A synonymous variant in scavenger receptor, class B, type I gene is associated with lower SR-BI protein expression and function

Objective: A synonymous variant within scavenger receptor class B type I gene (SCARB1), exon 8 rs5888, has been associated with altered lipid levels and cardiovascular risk in humans. The objective was to determine if rs5888 decreased SR-BI protein expression and function in vitro. Methods: SR-BI RNA secondary structure, turnover, polysomal distribution and protein expression were examined in COS cells transfected with wild-type or rs5888-SR-BI plasmids by selective 2′-hydroxyl acylation and primer extension assays, actinomycin D inhibition, polysomal profiling, and western blotting. SR-BI function in murine macrophages stably expressing wild-type or rs5888-SR-BI was assessed by measuring the specific cell association of ¹²⁵I,³H-cholesteryl ester (CE) radiolabeled HDL. Results: Rs5888 changed RNA secondary structure and led to marked differences in the polysomal profiles compared with wild-type transcript (p<0.02). As compared to wild-type cells, COS cells expressing rs5888 had significantly lower SR-BI protein expression (p<0.04), but no difference in total RNA transcript levels. There were no differences in SR-BI RNA turnover in murine macrophages, whereas specific cell association of ¹²⁵I (p<0.0001) or ³H-CE (p<0.00001) was significantly lower in rs5888 cells. Conclusions: The rs5888 variant affected SR-BI RNA secondary structure, protein translation, and was significantly associated with reduced SR-BI protein expression and function in vitro.