Ezrin is a cyclic AMP-dependent protein kinase anchoring protein

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Abstract
CAMP‐dependent protein kinase (A‐kinase) anchoring proteins (AKAPs) are responsible for the subcellular sequestration of the type II A‐kinase. Previously, we identified a 78 kDa AKAP which was enriched in gastric parietal cells. We have now purified the 78 kDa AKAP to homogeneity from gastric fundic mucosal supernates using type II A‐kinase regulatory subunit (RII) 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 cells or bacteria also bound RII. Recombinant radixin and moesin, ezrin‐related proteins, also bound RII in blot overlay. Analysis of recombinant truncations of ezrin mapped the RII binding site to a region between amino acids 373 and 439. This region contained a 14‐amino‐acid amphipathic α‐helical putative RII binding region. A synthetic peptide containing the amphipathic helical region (ezrin409–438) blocked RII binding to ezrin, but a peptide with a leucine to proline substitution at amino acid 421 failed to inhibit RII binding. In mouse fundic mucosa, RIIimmunoreactivity redistributed from a predominantly cytosolic location in resting parietal cells, to a canalicular pattern in mucosa from animals stimulated with gastrin. These results demonstrate that ezrin is a major AKAP in gastric parietal cells and may function to tether type II A‐kinase to a region near the secretory canaliculus.