ACTIONS AND EXPRESSION OF RAB-GDP DISSOCIATION INHIBITOR IN DISPERSEDCHIEF CELLS FROM GUINEA-PIG STOMACH

Rab proteins are a family of ras-like proteins that are involved in in tracellular membrane trafficking. Rab-GDP dissociation inhibitor preve nts dissociation of GDP from Rab proteins and extracts Rab proteins fr om cell membranes in vitro. In the present study, we examined the effe cts of recombinant rab-GDI on Rab proteins in gastric chief cells. Rab -GDI extracted GTP-binding proteins, including Rab3 and Rab5, from chi ef cell membranes in a dose-dependent manner. Maximal concentrations o f rab-GDI (greater than or equal to 50 mu g/ml) removed approx. 40% of membrane-associated Rab3. Moreover, preincubation of permeabilized ch ief cells with rab-GDI resulted in a 35% decrease in GTP gamma S(100 m u M)-induced pepsinogen secretion, suggesting that membrane-associated Rab proteins are involved in the final stages of secretion, Immunosta ining of chief cell cytosolic and membrane fractions with GDI-specific antisera revealed bands at 56 and 48 kDa, respectively, indicating th at chief cells express two isoforms of rab-GDI. In gastric chief cells , regulation of Rab proteins by rab-GDI plays an important role in med iating exocytosis. (C) 1996 Academic Press, Inc.