RAB5A effector molecule that is involved in vesicular trafficking of early endosomes (PubMed:16476778). Mediates the recruitment of HTT by RAB5A onto early endosomes. The HTT- F8A1/F8A2/F8A3-RAB5A complex stimulates early endosomal interaction with actin filaments and inhibits interaction with microtubules, leading to the reduction of endosome motility (PubMed:16476778). . This is the function of F8A3 (coagulation factor VIII associated 3, ENSG00000277150).