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1-Adrenoceptor-Mediated Phosphorylation of MYPT1 and CPI-17 in the Uterine Artery: Role of ERK/PKC
1 Center for Perinatal Biology, Department of Physiology & Pharmacology, Loma Linda University School of Medicine, Loma Linda, CA, USA
* To whom correspondence should be addressed. E-mail: lzhang{at}som.llu.edu.
Previously, we have demonstrated that ERK/PKC signaling pathways play a key role in the regulation of Ca2+ sensitivity and contractility of the uterine artery. The present study tested the hypothesis that ERK and PKC differentially regulate myosin light chain phosphatase (MLCP) activity by phosphorylation of the MLCP regulatory subunit MYPT1 and CPI-17. Agonist-induced contractions and phosphorylation of MYPT1/Thr696, MYPT1/Thr850, and CPI-17/Thr38 were measured simultaneously in the same tissues of isolated near-term pregnant ovine uterine arteries. Phenylephrine produced time-dependent concurrent increases in the phosphorylation of ERK44/42 and MYPT1/Thr850, which preceded contractions. In addition, phenylephrine induced phosphorylation of CPI-17/Thr38 that was concurrent with the contractions. In contrast, phenylephrine did not induce phosphorylation of MYPT1/Thr696. PD098059 inhibited phosphorylation of ERK44/42 and the initial peak phosphorylation of MYPT1/Thr850, but did not affect CPI-17/Thr38 phosphorylation. PKC activation by PDBu induced a time-dependent phosphorylation of CPI-17/Thr38 that preceded the contractions of the uterine artery. In addition, PDBu activated PKC
, and induced co-immunoprecipitation of PKC
with caldesmon. The results suggest that phosphorylation of MYPT1/Thr850 and CPI-17/Thr38 play important roles in the regulation of agonist-mediated Ca2+ sensitivity in the uterine artery, which are regulated in part by ERK and PKC, respectively. In addition, phosphorylated CPI-17 may regulate the Ca2+ sensitivity through the thin filament regulatory pathway in the uterine artery.
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