Citron kinase, a Rho-dependent kinase, induces di-phosphorylation of regulatory light chain of myosin II.
Citron kinase is a Rho-effector protein kinase that is related to Rho-associated kinases of ROCK/ROK/Rho-kinase family. Both ROCK and citron kinase are suggested to play a role in cytokinesis. However, no substrates are known for citron kinase. We found that citron kinase phosphorylated regulatory light chain (MLC) of myosin II at both Ser-19 and Thr-18 in vitro. Unlike ROCK, however, citron kinase did not phosphorylate the myosin binding subunit of myosin phosphatase, indicating that it does not inhibit myosin phosphatase. We found that the expression of the kinase domain of citron kinase resulted in an increase in MLC di-phosphorylation. Furthermore, the kinase domain was able to increase di-phosphorylation and restore stress fiber assembly even when ROCK was inhibited with a specific inhibitor, Y-27632. The expression of full-length citron kinase also increased di-phosphorylation during cytokinesis. These observations suggest that citron kinase phosphorylates MLC to generate di-phosphorylated MLC in vivo. Although both mono- and di-phosphorylated MLC were found in cleavage furrows, di-phosphorylated MLC showed more constrained localization than did mono-phosphorylated MLC. Because citron kinase is localized in cleavage furrows, citron kinase may be involved in regulating di-phosphorylation of MLC during cytokinesis.
Yamashiro
Shigeko
S
Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, New Jersey 08855, USA. yamashiro@mbcl.rutgers.edu
Totsukawa
Go
G
Yamakita
Yoshihiko
Y
Sasaki
Yasuharu
Y
Madaule
Pascal
P
Ishizaki
Toshimaa
T
Narumiya
Shuh
S
Matsumura
Fumio
F
D000818:Animals; D019556:COS Cells; D047908:Intracellular Signaling Peptides and Proteins; D007700:Kinetics; D018994:Myosin Light Chains / Q000378:metabolism*; D024462:Myosin Type II / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*
D047908:Intracellular Signaling Peptides and Proteins; D018994:Myosin Light Chains; C115635:citron-kinase; D017346:Protein Serine-Threonine Kinases; D024462:Myosin Type II