Cytokine-mediated down-regulation of the transcription factor cAMP-response element-binding protein in pancreatic beta-cells.
Cytokines are known to induce apoptosis of pancreatic beta-cells. Impaired expression of the anti-apoptotic gene bcl-2 is one of the mechanisms involved. In this study, we identified a defect involving transcription factor cAMP-response element-binding protein (CREB) in the expression of bcl-2. Exposure of mouse pancreatic beta-cell line, MIN6 cells, to cytokines (interleukin-1beta, tumor necrosis factor-alpha, and interferon-gamma) led to a significant (p < 0.01) decrease in Bcl-2 protein and mRNA levels. Cytokines decreased (56%) the activity of the bcl-2 promoter that contains a cAMP-response element (CRE) site. Similar decreases were seen with a luciferase reporter gene driven by tandem repeats of CRE and a CREB-specific Gal4-luciferase reporter, suggesting a defect at the level of CREB. The active phospho form (serine 133) of CREB diminished significantly (p < 0.01) in cells exposed to cytokines. Examination of signaling pathways upstream of CREB revealed a reduction in the active form of Akt. Cytokine-induced decrease of bcl-2 promoter activity was partially restored when cells were cotransfected with a constitutively active form of Akt. Several end points of cytokine action including decreases in phospho-CREB, phospho-Akt, and BCl-2 levels and activation of caspase-9 were observed in isolated mouse islets. Overexpression of wild-type CREB in MIN6 cells by plasmid transfection and adenoviral infection led to protection against cytokine-induced apoptosis. Adenoviral transfer of dominant-negative forms of CREB, on the other hand, resulted in activation of caspase-9 and exaggeration of cytokine-induced beta-cell apoptosis. Together, these results point to CREB as a novel target for strategies aimed at improving the survival of beta-cells.
Jambal
Purevsuren
P
Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
Masterson
Sara
S
Nesterova
Albina
A
Bouchard
Ron
R
Bergman
Barbara
B
Hutton
John C
JC
Boxer
Linda M
LM
Reusch
Jane E-B
JE
Pugazhenthi
Subbiah
S
D000818:Animals; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000187:drug effects / Q000235:genetics*; D016207:Cytokines / Q000494:pharmacology*; D005786:Gene Expression Regulation / Q000187:drug effects*; D017930:Genes, Reporter; D007515:Islets of Langerhans / Q000187:drug effects / Q000502:physiology*; D008156:Luciferases / Q000235:genetics; D051379:Mice; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics
D017362:Cyclic AMP Response Element-Binding Protein; D016207:Cytokines; D019253:Proto-Oncogene Proteins c-bcl-2; D008156:Luciferases