Guanine nucleotide exchange factor (GEF) which may activate RAB6A and RAB39A and/or RAB39B. Promotes the exchange of GDP to GTP, converting inactive GDP-bound Rab proteins into their active GTP-bound form. Involved in the negative regulation of neurite outgrowth (By similarity). {ECO:0000250|UniProtKB:G3V7Q0, ECO:0000269|PubMed:20937701}. This is the function of Ensembl gene identifier ENSG00000184014 (DENND5A, DENN domain containing 5A).