Identification of the human analog of SR‐BI and LOX‐1 as receptors for hypochlorite‐modified high‐density lipoprotein on human umbilical venous endothelial cells

As HOCl‐modified (lipo)proteins colocalize with endothelial cells in viivo , the interaction of HOCl‐modified high‐density lipoprotein (HOCl‐HDL 3 ) with human umbilical venous endothelial cells (HUVECs) was studied. HUVECs have much higher binding capacity and holoparticle turnover for HOCl‐HDL3 than for HDL3. The cholesterylester (CE)‐uptake from HDL3 and HOCl‐HDL3 in excess of holoparticle uptake suggested involvement of the human analog of scavenger receptor class B, type I (hSR‐BI). hSR‐BI could be identified by RT‐PCR and Northern and Western blots on HUVECs. Also, CHO‐cells overexpressing SR‐BI revealed high‐affinity binding and pronounced increase in selective CE‐uptake from HDL3 and HOCl‐HDL3. However, that intracellular degradation of HOCl‐HDL3 by HUVECs increased with degree of HOCl‐modification (which could partially be inhibited by chloroquine) pointed towards another pathway that involves receptor‐mediated endocytosis. We identified in ligand blots a single binding protein for HOCl‐HDL3 comigrating with lectin‐like oxidized‐LDL receptor (LOX‐1). Preincubation of nitrocellulose strips with anti‐LOX‐1 IgG revealed pronounced inhibition of HOCl‐HDL3 binding. Competition studies with known ligands performed on intact cells corroborated involvement of LOX‐1 in binding of HOCl‐HDL3. We conclude that hSR‐BI and LOX‐1 act in concert, with the first primarily mediating selective CE‐uptake and the latter responsible for holoparticle uptake and lysosomal degradation of HOCl‐HDL3.