KETOCONAZOLE AND 25-HYDROXYCHOLESTEROL PRODUCE RECIPROCAL CHANGES IN THE RATE OF TRANSCRIPTION OF THE HUMAN LDL RECEPTOR GENE

Sterol-dependent regulation of low-density lipoprotein (LDL) receptor gene expression was studied in the human hepatoma HepG2 cellline. Incu bation of HepG2 cells with 20 mu M ketoconazole increased the level of LDL receptor mRNA. After a lag of approx. 1.0 h the level rose 6.5-fo ld within 8.0 h and remained elevated for up to 24 h. Incubation with 10 mu g 25-hydroxycholesterol/ml for 24 h produced a 40-50% reduction in the level of LDL receptor mRNA. Ketoconazole- and 25-hydroxrycholes terol-induced changes in LDL receptor mRNA accumulation were due to al terations in the relative rate of LDL receptor gene transcription as m easured by nuclear run-on transcription. Incubation with 20 mu M ketoc onazole for 4 h or 10 mu g 25-hydroxycholesterol/ml for 24 h produced a 3.6-fold increase and a 40% reduction, respectively, in the transcri ption rate of LDL receptor gene. Removal of the Alu-like sequence elem ents within the LDL receptor cDNA was required to consistently measure changes in LDL receptor gene transcription. No significant changes we re noted in the half-life of LDL receptor mRNA in ketoconazole or 25-h ydroxycholesterol-treated cells. These data demonstrate that sterol-de pendent changes in the level of LDL receptor mRNA can be completely ac counted for by changes in the rate of LDL receptor gene transcription.