Rad is a p53 direct transcriptional target that inhibits cell migration and is frequently silenced in lung carcinoma cells

The p53 tumor suppressor exerts its function mainly as a transcriptional activator. Here we show that the Ras-related small GTPase Rad, an inhibitor of Rho kinase, is a direct transcriptional target of p53. Expression of Rad messenger RNA (mRNA) and protein was induced by DNA damage in a p53-dependent manner. The −2934/−2905-bp Rad promoter region, to which p53 bound, was required for p53-mediated Rad gene activation. Treatment by DNA damaging agents increased p53 occupancy and histone acetylation in the region of Rad promoter containing the p53-binding site. Expression of Rad diminished the inhibitory phosphorylation at Ser3 of cofilin, a regulator of actin dynamics, and suppressed migration and invasiveness of cancer cells. Knockdown of Rad promoted cell migration and alleviated the p53-mediated migration suppression. Frequent loss of Rad mRNA and protein expression was observed in non-small cell lung carcinoma tissues. Together our results reveal a mechanism that p53 may inhibit cell migration by disrupting actin dynamics via Rad activation and implicate a tumor suppressor role of Rad in lung cancer.