Myosin Phosphatase Target Subunit 1 (MYPT1) Regulates the Contraction and Relaxation of Vascular Smooth Muscle and Maintains Blood Pressure

Yan-Ning Qiao,Wei-Qi He,Cai-Ping Chen,Cheng-Hai Zhang,Wei Zhao,Pei Wang,Lin Zhang,Yan-Ze Wu,Xiao Yang,Ya-Jing Peng,Ji-Min Gao,Kristine E Kamm,James T Stull,Min-Sheng Zhu

doi:10.1074/jbc.m113.525444

Abstract

Myosin light chain phosphatase with its regulatory subunit, myosin phosphatase target subunit 1 (MYPT1) modulates Ca(2+)-dependent phosphorylation of myosin light chain by myosin light chain kinase, which is essential for smooth muscle contraction. The role of MYPT1 in vascular smooth muscle was investigated in adult MYPT1 smooth muscle specific knock-out mice. MYPT1 deletion enhanced phosphorylation of myosin regulatory light chain and contractile force in isolated mesenteric arteries treated with KCl and various vascular agonists. The contractile responses of arteries from knock-out mice to norepinephrine were inhibited by Rho-associated kinase (ROCK) and protein kinase C inhibitors and were associated with inhibition of phosphorylation of the myosin light chain phosphatase inhibitor CPI-17. Additionally, stimulation of the NO/cGMP/protein kinase G (PKG) signaling pathway still resulted in relaxation of MYPT1-deficient mesenteric arteries, indicating phosphorylation of MYPT1 by PKG is not a major contributor to the relaxation response. Thus, MYPT1 enhances myosin light chain phosphatase activity sufficient for blood pressure maintenance. Rho-associated kinase phosphorylation of CPI-17 plays a significant role in enhancing vascular contractile responses, whereas phosphorylation of MYPT1 in the NO/cGMP/PKG signaling module is not necessary for relaxation.

Highlights

myosin phosphatase target subunit 1 (MYPT1) is a regulatory subunit of myosin phosphatase
Because vascular smooth muscles predominantly express CPI-17, which inhibits PP1c␦ activity after phosphorylation by PKC or Rho-associated kinase (ROCK), we hypothesized that CPI-17 phosphorylation might inhibit PP1c␦ activity and, relax vessels in the absence of MYPT1
In MYPT1-deficient segments pretreated with calyculin A, the attenuation of the H1152-mediated relaxation effect was greater compared with CTR (Fig. 8, B and C)

Summary

Introduction

Results: Deleting MYPT1 in vascular smooth muscle enhances myosin phosphorylation, contractility, and blood pressure. Significance: MYPT1 is not essential for vascular smooth muscle contractility, it contributes to blood pressure maintenance in vivo through signaling to myosin phosphorylation. MYPT1 deletion enhanced phosphorylation of myosin regulatory light chain and contractile force in isolated mesenteric arteries treated with KCl and various vascular agonists. The contractile responses of arteries from knock-out mice to norepinephrine were inhibited by Rho-associated kinase (ROCK) and protein kinase C inhibitors and were associated with inhibition of phosphorylation of the myosin light chain phosphatase inhibitor CPI-17. MYPT1 enhances myosin light chain phosphatase activity sufficient for blood pressure maintenance. Rho-associated kinase phosphorylation of CPI-17 plays a significant role in enhancing vascular contractile responses, whereas phosphorylation of MYPT1 in the NO/cGMP/PKG signaling module is not necessary for relaxation

Results

Discussion

Conclusion