Role of ROCK in G1/S Transition of Corneal Epithelial Cells: Regulation of CDK4 and Cyclins D1 and D3

Abstract

Abstract: : Purpose: We have observed that the inhibition of a Rho–associated serine/threonine kinase (ROCK) delayed cell cycle progression in corneal epithelial cells. The purpose of the present study was to identify the cell cycle modulators that are regulated by Rho/ROCK pathway. Methods: Rabbit corneal epithelial cells in culture were arrested in the G₀ phase of the cell cycle by TGFß1 treatment. TheTGFß1 block was then removed to allow the cells to progress through G₁ and S phase, in the presence or absence of the ROCK inhibitor (Y27632). BrdU labeling was employed to estimate the number of cells in the S phase and western blot analyses was performed to determine relative levels of specific cyclins and CDKs. Results: TGFß1 treatment of P₁ cultures of rabbit corneal epithelial cells resulted in arrest of the cells in G₀ with less than 1% of the cells in the S phase. While without ROCK inhibition 25+3.5% of the cells had entered the S phase at 24 hours after the removal of the TGFß1 block, with ROCK inhibition only 8.1+ 2.6% were in the S phase. The difference was less apparent at 36 hours. ROCK inhibition during the progression of G₁/S, resulted in decreased levels of cyclins D1 and D3 and CDK4 as compared to control cells which were not exposed to Y27632. The differences in the relative levels of these proteins between the ROCK–inhibited and non–inhibited cells were evident at 12 hours and maximum at 36 hours after the removal of the TGFß1 block. Conclusions: The Rho/ROCK pathway is involved in the control of G₁/S progression of the cell cycle of corneal epithelial cells in culture. Intracellular levels of at least three components of G₁ progression, including CDK4 and cyclins D1, D3, are regulated by Rho/ROCK activity.

Keywords: cornea: epithelium • proliferation • signal transduction