Abstract
Exposure of islet beta-cells to elevated glucose concentrations (30 versus 3 mm) prompts enhanced preproinsulin (PPI) gene transcription and the trans-location to the nucleoplasm of pancreatic duodenum homeobox-1 (PDX-1; Rafiq, I., Kennedy, H., and Rutter, G. A. (1998) J. Biol. Chem. 273, 23241-23247). Here, we show that in MIN6 beta-cells, over-expression of p110.CAAX, a constitutively active form of phosphatidylinositol 3-kinase (PI3K) mimicked the activatory effects of glucose on PPI promoter activity, whereas Deltap85, a dominant negative form of the p85 subunit lacking the p110-binding domain, and the PI3K inhibitor LY 294002, blocked these effects. Similarly, glucose-stimulated nuclear trans-location of endogenous PDX-1 was blocked by Deltap85 expression, and wortmannin or LY 294002 blocked the trans-location from the nuclear membrane to the nucleoplasm of epitope-tagged PDX-1.c-myc. By contrast, SB 203580, an inhibitor of stress-activated protein kinase-2 (SAPK2)/p38 MAP kinase, had no effect on any of the above parameters, and PPI promoter activity and PDX-1.c-myc localization were unaffected by over-expression of the upstream kinase MKK6 (MAP kinase kinase-6) or wild-type p38/SAPK2, respectively. Furthermore, no change in the activity of extracted p38/SAPK2 could be detected after incubation of cells at either 3 or 30 mm glucose. These data suggest that stimulation of PI3K is necessary and sufficient for the effects of glucose on PPI gene transcription, acting via a downstream signaling pathway that does not involve p38/SAPK2.
Original language | English |
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Pages (from-to) | 15977-84 |
Number of pages | 8 |
Journal | Journal of Biological Chemistry |
Volume | 275 |
Issue number | 21 |
Publication status | Published - 26 May 2000 |
Keywords
- Androstadienes/pharmacology
- Animals
- Calcium-Calmodulin-Dependent Protein Kinases/metabolism
- Cell Line
- Cell Nucleus/metabolism
- Chromones/pharmacology
- Enzyme Activation
- Enzyme Inhibitors/pharmacology
- Gene Expression Regulation/drug effects
- Glucose/pharmacology
- Homeodomain Proteins/genetics
- Imidazoles/pharmacology
- Insulin
- Islets of Langerhans/metabolism
- MAP Kinase Kinase 6
- Microscopy, Confocal
- Mitogen-Activated Protein Kinases/genetics
- Morpholines/pharmacology
- Phosphatidylinositol 3-Kinases/genetics
- Proinsulin/genetics
- Promoter Regions, Genetic
- Protein Kinase C/antagonists & inhibitors
- Protein Precursors/genetics
- Pyridines/pharmacology
- Signal Transduction
- Trans-Activators/genetics
- Transfection
- p38 Mitogen-Activated Protein Kinases