[The family of HDL receptor].

Several HDL binding proteins have recently cloned and their roles in HDL metabolism have been gradually elucidated. HBP (vigilin), which lacks a transmembrane domain, is responsive to cell cholesterol levels, however, its physiological roles remain unknown. SR-B1, a member of the class B scavenger receptor, has been reported to bind with not only oxidized LDL but also HDL. The level of SR-B1 expression correlates with both the selective cholesterol transfer into cells and cholesterol efflux from cells. These data suggest that SR-B1 plays important roles in steroid hormone production. HB2 shows high sequence homology with ALCAM (activated leukocyte-cell adhesion molecule). When overexpressed with HB2, HDL binding is increased in the cells. After PMA-induced differentiation of monocytes into macrophages, HB2 mRNA is elevated, which correlates with increased binding of HDL, but is down-regulated by cholesterol loading of macrophages. However, physiological role of HB2 also remains unknown.