FATTY-ACIDS AND FIBRATES ARE POTENT INDUCERS OF TRANSCRIPTION OF THE PHOSPHENOLPYRUVATE CARBOXYKINASE GENE IN ADIPOCYTES

Cytosolic phosphoenolpyruvate carboxykinase (PEPCK) plays a critical r ole in adipose tissue glyceroneogenesis. We have previously shown that transcription of the PEPCK gene was stimulated by isoprenaline and re tinoic acid in 3T3-F442A adipocytes. We also showed that oleate increa sed PEPCK mRNA. Here, we analysed the effect that fatty acids of vario us chain lengths anti unsaturation degrees exerted on PEPCK gene expre ssion in 3T3-F442A adipocytes. When maintained in serum-free, glucose- free medium, differentiated cells responded to unsaturated long-chain fatty acids by a large increase in PEPCK mRNA whereas saturated fatty acids were inefficient. A maximum fivefold stimulation by oleate was a ttained at 4 h of treatment with 1 mM fatty acid bound to albumin in a 6:1 ratio. The poly-unsaturated very long-chain fatty acid all-cis-4, 7,10,13,16,19-docosahexaenoic acid (C-22:6) was even more potent and p roduced a tenfold increase. The expression of the genes encoding glyce rol-3-phosphate dehydrogenase, hormone-sensitive lipase or actin remai ned unaffected by oleate exposure. A 4-h treatment by the hypolipidemi c drug clofibrate, 0.5-2 mM, also produced a large (3-9-fold) increase in PEPCK mRNA. When used at non-saturating concentrations, oleate and clofibrate acted in an additive manner. At maximally effective concen trations, additivity was lost, suggesting that fatty acids and fibrate s might act through similar mechanisms. Nuclear transcription experime nts showed that oleate and clofibrate: stimulated the transcription ra te of the gene. 3T3-F442A cells were stably transfected with a plasmid containing the base pairs -2100 to +69 of the PEPCK gene promoter fus ed to the chloramphenicol acetyltransferase gene, These differentiated stable transfectants responded to oleate and clofibrate by a specific increase in chloramphenicol acetyltransferase activity. Adipocytes ex press various isoforms of peroxisome-proliferator-activated receptors that can be activated by fibrates and fatty acids. Potential recogniti on sequences for peroxisome-proliferator-activated receptors are prese nt in the -2100 to +69 fragment of the PEPCK gene promoter. Thus, this gene represents an ideal molecular target for understanding the compl ex transcriptional control exerted by fatty acids and peroxisome proli ferators.