title: Reduction in ATP levels triggers immunoproteasome activation by the 11S (PA28) regulator during early antiviral response mediated by IFNβ in mouse pancreatic β-cells.
abstract: Autoimmune destruction of insulin producing pancreatic β-cells is the hallmark of type I diabetes. One of the key molecules implicated in the disease onset is the immunoproteasome, a protease with multiple proteolytic sites that collaborates with the constitutive 19S and the inducible 11S (PA28) activators to produce immunogenic peptides for presentation by MHC class I molecules. Despite its importance, little is known about the function and regulation of the immunoproteasome in pancreatic β-cells. Of special interest to immunoproteasome activation in β-cells are the effects of IFNβ, a type I IFN secreted by virus-infected cells and implicated in type I diabetes onset, compared to IFNγ, the classic immunoproteasome inducer secreted by cells of the immune system. By qPCR analysis, we show that mouse insulinoma MIN6 cells and mouse islets accumulate the immune proteolytic β1(i), β2(i) and β5(i), and 11S mRNAs upon exposure to IFNβ or IFNγ. Higher concentrations of IFNβ than IFNγ are needed for similar expression, but in each case the expression is transient, with maximal mRNA accumulation in 12 hours, and depends primarily on Interferon Regulatory Factor 1. IFNs do not alter expression of regular proteasome genes, and in the time frame of IFNβ-mediated response, the immune and regular proteolytic subunits co-exist in the 20S particles. In cell extracts with ATP, these particles have normal peptidase activities and degrade polyubiquitinated proteins with rates typical of the regular proteasome, implicating normal regulation by the 19S activator. However, ATP depletion rapidly stimulates the catalytic rates in a manner consistent with levels of the 11S activator. These findings suggest that stochastic combination of regular and immune proteolytic subunits may increase the probability with which unique immunogenic peptides are produced in pancreatic β-cells exposed to IFNβ, but primarily in cells with reduced ATP levels that stimulate the 11S participation in immunoproteasome function.
authors: Edward A. Doisy Department of Biochemistry and Molecular Biology, Saint Louis University School of Medicine, Saint Louis, Missouri, United States of America.
authors: Wieke
authors: W
authors: Freudenburg
authors: Madhav
authors: M
authors: Gautam
authors: Pradipta
authors: P
authors: Chakraborty
authors: Jared
authors: J
authors: James
authors: Jennifer
authors: J
authors: Richards
authors: Alison S
authors: AS
authors: Salvatori
authors: Aaron
authors: A
authors: Baldwin
authors: Jill
authors: J
authors: Schriewer
authors: R Mark L
authors: RM
authors: Buller
authors: John A
authors: JA
authors: Corbett
authors: Dorota
authors: D
authors: Skowyra
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D045744:Cell Line, Tumor; D002851:Chromatography, High Pressure Liquid; D017931:DNA Primers / Q000235:genetics; D047468:Immunoprecipitation; D050417:Insulin-Secreting Cells / Q000276:immunology* / Q000821:virology; D050856:Interferon Regulatory Factor-1 / Q000235:genetics / Q000378:metabolism; D016899:Interferon-beta / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009124:Muscle Proteins / Q000378:metabolism*; D017830:Octoxynol; D016133:Polymerase Chain Reaction; D046988:Proteasome Endopeptidase Complex / Q000276:immunology* / Q000378:metabolism
chemical_list: D017931:DNA Primers; D050856:Interferon Regulatory Factor-1; C494258:Irf1 protein, mouse; D009124:Muscle Proteins; C085047:PSME1 protein, human; D016899:Interferon-beta; D000255:Adenosine Triphosphate; D017830:Octoxynol; D046988:Proteasome Endopeptidase Complex
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