Signaling through myosin light chain kinase in smooth muscles.
Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK) phosphorylates smooth muscle myosin regulatory light chain (RLC) to initiate contraction. We used a tamoxifen-activated, smooth muscle-specific inactivation of MLCK expression in adult mice to determine whether MLCK was differentially limiting in distinct smooth muscles. A 50% decrease in MLCK in urinary bladder smooth muscle had no effect on RLC phosphorylation or on contractile responses, whereas an 80% decrease resulted in only a 20% decrease in RLC phosphorylation and contractile responses to the muscarinic agonist carbachol. Phosphorylation of the myosin light chain phosphatase regulatory subunit MYPT1 at Thr-696 and Thr-853 and the inhibitor protein CPI-17 were also stimulated with carbachol. These results are consistent with the previous findings that activation of a small fraction of MLCK by limiting amounts of free Ca(2+)/calmodulin combined with myosin light chain phosphatase inhibition is sufficient for robust RLC phosphorylation and contractile responses in bladder smooth muscle. In contrast, a 50% decrease in MLCK in aortic smooth muscle resulted in 40% inhibition of RLC phosphorylation and aorta contractile responses, whereas a 90% decrease profoundly inhibited both responses. Thus, MLCK content is limiting for contraction in aortic smooth muscle. Phosphorylation of CPI-17 and MYPT1 at Thr-696 and Thr-853 were also stimulated with phenylephrine but significantly less than in bladder tissue. These results indicate differential contributions of MLCK to signaling. Limiting MLCK activity combined with modest Ca(2+) sensitization responses provide insights into how haploinsufficiency of MLCK may result in contractile dysfunction in vivo, leading to dissections of human thoracic aorta.
Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390.
Ning
N
Gao
Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390.
Jian
J
Huang
Model Animal Research Center and Ministry of Education Key Laboratory of Model Animal for Disease Study, Nanjing University, 210061 Nanjing, China.
Weiqi
W
He
Model Animal Research Center and Ministry of Education Key Laboratory of Model Animal for Disease Study, Nanjing University, 210061 Nanjing, China.
Minsheng
M
Zhu
Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390.
Kristine E
KE
Kamm
Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390. Electronic address: james.stull@utsouthwestern.edu.
James T
JT
Stull
D000818:Animals; D001011:Aorta / Q000201:enzymology / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D004591:Electrophoresis, Polyacrylamide Gel; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D008822:Mice, Transgenic; D009119:Muscle Contraction; D009124:Muscle Proteins / Q000378:metabolism; D009130:Muscle, Smooth / Q000166:cytology / Q000201:enzymology*; D009219:Myosin-Light-Chain Kinase / Q000235:genetics* / Q000378:metabolism*; D010656:Phenylephrine / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D015398:Signal Transduction; D001743:Urinary Bladder / Q000378:metabolism
D002147:Calmodulin; D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins; D010750:Phosphoproteins; C491520:Ppp1r14a protein, mouse; D010656:Phenylephrine; D002217:Carbachol; D009219:Myosin-Light-Chain Kinase