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Cholesterol and lipoprotein metabolism of human promyelocytic leukemic HL-60 induced macrophages.
AuthorEl-Jouni, Zeinab Ezzuddine.
AdvisorMcNamara, Donald J.
MetadataShow full item record
PublisherThe University of Arizona.
RightsCopyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
AbstractHuman promyelocytic leukemic cells (HL-60) possess well regulated expression of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase, acylCoA:cholesterol acyltransferase (ACAT), and receptor-mediated low density lipoprotein (LDL) catabolism, but lack receptor-mediated acetyl-LDL processing. Differentiation of HL-60 cells with tetramyristic phorbol acetate (TPA) is accompanied by the loss of receptor-mediated LDL degradation and no expression of a functionally active scavenger receptor. 1,25-Dihydroxyvitamin D₃ (D₃)-induced HL-60 macrophages possess specific and saturable receptor-mediated binding for LDL, with an apparent K(d) of 29 μg/ml and a B(max) of 219 ng/mg. Receptor-mediated LDL degradation is specific for apoB and apoE containing lipoproteins; it is calcium dependent, and is inhibited by pronase and chloroquine. Differentiation of HL-60 cells with D₃ for 2 days induces a 45-fold increase in acetyl-LDL degradation rate compared to undifferentiated cells. Receptor-mediated degradation of acetyl-LDL is specific for acetyl-LDL, calcium independent, inhibited by chloroquine, pronase and fucoidin treatment, and is not regulated by cellular cholesterol. Acetyl-LDL binding studies demonstrated a K(d) of 36 μg/ml and a B(max) 313 ng/mg. Delivery of cholesterol via receptor-mediated catabolism of LDL or acetyl-LDL results in significant suppression of sterol synthesis and HMG-CoA reductase activity, and significant induction of ACAT activity relative to macrophages incubated with LPDS (P < 0.001). However, receptor-mediated degradation of acetyl-LDL, but not LDL, significantly increases cholesteryl ester content (P < 0.001). D₃-induced HL-60 macrophages incubated with or without LDL for 48 hr exhibited large empty vacuoles with little or no lipid stainable material. In contrast, macrophages incubated with acetyl-LDL exhibited a dramatic increase in lipid stainable material which imparted the macrophages with a foamy appearance. In conclusion, HL-60 cells treated with D₃ for 48 hr undergo activation differentiation assuming the structural and functional characteristics of human monocyte-derived macrophages. Thus, D₃-induced HL-60 macrophages are a suitable in vitro system to study lipoproteins and cholesterol regulation as related to macrophage involvement in atherosclerosis.
Degree ProgramNutritional Sciences