Coagulation factor VIII-associated 2 (F8A2)

Coagulation factor VIII-associated 2 (F8A2), commonly referred to as HAP40 (huntingtin-associated protein 40), is a protein primarily recognized as an effector of the small GTPase RAB5A and a binding partner of huntingtin (HTT)[5]. F8A2 mediates the recruitment of huntingtin by RAB5A onto early endosomes, influencing vesicular trafficking by stimulating the interaction of early endosomes with actin filaments and inhibiting their interaction with microtubules, thereby reducing endosome motility[5]. The F8A2 gene is located as a repeat within the X chromosome, including within intron 22 of the factor VIII gene, and has two nearly identical paralogs (F8A1, F8A3). While F8A2 is robustly transcribed in various tissues, its precise physiological or disease relevance in humans is unclear, with current data pointing toward a supporting role in intracellular trafficking rather than in coagulation or as a drug target[5][4]. There are no therapeutic drugs or biomarker utilities described for F8A2, and its function is independent from classical coagulation factor VIII function[5][4].

Other names

HAP4040-kDa huntingtin-associated proteinF8A1 (note: technically a paralog, not a strict alias)CpG island proteinFactor VIII intron 22 proteinCoagulation factor VIII-associated (intronic transcript) 2F8A3 (closely related paralog)