Phosphorylation of connexin-32 by protein kinase C prevents its proteolysis by mu-calpain and m-calpain.
Isolated connexin-32s from rat and mouse liver are proteolyzed in vitro by the intracellular Ca(2+)-dependent neutral proteases, mu-calpain and m-calpain, producing a major fragment of 26 kDa. Connexin-26 is not proteolyzed by calpain. Calpain cleaves connexin-32 at its C-terminal end as shown by 125I-calmodulin binding experiments. Connexin-32, but not connexin-26, is phosphorylated by both protein kinase A and protein kinase C in serine residues and the sites of phosphorylation by both kinases remain in the major 26-kDa fragment resulting from calpain proteolysis. Phosphorylation of connexin-32 by protein kinase C, but not by protein kinase A, prevents the proteolytic attack of mu-calpain and m-calpain. Phosphorylation of connexin-32 by protein kinase A and protein kinase C does not prevent its proteolysis by papain, alpha-chymotrypsin, proteinase K, and trypsin.
Elvira
M
M
Instituto de Investigaciones Biomédicas, Consejo Superior de Investigaciones Cientificas, Madrid, Spain.
Díez
J A
JA
Wang
K K
KK
Villalobo
A
A
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D015153:Blotting, Western; D002147:Calmodulin / Q000378:metabolism; D002154:Calpain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D017630:Connexins; D004912:Erythrocytes / Q000378:metabolism*; D006801:Humans; D007527:Isoenzymes / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D008565:Membrane Proteins / Q000302:isolation & purification / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D009132:Muscles / Q000201:enzymology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011494:Protein Kinases / Q000378:metabolism; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D012694:Serine
D002147:Calmodulin; D017630:Connexins; D007527:Isoenzymes; D008565:Membrane Proteins; D012694:Serine; D011494:Protein Kinases; D011493:Protein Kinase C; D002154:Calpain