. Patients have increased apoptosis in their bone marrow cells leading to low peripheral blood counts. The full complement of gene mutations that contribute to increased apoptosis in MDS remains unknown. Up to 25% of MDS patients harbor and acquired interstitial deletion on the long arm of chromosome 5 [del(5q)], creating haploinsufficiency for a large set of genes including HSPA9. Knockdown of HSPA9 in primary human CD34+ hematopoietic progenitor cells significantly inhibits growth and increases apoptosis. We show here that HSPA9 knockdown is associated with increased TP53 expression and activity, resulting in increased expression of target genes BAX and p21. HSPA9 protein interacts with TP53 in CD34+ cells and knockdown of HSPA9 increases nuclear TP53 levels, providing a possible mechanism for regulation of TP53 by HSPA9 haploinsufficiency in hematopoietic cells. Concurrent knockdown of TP53 and HSPA9 rescued the increased apoptosis observed in CD34+ cells following knockdown of HSPA9. Reduction of HSPA9 below 50% results in severe inhibition of cell growth, suggesting that del(5q) cells may be preferentially sensitive to further reductions of HSPA9 below 50%, thus providing a genetic vulnerability to del(5q) cells. Treatment of bone marrow cells with MKT-077, an HSPA9 inhibitor, induced apoptosis in a higher percentage of cells from MDS patients with del(5q) compared to non-del(5q) MDS patients and normal donor cells. Collectively, these findings indicate that reduced levels of HSPA9 may contribute to TP53 activation and increased apoptosis observed in del(5q)-associated MDS.
| S-EPMC5298293 | biostudies-literature
Project description:The autophagy-mediated degradation of peroxisomes, pexophagy, serves as a rheostat for peroxisome homeostasis. However, disturbing this process has yet to be investigated in the context of therapy treatment and resistance in cancer. In Vorinostat (Vor)-resistant lymphoma (B8) cells, an autophagosome enrichment procedure, followed by mass spectrometry (MS), revealed an abundance of peroxisomal proteins, indicative of elevated pexophagy. This was validated by immunofluorescence colocalization and co-immunoprecipitation of PEX5 with the pexophagy receptor p62. Using Vor-resistant B8 cells, we triggered apoptosis by genetically silencing PEX1, PEX6 and PEX26, members of the exportomer complex, which negatively regulates pexophagy. To further explore PEX26 in other model systems, we genetically silenced the exportomer component in A549 (lung adenocarcinoma), 1205Lu (melanoma) and in 1205Lu cells with acquired resistance to MAPK-targeted therapies (VCR5). Here, we observed that silencing PEX26 promotes therapy sensitivity under otherwise therapy-resistant conditions. Using gene expression data from lymphoma (DLBCL), melanoma and lung adenocarcinoma cohorts, we found that low gene expression of PEX26, a component of the “negative regulation of pexophagy” signature, was significantly associated with prolonged patient survival. Clinically, gene expression levels of this signature could be utilized as a prognostic indicator in DLBCL, lung adenocarcinoma, melanoma, and perhaps other cancers. In conclusion, we provide precedence for the development and use of therapies that promote pexophagy in cancer. Furthermore, the MS-based identification of autophagosome cargos provides a platform towards identifying proteins unique to pro-death and pro-survival autophagosomes in cancer model systems, which could illuminate therapeutic use and development.
2022-08-11 | PXD013926 | Pride
Project description:Tankyrase is a poly (ADP-ribose) polymerase that leads to ubiquitination and degradation of target proteins. Since tankyrase inhibitors suppress the degradation of AXIN protein, a negative regulator of the canonical Wnt pathway, they effectively act as Wnt inhibitors. Small molecule tankyrase inhibitors are being investigated as drug candidates for cancer and fibrotic diseases, in which the Wnt pathways are aberrantly activated. Tankyrase is also reported to degrade the adaptor protein SH3BP2 (SH3 domain-binding protein 2). We have previously shown that SH3BP2 gain-of-function mutation enhances receptor activator of nuclear factor-?B ligand (RANKL)-induced osteoclastogenesis in murine bone marrow-derived macrophages (BMMs). Although the interaction between tankyrase and SH3BP2 has been reported, it is not clear whether and how the inhibition of tankyrase affects bone cells and bone mass. Here, we have demonstrated that tankyrase inhibitors (IWR-1, XAV939, and G007-LK) enhanced RANKL-induced osteoclast formation and function in murine BMMs and human peripheral blood mononuclear cells through the accumulation of SH3BP2, subsequent phosphorylation of SYK, and nuclear translocation of NFATc1. Tankyrase inhibitors also enhanced osteoblast differentiation and maturation, represented by increased expression of osteoblast-associated genes accompanied by the accumulation of SH3BP2 protein and enhanced nuclear translocation of ABL, TAZ, and Runx2 in primary osteoblasts. Most importantly, pharmacological inhibition of tankyrase in mice significantly decreased tibia and lumbar vertebrae bone volumes in association with increased numbers of osteoclasts. Our findings uncover the role of tankyrase inhibition in bone cells and highlight the potential adverse effects of the inhibitor on bone.
| S-EPMC6912859 | biostudies-literature