The function of integrin linked-kinase (ILK) in normal and activated stellate cells–implications for fibrogenesis in wound healing

Integrin-linked kinase (ILK) is a multidomain focal adhesion protein implicated in signal transduction between integrins and growth factor/extracellular receptors. We have previously shown that ILK expression is increased in liver fibrosis and that ILK appears to be a key regulator of fibrogenesis in rat hepatic stellate cells, effectors of the fibrogenic response. Here we hypothesized that the mechanism by which ILK mediates the fibrogenic phenotype is by engaging the small GTPase, Rho in a signal transduction pathway linked to fibrogenesis. METHODS: ILK function in quiescent (non fibrogenic) and activated (fibrogenic) stellate cells was examined in cells isolated from rat livers. ILK, Rho, and Gα(12/13) signaling were manipulated using established chemical agents or specific adenoviral constructs. RESULTS: ILK activity was minimal in quiescent stellate cells, but prominent in activated stellate cells; inhibition of ILK activity had no effect in quiescent cells, but had prominent effects in activated cells. Overexpression of ILK in activated stellate cells increased Rho activity, but had no effect in quiescent cells. Further, endothelin-1 (ET-1) stimulated Rho activity in activated stellate cells, but not in quiescent cells. Rho, RhoGEF and Gα(12/13) expression were increased after stellate cell activation. Inhibition of Gα(12/13) signaling, by expression of the RGS domain of the p115-Rho- specific guanine nucleotide exchange factor (p115-RGS) in activated stellate cells, significantly inhibited type I collagen and smooth muscle α actin expression, both classically upregulated after stellate cell activation. The data suggest that ILK mediates Rho dependent functional effects in activated stellate cells, and raise the possibility that ILK is important in cross talk with the GPCR system.