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RHO protein regulation of contraction in the human uterus

Medical School, Institute of Cellular Medicine, University of Newcastle, 3rd Floor, William Leech Building, Framlington Place, Newcastle upon Tyne NE2 4HH, UK¹ Division of Obstetrics and Gynaecology, Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, Clinical Sciences South Bristol, University of Bristol, Dorothy Hodgkin Building, Whitson Street, Bristol BS1 3NY, UK

Correspondence should be addressed to J Lartey; Email: jon.lartey{at}ncl.ac.uk

The state of contraction in smooth muscle cells of the human uterus is dependent on the interaction of activated forms of actin and myosin. Ras homology (RHO) proteins are small monomeric GTP-binding proteins that regulate actin polymerisation and myosin phosphorylation in smooth muscle cells. Their action is determined by their level of expression, GTP-bound state, intracellular localisation and phosphorylated status. Agonist activated RHO proteins bind to effector kinases such as RHO kinase (ROCK) and diaphanous proteins (DIAPH) to regulate smooth muscle contraction by two mechanisms: ROCK activates smooth muscle myosin either by direct phosphorylation at Ser19/Thr18 or through inhibition of myosin phosphatase which is a trimeric protein regulated by ROCK and by other protein kinases. Actin-polymerising proteins such as DIAPH homolog 1 increase filamentous actin assembly to enhance acto-myosin cross bridge formation and contraction. This review explores recent advances in RHO protein signalling in human myometrium and proposes areas of further research to investigate the involvement of these proteins in the regulation of uterine contractility in pregnancy and labour.