Oxytocin modulation of myosin II phosphatase targeting subunit (MYPT1) binding proteins in the pregnant human uterus

Introduction Myosin phosphatase (MLCP) is a trimeric phosphatase that dephosphorylates regulatory myosin light chains (MLC20) to induce relaxation in smooth muscle tissues. Activity of the phosphatase is regulated by the Myosin phosphatase targeting (MYPT) subunit which directs the phosphatase complex to MLC20. Activated GTP RHOA, RHO-kinase and CPI-17 bind to different regions of MYPT1 to regulate MLC20 phosphorylation. Aims and methods Freshly harvested myometrial tissue strips were treated with 10 nM oxytocin. Changes in GTP-RHOA, phospho-RHOA Ser188, phospho-MYPT1 Thr696, phospho-CPI-17 Thr38 and phospho-MLC Ser 18/Thr19 expression were normalised to total non-phosphorylated protein content. Results Oxytocin induced a peak 2–3 fold increases in MYPT1, and MLC20 phosphorylation at 1 min (p<0.01) which was reduced to a 1–2 fold increase at 5 min (p<0.05). Three fold increases in phospho-CPI-17 Thr38 expression was observed at 5 min. These changes further enhance our understanding of regulation of myosin phosphorylation in uterine smooth muscle tissues.