Premium
Tumor necrosis factor up‐regulates expression of low‐density lipoprotein receptors on HepG2 cells
Author(s) -
Liao Wei,
Florén ClaesHenrik
Publication year - 1993
Publication title -
hepatology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.488
H-Index - 361
eISSN - 1527-3350
pISSN - 0270-9139
DOI - 10.1002/hep.1840170521
Subject(s) - tumor necrosis factor alpha , receptor , cancer research , ldl receptor , microbiology and biotechnology , medicine , tumor necrosis factor α , lipoprotein , endocrinology , chemistry , biology , cholesterol
Tumor necrosis factor mediates most biological activities of endotoxin and also, in part, mediates endotoxin‐induced disturbances in lipid metabolism. In this study, the effect of tumor necrosis factor on low‐density lipoprotein receptor activity was investigated in cells of HepG2, a well‐differentiated human hepatoma cell line. Pretreatment of the cells with tumor necrosis factor leads to enhanced binding, uptake and degradation of 125 I‐labeled low‐density lipoprotein. This effect of tumor necrosis factor was dose and time dependent. Tumor necrosis factor‐stimulated enhancement of low‐density lipoprotein binding occurred at all stages of cell growth. However, addition of an excess of unlabeled low‐density lipoprotein, to down‐regulate low‐density lipoprotein receptors before exposure to tumor necrosis factor of the cells, completely abolished the effects of tumor necrosis factor. Competition experiments using unlabeled low‐density lipoprotein and blockage experiments with a monoclonal low‐density lipoprotein receptor antibody showed that tumor necrosis factor‐stimulated low‐density lipoprotein binding takes place through stimulation of low‐density lipoprotein receptors. Comparison of the kinetics of specific low‐density lipoprotein binding in the unstimulated cells and in the tumor necrosis factor‐stimulated cells indicated that tumor necrosis factor caused a 30% increase in maximum velocity with no significant change in Michaelis constant, suggesting that tumor necrosis factor increases the number of low‐density lipoprotein receptors on the cells rather than changing binding affinity. Preincubation of the cells with cycloheximide or actinomycin D totally abolished the up‐regulatory effect of tumor necrosis factor on low‐density lipoprotein receptors. Tumor necrosis factor did not stimulate proliferation of HepG2 cells, as judged by cell protein determination or by [ 3 H]thymidine incorporation. In conclusion, this study suggests that tumor necrosis factor up‐regulates expression of low‐density lipoprotein receptors on HepG2 cells by stimulation of de novo synthesis of receptors, independent of cell growth. (H EPATOLOGY 1993;17:898–907.)