Metabolism of normal and modified low-density lipoproteins by macrophage cell lines of murine and human origin

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 P388D, 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 · 10⁵ receptors, with an apparent K_d of 3 · 10^-8 M, were present on P388D₁ cells. P388D₁ cells metabolized 30% as much acetyl-LDL as murine peritoneal macrophages at 37°C and bound 60% as much at 4°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.