DNA regions mediating basal and insulin responsive tyrosine aminotransferase transcription

cis-acting DNA regions which mediate the transcriptional effects of insulin show little similarity among insulin-regulated genes. This study, using mutant promoter constructs transiently transfected into the KRC-7 rat hepatoma cell line, identified an insulin-responsive element (IRE) in the promoter of the gene encoding tyrosine aminotransferase (TAT). This IRE is required for insulin inhibition of both basal and cAMP-responsive transcription, and is located near a basal enhancer (BE) required for full basal expression and cAMP sensitivity. It is also distinct from a more proximal region required for insulin inhibition of glucocorticoid-induced transcription. In addition, the sufficiency of the BE for basal transcription was examined. A proximal TAT promoter region not essential for glucocorticoid-induced expression was found to be required for mediation of the BE's effect.