Up-regulation of myometrial RHO effector proteins (PKN1 and DIAPH1) and CPI-17 (PPP1R14A) phosphorylation in human pregnancy is associated with increased GTP-RHOA in spontaneous preterm labor.
RHO GTP-binding proteins are important regulators of actin-myosin interactions in uterine smooth muscle cells. Active (GTP-bound) RHOA binds to RHO-associated protein kinase (ROCK1), which inhibits the myosin-binding subunit (PPP1R12A) of myosin light chain phosphatase, leading to calcium-independent increases in myosin light chain phosphorylation and tension, which are termed "calcium sensitization." The RHO effector protein kinase N (PKN1) also increases calcium sensitization by phosphorylating the protein kinase C (PRKCB)-dependent protein CPI-17 (PPP1R14A) to inhibit the PPP1c subunit of myosin phosphatase. Moreover, other RHO proteins, such as RHOB, RHOD, and their effectors (DIAPH1 and DIAPH2), may modulate PKN1/ ROCK1 signaling to effect changes in myosin phosphatase activity and myosin light chain phosphorylation. The increases in contractile activity observed in term and preterm labor may be due to an increase in RHO activity and/or changes in RHO-related proteins. We found that the RHOA and RHOB mRNA levels in the myometrium were increased in pregnancy, although the expression levels of the RHOA and RHOB proteins did not change with pregnancy or labor. GTP-bound RHOA was increased in pregnancy, and this increase was significant in spontaneous preterm labor myometrium. PKN1 expression and PPP1R14A phosphorylation were dramatically increased in the pregnant myometrium. We also observed increases in DIAPH1 expression in spontaneous term and preterm labor myometrial tissues. The present study shows that human pregnancy is characterized by increases in PKN1 expression and PPP1R14A phosphorylation in the myometrium. Moreover, increases in GTP-bound RHOA and DIAPH1 expression may contribute to the increase in uterine activity in idiopathic preterm labor.
Lartey
J
J
Clinical Sciences at South Bristol, Division of Obstetrics and Gynaecology, Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, Dorothy Hodgkin Building, University of Bristol, Bristol BS1 3NY, United Kingdom.
Smith
M
M
Pawade
J
J
Strachan
B
B
Mellor
H
H
López Bernal
A
A
D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D002478:Cells, Cultured; D005260:Female; D000080865:Formins; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D008954:Models, Biological; D009124:Muscle Proteins; D009215:Myometrium / Q000378:metabolism*; D007752:Obstetric Labor, Premature / Q000378:metabolism*; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D010766:Phosphorylation; D011247:Pregnancy; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D047929:Term Birth / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation; D020741:rho GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020742:rhoA GTP-Binding Protein / Q000235:genetics* / Q000378:metabolism; D020743:rhoB GTP-Binding Protein / Q000235:genetics / Q000378:metabolism
D048868:Adaptor Proteins, Signal Transducing; C108962:DIAPH1 protein, human; D000080865:Formins; D047908:Intracellular Signaling Peptides and Proteins; D009124:Muscle Proteins; C107507:PPP1R14A protein, human; D012333:RNA, Messenger; C061570:protein kinase N; D011493:Protein Kinase C; D010749:Phosphoprotein Phosphatases; C105243:RHOD protein, human; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D020743:rhoB GTP-Binding Protein