Characterization of CLA-1, a human homologue of rodent scavenger receptor BI, as a receptor for high density lipoprotein and apoptotic thymocytes

Abstract

Recently, a murine scavenger receptor type B class I (SR-BI) was identified that binds high density lipoprotein (HDL) and mediates the selective uptake of cholesterol esters. The human CD36 and LIMPII analogous- 1 (CLA-1) receptor shows high sequence homology with SR-BI, but their functional relationship has not been determined. Transfected cells expressing CLA-1 bound HDL with a K(d) of about 35 μg/ml, similar to the K(d) for HDL binding to rodent SR-BI. This binding resulted in an intracellular accumulation of HDL-derived [3H]cholesterol esters without internalization or degradation of 125I-apolipoprotein. CLA-1 was strongly expressed in the adrenal gland and was also abundant in liver and testis, suggesting that CLA- 1, like SR-BI, could play a role in the metabolism of HDL. However, CLA-1 was also expressed in monocytes and, like SR-BI, recognized modified forms of low density lipoproteins as well as native LDL and anionic phospholipids. These findings suggest that CLA-1 might have additional physiological functions. We found that CLA-1 recognizes apoptotic thymocytes. Our results demonstrate that CLA-1, a close structural homologue of SR-BI, is also functionally related to SR-BI and may play an important role as a 'docking receptor' for HDL in connection with selective uptake of cholesterol esters. An additional role in recognition of damaged cells is suggested by these studies.