EZRIN-CALPAIN-I INTERACTIONS IN GASTRIC PARIETAL-CELLS

Gastric ezrin, a membrane-cytoskeletal linker with sequence homology t o talin and erythrocyte band 4.1, has been associated with the remodel ing of parietal cell apical membrane that occurs with adenosine 3',5'- cyclic monophosphate (cAMP)-dependent protein kinase stimulation. Here we examine the interrelationship between parietal cell ezrin and Ca2-dependent protease activity. Addition of Ca2+ to Sonicated gastric gl and preparations rendered a relatively selective proteolysis of the 80 -kDa ezrin, accompanied by the appearance of a 55-kDa breakdown produc t. Ca2+-dependent proteolysis of ezrin was blocked by E64, a cysteine protease inhibitor, or calpastatin, indicating calpain as the responsi ble protease. Degradation of ezrin in intact gastric glands was achiev ed by varying extracellular [Ca2+] and [ionomycin]. Ezrin degradation in situ was rapid and relatively selective, although Ca2+-dependent de gradation of some spectrin-like bands was also observed. The effect of activated calpain I on parietal cell function was assessed by probing the secretory response to histamine stimulation using [C-14]aminopyri ne uptake, along with parallel measurements of calpain activity, over a wide range of ionomycin. Activation of calpain, as evidenced by loss of parietal cell ezrin, was correlated with decreased AP uptake by st imulated gastric glands, supporting a role for ezrin in the oxyntic se cretory process. The calpain-ezrin interaction established here, and t he similarities of calpain with talin and erythrocyte band 4.1, sugges t a common feature to this family of ezrin/band 4.1/talin proteins tha t have been implicated in membrane-cytoskeletal association.