GTPase-activating protein for RhoA, and perhaps for Cdc42. May be involved in regulation of cytoskeletal reorganization, cell proliferation and cell motility. Acts a tumor suppressor in hepatocellular carcinoma cells. {ECO:0000269|PubMed:14697242, ECO:0000269|PubMed:16217026}. This is the function of Ensembl gene identifier ENSG00000133121 (STARD13, StAR related lipid transfer domain containing 13).