A morphological study of the expression of the small G protein RhoA in resting and activated MDCK cells

The small G protein Rho subfamily controls several cellular events such as growth, movement, proliferation and differentiation by rearranging actin an d cytoskeleton proteins. Most of these effects are mediated by the activati on of growth factor and extracellular matrix molecule receptors, suggesting a role for Rho molecules in the transduction pathway of these receptors. D espite the importance of Rho peptides in fundamental cellular events, data on their subcellular immunolocalisation are sparse: here we investigated th e expression and subcellular localisation of RhoA in resting (cultured on p lastic) and activated (Matri-cell or hepatocyte growth factor) MDCK cells b y immunoperoxidase and immunogold techniques. Resting MDCK cells contain de tectable amounts of RhoA mainly localised in the cytoplasm; RhoA expression is significantly enhanced by Matri-cell substrates that promote translocat ion of RhoA at the membrane level. This enhancing effect is reduced after e xposure to hepatocyte growth factor.