Bovine pyruvate carboxylase gene proximal promoter activity is regulated by saturated and unsaturated fatty acids in Madin-Darby bovine kidney cells

An increase in bovine pyruvate carboxylase (PC; EC 6.4.1.1) at calving and during feed restriction corresponds with increased circulating nonesterified fatty acids as a consequence of negative energy balance. Regulation of PC mRNA and effect of specific combinations of saturated and unsaturated fatty acid profiles has yet to be explored. Our objective was to determine the effects of chain length, degree of saturation, and copresence of saturated and unsaturated fatty acids on activity of bovine PC promoter 1 (PCP1). For these experiments, Madin-Darby bovine kidney cells were transfected with a full-length bovine PCP1 construct from -1002 to +3 bp relative to the bovine PC gene transcription start site (bovine PCP1((-1002 _+3))) ligated to a Firefly luciferase reporter, or with one of a series of nested 5' serial truncations (bovine PCP1((-773_+3)), bovine PCP1((- 494 _+3)), or bovine PCP1((-222_+3))). Cells were exposed for 23 h to either individual fatty acids (C16:0, C18:0, or C18:3n-3 cis) bound to BSA or to fatty acid mixtures in ratios of 90:10, 75:25, 50:50, or 25:75, corresponding to combinations of C16:0: C18:3n-3 cis or C18:0: C18:3n-3 cis. Total fatty acid concentration was 1.00 mM. Exposure to either C16:0 or C18:3n-3 cis alone elicited a significant increase in capacity to drive bovine PCP1((-1002_+3)) activity compared with 1% BSA in Dulbecco's Modified Eagle's Medium control treatment (2.29, 2.89, and 1.00 +/- 0.26 fold of promoter induction for C16:0, C18:3n-3 cis, and control, respectively). Treatment with C18:3n-3 cis alone caused a greater increase in promoter activity compared with C16:0 alone, indicating a lesser response to C16:0 alone for bovine PCP1((-1002 _+3)). Interestingly, inclusion of C18:3n-3 cis, at any level of fatty acid ratios examined, in combination with C16:0 increased promoter activity of bovine PCP1((-773_+3)) or bovine PCP1((-222_+3)) compared with treatment with C16:0 alone or control. Data from the bovine PCP1 truncation and fatty acid copresence experiments reveal the potential for response elements of unsaturated fatty acids or fatty acid ligands in several bovine PCP1 promoter regions. In silico analysis of bovine PCP1 identified putative peroxisome proliferator-activated receptor alpha and sterol regulatory element binding protein binding sites which may be implicated in fatty acid signaling to alter bovine PCP1 activity. Pyruvate carboxylase promoter 1 activity that is mediated by unsaturated fatty acids acting through elements within -1002 and -222 bp of bovine PCPI may determine PC response during periods of negative energy balance in dairy cows.

Automated summary

The study explored the effects of different fatty acids on the activity of the bovine PCP1 promoter, with C18:3n-3 cis showing a greater impact on promoter activity and enhancing the activity when combined with C16:0.