Identification of Protein Phosphatase that Controls the Activity of Myosin Light Chain Phosphatase

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In this study, we utilized affinity chromatography technique using MYPT1 fragment that was thiophosphorylated at Thr-696 (tp-MYPT) as ligand for isolation of MYPT1-phosphatases. By peptide mass fingerprinting analysis, we identified PP1cδ as one of the proteins that specifically bound to tp-MYPT but not unphosphorylated (unp)-MYPT Sepharose resin. Furthermore, overexpression of PP1cδ in smooth muscle cell line resulted the inhibition of the MYPT1 phosphorylation at Thr-696 induced by endothelin-1 sitimulation. Our results indicate that PP1cδ facilitates the dis-inhibition of MLCP activity by auto-dephosphorylating MYPT1.