Differential regulation of bovine pyruvate carboxylase promoters by fatty acids and peroxisome proliferator-activated receptor-α agonist

Pyruvate carboxylase (PC) is a critical enzyme in supplying carbon for gluconeogenesis and oxaloacetate for the tricarboxylic acid cycle. The bovine PC (EC 6.4.1.1) gene contains 3 promoter sequences (P3, P2, and P1 from 5' to 3'). Physiological stressors, including the onset of calving and feed restriction, lead to elevated nonesterified fatty acids and glucocorticoid levels that coincide with an increase in PC mRNA expression. The effects of elevated fatty acids on bovine PC mRNA expression and promoter function have not been determined. The objective of this experiment was to determine the direct effects of stearic, oleic, and linoleic acids, dexamethasone, and Wy14643 (a peroxisome proliferator-activated receptor-alpha agonist) on bovine PC promoter activity. Promoter-luciferase constructs, containing 1,005 bp of P1, 1,079 bp of P2, or 1,010 bp of P3, were transiently transfected into rat hepatoma (H4IIE) cells. Cells were then treated with 1 mM stearic, oleic, or linoleic acids, 1 mu M dexamethasone, or 10 mu M Wy14643 for 23 h. Activity of P1 was suppressed with exposure to stearic acid (1.58 vs. 6.19 +/- 0.81 arbitrary units for stearic vs. control, respectively) and enhanced with exposure to Wy14643 (9.26 vs. 6.19 +/- 0.81 arbitrary units for Wy14643 vs. control, respectively). Conversely, stearic acid enhanced P3 activity (2.55 vs. 0.40 +/- 0.33 arbitrary units for stearic vs. control, respectively). Dexamethasone, linoleic acid, and oleic acid failed to elicit a response from any of the promoters tested. These data demonstrate the direct role of fatty acids in regulating PC expression and indicate that fatty acids provide promoter-specific regulation of PC promoters.