Effects of dehydroepiandrosterone on rat apolipoprotein Al gene expression in the human hepatoma cell line, HepG2

Serum apolipoprotein Al (apoAl) levels correlate with the risk of developing atherosclerosis. Previous studies have suggested that dehydroepiandrosterone (DHEA) lowers high-density lipoprotein (HDL)-cholesterol levels. We investigated whether or not DHEA may lower HDL-cholesterol levels by suppressing apoAl gene transcription in hepatocytes. ApoAl mRNA levels, assessed by Northern blotting, were suppressed in HepG2 cells treated with DHEA (34%) (10 mug/mL) or testosterone (36%) (T, 1 mug/mL). Estradiol alone (E-2, 1 mug/mL) had relatively little effect on apoAl mRNA levels, while E-2 in combination with DHEA prevented a decrease in apoAl mRNA levels compared to DHEA alone. To determine whether these effects were due to changes in apoAl gene transcription, HepG2 cells were transfected with a plasmid carrying the full-length promoter of the rat apoAI gene ligated into a chloramphenicol acetyltransferase (CAT) reporter construct. The plasmid pCMV.SPORT-beta-gal was included in each transfection to normalize the data to transfection efficiency. Cells were then cultured in the presence or absence of DHEA (10 mug/mL), T (1 mug/mL), 17alpha-methyltestosterone (MTT, 1 mug/mL), 5alpha-dihydrotestosterane (DHT, 1 mug/mL), E-2 (1 mug/mL), or a combination of DHEA plus E-2, T plus E-2, MTT plus E-2, and DHT plus E-2, for 24 hours. CAT activity, relative to beta-galactosidase activity, was reduced by 19.6%, 57.6%, 38.6%, and 54.6% with DHEA, T, DHT, and MTT addition, respectively. E-2 increased CAT activity by 43.8%. When the androgens (ie, DHEA, T, DHT, or MTT) were combined with E-2, apoAl promoter activity was suppressed. We conclude, therefore, that androgens downregulate apoAl promoter activity in the presence or absence of E-2. However, the changes in mRNA levels do not always reflect changes in promoter activity, suggesting that these steroids may have additional post-transcriptional effects on steady-state apoAl mRNA levels. It remains to be established if the transcriptional effects we observed are mediated through an androgen response element. Copyright (C) 2002 by W.B. Saunders Company.