Phosphorylation of myosin light chain kinase by the multifunctional calmodulin-dependent protein kinase II in smooth muscle cells.
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.
Tansey
M G
MG
Department of Physiology, University of Texas Southwestern Medical Center, Dallas 75235.
Word
R A
RA
Hidaka
H
H
Singer
H A
HA
Schworer
C M
CM
Kamm
K E
KE
Stull
J T
JT
D000818:Animals; D002118:Calcium / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002417:Cattle; D002478:Cells, Cultured; D015180:Electrophoresis, Gel, Two-Dimensional; D007700:Kinetics; D009130:Muscle, Smooth / Q000166:cytology / Q000201:enzymology*; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*
D011494:Protein Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D009219:Myosin-Light-Chain Kinase; D002118:Calcium