EZRIN IS A CYCLIC-AMP-DEPENDENT PROTEIN-KINASE ANCHORING PROTEIN

cAMP-dependent protein kinase (A-kinase) anchoring proteins (AKAPs) ar e responsible for the subcellular sequestration of the type II A-kinas e. Previously, we identified a 78 kDa AKAP which was enriched in gastr ic parietal cells. We have now purified the 78 kDa AKAP to homogeneity from gastric fundic mucosal supernates using type II A-kinase regulat ory subunit (R(II)) affinity chromatography. The purified 78 kDa AKAP was recognized by monoclonal antibodies against ezrin, the canalicular actin-associated protein. Recombinant ezrin produced in either Sf9 ce lls or bacteria also bound R(II). Recombinant radixin and moesin, ezri n-related proteins, also bound R(II) in blot overlay. Analysis of reco mbinant truncations of ezrin mapped the R(II) binding site to a region between amino acids 373 and 439. This region contained a lit-aminoaci d amphipathic alpha-helical putative R(II) binding region. A synthetic peptide containing the amphipathic helical region (ezrin(409-438)) bl ocked R(II) binding to ezrin, but a peptide with a leucine to proline substitution at amino acid 421 failed to inhibit R(II) binding. In mou se fundic mucosa, R(II) immunoreactivity redistributed from a predomin antly cytosolic location in resting parietal cells, to a canalicular p attern in mucosa from animals stimulated with gastrin. These results d emonstrate that ezrin is a major AKAP in gastric parietal cells and ma y function to tether type II A-kinase to a region near the secretory c analiculus.