ENHANCEMENT OF LOW-DENSITY-LIPOPROTEIN BINDING TO BOTH LOW-DENSITY-LIPOPROTEIN RECEPTOR-POSITIVE AND RECEPTOR-NEGATIVE CELLS BY TETRACYCLINE ANTIBIOTICS

Some tetracycline (TC) antibiotics, including TC and anhydrotetracycli ne, have been found to enhance specific binding of row density lipopro tein (LDL) to both LDL receptor-positive and -negative cells at relati vely higher concentrations. When incubated at 37 degrees C, the abilit y of LDL receptor-negative human fibroblasts to bind I-125-LDL was inc reased from <2 to 45 ng/mg by 170 mu M TC. In normal human fibroblasts and Hep G2 cells, I-125-LDL binding was elevated 1.4- to 2-fold by 11 3 mu M TC. The I-125-LDL binding in the presence of TC was diminished by both heparin and EDTA. The enhancement by TC was not observed when I-125-LDL binding was assayed at 4 degrees C. TC enhanced LDL binding to paraformaldehyde-fixed Hep G2 cells, excluding LDL receptor inducti on in the mechanism. These results demonstrated that TC enhanced cellu lar LDL binding through a process not involving functional LDL recepto rs.