The function of MCF2L (MCF.2 cell line derived transforming sequence like, ENSG00000126217) is as follows. Guanine nucleotide exchange factor that catalyzes guanine nucleotide exchange on RHOA and CDC42, and thereby contributes to the regulation of RHOA and CDC42 signaling pathways (By similarity). Seems to lack activity with RAC1. Becomes activated and highly tumorigenic by truncation of the N-terminus (By similarity). Isoform 5 activates CDC42 (PubMed:15157669). {ECO:0000250|UniProtKB:Q63406, ECO:0000269|PubMed:15157669}. [Isoform 3]: Does not catalyze guanine nucleotide exchange on CDC42 (PubMed:15157669). .