Functional role of RhoA in growth regulation of primary hepatocytes

The expression, activation and involvement in growth regulation of a small GTPase, RhoA, were examined in rat primary hepatocyte cultures. Hepatocytes freshly isolated from liver expressed RhoA protein at high levels. The total level of RhoA protein in the cells decreased markedly within a day in monolayer cultures. Thereafter, RhoA expression recovered as cell-cell attachment occurred during the culture. On the other hand, the level of the active form of RhoA decreased as the culture proceeded. Ca²⁺ depletion in the medium to disrupt cadherin engagement triggered RhoA activation without de novo protein synthesis, indicating cadherin engagement regulates RhoA activation in hepatocytes. Hepatocyte growth stimulation by HGF was enhanced by Ca ²⁺ depletion or introduction of a constitutively active form of RhoA. The Clostridium botulinum C3 enzyme inhibited hepatocyte growth with stimulation by HGF. These results suggest that RhoA has a crucial role in hepatocyte growth control.