Radil is a KRas‐interacting protein involved in regulating cell adhesion and migration

Abstract

Ras proteins regulate a variety of cellular processes including cell survival, proliferation, and differentiation. Ras genes are among the most frequently mutated oncogenes in human malignancies. To date, there are no successful anti‐cancer drugs in the clinic that target Ras proteins or their pathways. Therefore, it is imperative to identify and characterize new components that regulate Ras activities or mediate their downstream signaling pathways. Recently, we have identified a series of proteins that are associated with KRas using a combination of immunoprecipitation and mass spectrometry. We have initially focused on Radil, a gene product with Ras‐association (RA) and DIL domains. Radil is known to be a downstream effector of RAP1, inhibiting RhoA signaling in the regulation of cell survival, adhesion, and migration. We have demonstrated that Radil interacted with all three isoforms of Ras including HRas, NRas, and KRas although it exhibits the strongest interaction with the latter. Radil knockdown does not seem to affect MEK phosphorylation induced by KRasV12, suggesting that it may lie upstream of KRas regulatory pathway. Intriguingly, ectopic expression of Radil only transiently activates MEK and ERK whereas high levels of Radil are correlated with downregulation of KRas downstream components, suggesting a biphasic regulation of KRas signaling. Moreover, Radil knockdown greatly reduced the number of adhesion foci and depolymerized actin filaments, which was associated with reduced FAK activity, deceased cell proliferation, and downregulation of Vimentin and Snail (two mesenchymal cell markers). Taken together, our current studies strongly suggest that Radil may be important for regulating Ras signaling and the epithelial‐mesenchymal transition.