Myosin light chain phosphatase inhibitors

Specific myosin light chain phosphatase inhibitors as potential therapeutic agents for human prostate cancer... 

If MLCK activates contraction by increasing myosin phosphorylation, then an increase in the activity of myosin light chain phosphatase, MLCP, by decreasing the fraction of myosin which is phosphorylated, should lead to relaxation from the active (contractile) state. Cyclic adenosine monophosphate (AMP) is a strong inhibitor of smooth muscle contraction and it has been suggested that activation of MLCP could result from its phosphorylation via cAMP activated protein kinase (see Figure 5). 

Alteration of MLC phosphorylation can occur at four possible sites inhibition of Ca + binding to calmodulin, inhibition of calmodulin activation of MLCK, direct inhibition of MLCK catalytic activity, or activation of myosin light chain phosphatase (MLCP). Although inhibitors of MLCP, such as okadaic acid, are well characterized, there are no known specific activators of MLCP. 

As pointed out by Butler et al. (1994), the a-toxin-permeabilized preparation used by Kitazawa et al. might contain endogenous phosphatase inhibitors that have been lost in the Triton-skinned preparation. This could at least partially explain the observed difference in phosphatase rate, and is an intriguing possibility relating to the demonstration that receptor agonists are able to increase Ca2+ sensitivity in neuroeffector-coupled permeabilized preparations by a mechanism involving inhibited myosin light chain phosphatase (MLCP) activity (Kitazawa et al., 1991 Kubota et al.,... 

Gong MC, Cohen P, Kitazawa T, Ikebe M, Masuo M, Somlyo AP, Somlyo AV (1992) Myosin light chain phosphatase activities and the effects of phosphatase inhibitors in tonic and phasic smooth muscle. J Biol Chem 267 14662-14668 Gong MC, Fujihara H, Somlyo AV, Somlyo AP (1997) Translocation of rhoA associated with sensitization of smooth muscle. J Biol Chem 272 10704-10709 Gong MC, lizuka K, Nixon G, Browne JP, Hall A, Eccleston JF, Sugai M, Kobayashi S, Somlyo AV, Somlyo AP (1996) Role of guanine nucleotide-binding proteins - ras family or trimeric proteins or both - in Ca sensitization of smooth muscle. Proc Natl Acad Sci USA 93 1340-1345... 

Myosin light chain phosphatase (MLCP) is an important protein in the regulation of cellular motility and division. We developed and synthesized a fluorescent small molecule (17e) that selectively inhibits MLCP. We found the growth of human prostate cancer cell lines with upregulated amounts of MLCP proves to be more sensitive when treated with our selective MLCP inhibitor. We used the fluorescent properties of 17e to image its entry and compartmentalization in human prostate cancer... 

Tokui T, Brozovich, F, Ando S, Ikebe M (1996) Enhancement of smooth muscle contraction with protein phosphatase inhibitor 1 Activation of inhibitor 1 by cGMP dependent protein kinase. Biochem Biophys Res Commun 220 777-783 Tdrbk K, Trentham DR (1994) Mechanism of 2-chloro-(epsilon-amino-Lys75)-[6-[4-(Nd -diethylamino)phenyl]-l,3,5-triazin-4-yl]calmodulin interactions with smooth muscle myosin light chain kinase and derived peptides. Biochemistry 33 12807-12820... 

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