title: Pennogenin tetraglycoside induces rat myometrial contraction and MLC20 phosphorylation via PLC-IP(3) and RhoA/Rho kinase signaling pathways.
abstract: BACKGROUND
  Total steroidal saponins extracted from the rhizome of Paris polyphylla Sm. var. yunnanensis (TSSPs) have been widely used in China for the treatment of abnormal uterine bleeding. We previously studied the main active constituents of TSSPs and their structure-activity relationships with respect to rat myometrial contractions. Tg (pennogenin tetraglycoside) was identified as one of the active ingredients in TSSPs able to induce rat myometrial contractions. However, the mechanisms underlying the pharmacological actions on uterine activity have not been described clearly.
  
  
  METHODS
  Here Tg was screened for effects on contractile activity in isolated uterine strips from estrogen-primed rats and on MLC20 phosphorylation and related signaling pathways in cultured rat myometrial cells as determined by Western blot. Intracellular calcium ([Ca(2+)](i)) was monitored under a confocal microscope using Fluo-4 AM-loaded myometrial cells.
  
  
  RESULTS
  Tg dose-dependently stimulated rat myometrial contractions as well as MLC20 phosphorylation in vitro, which could be completely suppressed by an inhibitor of myosin light chain kinase (MLCK). Use of Ca(2+) channel blockers and kinase inhibitors demonstrated that Tg-induced myometrial contractions are mediated by activation of the phospholipase C (PLC)-inositol triphosphate (IP3) signaling pathway, resulting in increased MLC20 phosphorylation. Furthermore, Y27632, a specific inhibitor of Rho kinase (ROK), notably suppressed Tg-stimulated myometrial contractions and decreased MLC20 phosphorylation.
  
  
  CONCLUSIONS
  These data provide evidence that rat myometrial contractility induced by Tg results from enhanced MLC20 phosphorylation, while both PLC-IP3 and RhoA/ROK signaling pathways mediate the process. These mechanisms may be responsible for the therapeutic effects of TSSPs on abnormal uterine bleeding.
authors.affiliation: Department of Pathophysiology, Beijing Institute of Radiation Medicine, Beijing, China.
authors.forename: Limei
authors.initials: L
authors.lastname: Wang
authors.forename: Chao
authors.initials: C
authors.lastname: Jia
authors.forename: Zuyin
authors.initials: Z
authors.lastname: Yu
authors.forename: Xiaolan
authors.initials: X
authors.lastname: Liu
authors.forename: Liping
authors.initials: L
authors.lastname: Kang
authors.forename: Yue
authors.initials: Y
authors.lastname: Cong
authors.forename: Yajun
authors.initials: Y
authors.lastname: Shan
authors.forename: Zhenhu
authors.initials: Z
authors.lastname: Zhao
authors.forename: Baiping
authors.initials: B
authors.lastname: Ma
authors.forename: Yuwen
authors.initials: Y
authors.lastname: Cong
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002147:Calmodulin / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D066298:In Vitro Techniques; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D018994:Myosin Light Chains / Q000378:metabolism*; D009219:Myosin-Light-Chain Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects; D013150:Spirostans / Q000737:chemistry / Q000494:pharmacology*; D013997:Time Factors; D010738:Type C Phospholipases / Q000378:metabolism*; D014590:Uterine Contraction / Q000187:drug effects*; D054460:rho-Associated Kinases / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000378:metabolism*
chemical_list: D002147:Calmodulin; D018994:Myosin Light Chains; D013150:Spirostans; C036302:pennogenin tetraglycoside; D015544:Inositol 1,4,5-Trisphosphate; D054460:rho-Associated Kinases; D009219:Myosin-Light-Chain Kinase; D010738:Type C Phospholipases; D020742:rhoA GTP-Binding Protein; D002118:Calcium