Mastoparan-induced insulin secretion from insulin-secreting βTC3 and INS-1 cells: Evidence for its regulation by rho subfamily of G proteins

Rajesh H. Amin, Hai Qing Chen, Rajakrishnan Veluthakal, Robert B. Silver, Jingsong Li, Guodong Li, Anjaneyulu Kowluru

Research output: Contribution to journalArticle

44 Scopus citations

Abstract

Mastoparan, a tetradecapeptide from wasp venom, stimulates insulin secretion from the islet β-cells, presumably via activation of trimeric G proteins. Herein, we used Clostridial toxins, which selectively modify and inactivate the Rho subfamily of G proteins, to examine whether mastoparan-induced insulin secretion also involves activation of these signaling proteins. Mastoparan, but not mastoparan 17 (an inactive analog of mastoparan), significantly stimulated insulin secretion from βTC3 and INS-1 cells. Preincubation of βTC3 cells with either Clostridium difficille toxin B, which inactivates Rho, Cdc42, and Rac, or Clostridium sordellii toxin, which inactivates Ras, Rap, and Rac, markedly attenuated the mastoparan-induced insulin secretion, implicating Rac in this phenomenon. Mastoparan-stimulated insulin secretion was resistant to GGTI-2147, a specific inhibitor of geranylgeranylation of Rho G proteins (e.g. Rac), suggesting that mastoparan induces direct activation of Rac via GTP/GDP exchange. This was confirmed by a pull-down assay that quantifies the binding of activated (i.e. GTP-bound) Rac to p21-activated kinase. However, glucose-induced insulin secretion from these cells was abolished by toxin B or GGTI-2147, suggesting that the geranylgeranylation step is critical for glucose-stimulated secretion. Mastoparan significantly increased the translocation of cytosolic Rac and Cdc42 to the membrane fraction. Confocal light microscopy revealed a substantial degree of colocalization of Rac (and, to a lesser degree, Cdc42) with insulin in β-cells exposed to mastoparan. Further, stable expression of a dominant negative (N17Rac) form of Rac into INS-1 cells resulted in a significant reduction in mastoparan-stimulated insulin secretion from these cells. Taken together, our findings implicate Rho G proteins, specifically Rac, in mastoparan-induced insulin release.

Original languageEnglish (US)
Pages (from-to)4508-4518
Number of pages11
JournalEndocrinology
Volume144
Issue number10
DOIs
StatePublished - Oct 1 2003
Externally publishedYes

ASJC Scopus subject areas

  • Endocrinology

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