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The Heterotrimeric G-protein Gi Is Localized to the Insulin Secretory Granules of Beta-Cells and Is Involved in Insulin Exocytosis

The Heterotrimeric G-protein Gi Is Localized to the Insulin Secretory Granules of Beta-Cells and Is Involved in Insulin Exocytosis

R J Konrad, R A Young, R D Record, R M Smith, P Butkerait, D Manning, L Jarett, B A Wolf

J Biol Chem. 1995 May 26;270(21):12869-76.

PMID: 7759545

Abstract:

Mastoparan, a tetradecapeptide found in wasp venom that stimulates G-proteins, increases insulin secretion from beta-cells. In this study, we have examined the role of heterotrimeric G-proteins in mastoparan-induced insulin secretion from the insulin-secreting beta-cell line beta-TC3. Mastoparan stimulated insulin secretion in a dose-dependent manner from digitonin-permeabilized beta-TC3 cells. Active mastoparan analogues mastoparan 7, mastoparan 8, and mastoparan X also stimulated secretion. Mastoparan 17, an inactive analogue of mastoparan, did not increase insulin secretion from permeabilized beta-TC3 cells. Mastoparan-induced insulin secretion from permeabilized beta-TC3 cells was inhibited by pretreatment of the cells with pertussis toxin, suggesting that mastoparan-induced insulin secretion is mediated through a pertussis toxin-sensitive G-protein present distally in exocytosis. Enriched insulin secretory granules (ISG) were prepared by sucrose/nycodenz ultracentrifugation. Western immunoblotting performed on beta-TC3 homogenate and ISG demonstrated that G alpha i was dramatically enriched in ISG. Levels of G alpha o and G alpha q were comparable in homogenate and ISG. Mastoparan stimulated ISG GTPase activity in a pertussis toxin-sensitive manner. Mastoparan 7 and mastoparan 8 also stimulated GTPase activity in the ISG, while the inactive analogue mastoparan 17 had no effect. Selective localization of G alpha i to ISG was confirmed with electron microscopic immunocytochemistry in beta-TC3 cells and beta-cells from rat pancreas. In contrast to G alpha o and G alpha q, G alpha was clearly localized to the ISG. Together, these data suggest that mastoparan may act through the heterotrimeric G-protein G alpha i located in the ISG of beta-cells to stimulate insulin secretion.

Chemicals Related in the Paper:

Catalog Number	Product Name	Structure	CAS Number	Price
AP145854611	Mastoparan 17		145854-61-1	Price

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