Lipid transporter involved in lipid countertransport between the Golgi complex and membranes of the endoplasmic reticulum: specifically exchanges sterol (cholesterol) with phosphatidylinositol 4-phosphate (PI4P, 1,2-diacyl-sn-glycero-3-phospho-(1D-myo-inositol 4- phosphate)), delivering sterol to the Golgi in exchange for PI4P, which is subsequently degraded by the SAC1/SACM1L phosphatase in the endoplasmic reticulum (PubMed:24209621, PubMed:28978670). 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 the stability of the relatively short lived ABCA1 protein (an important point of control for cholesterol efflux activity) (PubMed:18450749). {ECO:0000269|PubMed:15746430, ECO:0000269|PubMed:17428193, ECO:0000269|PubMed:18450749, ECO:0000269|PubMed:24209621, ECO:0000269|PubMed:28978670}. This is the function of OSBP (oxysterol binding protein, Ensembl gene identifier ENSG00000110048).