| Abstract: | Four murine macrophage-like continuous cell lines (P388D1, J774.1, RAW 264.7, and PU5-1.8) and two human cell lines displaying macrophage-monocyte characteristics (HL-60, U-937) have been examined for their ability to degrade both normal and acetylated low-density lipoproteins. All of these cell lines, except PU5-1.8, were demonstrated to have LDL receptors that were induced 2-5-fold by preincubation in lipoprotein-deficient serum. Metabolism of dextran sulfate-LDL complexes by all lines except PU5-1.8 was observed. Three cell lines, P388D1, J774.1 and RAW 264.7, while exhibiting individual differences in their metabolism of acetyl-LDL, all processed acetyl-LDL in a fashion qualitatively analogous to that by murine peritoneal macrophages and human monocytes. Cell lines PU5-1.8, U-937 and HL-60 did not bind or degrade significant quantities of acetyl-LDL. In P388D1 cells, metabolism of acetyl-LDL exhibited time and concentration dependence, was reversibly inhibited by chloroquine, blocked by fucoidan and dextran sulfate, and was calcium independent. Approximately 4 X 10(5) receptors, with an apparent Kd of 3 X 10(-8) M, were present on P388D1 cells. P388D1 cells metabolized 30% as much acetyl-LDL as murine peritoneal macrophages at 37 degrees C and bound 60% as much at 4 degrees C. Chemical measurement demonstrated a 250-fold increase in the cholesteryl ester content of P388D1 cells over 96 h. The accumulation of cholesteryl esters was reversible in the presence of HDL3 and involved continuous hydrolysis and reesterification. These lines represent a convenient resource for examining the metabolism of chemically modified lipoproteins, for isolation of cell mutants, and for isolation of specific lipoprotein receptors. |
