title: Proteasome regulates turnover of toxic human amylin in pancreatic cells.
abstract: Toxic human amylin (hA) oligomers and aggregates are implicated in the pathogenesis of type 2 diabetes mellitus (T2DM). Although recent studies demonstrated a causal connection between hA uptake and toxicity in pancreatic cells, the mechanism of amylin's clearance following its internalization and its relationship to toxicity is yet to be determined, and hence was investigated here. Using pancreatic rat insulinoma β-cells and human islets as model systems, we show that hA, following its internalization, first accumulates in the cytosol followed by its translocation into nucleus, and to a lesser extent lysosomes, keeping the net cytosolic amylin content low. An increase in hA accumulation in the nucleus of pancreatic cells correlated with its cytotoxicity, suggesting that its excessive accumulation in the nucleus is detrimental. hA interacted with 20S core and 19S lid subunits of the β-cell proteasomal complex, as suggested by immunoprecipitation and confocal microscopy studies, which subsequently resulted in a decrease in the proteasome's proteolytic activity in these cells. In vitro binding and activity assays confirmed an intrinsic and potent ability of amylin to interact with the 20S core complex thereby modulating its proteolytic activity. Interestingly, less toxic and aggregation incapable rat amylin (rA) showed a comparable inhibitory effect on proteasome activity and protein ubiquitination, decoupling amylin aggregation/ toxicity and amylin-induced protein stress. In agreement with these studies, inhibition of proteasomal proteolytic activity significantly increased intracellular amylin content and toxicity. Taken together, our results suggest a pivotal role of proteasomes in amylin's turnover and detoxification in pancreatic cells.
authors.affiliation: Department of Biological Sciences, The George Washington University, 800 22nd Street, N.W., Washington D.C. 20052, U.S.A.
authors.forename: Sanghamitra
authors.initials: S
authors.lastname: Singh
authors.affiliation: Department of Biological Sciences, The George Washington University, 800 22nd Street, N.W., Washington D.C. 20052, U.S.A.
authors.forename: Saurabh
authors.initials: S
authors.lastname: Trikha
authors.affiliation: Department of Biological Sciences, The George Washington University, 800 22nd Street, N.W., Washington D.C. 20052, U.S.A.
authors.forename: Anjali
authors.initials: A
authors.lastname: Sarkar
authors.affiliation: Department of Biological Sciences, The George Washington University, 800 22nd Street, N.W., Washington D.C. 20052, U.S.A. jerema@gwu.edu.
authors.forename: Aleksandar M
authors.initials: AM
authors.lastname: Jeremic
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D058228:Islet Amyloid Polypeptide / Q000378:metabolism* / Q000633:toxicity; D018613:Microscopy, Confocal; D010179:Pancreas / Q000166:cytology / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D051381:Rats
chemical_list: D058228:Islet Amyloid Polypeptide; D046988:Proteasome Endopeptidase Complex
keywords: human amylin; lysosome; proteasome; protein aggregation; proteotoxicity