RhoA/Rho-Kinase Cascade Is Involved in Oxytocin-Induced Rat Uterine Contraction

Abstract

The RhoA/Rho-kinase cascade is involved in various cellular functions, including migration, proliferation, and smooth muscle contraction. We examined the potential role of this pathway in oxytocin-induced uterine contraction. The specific Rho-kinase inhibitor Y-27632 inhibited oxytocin-induced rat uterine contraction on d 21 of pregnancy in a concentration-dependent manner, whereas the extent of this inhibition was reduced in the nonpregnant uterus. Y-27632 had no effect on oxytocin-induced intracellular Ca(2+) mobilization in myometrial cells. Immunoblot analysis showed that oxytocin increased the level of myosin light chain phosphorylation, and this increase was attenuated by Y-27632. Oxytocin increased the phosphorylation of myosin-binding subunit of myosin phosphatase, one of the major substrates of Rho-kinase, and this increase was reduced by Y-27632. The expression of Rho-kinase protein was shown to increase in the uterus during pregnancy compared with the nonpregnant uterus, whereas the expression of RhoA protein remained at the same level during pregnancy. RT-PCR and Northern blot analysis showed that the expression of Rho-kinase was up-regulated at the transcriptional level during pregnancy. These results suggest that the RhoA/Rho-kinase pathway may have an important role in oxytocin-induced uterine contraction, and that up-regulation of Rho-kinase is involved in the mechanism underlying the increased contractility of the pregnant myometrium.

Adult Cardiac Sca-1-positive Cells Differentiate into Beating Cardiomyocytes

“…Oxytocin inhibits the proliferation of human brain tumors (43), breast cancer cells (44), and adenocarcinoma of endometrium (45) via the cyclic adenosine monophosphate-protein kinase A pathway. Tahara et al (46) have reported that the RhoA/Rho-kinase cascade is involved in oxytocin-induced rat uterine contraction. Among the considerable diversity of oxytocin-mediated signaling pathways, the specific pathway that activates cardiogenesis is currently unknown.…”

Expression of RND Proteins in Human Myometrium1

“…Furthermore, exposure of human uterine smooth muscle cells to agonists like thromboxane induces an increase in ROCK1 [19]. In rat, mouse, and human myometrium, the ROCK inhibitor Y27632 affected oxytocin-, thromboxane-, and carbachol-induced increases in tension and MYL phosphorylation without a reduction in [Ca 2þ ] i [5,20,21; also see Note Added in Proof]. Recently, the use of Y27632 in pregnant rats with lipopolysaccharide and prostaglandin F2alpha induced preterm labor, leading to lower delivery rates [22].…”

“…However, during agonistinduced contractions, the increase in MYL phosphorylation and tension observed is usually higher than the corresponding increase in [Ca 2þ ] i . This increase in calcium-independent tension is termed ''Ca 2þ sensitization'' [4,5]. Dephosphorylation of the phosphorylated MYL by a myosin phosphatase results in relaxation [6].…”

“…Moreover, ROCK directly phosphorylates MYL at Ser 19 [13,14]. Both mechanisms lead to an increase in MYL phosphorylation and Ca 2þ independent increase in tension [4,5]. Thus, stimulation of the RHOA-ROCK pathway sensitizes myometrium to the effects of agonists by the process of Ca 2þ sensitization [15,16].…”

The regulation of myosin phosphatase in pregnant human myometrium

“…Enzymes capable of phosphorylating MYPT1 in vitro include ROCK [41], ZIPK [42] and ILK [43]. ROCK-dependent phosphorylation of one or both of these sites has been demonstrated in smooth muscle cells [44][45][46][47] and rat uterine strips [48], and phospho-MYPT1 (Thr 853 ) can be increased during Ca 2 + -sensitization of permeabilized vascular smooth muscle induced by phenylephrine or GTP[S] (guanosine 5-[γ -thio]triphosphate) [47]. However, evidence for phosphorylation of MYPT1 at these sites in human myometrial tissue is lacking, and inhibition of MYLP activity as a method of Ca 2 + -sensitization in this tissue remains speculative.…”