Myosin light chain kinase phosphorylation in tracheal smooth muscle.
Purified myosin light chain kinase from smooth muscle is phosphorylated by cyclic AMP-dependent protein kinase, protein kinase C, and the multifunctional calmodulin-dependent protein kinase II. Because phosphorylation in a specific site (site A) by any one of these kinases desensitizes myosin light chain kinase to activation by Ca2+/calmodulin, kinase phosphorylation could play an important role in regulating smooth muscle contractility. This possibility was investigated in 32P-labeled bovine tracheal smooth muscle. Treatment of tissues with carbachol, KCl, isoproterenol, or phorbol 12,13-dibutyrate increased the extent of kinase phosphorylation. Six primary phosphopeptides (A-F) of myosin light chain kinase were identified. Site A was phosphorylated to an appreciable extent only with carbachol or KCl, agents which contract tracheal smooth muscle. The extent of site A phosphorylation correlated to increases in the concentration of Ca2+/calmodulin required for activation. These results show that cyclic AMP-dependent protein kinase and protein kinase C do not affect smooth muscle contractility by phosphorylating site A in myosin light chain kinase. It is proposed that phosphorylation of myosin light chain kinase in site A in contracting tracheal smooth muscle may play a role in the reported desensitization of contractile elements to activation by Ca2+.
Department of Physiology, University of Texas Southwestern Medical Center, Dallas 75235.
J T
JT
Stull
L C
LC
Hsu
M G
MG
Tansey
K E
KE
Kamm
D000818:Animals; D001345:Autoradiography; D002217:Carbachol / Q000494:pharmacology; D002417:Cattle; D015180:Electrophoresis, Gel, Two-Dimensional; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D007700:Kinetics; D009130:Muscle, Smooth / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology; D009219:Myosin-Light-Chain Kinase / Q000378:metabolism*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D010748:Phosphopeptides / Q000302:isolation & purification; D010761:Phosphorus Radioisotopes; D010766:Phosphorylation; D011189:Potassium Chloride / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D014132:Trachea / Q000187:drug effects / Q000201:enzymology* / Q000502:physiology; D014357:Trypsin
D010748:Phosphopeptides; D010761:Phosphorus Radioisotopes; D015240:Phorbol 12,13-Dibutyrate; D011189:Potassium Chloride; D002217:Carbachol; D011493:Protein Kinase C; D009219:Myosin-Light-Chain Kinase; D014357:Trypsin; D007545:Isoproterenol