Rac-induced increase of phosphorylation of myosin regulatory light chain in HeLa cells.

The pathways by which activation of the small GTP-binding protein Rac causes cytoskeletal changes are not fully understood but are likely to involve both assembly of new actin filaments and reorganization of actin filaments driven by the actin-dependent ATPase activity of myosin II. Here we show that expression of active RacQ61 in growing HeLa cells, in addition to inducing ruffling, substantially enhances the level of phosphorylation of serine-19 of the myosin II regulatory light chain (MLC), which would increase actomyosin II ATPase and motor activities. Phosphorylated myosin was localized to RacQ61-induced ruffles and stress fibers. RacQ61-induced phosphorylation of MLC was reduced by a maximum of about 38% by an inhibitor (Tat-PAK) of p21-activated kinase (PAK), about 35% by an inhibitor (Y-27632) of Rho kinase, 51% by Tat-PAK plus Y-27632, and 10% by an inhibitor (ML7) of myosin light chain kinase. Staurosporine, a non-specific inhibitor of serine/threonine kinases, reduced RacQ61-induced phosphorylation of MLC by about 58%, at the maximum concentration that did not kill cells. Since Rac activates PAK and PAK can phosphorylate MLC, these data strongly suggest that PAK is responsible for a significant fraction of RacQ61-induced MLC phosphorylation. To our knowledge, this is the first evidence that active Rac causes phosphorylation of MLC in cells, thus implicating activation of the ATPase activity of actomyosin II as one of the ways by which Rac may induce cytoskeletal changes.

Brzeska H ，Szczepanowska J ，Matsumura F ，Korn ED ... -  《cell motility and the cytoskeleton》

Role of Rho, Rac, and Rho-kinase in phosphorylation of myosin light chain, development of polarity, and spontaneous migration of Walker 256 carcinosarcoma cells.

Gutjahr MC ，Rossy J ，Niggli V 《EXPERIMENTAL CELL RESEARCH》

Thrombin-induced phosphorylation of the regulatory light chain of myosin II in cultured bovine corneal endothelial cells.

Satpathy M ，Gallagher P ，Lizotte-Waniewski M ，Srinivas SP ... -  《EXPERIMENTAL EYE RESEARCH》

Rho-kinase contributes to diphosphorylation of myosin II regulatory light chain in nonmuscle cells.

Ueda K ，Murata-Hori M ，Tatsuka M ，Hosoya H ... -  《ONCOGENE》

Inhibition by Rho-kinase and protein kinase C of myosin phosphatase is involved in thrombin-induced shape change of megakaryocytic leukemia cell line UT-7/TPO.

Yazaki A ，Tamaru S ，Sasaki Y ，Komatsu N ，Wada H ，Shiku H ，Nishikawa M ... -  《CELLULAR SIGNALLING》