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Activation of myosin phosphatase targeting subunit by mitosis-specific phosphorylation.

Totsukawa G, Yamakita Y, Yamashiro S, Hosoya H, Hartshorne DJ, Matsumura F - J. Cell Biol. (1999)

Bottom Line: We have found that the myosin phosphatase targeting subunit (MYPT) undergoes mitosis-specific phosphorylation and that the phosphorylation is reversed during cytokinesis.MYPT phosphorylated either in vivo or in vitro in the mitosis-specific way showed higher binding to myosin II (two- to threefold) compared to MYPT from cells in interphase.The mitosis-specific effect of phosphorylation is lost on exit from mitosis, and the resultant increase in myosin phosphorylation may act as a signal to activate cytokinesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08855, USA.

ABSTRACT
It has been demonstrated previously that during mitosis the sites of myosin phosphorylation are switched between the inhibitory sites, Ser 1/2, and the activation sites, Ser 19/Thr 18 (Yamakita, Y., S. Yamashiro, and F. Matsumura. 1994. J. Cell Biol. 124:129- 137; Satterwhite, L.L., M.J. Lohka, K.L. Wilson, T.Y. Scherson, L.J. Cisek, J.L. Corden, and T.D. Pollard. 1992. J. Cell Biol. 118:595-605), suggesting a regulatory role of myosin phosphorylation in cell division. To explore the function of myosin phosphatase in cell division, the possibility that myosin phosphatase activity may be altered during cell division was examined. We have found that the myosin phosphatase targeting subunit (MYPT) undergoes mitosis-specific phosphorylation and that the phosphorylation is reversed during cytokinesis. MYPT phosphorylated either in vivo or in vitro in the mitosis-specific way showed higher binding to myosin II (two- to threefold) compared to MYPT from cells in interphase. Furthermore, the activity of myosin phosphatase was increased more than twice and it is suggested this reflected the increased affinity of myosin binding. These results indicate the presence of a unique positive regulatory mechanism for myosin phosphatase in cell division. The activation of myosin phosphatase during mitosis would enhance dephosphorylation of the myosin regulatory light chain, thereby leading to the disassembly of stress fibers during prophase. The mitosis-specific effect of phosphorylation is lost on exit from mitosis, and the resultant increase in myosin phosphorylation may act as a signal to activate cytokinesis.

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Model of the regulation of myosin phosphatase during  cell division. MYPT has two functionally different phosphorylation sites. One is the mitosis-specific phosphorylation site(s) including Ser 430 that activate myosin phosphatase activity, and the  other is Rho-kinase site(s) that inhibit myosin phosphatase activity. See text for details.
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Figure 6: Model of the regulation of myosin phosphatase during cell division. MYPT has two functionally different phosphorylation sites. One is the mitosis-specific phosphorylation site(s) including Ser 430 that activate myosin phosphatase activity, and the other is Rho-kinase site(s) that inhibit myosin phosphatase activity. See text for details.

Mentions: The positive regulatory mechanism of myosin phosphatase described above contrasts the negative regulation by phosphorylation of MYPT with Rho-kinase. It is possible that both mechanisms collaborate to regulate the massive reorganization of microfilaments during cell division. Our current model for regulation of myosin phosphatase during cell division is shown in Fig. 6. This incorporates two phosphorylation steps: an activation via the mitosis-specific kinase(s), and an inhibition via Rho-kinase (Amano et al., 1996; Kimura et al., 1996). It is therefore reasonable to suggest that there are at least two functional phosphorylation sites to reflect the positive and negative regulatory effects. When cells enter prophase it is proposed that the mitosis-specific phosphorylation occurs (via unknown kinase) and this causes activation of myosin phosphatase and a decrease in the level of myosin phosphorylation (at Ser 19). The result is disassembly of stress fibers and cell rounding. On exit from mitosis and before, or during cytokinesis, the activating site(s) on MYPT are dephosphorylated. At the same phase of the cell cycle it is suggested that inhibition of myosin phosphatase occurs via phosphorylation of MYPT by Rho-kinase. Here the next result would be an increase in the level of myosin phosphorylation (at Ser 19) and activation of myosin for cell division. There are important components of this scheme that must be identified before a plausible mechanism can be established, these include the kinase(s) and phosphatase(s) involved at the mitosis-specific stage.


Activation of myosin phosphatase targeting subunit by mitosis-specific phosphorylation.

Totsukawa G, Yamakita Y, Yamashiro S, Hosoya H, Hartshorne DJ, Matsumura F - J. Cell Biol. (1999)

Model of the regulation of myosin phosphatase during  cell division. MYPT has two functionally different phosphorylation sites. One is the mitosis-specific phosphorylation site(s) including Ser 430 that activate myosin phosphatase activity, and the  other is Rho-kinase site(s) that inhibit myosin phosphatase activity. See text for details.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2132942&req=5

Figure 6: Model of the regulation of myosin phosphatase during cell division. MYPT has two functionally different phosphorylation sites. One is the mitosis-specific phosphorylation site(s) including Ser 430 that activate myosin phosphatase activity, and the other is Rho-kinase site(s) that inhibit myosin phosphatase activity. See text for details.
Mentions: The positive regulatory mechanism of myosin phosphatase described above contrasts the negative regulation by phosphorylation of MYPT with Rho-kinase. It is possible that both mechanisms collaborate to regulate the massive reorganization of microfilaments during cell division. Our current model for regulation of myosin phosphatase during cell division is shown in Fig. 6. This incorporates two phosphorylation steps: an activation via the mitosis-specific kinase(s), and an inhibition via Rho-kinase (Amano et al., 1996; Kimura et al., 1996). It is therefore reasonable to suggest that there are at least two functional phosphorylation sites to reflect the positive and negative regulatory effects. When cells enter prophase it is proposed that the mitosis-specific phosphorylation occurs (via unknown kinase) and this causes activation of myosin phosphatase and a decrease in the level of myosin phosphorylation (at Ser 19). The result is disassembly of stress fibers and cell rounding. On exit from mitosis and before, or during cytokinesis, the activating site(s) on MYPT are dephosphorylated. At the same phase of the cell cycle it is suggested that inhibition of myosin phosphatase occurs via phosphorylation of MYPT by Rho-kinase. Here the next result would be an increase in the level of myosin phosphorylation (at Ser 19) and activation of myosin for cell division. There are important components of this scheme that must be identified before a plausible mechanism can be established, these include the kinase(s) and phosphatase(s) involved at the mitosis-specific stage.

Bottom Line: We have found that the myosin phosphatase targeting subunit (MYPT) undergoes mitosis-specific phosphorylation and that the phosphorylation is reversed during cytokinesis.MYPT phosphorylated either in vivo or in vitro in the mitosis-specific way showed higher binding to myosin II (two- to threefold) compared to MYPT from cells in interphase.The mitosis-specific effect of phosphorylation is lost on exit from mitosis, and the resultant increase in myosin phosphorylation may act as a signal to activate cytokinesis.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08855, USA.

ABSTRACT
It has been demonstrated previously that during mitosis the sites of myosin phosphorylation are switched between the inhibitory sites, Ser 1/2, and the activation sites, Ser 19/Thr 18 (Yamakita, Y., S. Yamashiro, and F. Matsumura. 1994. J. Cell Biol. 124:129- 137; Satterwhite, L.L., M.J. Lohka, K.L. Wilson, T.Y. Scherson, L.J. Cisek, J.L. Corden, and T.D. Pollard. 1992. J. Cell Biol. 118:595-605), suggesting a regulatory role of myosin phosphorylation in cell division. To explore the function of myosin phosphatase in cell division, the possibility that myosin phosphatase activity may be altered during cell division was examined. We have found that the myosin phosphatase targeting subunit (MYPT) undergoes mitosis-specific phosphorylation and that the phosphorylation is reversed during cytokinesis. MYPT phosphorylated either in vivo or in vitro in the mitosis-specific way showed higher binding to myosin II (two- to threefold) compared to MYPT from cells in interphase. Furthermore, the activity of myosin phosphatase was increased more than twice and it is suggested this reflected the increased affinity of myosin binding. These results indicate the presence of a unique positive regulatory mechanism for myosin phosphatase in cell division. The activation of myosin phosphatase during mitosis would enhance dephosphorylation of the myosin regulatory light chain, thereby leading to the disassembly of stress fibers during prophase. The mitosis-specific effect of phosphorylation is lost on exit from mitosis, and the resultant increase in myosin phosphorylation may act as a signal to activate cytokinesis.

Show MeSH