Distinct C/EBPalpha motifs regulate lipogenic and gluconeogenic gene expression in vivo.

The C/EBPα transcription factor regulates hepatic nitrogen, glucose, lipid and iron metabolism. However, how it is able to independently control these processes is not known. Here, we use mouse knock-in mutagenesis to identify C/EBPα domains that specifically regulate hepatic gluconeogenesis and lipogenesis. In vivo deletion of a proline-histidine rich domain (PHR), dephosphorylated at S193 by insulin signaling, dysregulated genes involved in the generation of acetyl-CoA and NADPH for triglyceride synthesis and led to increased hepatic lipogenesis. These promoters bound SREBP-1 as well as C/EBPα, and the PHR was required for C/EBPα-SREBP transcriptional synergy. In contrast, the highly conserved C/EBPα CR4 domain was found to undergo liver-specific dephosphorylation of residues T222 and T226 upon fasting, and alanine mutation of these residues upregulated the hepatic expression of the gluconeogenic G6Pase and PEPCK mRNAs, but not PGC-1α, leading to glucose intolerance. Our results show that pathway-specific metabolic regulation can be achieved through a single transcription factor containing context-sensitive regulatory domains, and indicate C/EBPα phosphorylation as a PGC-1α-independent mechanism for regulating hepatic gluconeogenesis.