The effector loop and prenylation site of R-Ras are involved in the regulation of integrin function

The closely related small GTP-binding proteins H-Ras and R-Ras have opposing effects on the regulation of integrin cell adhesion receptors, To gain insight into the properties of R-Ras with respect to the regulation of integrin function and interactions with downstream effecters we performed an analysis of R-Ras variants containing mutations in the effector binding domain and C-terminal prenylation site. We found that the activation of the downstream effector PI 3-kinase was sensitive to mutations in the effector binding domain, as was the binding to the effecters, Ral-GDS, Raf-1 and the novel effector Norel, Furthermore, specific mutations in the effector binding loop and C-terminal prenylation motif impaired the ability of R-Ras to regulate integrin function in CHO cells. However, the ability of the R-Ras effector loop mutants to bind, and activate known effecters did not correlate with their ability to regulate integrin function. Thus, the known R-Ras effecters are not critical for regulating integrin activation, at least in CHO cells, Consequently, these studies provide insight into the structural basis of the interactions between R-Ras and its candidate effecters and suggest the existence of novel mechanisms through which this GTPase could regulate cell adhesion.