DOMINANT-NEGATIVE MUTATIONS OF THE SCAVENGER RECEPTOR - NATIVE RECEPTOR INACTIVATION BY EXPRESSION OF TRUNCATED VARIANTS

The bovine scavenger receptor was truncated at amino acid 266 or 310 t o delete either all or part, respectively, of the collagen-like domain . The truncated receptors were inactive in the binding and internaliza tion of acetyl (Ac) low density lipoprotein (LDL). Coexpression of tru ncated receptor with the native receptor dramatically reduced the perc entage of cells internalizing fluorescently labeled Ac LDL, compared w ith cells expressing the native receptor alone. The mutant truncated a t amino acid 266 was most effective in receptor inactivation, resultin g in a 42% or 80% decrease in the percentage of cells expressing activ e receptor when transfected in a 1:1 or 1:2 molar ratio (native:mutant ), respectively, with native receptor. Degradation of I-125-Ac LDL was reduced up to 90% when the native and truncated mutant receptors were coexpressed. Scavenger receptor inhibition was specific because the a ctivity of the LDL receptor was not altered. Transient transfection of the mouse macrophage cell line P388D1 with truncated scavenger recept or resulted in a 65% decrease in the uptake and degradation of Ac LDL but did not decrease the degradation of beta-migrating very low densit y lipoprotein, which is LDL receptor-mediated. These results demonstra te that expression of truncated bovine scavenger receptor inactivates both the native bovine and murine scavenger receptors, producing a dom inant negative phenotype in vitro.