Glucose regulation of mouse S(14) gene expression in hepatocytes. Involvement of a novel transcription factor complex

Abstract

Transcription of genes encoding enzymes required for lipogenesis is induced in hepatocytes in response to elevated glucose metabolism. We have previously mapped the carbohydrate-response elements (ChoREs) of the rat liver-type pyruvate kinase (L-PK) and S(14) genes and found them to share significant sequence similarity. However, progress in unraveling this signaling pathway has been hampered due to the difficulty in identifying the key factor(s) that bind to these ChoREs. To gain further insight into the nature of the carbohydrate-responsive transcription factor, the glucose regulatory sequences from the mouse S(14) gene were examined in primary hepatocytes. Three elements were found to be essential for supporting the glucose response: a thyroid hormone-response element between -1522 and -1494, an accessory factor site between -1421 and -1392, and the ChoRE between -1450 and -1425. Of these, only the accessory factor site was conserved between the rat and mouse S(14) genes. Investigation of the ChoRE sequence indicated that two half E box motifs are critical for the response to glucose. Electrophoretic mobility shift assays revealed a complex formed between the mouse S(14) ChoRE and liver nuclear proteins. This complex was also formed by ChoREs from the rat S(14) and L-PK genes but not by mutants of these sites that are inactive in supporting the glucose response. These results suggest the presence of a novel transcription factor complex that mediates the glucose-regulated transcription of S(14) and L-PK genes.