Isoform specific expression of the neuronal F-actin binding protein, drebrin, in specialized cells of stomach and kidney epithelia

To further understand the functional role that the F-actin binding protein, drebrin (developmentally regulated brain protein), plays in the regulation of F-actin, we characterized its expression in non-neuronal cells. Using n anoelectrospray mass spectrometry methods, we initially identified drebrin in non-neuronal cultured cells. Using a drebrin-specific monoclonal antibod y, we were able to detect drebrin protein in several different cell lines d erived from fibroblasts, astrocytomas, and simple epithelia, but not in cel l lines derived from stratified epithelia. Double-label immunofluorescence experiments of cultured cell monolayers revealed the localization of drebri n at the apical plasma membrane together with a pool of submembranous F-act in, Immunoblot analysis of mouse organs revealed that, in addition to its h igh levels of expression in brain, drebrin was present in stomach and to a lesser degree in kidney, colon, and urinary bladder. Drebrin protein detect ed in the non-brain organs migrated faster through SDS-PAGE gels, indicatin g that the lower molecular weight embryonic brain isoform (E2) may be the p rominent isoform in these organs, RT-PCR experiments confirmed the specific expression of the E2 isoform in adult stomach, kidney, and cultured cells. In situ immunofluorescence experiments revealed a cell-type specific patte rn in both stomach and kidney. In stomach, drebrin was specifically express ed in the acid-secreting parietal cells of the fundic glands, where it accu mulated at the extended apical membrane of the canaliculi. In kidney, drebr in was expressed in acid-secreting type A intercalated cells, where it loca lized specifically to the apical plasma membrane. Drebrin was expressed as well in the distal tubule epithelial cells where the protein was concentrat ed at the luminal surface and present at the interdigitations of the basola teral membranes.