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Vol. 18, Issue 2, 605-616, February 2007

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Regulation of Myosin II Dynamics by Phosphorylation and Dephosphorylation of Its Light Chain in Epithelial Cells

Toshiyuki Watanabe^*,, Hiroshi Hosoya, and Shigenobu Yonemura^*

*RIKEN, Center for Developmental Biology, Kobe 650-0047, Japan; Department of Life Science, Graduate School of Science and Technology, Kobe University, Kobe 657-8501, Japan; and Department of Biological Science, Graduate School of Science, Hiroshima University, Hiroshima, 739-8526, Japan

Submitted July 10, 2006; Revised November 17, 2006; Accepted November 22, 2006
Monitoring Editor: Erika Holzbaur

Nonmuscle myosin II, an actin-based motor protein, plays an essential role in actin cytoskeleton organization and cellular motility. Although phosphorylation of its regulatory light chain (MRLC) is known to be involved in myosin II filament assembly and motor activity in vitro, it remains unclear exactly how MRLC phosphorylation regulates myosin II dynamics in vivo. We established clones of Madin Darby canine kidney II epithelial cells expressing MRLC-enhanced green fluorescent protein or its mutants. Time-lapse imaging revealed that both phosphorylation and dephosphorylation are required for proper dynamics of myosin II. Inhibitors affecting myosin phosphorylation and MRLC mutants indicated that monophosphorylation of MRLC is required and sufficient for maintenance of stress fibers. Diphosphorylated MRLC stabilized myosin II filaments and was distributed locally in regions of stress fibers where contraction occurs, suggesting that diphosphorylation is involved in the spatial regulation of myosin II assembly and contraction. We further found that myosin phosphatase or Zipper-interacting protein kinase localizes to stress fibers depending on the activity of myosin II ATPase.

The online version of this article contains supplemental material at MBC Online (http://www.molbiolcell.org).

Address correspondence to: Shigenobu Yonemura (yonemura{at}cdb.riken.jp)

Abbreviations used: 0P-, nonphosphorylated; 1P-, monophosphorylated; 2P-, diphosphorylated; MLCK, myosin light chain kinase; MRLC, myosin regulatory light chain; MYPT1, myosin phosphatase targeting subunit 1; NMHC, nonmuscle myosin heavy chain; ZIP, zipper-interacting protein.

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