PKA-mediated protein phosphorylation protects ezrin from calpain I cleavage.
Ezrin is localized to the apical membrane of parietal cells and couples the cAMP-dependent protein kinase (PKA) activation cascade to the regulated HCl secretion in gastric parietal cells. Our recent studies demonstrate the functional relevance of PKA-mediated phosphorylation of ezrin in parietal cell secretion [R. Zhou, X. Cao, C. Watson, Y. Miao, Z. Guo, J.G. Forte, X. Yao, Characterization of protein kinase A-mediated phosphorylation of ezrin in gastric parietal cell activation, J. Biol. Chem. 278 (2003) 35651]. Here we show that activation of PKA protects ezrin from calpain I-mediated proteolysis without alteration of calpain I activation and fodrin breakdown. To determine whether phosphorylation of Ser66 by PKA affects the insensitivity to the calpain I-mediated cleavage, recombinant proteins of ezrin, both wild type and S66A/D mutants, were incubated with the purified calpain I. Indeed, phosphorylation-like S66D mutant ezrin is resistant to calpain I-mediated proteolysis while wild type and S66A mutant were sensitive. In fact, expression of phosphorylation-like S66D, but not S66A, mutant in parietal cells confers its resistance to calpain I-mediated proteolysis. Taken together, these results indicate that phosphorylation of ezrin by PKA modulates its sensitivity to calpain I cleavage.
Wang
Hongmei
H
Laboratory of Cell Dynamics, University of Science and Technology of China, Hefei 230027, China.
Guo
Zhen
Z
Wu
Fang
F
Long
Fei
F
Cao
Xinwang
X
Liu
Bingya
B
Zhu
Zhengang
Z
Yao
Xuebiao
X
D000818:Animals; D002154:Calpain / Q000378:metabolism*; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D003598:Cytoskeletal Proteins; D004789:Enzyme Activation; D006632:Histamine / Q000494:pharmacology; D010295:Parietal Cells, Gastric / Q000187:drug effects / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011817:Rabbits; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D000099149:Ezrin
D002154:Calpain; D017868:Cyclic AMP-Dependent Protein Kinases; D003598:Cytoskeletal Proteins; D006632:Histamine; D010447:Peptide Hydrolases; D010750:Phosphoproteins; D000099149:Ezrin