Guanine nucleotide exchange factor (GEF) that modulates the Rho family of GTPases. Promotes the conversion of some member of the Rho family GTPase from the GDP-bound to the GTP-bound form. Isoform 1 exhibits no activity toward RHOA, RAC1 or CDC42. Isoform 2 exhibits decreased GEF activity toward CDC42. Isoform 3 exhibits a weak but significant activity toward RAC1 and CDC42. Isoform 4 exhibits significant activity toward RHOA and CDC42. The truncated DBL oncogene is active toward RHOA, RAC1 and CDC42. Interacts with an array of inositol phospholipids such as phosphatidylinositol 3-phosphate (PI3P), phosphatidylinositol 4-phosphate (PI4P) and phosphatidylinositol 5-phosphate (PI5P). May interact with CCPG1. Colocalizes with CDC42 to plasma membrane. Isoform 1 is expressed only in brain. Isoform 3 is expressed in heart, kidney, spleen, liver and testis. Isoform 4 is expressed in brain, heart, kidney, testis, placenta, stomach and peripheral blood. The protein is detectable in brain, heart, kidney, intestine, muscle, lung and testis. The CRAL-TRIO domain is involved in interaction with inositol phospholipids. The DH domain is essential for transforming activity and directly catalyzes GDP-GTP exchange activity. It may interact with CCPG1. Phosphorylation by TNK2 enhances guanine nucleotide exchange factor (GEF) activity toward Rho family proteins. MCF2 and DBL represent two activated versions of the same proto-oncogene. Belongs to the MCF2 family.