Lipid transporter involved in lipid countertransport between the Golgi complex and membranes of the endoplasmic reticulum: specifically exchanges sterol with phosphatidylinositol 4-phosphate (PI4P), delivering sterol to the Golgi in exchange for PI4P, which is degraded by the SAC1/SACM1L phosphatase in the endoplasmic reticulum (PubMed:24209621). Binds cholesterol and a range of oxysterols including 25-hydroxycholesterol (PubMed:15746430, PubMed:17428193). Cholesterol binding promotes the formation of a complex with PP2A and a tyrosine phosphatase which dephosphorylates ERK1/2, whereas 25-hydroxycholesterol causes its disassembly (PubMed:15746430). Regulates cholesterol efflux by decreasing ABCA1 stability (PubMed:18450749). Homodimer or homotrimer. Interacts (via FFAT motif) with VAPA (PubMed:24209621, PubMed:20178991). Interacts (via C-terminus) with RELCH (via the third HEAT repeat) (By similarity). Found in a complex composed of RELCH, OSBP1 and RAB11A (By similarity). Predominantly cytosolic. Widely expressed. The FFAT motif is required for interaction with VATA and proper localization of the protein. The PH and the Ala/Gly-rich domains control cholesterol binding without affecting 25-hydroxycholesterol binding. The second coiled-coil domain is required for interaction with the tyrosine phosphatase. Belongs to the OSBP family. Aberrant splicing.