Fatty Acids and Fibrates are Potent Inducers of Transcription of the Phosphenol pyruvate Carboxykinase Gene in Adipocytes

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Abstract
Cytosolic phosphoenolpyruvate carboxykinase (PEPCK) plays a critical role in adipose tissue glyceroneogenesis. We have previously shown that transcription of the PEPCK gene was stimulated by isoprenaline and retinoic acid in 3T3‐F442A adipocytes. We also showed that oleate increased PEPCK mRNA. Here, we analysed the effect that fatty acids of various chain lengths and unsaturation degrees exerted on PEPCK gene expression 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 attained at 4h 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 (C22:6) was even more potent and produced a tenfold increase. The expression of the genes encoding glycerol‐3‐phosphate dehydrogenase, hormone‐sensitive lipase or actin remained unaffected by oleate exposure. A 4‐h treatment by the hypolipidemic 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 concentrations, additivity was lost, suggesting that fatty acids and fibrates might act through similar mechanisms. Nuclear transcription experiments showed that oleate and clofibrate stimulated the transcription rate of the gene. 3T3‐F442A cells were stably transfected with a plasmid containing the base pairs–2100 to +69 of the PEPCK gene promoter fused to the chloramphenicol acetyltransferase gene. These differentiated stable transfectants responded to oleate and clofibrate by a specific increase in chloramphenicol acetyltransferase activity. Adipocytes express various isoforms of peroxisome‐proliferator‐activated receptors that can be activated by fibrates and fatty acids. Potential recognition sequences for peroxisome‐proliferator‐activated receptors are present in the–2100 to +69 fragment of the PEPCK gene promoter. Thus, this gene represents an ideal molecular target for understanding the complex transcriptional control exerted by fatty acids and peroxisome proliferators.