Involvement of a unique carbohydrate-responsive factor in the glucose regulation of rat liver fatty-acid synthase gene transcription.
Refeeding carbohydrate to fasted rats induces the transcription of genes encoding enzymes of fatty acid biosynthesis, e.g. fatty-acid synthase (FAS). Part of this transcriptional induction is mediated by insulin. An insulin response element has been described for the fatty-acid synthase gene region of -600 to +65, but the 2-3-fold increase in fatty-acid synthase promoter activity attributable to this region is small compared with the 20-30-fold induction in fatty-acid synthase gene transcription observed in fasted rats refed carbohydrate. We have previously reported that the fatty-acid synthase gene region between -7382 and -6970 was essential for achieving high in vivo rates of gene transcription. The studies of the current report demonstrate that the region of -7382 to -6970 of the fatty-acid synthase gene contains a carbohydrate response element (CHO-RE(FAS)) with a palindrome sequence (CATGTGn(5)GGCGTG) that is nearly identical to the CHO-RE of the l-type pyruvate kinase and S(14) genes. The glucose responsiveness imparted by CHO-RE(FAS) was independent of insulin. Moreover, CHO-RE(FAS) conferred glucose responsiveness to a heterologous promoter (i.e. l-type pyruvate kinase). Electrophoretic mobility shift assays demonstrated that CHO-RE(FAS) readily bound a unique hepatic ChoRF and that CHO-RE(FAS) competed with the CHO-RE of the l-type pyruvate kinase and S(14) genes for ChoRF binding. In vivo footprinting revealed that fasting reduced and refeeding increased ChoRF binding to CHO-RE(FAS). Thus, carbohydrate responsiveness of rat liver fatty-acid synthase appears to require both insulin and glucose signaling pathways. More importantly, a unique hepatic ChoRF has now been shown to recognize glucose responsive sequences that are common to three different genes: fatty-acid synthase, l-type pyruvate kinase, and S(14).
Rufo
C
C
Division of Nutritional Sciences and the Institute for Cellular and Molecular Biology, The University of Texas, Austin, Texas, 78712, USA.
Teran-Garcia
M
M
Nakamura
M T
MT
Koo
S H
SH
Towle
H C
HC
Clarke
S D
SD
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002478:Cells, Cultured; D018983:DNA Footprinting; D064429:Fatty Acid Synthases / Q000235:genetics*; D015971:Gene Expression Regulation, Enzymologic; D005947:Glucose / Q000494:pharmacology*; D022781:Hepatocytes / Q000201:enzymology*; D008099:Liver / Q000201:enzymology*; D008156:Luciferases / Q000235:genetics; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism; D011770:Pyruvate Kinase / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D016415:Sequence Alignment; D012689:Sequence Homology, Nucleic Acid; D014158:Transcription, Genetic / Q000502:physiology*; D014162:Transfection
D009687:Nuclear Proteins; D008156:Luciferases; D064429:Fatty Acid Synthases; D011770:Pyruvate Kinase; D005947:Glucose