9-cis-retinoic acid increases apolipoprotein AI secretion and mRNA expression in HepG2 cells.
HepG2 cells were studied as a model for regulation of hepatic apolipoprotein AI (apo AI) secretion and gene expression by 9-cis-retinoic acid. HepG2 cells cultured on plastic dishes were exposed to 9-cis-retinoic acid (9-cis-RA) for 48 h with a complete media change at 24 h. Apo AI mass in cultured media was determined by ELISA, by quantitative immunoblotting and by steady-state 35S-methionine labeling. Messenger RNA levels were determined by RNase protection using probes for apo AI and the housekeeping gene, glyceraldehyde 3-phosphate dehydrogenase (G3PDH). 9-cis-RA increased secretion of apo AI by 52% at doses of 10 and 1 microM (6.3 +/- 0.6 vs. 4.2 +/- 0.3; P < 0.005; 6.1 +/- 0.3 vs. 4.0 +/- 0.7 ng of apo AI/mg cell protein, P < 0.05) and by 35% at 0.1 microM (5.5 +/- 0.6 vs. 4.1 +/- 0.4 ng apo AI/mg protein, P < 0.05, n = 4). Immunoblotting results were consistent with results from ELISA (70% increase at 10 microM 9-cis-RA, P < 0.001; 34% increase at 1 microM, P < 0.005, n = 3). Metabolically labeled apoAI in the medium was increased by 39% following steady-state labeling in the presence of 10 microM 9-cis-RA (597 +/- 7 vs. 430 +/- 13 DPM/microliters media; P < 0.001; n = 4). 9-cis-RA (10 microM) also increased HepG2 cell apo AI mRNA expression by 76% (68 700 +/- 400 vs. 38 900 +/- 2700 DPM, P < 0.01, n = 4), whereas expression of G3PDH mRNA was slightly decreased (14%, P < 0.05). Thus, 9-cis-RA stimulates apo AI expression in HepG2 cells, suggesting a role for retinoids in activating endogenous apo AI gene expression.
Haghpassand
M
M
Department of Cardiovascular and Metabolic Diseases, Pfizer, Inc., Groton, CT 06340, USA.
Moberly
J B
JB
D000818:Animals; D016632:Apolipoprotein A-I / Q000235:genetics* / Q000378:metabolism*; D002478:Cells, Cultured; D004797:Enzyme-Linked Immunosorbent Assay; D015870:Gene Expression / Q000187:drug effects; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases / Q000235:genetics; D015151:Immunoblotting; D008099:Liver / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental; D051379:Mice; D012333:RNA, Messenger / Q000378:metabolism*; D014212:Tretinoin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D016632:Apolipoprotein A-I; D012333:RNA, Messenger; D014212:Tretinoin; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases