Redistribution of a 120 kDa phosphoprotein in the parietal cell associatedwith stimulation

When rabbit isolated gastric glands were stimulated via the cyclic AMP path way, a phosphorylated protein band of about 120 kDa (pp 120) was markedly i ncreased in the apical membrane-rich fraction, concomitant with an increase in the amount of H,K-ATPase and the phosphorylation of the cytoskeletal pr otein ezrin in the same fraction. The cytosolic fraction, but not other mem brane fractions, also contained a protein with common features to the membr ane-bound pp120, i.e., comigration in two-dimensional gels with a pi of sim ilar to 4.5, anomalous mobility in SDS-PAGE, reactivity to antibodies, and phosphorylation, indicating that these two proteins were identical. The pos sibility that pp120 is vinculin was completely excluded. Using antibody aga inst pp120, this protein was found to be almost exclusively in the gastric parietal cell. Biochemical and immunohistochemical analyses suggest that pp 120 exists mainly in the cytosol, and that a small part of the protein bind s to the apical membrane when the parietal cell is stimulated via the cycli c AMP pathway. In the presence of histone, purified pp120 produced phosphor ylation on pp120 as well as histone. The inhibitor profile of this kinase a ctivity is not consistent with any known kinase. We conclude that pp120 is closely associated with a new type of kinase, and translocates from cytosol to the apical membrane when the parietal cell is stimulated.