Abstract
U937 is a monocytic cell-line originally derived from a histiocytic lymphoma. In serum-free medium the growth of U937 cells was stimulated by addition of low density lipoprotein (LDL). Methylation of LDL impaired its ability to be taken up in U937 cells as well as the capacity to stimulate the growth of these cells. Pretreatment of U937 cells with a monoclonal antibody against the LDL receptor was also found to completely block the growth-promoting effect of LDL. Exposure of U937 cells to liposomes with a lipid composition similar to that of LDL did not stimulate the growth rate. These findings demonstrate that growth of U937 cells under serum-free conditions is related to the amount of LDL ingested by the cells and that this uptake is mediated by binding of LDL to the LDL receptor. To determine if LDL-induced growth of U937 cells can be used to identify LDL with decreased binding to the LDL receptor, U937 cells were incubated with LDL isolated from a patient with familial defective apolipoprotein B-100 and from subjects with various lipoprotein phenotypes. LDL containing defective apolipoprotein B-100 was found to be less than half as effective as LDL from normolipidemic controls in stimulating growth of U937 cells. LDL isolated from patients with hyperlipoproteinemia type IIa and IV did not differ from normal LDL in their ability to promote growth of U937 cells. The present results suggest that LDL-induced growth of U937 cells may be used as an assay to identify defective receptor binding of LDL.
Highlights
U937 is a monocytic cell-line originally derived from a histiocytic lymphoma
Studies on patients with familial hypercholesterolemia (FH) and on Watanabe heritable hyperlipidemic rabbits have demonstrated that defective receptor binding of apolipoprotein B-100 (apoB) leads to hypercholesterolemia and to premature development of atherosclerosis [2]
U937 cells grown in lipoprotein-deficient serum showed only a limited increase in cell number over a 48-h period (Fig l), indicating either that lipoproteins are major growth factors for U937 cells or they contain an essential
Summary
U937 is a monocytic cell-line originally derived from a histiocytic lymphoma. In serum-free medium the growth of U937 cells was stimulated by addition of low density lipoprotein (LDL). When searching for an alternative method to determine the binding properties of LDL, we took advantage of the fact that most cell types require cholesterol for de novo membrane synthesis in order to Abbreviations: VLDL, very low density lipoprotein: HDL, high density lipoprotein; LDL, low density lipoprotein; FH, familial hypercholesterolemia; RFLP, restriction fragment length polymorphism. U937 is a monocytic cell line derived from a histiocytic lymphoma and has been used as a model for studies of monocyte/macrophage function (LO) These cells have been shown to lack the qualities required for endogenous cholesterol synthesis, and cultivation of the cells in a medium supplemented with delipidated serum results in depletion of cellular cholesterol content and arrest of cell growth within 48 h [11]. We here confirm this finding and report that the growth rate of U937 cells is dependent on the binding of LDL particles to the LDL receptor and that the growth response of these cells can be used to determine the binding properties of LDL
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