Regulation of insulin secretion by phosphatidylinositol-4,5-bisphosphate.
The role of PIP(2) in pancreatic beta cell function was examined here using the beta cell line MIN6B1. Blocking PIP(2) with PH-PLC-GFP or PIP5KIgamma RNAi did not impact on glucose-stimulated secretion although susceptibility to apoptosis was increased. Over-expression of PIP5KIgamma improved cell survival and inhibited secretion with accumulation of endocytic vacuoles containing F-actin, PIP(2), transferrin receptor, caveolin 1, Arf6 and the insulin granule membrane protein phogrin but not insulin. Expression of constitutively active Arf6 Q67L also resulted in vacuole formation and inhibition of secretion, which was reversed by PH-PLC-GFP co-expression. PIP(2) co-localized with gelsolin and F-actin, and gelsolin co-expression partially reversed the secretory defect of PIP5KIgamma-over-expressing cells. RhoA/ROCK inhibition increased actin depolymerization and secretion, which was prevented by over-expressing PIP5KIgamma, while blocking PIP(2) reduced constitutively active RhoA V14-induced F-actin polymerization. In conclusion, although PIP(2) plays a pro-survival role in MIN6B1 cells, excessive PIP(2) production because of PIP5KIgamma over-expression inhibits secretion because of both a defective Arf6/PIP5KIgamma-dependent endocytic recycling of secretory membrane and secretory membrane components such as phogrin and the RhoA/ROCK/PIP5KIgamma-dependent perturbation of F-actin cytoskeleton remodelling.
Department of Genetic Medicine and Development, University of Geneva Medical School, Geneva, Switzerland. Alejandra.TomasCatala@unige.ch
Alejandra
A
Tomas
Barbara
B
Yermen
Romano
R
Regazzi
Jeffrey E
JE
Pessin
Philippe A
PA
Halban
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D018929:Cell Culture Techniques; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D004591:Electrophoresis, Polyacrylamide Gel; D004705:Endocytosis / Q000187:drug effects; D005947:Glucose / Q000494:pharmacology; D020287:In Situ Nick-End Labeling; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D051379:Mice; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D019269:Phosphatidylinositol 4,5-Diphosphate / Q000037:antagonists & inhibitors / Q000502:physiology*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D021381:Protein Transport; D014617:Vacuoles / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism
D007328:Insulin; D019269:Phosphatidylinositol 4,5-Diphosphate; D017853:Phosphotransferases (Alcohol Group Acceptor); C020077:1-phosphatidylinositol-4-phosphate 5-kinase; D005947:Glucose