ABSTRACT
Fatty acid synthase (Fasn) is a key component of energy metabolism that is dynamically induced by food intake. Although extensive studies have revealed a number of transcription factors involved in the fasting/refeeding transition of Fasn expression in hepatocytes, much less evidence is available for adipocytes. Using the in vivo Ad-luc analytical system, we identified the inverted CCAAT element (ICE) around -100 nucleotides in the Fasn promoter as a critical cis-element for the refeeding response in adipocytes. Electrophoretic mobility shift assays and chromatin immunoprecipitation show that nuclear factor Y (NF-Y) binds to ICE specifically in refeeding states. Notably, the NF-Y binding to ICE is differently regulated between adipocytes and hepatocytes. These findings provide insights into the specific mechanisms controlling energy metabolism in adipocytes.
Subject(s)
Adipocytes/metabolism , CCAAT-Binding Factor/metabolism , Fatty Acid Synthases/metabolism , Feeding Behavior , 3T3-L1 Cells , Adenoviridae/genetics , Adipocytes/cytology , Adipose Tissue, White/metabolism , Animals , Base Sequence , CCAAT-Binding Factor/genetics , Chromatin Immunoprecipitation , Electrophoretic Mobility Shift Assay , Fatty Acid Synthases/genetics , Gene Expression Regulation , Immunoblotting , Liver/metabolism , Luciferases/genetics , Luciferases/metabolism , Male , Mice , Mice, Inbred C57BL , Mice, Inbred ICR , Mutation , Promoter Regions, Genetic/genetics , Protein Binding , Response Elements/genetics , Reverse Transcriptase Polymerase Chain ReactionABSTRACT
Hepatic lipogenesis is nutritionally regulated (i.e., downregulated during fasting and upregulated during the postprandial state) as an adaptation to the nutritional environment. While alterations in the expression level of the transcription factor SREBP-1c are known to be critical for nutritionally regulated lipogenesis, upstream mechanisms governing Srebf1 expression remain unclear. Here, we show that the fasting-induced transcription factor KLF15, a key regulator of gluconeogenesis, forms a complex with LXR/RXR, specifically on the Srebf1 promoter. This complex recruits the corepressor RIP140 instead of the coactivator SRC1, resulting in reduced Srebf1 and thus downstream lipogenic enzyme expression during the early and euglycemic period of fasting prior to hypoglycemia and PKA activation. Through this mechanism, KLF15 overexpression specifically ameliorates hypertriglyceridemia without affecting LXR-mediated cholesterol metabolism. These findings reveal a key molecular link between glucose and lipid metabolism and have therapeutic implications for the treatment of hyperlipidemia.
Subject(s)
DNA-Binding Proteins/genetics , Genome , Gluconeogenesis/genetics , Hepatocytes/metabolism , Lipogenesis/genetics , Sterol Regulatory Element Binding Protein 1/genetics , Transcription Factors/genetics , Animals , Cyclic AMP-Dependent Protein Kinases/genetics , Cyclic AMP-Dependent Protein Kinases/metabolism , DNA-Binding Proteins/metabolism , Fasting , Genes, Reporter , Hepatocytes/cytology , Kruppel-Like Transcription Factors , Liver/cytology , Liver/metabolism , Liver X Receptors/genetics , Liver X Receptors/metabolism , Luciferases/genetics , Luciferases/metabolism , Male , Mice , Mice, Inbred ICR , Mice, Knockout , Nuclear Receptor Co-Repressor 1/genetics , Nuclear Receptor Co-Repressor 1/metabolism , Primary Cell Culture , Promoter Regions, Genetic , Protein Binding , Retinoid X Receptors/genetics , Retinoid X Receptors/metabolism , Signal Transduction , Sterol Regulatory Element Binding Protein 1/metabolism , Transcription Factors/metabolism , Transcriptional ActivationABSTRACT
Fatty acid elongase 5 (ELOVL5) is an enzyme involved in the synthesis of polyunsaturated fatty acids. Sterol Regulatory Element-binding Protein (SREBP)-1 activates ELOVL5 and increases polyunsaturated fatty acid synthesis, which in turn negatively affects SREBP-1 expression. Thus, ELOVL5 has been established as an SREBP-1 target gene and an important component of the negative feedback loop of de novo lipogenesis. However, the human ELOVL5 promoter/enhancer has not been fully analyzed and the location of SREBP biding sites around the ELOVL5 gene has yet to be defined. Here we performed a detailed promoter/enhancer analysis of human ELOVL5 gene, and identified two new SREBP binding sites, one in the 10 kb upstream region and one in the exon 1. These two SRE motifs are conserved among mammals and the mechanism found in the present study by which SREBP activates ELOVL5 is considered to be common in mammals. Through these findings, we clarified the molecular mechanism how SREBP activates ELOVL5, an important regulator of de novo lipogenesis.