Insulin granule recruitment and exocytosis is dependent on p110gamma in insulinoma and human beta-cells.
OBJECTIVE
Phosphatidylinositol 3-OH kinase (PI3K) has a long-recognized role in beta-cell mass regulation and gene transcription and is implicated in the modulation of insulin secretion. The role of nontyrosine kinase receptor-activated PI3K isoforms is largely unexplored. We therefore investigated the role of the G-protein-coupled PI3Kgamma and its catalytic subunit p110gamma in the regulation of insulin granule recruitment and exocytosis.


METHODS
The expression of p110gamma was knocked down by small-interfering RNA, and p110gamma activity was selectively inhibited with AS605240 (40 nmol/l). Exocytosis and granule recruitment was monitored by islet perifusion, whole-cell capacitance, total internal reflection fluorescence microscopy, and electron microscopy in INS-1 and human beta-cells. Cortical F-actin was examined in INS-1 cells and human islets and in mouse beta-cells lacking the phosphatase and tensin homolog (PTEN).


RESULTS
Knockdown or inhibition of p110gamma markedly blunted depolarization-induced insulin secretion and exocytosis and ablated the exocytotic response to direct Ca(2+) infusion. This resulted from reduced granule localization to the plasma membrane and was associated with increased cortical F-actin. Inhibition of p110gamma had no effect on F-actin in beta-cells lacking PTEN. Finally, the effect of p110gamma inhibition on granule localization and exocytosis could be rapidly reversed by agents that promote actin depolymerization.


CONCLUSIONS
The G-protein-coupled PI3Kgamma is an important determinant of secretory granule trafficking to the plasma membrane, at least in part through the negative regulation of cortical F-actin. Thus, p110gamma activity plays an important role in maintaining a membrane-docked, readily releasable pool of secretory granules in insulinoma and human beta-cells.
Pigeau
Gary M
GM
Department of Pharmacology and the Alberta Diabetes Institute, University of Alberta, Alberta, Canada.
Kolic
Jelena
J
Ball
Brandon J
BJ
Hoppa
Michael B
MB
Wang
Ying W
YW
Rückle
Thomas
T
Woo
Minna
M
Manning Fox
Jocelyn E
JE
MacDonald
Patrick E
PE
D000199:Actins / Q000378:metabolism; D000818:Animals; D015220:Calcium Channels / Q000502:physiology; D045744:Cell Line, Tumor; D058544:Class Ib Phosphatidylinositol 3-Kinase; D005089:Exocytosis / Q000502:physiology; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D000078790:Insulin Secretion; D050417:Insulin-Secreting Cells / Q000166:cytology* / Q000378:metabolism*; D007340:Insulinoma; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008564:Membrane Potentials / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D010190:Pancreatic Neoplasms; D018408:Patch-Clamp Techniques; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011810:Quinoxalines / Q000494:pharmacology; D034741:RNA, Small Interfering; D022142:Secretory Vesicles / Q000378:metabolism*; D045162:Thiazolidinediones / Q000494:pharmacology
D000199:Actins; D015220:Calcium Channels; D058544:Class Ib Phosphatidylinositol 3-Kinase; D007328:Insulin; D007527:Isoenzymes; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011810:Quinoxalines; D034741:RNA, Small Interfering; D045162:Thiazolidinediones; C505144:5-quinoxalin-6-ylmethylenethiazolidine-2,4-dione; C546760:PIK3CG protein, human; C546764:Pik3cg protein, mouse