Editors' ChoiceMuscle contraction

Maintaining Smooth Muscle Tone

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Science's STKE  23 Nov 1999:
Vol. 1999, Issue 9, pp. tw7
DOI: 10.1126/stke.1999.9.tw7

Contraction of smooth muscle cells, such as those that line blood vessels, is regulated through phosphorylation of the myosin light chain. Phosphorylation by myosin light-chain kinase (and consequent increased contraction) is opposed by dephosphorylation (and consequent relaxation) catalyzed by the myosin light-chain phosphatase (PP1M). Some agents that control blood pressure act by modulating this regulatory system. Nitric oxide, a vasodilator, causes increased intracellular production of cyclic guanosine monophosphate (cGMP), which in turn activates cGMP-dependent protein kinase (cGKIα). Surks et al. provide evidence that cGKIα localizes as part of a multienzyme complex at the contractile apparatus through direct interaction with the myosin-binding subunit (MBS) of PP1M. This association was required for cGMP-dependent activation of PP1M and dephosphorylation of myosin light chain. The CGKIα enzyme adds yet another component to the cluster of regulatory components bound to the MBS, which includes the catalytic subunit of PP1M and another protein kinase, Rho-associated kinase, which has an opposite (inhibitory) action on PP1M.

Surks, H.K., Mochizuki, N., Kasai, Y., Georgescu, S.P., Tang, K.M., Ito, M., Lincoln, T.M., and Mendelsohn, M.D. (1999) Regulation of myosin phosphatase by a specific interaction with cGMP- dependent protein kinase Iα. Science 286: 1583-1587. [Abstract] [Full Text]

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