Phosphorylation of myosin light chain kinase by the multifunctional calmodulin-dependent protein kinase II in smooth muscle cells. |
| |
Authors: | M G Tansey R A Word H Hidaka H A Singer C M Schworer K E Kamm J T Stull |
| |
Institution: | Department of Physiology, University of Texas Southwestern Medical Center, Dallas 75235. |
| |
Abstract: | Stimulation of tracheal smooth muscle cells in culture with ionomycin resulted in a rapid increase in cytosolic free Ca2+ concentration (Ca2+]i) and an increase in both myosin light chain kinase and myosin light chain phosphorylation. These responses were markedly inhibited in the absence of extracellular Ca2+. Pretreatment of cells with 1-N-O-bis(5-isoquinolinesulfonyl)-N- methyl-L-tyrosyl]-4-phenylpiperazine (KN-62), a specific inhibitor of the multifunctional calmodulin-dependent protein kinase II (CaM kinase II), did not affect the increase in Ca2+]i but inhibited ionomycin-induced phosphorylation of myosin light chain kinase at the regulatory site near the calmodulin-binding domain. KN-62 inhibited CaM kinase II activity toward purified myosin light chain kinase. Phosphorylation of myosin light chain kinase decreased its sensitivity to activation by Ca2+ in cell lysates. Pretreatment of cells with KN-62 prevented this desensitization to Ca2+ and potentiated myosin light chain phosphorylation. We propose that the Ca(2+)-dependent phosphorylation of myosin light chain kinase by CaM kinase II decreases the Ca2+ sensitivity of myosin light chain phosphorylation in smooth muscle. |
| |
Keywords: | |
|
|