Actions and expression of RAB-GDP dissociation inhibitor in dispersed chief cells from guinea pig stomach.

Rab proteins are a family of ras-like proteins that are involved in intracellular membrane trafficking. Rab-GDP dissociation inhibitor prevents dissociation of GDP from Rab proteins and extracts Rab proteins from cell membranes in vitro. In the present study, we examined the effects of recombinant rab-GDI on Rab proteins in gastric chief cells. Rab-GDI extracted GTP-binding proteins, including Rab3 and Rab5, from chief cell membranes in a dose-dependent manner. Maximal concentrations of rab-GDI (> or = 50 micrograms/ml) removed approx. 40% of membrane-associated Rab3. Moreover, preincubation of permeabilized chief cells with rab-GDI resulted in a 35% decrease in GTP gamma S(100 microM)-induced pepsinogen secretion, suggesting that membrane-associated Rab proteins are involved in the final stages of secretion. Immunostaining of chief cell cytosolic and membrane fractions with GDI-specific antisera revealed bands at 56 and 48 kDa, respectively, indicating that chief cells express two isoforms of rab-GDI. In gastric chief cells, regulation of Rab proteins by rab-GDI plays an important role in mediating exocytosis.