Open AccessHormonal regulation of low‐density lipoprotein (LDL) receptor activity in human hepatoma Hep G2 cells
Author(s) -
WADE David P.,
KNIGHT Brian L.,
SOUTAR Anne K.
Publication year - 1988
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1988.tb14084.x
Subject(s) - ldl receptor , receptor , medicine , endocrinology , low density lipoprotein , lipoprotein , blot , chemistry , biochemistry , biology , cholesterol , gene
Low‐density lipoprotein (LDL) receptors of approximate M r 130000 on non‐reduced gels have been identified in Hep G2 cells by immuno‐ and ligand‐blotting of cell extracts. Measurement of LDL receptor protein by scanning ligand blots was correlated with the specific binding, uptake and degradation of 125 I‐labelled LDL by intact cells, confirming that this is mediated by the LDL receptor. Cells incubated in medium with serum expressed significant LDL receptor activity. This increased when cells were transferred to medium containing lipoprotein‐deficient serum (LPDS) but was not maximal because a further increase occurred when compactin was included in the medium. Inclusion of 17α‐ethinyl estradiol or 17β‐estradiol in the medium at concentrations up to 500 ng/ml had no effect on LDL receptor activity in the cells as assayed by ligand blotting. Inclusion of insulin (100 mU/ml) in the preincubation medium containing LPDS resulted in a twofold increase in LDL‐receptor protein and of LDL binding and degradation by intact cells. Insulin also diminished the suppressive effect of LDL on LDL receptor activity. If insulin exerts this effect in vivo it may partly explain why the liver expresses LDL receptors despite high levels of LDL in plasma and interstitial fluid.