Binds GDP/GTP and possesses intrinsic GTPase activity. Has higher affinity for GDP than for GTP. In cell lines overexpression leads to a reduction in the rate of proliferation, colony formation and in tumorigenic potential. GTP + H2O = GDP + H(+) + phosphate Detected in heart, brain, placenta, lung, liver, skin, kidney and pancreas. Detected in estrogen receptor-positive breast-derived cell lines, but not in estrogen receptor-negative cell lines. Expression is decreased or lost in a significant proportion of primary breast tumors with poor clinical prognosis. Up-regulated by estradiol. Down-regulated by tamoxifen. Belongs to the small GTPase superfamily. Ras family.