Characterization of the Responsive Elements to Hormones in the Rat Aldolase B Gene

Transcription of the aldolase B gene, AldB, in the liver is regulated by hormones such as insulin and glucagon. To characterize the elements that are responsive to these hormones in the upstream region of AldB, plasmids carrying various length of the upstream region of this gene were constructed and transfected to primary cultured rat hepatocytes. The promoter activities were gradually increased by progressive deletion of the 5′-upstream region, and high activities were observed for constructs carrying the sequence between −408 and −85 bp, suggesting the presence of suppressive element(s) in the upstream region of −409 bp. The transcription activities of the mutants containing the sequences between −228 and −85 bp were enhanced by insulin, and glucagon suppressed the transcription activities of those containing the sequence between −764 and −85 bp. Two sequence elements similar to the cAMP-responsive element (CRE), one from −89 to −82 bp and another from +13 to +20 bp, were found in the upstream sequence of the gene. The latter element is not functional because its deletion did not affect either the transcription efficiency or glucagon response. However, the deletion of the former element diminished both functions. A gel retardation assay showed that the nuclear factor binds to the former element, which was competitive with authentic CRE oligonucleotide but not with the mutant CRE one. These results suggest that the CRE-like element in the promoter region is prerequisite for both fundamental transcription efficiency of the gene and suppression by glucagon in hepatocytes.