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 opposin g effects on the regulation of integrin cell adhesion receptors, To gain in sight into the properties of R-Ras with respect to the regulation of integr in function and interactions with downstream effecters we performed an anal ysis of R-Ras variants containing mutations in the effector binding domain and C-terminal prenylation site. We found that the activation of the downst ream effector PI 3-kinase was sensitive to mutations in the effector bindin g domain, as was the binding to the effecters, Ral-GDS, Raf-1 and the novel effector Norel, Furthermore, specific mutations in the effector binding lo op and C-terminal prenylation motif impaired the ability of R-Ras to regula te integrin function in CHO cells. However, the ability of the R-Ras effect or loop mutants to bind, and activate known effecters did not correlate wit h their ability to regulate integrin function. Thus, the known R-Ras effect ers are not critical for regulating integrin activation, at least in CHO ce lls, Consequently, these studies provide insight into the structural basis of the interactions between R-Ras and its candidate effecters and suggest t he existence of novel mechanisms through which this GTPase could regulate c ell adhesion.