Ezrin-calpain I interactions in gastric parietal cells.
Gastric ezrin, a membrane-cytoskeletal linker with sequence homology to talin and erythrocyte band 4.1, has been associated with the remodeling 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 Ca(2+)-dependent protease activity. Addition of Ca2+ to sonicated gastric gland preparations rendered a relatively selective proteolysis of the 80-kDa ezrin, accompanied by the appearance of a 55-kDa breakdown product. Ca(2+)-dependent proteolysis of ezrin was blocked by E64, a cysteine protease inhibitor, or calpastatin, indicating calpain as the responsible protease. Degradation of ezrin in intact gastric glands was achieved by varying extracellular [Ca2+] and [ionomycin]. Ezrin degradation in situ was rapid and relatively selective, although Ca(2+)-dependent degradation 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 [14C]aminopyrine 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 stimulated gastric glands, supporting a role for ezrin in the oxyntic secretory process. The calpain-ezrin interaction established here, and the similarities of calpain with talin and erythrocyte band 4.1, suggest a common feature to this family of ezrin/band 4.1/talin proteins that have been implicated in membrane-cytoskeletal association.
Department of Molecular and Cell Biology, University of California, Berkeley 94720.
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Yao
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Thibodeau
J G
JG
Forte
D000818:Animals; D002118:Calcium / Q000378:metabolism; D002154:Calpain / Q000302:isolation & purification / Q000378:metabolism*; D003598:Cytoskeletal Proteins; D010450:Endopeptidases / Q000378:metabolism; D066298:In Vitro Techniques; D009994:Osmolar Concentration; D010295:Parietal Cells, Gastric / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D011522:Protons; D011817:Rabbits; D013010:Sonication; D013347:Subcellular Fractions / Q000378:metabolism; D000099149:Ezrin
D002118:Calcium; D002154:Calpain; D003598:Cytoskeletal Proteins; D010450:Endopeptidases; D010447:Peptide Hydrolases; D010750:Phosphoproteins; D011522:Protons; D000099149:Ezrin