TGF-β1-mediated activations of c-Src and Rac1 modulate levels of cyclins and p27Kip1 CDK inhibitor in hepatoma cells replated on fibronectin

Abstract

Integrin-mediated cell adhesion transduces signals to regulate actin cytoskeleton and cell proliferation. While understanding how integrin signals cross-talk with the TGF-beta 1 pathways, we observed lamellipodia formation and cyclin regulation in Hep3B cells, following TGF-beta 1 treatment. To answer if integrin signaling via actin organization might regulate cell cycle progression after TGF-beta 1 treatment, we analyzed cross-talk between the two receptor-mediated pathways in hepatoma cells on specific ECMs. We found that basal and TGF-beta 1-mediated activation of c-Src and Rac 1, expression of cyclins E and A, and suppression of p27(Kip1) were significant in cells replated on fibronectin, but not in cells on collagen 1, indicating a different integrin-mediated cellular response to TGF-beta 1 I treatment. Levels of tyrosine phosphorylation and actin-enriched lamellopodia on fibronectin were also more prominent than in cells on collagen I. Studies using pharmacological inhibitors or transient transfections revealed that the preferential TGF-beta 1 effects in cells on fibronectin required c-Src family kinase activity. These observations suggest that a specific cross-talk between TGF-beta 1 and fibronectin-binding integrin signal pathways leads to the activation of c-Src/Rac1/actin-organization, leading to changes in cell cycle regulator levels in hepatoma cells. Therefore, this study represents another mechanism to regulate cell cycle regulators when integrin signaling is collaborative with TGF-beta 1 pathways. (c) 2004 Elsevier B.V. All rights reserved.