It has been reported that Rho and Rho-kinase are involved in actin cytoskeleton organization and associated with carcinogenesis and progression of human cancers. However, the mechanism how the Rho/Rho-kinase pathway is involved in cell cycle progression has not been precisely characterized. In this study, we investigated the role of Rho-kinase in epidermal growth factor (EGF) signaling in SW480 colon cancer cells. We found that Y27632, a Rho-kinase inhibitor, dose-dependently induced cell proliferation in these cells. The blockade of EGF stimulation utilizing anti-EGF receptor neutralizing antibodies significantly suppressed cell growth, suggesting that EGF stimulation plays an important role in cell proliferation in SW480 cells. We also found that EGF induced Rho-kinase activation. Interestingly, EGF-induced phosphorylation of both Akt and glycogen synthase kinase-3β (GSK-3β), but not p44/p42 mitogen-activated protein (MAP) kinase, were dose-dependently enhanced when the cells were pretreated with Y27632 or fasudil, another Rho-kinase inhibitor. Moreover, whereas EGF increased the phosphorylation of retinoblastoma tumor suppressor protein as well as cyclin D1 protein expression level, pretreatment with Y27632 accelerated them. Taken together, our results suggest that Rho-kinase regulates negatively EGF-induced cell proliferation upstream of Akt/GSK-3β in colon cancer cells.

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