Guanine nucleotide exchange factor (GEF) which may activate RAB9A and RAB9B. Promotes the exchange of GDP to GTP, converting inactive GDP-bound Rab proteins into their active GTP-bound form. May be involved in cytoskeletal organization and tumorogenicity. Isoform 1 seems to be involved in a signaling transduction pathway leading to activation of MAPK1/ERK2. Isoform 3 may block ERK2 activation stimulated by ABL1. Isoform 3 may alter cell morphology and cell growth.Lichy J.H., Nucleic Acids Res. 24:4700-4708(1996).Amid C., Cytogenet. Cell Genet. 93:284-290(2001).Lichy J.H., Cell Growth Differ. 3:541-548(1992).