Guanine nucleotide exchange factor (GEF) regulating clathrin- mediated endocytosis through RAB35 activation. Promotes the exchange of GDP to GTP, converting inactive GDP-bound RAB35 into its active GTP- bound form. Regulates clathrin-mediated endocytosis of synaptic vesicles and mediates exit from early endosomes (PubMed:20154091, PubMed:20937701). Binds phosphatidylinositol-phosphates (PtdInsPs), with some preference for PtdIns(3)P (By similarity). {ECO:0000250|UniProtKB:Q8K382, ECO:0000269|PubMed:20154091, ECO:0000269|PubMed:20937701}. This is the function of DENND1A (DENN domain containing 1A, Ensembl gene identifier ENSG00000119522).