Acts as guanine nucleotide exchange factor (GEF) for RhoA GTPase. May be involved in activation of the SAPK/JNK pathway Stimulates genotoxic stress-induced RHOB activity in breast cancer cells leading to their cell death. Interacts with RHOA in its GTP- and GDP-bound states, and with CDC42 in its GTP-bound state. Interacts with the PDZ 1 domain of BAIAP1 (By similarity). Widely expressed. By TGFB1. Up-regulated by DNA damaging agents like H(2)O(2) or ionizing radiation (IR).