Interferon-gamma independently activates the MHC class I antigen processing pathway and diminishes glucose responsiveness in pancreatic beta-cell lines.
The mouse pancreatic beta TC3 and beta TC6-F7 cell lines were used to characterize the effects of interferon-gamma (IFN-y) on beta-cell phenotype and function. Initially, intracellular and secreted insulin were compared in glucose-stimulated cells over time. A significant reduction in insulin content and secretion was observed on a per-cell basis in glucose-stimulated beta TC3 and beta TC6-F7 cells after 12 h of exposure to IFN-gamma. The steadystate level of pre-proinsulin mRNA expression was not affected by IFN-gamma. Thus, we postulate that IFN-gamma's inhibitory actions occur after transcription of pre-proinsulin genes. Time-course analysis of IFN-gamma-regulated mRNA expression of the two intra-MHC-encoded subunits of the proteasome (low-molecular-mass polypeptide [Lmp]-2 and Lmp-7) revealed a correlation between their induction and the inhibitory effects of IFN-gamma on glucose-stimulated insulin production. Increased expression of Lmp-2 and Lmp-7 mRNA was accompanied by a corresponding induction of LMP2 and LMP7 protein expression. Subsequently, major histocompatibility complex (MHC) class I cell-surface expression was significantly increased in IFN-gamma-treated beta TC3 and beta TC6-F7 cells. Exposure of IFN-gamma-treated beta-cells to a peptide aldehyde inhibitor of the proteasome (MG132) significantly attenuated MHC class I cell-surface expression but did not prevent the negative effects of IFN-gamma on glucose responsiveness. Enhanced expression of the MHC class I antigen processing and presentation pathway and diminished insulin production appear to be distinct pathological alterations in beta-cells exposed to the insulitic cytokine IFN-gamma.
Baldeón
M E
ME
Division of Nutritional Sciences, University of Illinois at Urbana-Champaign, 61801, USA.
Neece
D J
DJ
Nandi
D
D
Monaco
J J
JJ
Gaskins
H R
HR
D000818:Animals; D017951:Antigen Presentation / Q000187:drug effects; D015152:Blotting, Northern; D015153:Blotting, Western; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000502:physiology*; D015395:Histocompatibility Antigens Class I / Q000276:immunology*; D007328:Insulin / Q000032:analysis / Q000378:metabolism; D007371:Interferon-gamma / Q000494:pharmacology*; D007515:Islets of Langerhans / Q000737:chemistry / Q000378:metabolism*; D007976:Leupeptins / Q000494:pharmacology; D008285:Major Histocompatibility Complex / Q000235:genetics; D051379:Mice; D009097:Multienzyme Complexes; D011384:Proinsulin / Q000235:genetics; D046988:Proteasome Endopeptidase Complex; D011498:Protein Precursors / Q000235:genetics; D011506:Proteins / Q000235:genetics; D012313:RNA / Q000032:analysis; D017471:Receptors, Interferon / Q000187:drug effects; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000187:drug effects; D000096743:Interferon gamma Receptor
D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors; D005947:Glucose; D015395:Histocompatibility Antigens Class I; D007328:Insulin; D007371:Interferon-gamma; D007976:Leupeptins; D009097:Multienzyme Complexes; D011384:Proinsulin; D046988:Proteasome Endopeptidase Complex; D011498:Protein Precursors; D011506:Proteins; D012313:RNA; D017471:Receptors, Interferon; D000096743:Interferon gamma Receptor; C071313:LMP-2 protein; C013737:preproinsulin; C077436:LMP7 protein; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde