Acts as guanine nucleotide exchange factor (GEF) for RHOA, RAC1 and CDC42 GTPases. Binding of APC may activate RAC1 GEF activity. The APC-ARHGEF4 complex seems to be involved in cell migration as well as in E-cadherin-mediated cell-cell adhesion. Required for MMP9 up-regulation via the JNK signaling pathway in colorectal tumor cells. Involved in tumor angiogenesis and may play a role in intestinal adenoma formation and tumor progression. Isoform 3 interacts with RHOA and RAC1, and (via ABR domain) with APC. Found in a complex consisting of ARHGEF4, APC and CTNNB1. Associated with membrane ruffles. Expressed at high levels in the brain, skeletal muscle and testis and at low levels in the kidney, lung, small intestine, ovary and prostate. Expression is aberrantly enhanced in most colorectal tumors. In an autoinhibited form the SH3 domain binds intramolecularly to the DH domain, thus blocking the Rac-binding site. Truncated N-terminus. Extended N-terminus.