Class A Scavenger receptor (SR‐A) mediated adhesion is regulated by lipid raft localization and cytoplasmic motifs

Abstract

SR‐A is a membrane receptor that mediates cell adhesion and ligand internalization. Previous studies suggest that SR‐A‐mediated macrophage adhesion, but not ligand internalization, activates signaling pathways that promote inflammation. We hypothesized that SR‐A function is regulated by localization of SR‐A in distinct plasma membrane domains; specifically, that SR‐A‐ mediated cell adhesion requires localization in cholesterol‐rich lipid rafts. To test this hypothesis, HEK cells were transfected to express either wild‐type (SR‐Aw/t) or a truncated receptor (SR‐AΔ1‐ 49), which lacks all but the membrane‐proximal 6 cytoplasmic amino acids and mediates only adhesion. A detergent‐free cell fractionation protocol was used to show that SR‐A and SR‐AΔ1–49 localized to a similar extent in lipid rafts. To determine if lipid raft localization was required for cell adhesion, cells were treated with methyl‐beta‐cyclodextrin (MβCD), which depletes cell cholesterol and disrupts lipid rafts. MβCD treatment inhibited the adhesion of cells expressing SR‐Aw/t, but did not affect adhesion mediated by SR‐AΔ1–49. Together, these results demonstrate that SR‐A localizes in lipid rafts, that this localization is required for cell adhesion, and that the membrane proximal amino acids are sufficient to localize the receptor in lipid rafts but not sufficient for functional regulation. Support: NIH‐HLRO1‐076682 and AHA Predoctoral fellowship AHA‐11PRE‐7950020.