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Growth modulation of low density lipoprotein receptor sterol sensitivity in cultured human fibroblasts
Author(s) -
Tatidis Loukas,
Vitols Sigurd
Publication year - 2001
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/s11745-001-0837-y
Subject(s) - sterol , ldl receptor , cholesterol , downregulation and upregulation , reductase , hmg coa reductase , receptor , low density lipoprotein , biology , cell growth , clinical chemistry , cell culture , lipoprotein , endocrinology , biochemistry , medicine , microbiology and biotechnology , enzyme , gene , genetics
Sterols regulate low density lipoprotein (LDL) receptor and 3‐hydroxy‐3‐methylglutaryl coenzyme A (HMG‐CoA) reductase gene expressions by end product repression. Studies on cultured cells have shown that growing cells have a higher LDL uptake than quiescent cells and that incubation of cells with growth factors or mitogenic compounds leads to sterol‐resistant upregulation of LDL receptor gene expression. The recent finding that elevated LDL receptor activity in acute myelogenous leukemia cells was characterized by a decreased sensitivity to downregulation by sterols raises the possibility that the mechanism behind this is related to the cellular growth rate. By using cultured human fibroblasts as a model system we therefore studied whether growth modulation of sterol sensitivity takes place in normal actively growing cells. Judging from the ability of sterols (25‐hydroxycholesterol+cholesterol) to inhibit 125 I‐LDL degradation, we found that the sensitivity to sterols varied markedly between cells of different densities. The lowest sensitivity to sterols and highest 125 I‐LDL degradation rate were found in subconfluent cells, whereas sparse and confluent cells were the most sensitive ones. In contrast to the LDL receptor, HMG‐CoA reductase sterol sensitivity did not appear to be growth regulated. We conclude that growth‐dependent modulation of sterol sensitivity and LDL receptor activity takes place in normal human fibroblasts. Modulation of sterol sensitivity may be an important mechanism to ensure an adequate cholesterol supply in growing cells.