Rab3a controls exocytosis in cholecystokinin-secreting cells

The expression of rab3A and rab3D isoforms in the enteroendocrine, cholecys tokinin-secreting, cell lines STC-1 and GLUTag is here demonstrated. In con trast, rab3B is undetectable in these two cell lines, and rab3C is only sli ghtly expressed in GLUTag cells. Using a transient co-transfection system w ith human growth hormone as reporter protein, we show that overexpression o f the GTPase-deficient mutant rab3AQ81L, but not rab3DQ81L, significantly d ecreases human growth hormone secretory responses to various agonists in ST C-1 cells. These results indicate that endocrine cell lines of intestinal o rigin express rab3A and rab3D proteins, but the GTP-bound form of rab3A Onl y acts as a negative modulator in the control of cholecystokinin secretion from STC-1 cells. (C) 2001 Federation of European Biochemical Societies. Pu blished by Elsevier Science B.V. All rights reserved.