Identification of clathrin and clathrin adaptors on tubulovesicles of gastric acid secretory (oxyntic) cells

Abstract

γ-Adaptin and clathrin heavy chain were identified on tubulovesicles of gastric oxyntic cells with the anti-γ-adaptin monoclonal antibody (MAb) 100/3 and an anti-clathrin heavy chain MAb (MAb 23), respectively. In Western blots, crude gastric microsomes from rabbit and rat and density gradient-purified, H-K-ATPase-rich microsomes from these same species were immunoreactive for γ-adaptin and clathrin. In immunofluorescent labeling of isolated rabbit gastric glands, anti-γ-adaptin and anti-clathrin heavy chain immunoreactivity appeared to be concentrated in oxyntic cells. In primary cultures of rabbit oxyntic cells, the immunocytochemical distribution of γ-adaptin immunoreactivity was similar to that of the tubulovesicular membrane marker in oxyntic cells, the H-K-ATPase. Further biochemical characterization of the tubulovesicular γ-adaptin-containing complex suggested that it has a subunit composition that is typical of that for a clathrin adaptor: in addition to the γ-adaptin subunit, it contains a β-adaptin subunit and other subunits of apparent molecular masses of 50 kDa and 19 kDa. From solubilized gastric microsomes from rabbit, γ-adaptin could be copurified with the major cargo protein of tubulovesicles, the H-K-ATPase. Thus this tubulovesicular coat may bind directly to the H-K-ATPase and may thereby mediate the regulated trafficking of the H-K-ATPase at the apical membrane of the oxyntic cell during the gastric acid secretory cycle. Given the similarities of the regulated trafficking of the H-K-ATPase with recycling of cargo through the apical recycling endosome of many epithelial cells, we propose that tubulovesicular clathrin and adaptors may regulate some part of an apical recycling pathway in other epithelial cells.