ANALYSIS OF THE GENE-REGULATION OF THE LD L-RECEPTOR IN HEPG2 CELLS AND IN FIBROBLASTS BY RT-PCR AND GEL-SHIFT EXPERIMENTS

The activity of the LDL-receptor is regulated by LDL-cholesterol and h ormones. We studied the influence of LDL-cholesterol, insulin and insu lin-like growth factor I (IGF-1) on the expression of the LDL-receptor gene in human fibroblasts and liver cells (HepG2). We used an transcr ipt-titration assay (RT-PCR) to measure the mRNA level. Application of LDL-cholesterol repressed the LDL-receptor mRNA in fibroblasts to 1/4 and in HepG2 cells to 1/2 as compared to the level in lipoprotein-def icient serum. Insulin and IGF-1 induced the gene expression of the LDL -receptor, which was repressed by cholesterol, in fibroblasts within 2 h 4- and 4,5-fold, respectively, and in HepG2 cells within 4 h 2-fold at maximum. Using gel-shift experiments we studied nuclear proteins w hich bound to the sterol-regulated element (SRE-1) and to the Spl-elem ent within the LDL-receptor gene promoter. Neither the repression by c holesterol nor the induction by insulin or IGF-1 resulted in a detecta ble change of protein binding to the SRE-1/Sp1-element.