Role of ADP-ribosylation Factor 6 (ARF6) in Gastric Acid Secretion

Jun Matsukawa, Kazuhisa Nakayama, Taku Nagao, Hidenori Ichijo, Tetsuro Urushidani
2003 Journal of Biological Chemistry  
ADP-ribosylation factor (ARF) proteins are monomeric GTPases that are essential for membrane transport and exocytosis in a number of secretory cells. We investigated ARF6, the activation of which is insensitive to brefeldin A, to determine whether it regulates membrane traffic in gastric parietal cells. ARF6 translocated from cytosol to tubulovesicle in the presence of GTP␥S, a potential inhibitor of acid secretion in permeabilized cells, whereas under the Mg 2؉ -chelated condition where
more » ... dition where activity of ARF-GTPase activating protein is inhibited, ARF6 translocated to the apical secretory membrane. Immunohistochemical examination revealed that ARF6 mainly located in parietal cell within the gastric glands, and it translocated from the cytosol to the intracellular canaliculi when the glands were stimulated. These results indicated that the distribution of ARF6 between cytosol and the two different membranes was regulated by its GTPase activity. In cultured gastric glands infected with adenovirus expressing ARF6 Q67L, a mutant lacking GTP hydrolysis activity, gastric acid secretion was inhibited. These results suggest that ARF6 regulates gastric acid secretion in parietal cell and that the GTP hydrolysis cycle of ARF6 is essential for the activation pathway. Activation of acid secretion in parietal cell involves mainly two steps: (a) translocation of the intracellular vesicles containing proton pump, so-called tubulovesicles or tubulocisternae, to the apical membrane, called intracellular canaliculus, and (b) the acquisition of potassium and chloride permeabilities, essential for operation of the pump, on the canalicular membrane. On the molecular level, this process is still unclear, but evidence has been found that suggests that regulated membrane trafficking and fusion events play the central role (1, 2). It is widely accepted that intracellular membrane traffic requires small monomeric GTPases (small G proteins), especially rab family proteins in various secretory cells (3). On the other hand, there are some observations opposing this idea. It was previously reported that GTP␥S 1 strongly inhibited gastric acid
doi:10.1074/jbc.m305444200 pmid:12860984 fatcat:6a5227jno5b4thgcmhgmuzbbda