Myosin phosphatase is inactivated by caspase-3 cleavage and phosphorylation of myosin phosphatase targeting subunit 1 during apoptosis |
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| Authors: | Takahiro Iwasaki Takeshi Katayama Kazuhiro Kohama Yaeta Endo Tatsuya Sawasaki |
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| Institution: | National Institutes of Health;aCell-Free Science and Technology Research Center and Venture Business Laboratory, Ehime University, Matsuyama, Ehime 790-8577, Japan;bDepartment of Molecular and Cellular Pharmacology, Gunma University Graduate School of Medicine, Maebashi, Gunma 371-8511, Japan;cProteo-Medicine Research Center, Ehime University, Toon, Ehime 791-0295, Japan;dRIKEN Systems and Structural Biology Center, Yokohama, Kanagawa 230-0045, Japan |
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| Abstract: | In nonapoptotic cells, the phosphorylation level of myosin II is constantly maintained by myosin kinases and myosin phosphatase. During apoptosis, caspase-3–activated Rho-associated protein kinase I triggers hyperphosphorylation of myosin II, leading to membrane blebbing. Although inhibition of myosin phosphatase could also contribute to myosin II phosphorylation, little is known about the regulation of myosin phosphatase in apoptosis. In this study, we have demonstrated that, in apoptotic cells, the myosin-binding domain of myosin phosphatase targeting subunit 1 (MYPT1) is cleaved by caspase-3 at Asp-884, and the cleaved MYPT1 is strongly phosphorylated at Thr-696 and Thr-853, phosphorylation of which is known to inhibit myosin II binding. Expression of the caspase-3 cleaved form of MYPT1 that lacked the C-terminal end in HeLa cells caused the dissociation of MYPT1 from actin stress fibers. The dephosphorylation activity of myosin phosphatase immunoprecipitated from the apoptotic cells was lower than that from the nonapoptotic control cells. These results suggest that down-regulation of MYPT1 may play a role in promoting hyperphosphorylation of myosin II by inhibiting the dephosphorylation of myosin II during apoptosis. |
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