Study Of Mechanism And Function Of Regulation Of ChREBP Transcription By HNF-4α

Transcription factor carbohydrate responsive element binding protein(ChREBP)is abundant in liver and adipose tissues.ChREBP promotes glycolysis and lipogenesis in metabolic tissues.ChREBP-α and ChREBP-β,which are two isoforms of ChREBP transcribed from different promoters,are both transcriptionally induced by glucose.However,the mechanism by which glucose increases ChREBP mRNA levels remains unclear.Here we report that hepatocyte nuclear factor 4 alpha(HNF-4α)is a key transcription factor for glucose-responsive ChREBP-α and ChREBP-β transcription.Ectopic HNF-4α expression increased ChREBP transcription while knockdown of HNF-4α greatly reduced ChREBP mRNA levels in liver cancer cells and mouse primary hepatocytes.We analyzed levels of ChREBP and HNF-4α in the liver of mice under fasting and feeding conditions and found that the expression of HNF-4α and ChREBP was positively correlated.HNF-4α not only directly bound to an E-box-containing region in intron 12 of the ChREBP gene,but also promoted ChREBP-β transcription by directly binding to DR1 sites of the ChREBP-β promoter.In addition,HNF-4α interacted with ChREBP-α and synergistically promoted ChREBP-β transcription.Functionally,HNF-4α suppression decreased glucose-dependent ChREBP induction.Increased expression and nuclear abundance of HNF-4α and its binding to cis-elements of ChREBP gene in response to glucose contributed to glucose-induced ChREBP transcription.ChREBP is required for high rate of glycolytic and anabolic activity as well as proliferation in liver cancer cells.However,the role of ChREBP in initiation and progression of liver remains unknown.We induced liver cancer in ChREBP+/+,+/-and-/-mice using the well-established hepatic carcinogen diethylnitrosamine(DEN)injection protocol followed by high-fat diet(HFD)feeding.We found that about 95% wild type or ChREBP +/-mice developed liver cancer at 9-month old whereas the tumor incidence decreased to about 50% in ChREBP-/-mice.Tumor number and size were significantly reduced in ChREBP-/-livers compared with age-matched controls.Ki67 and BrdU staining showed that deletion of ChREBP suppressed liver cell proliferation.The levels of AFP mRNA and protein decreased in ChREBP-/-livers compared with age-matched controls.Weight gain was slower in ChREBP-/-mice compared with age-matched controls.We found that ChREBP-/-liver alleviates cirrhosis compared with age-matched controls.Taken together,our results not only revealed the novel mechanism by which HNF-4α increased ChREBP transcription in response to glucose,but also demonstrated that ChREBP-α and HNF-4α synergistically promoted ChREBP-β transcription.The mechanism by which loss of ChREBP delays initiation and progression of DEN-induced liver cancer will be further studied.