Plays a role in regulation of vesicular cargo transport from the trans-Golgi network (TGN) to the plasma membrane (By similarity). Regulates Golgi phosphatidylinositol 4-phosphate (PtdIns(4)P) levels and activates the PtdIns(4)P phosphatase activity of SACM1L when it binds PtdIns(4)P in 'trans' configuration (By similarity). Binds preferentially to PtdIns(4)P (By similarity). Negatively regulates APOB secretion from hepatocytes (By similarity). Interacts with GTP-bound ARF1 (By similarity). Interacts with SACM1L and VAPA and/or VAPB to form a ternary complex (By similarity). Localizes to ER-trans Golgi network (TGN) contacts sites. The PH domain binds the small GTPase ARF1 and phosphatidylinositol-4-phosphate (PtdIns4P) with high selectivity, and is required for its recruitment to the trans-Golgi network (TGN).