The small GTPases Rab are key regulators of intracellular membrane trafficking, from the formation of transport vesicles to their fusion with membranes. Rabs cycle between an inactive GDP-bound form and an active GTP-bound form that is able to recruit to membranes different sets of downstream effectors directly responsible for vesicle formation, movement, tethering and fusion (PubMed:15907487, PubMed:16034420). RAB4A is involved in protein transport (PubMed:29425100). Also plays a role in vesicular traffic. Mediates VEGFR2 endosomal trafficking to enhance VEGFR2 signaling (PubMed:29425100). Acts as a regulator of platelet alpha-granule release during activation and aggregation of platelets (By similarity). {ECO:0000250|UniProtKB:P56371, ECO:0000269|PubMed:15907487, ECO:0000269|PubMed:16034420, ECO:0000269|PubMed:29425100}. This is the function of Ensembl gene identifier ENSG00000168118 (RAB4A, RAB4A, member RAS oncogene family).