HNF1alpha upregulates the human AE2 anion exchanger gene (SLC4A2) from an alternate promoter.

The human AE2 gene (SLC4A2) is transcribed in a widespread fashion from the upstream promoter, the resultant full-length transcript AE2a being encountered in most tissues. Moreover, alternate promoter sequences within intron 2 may drive tissue-restricted expression of variants AE2b(1) and AE2b(2), mainly in liver and kidney. AE2b(2) proximal promoter sequences are highly active in transfected liver-derived HepG2 cells and contain an HNF1 motif. Mutation-disruption of this motif dramatically decreased alternate promoter activity in HepG2 cells but not in prostate-derived PC-3 cells. Electromobility shift and supershift assays indicated that HNF1alpha from HepG2 nuclear extracts binds the HNF1 sequence. Transactivation studies in PC-3 cells showed enhanced activity of the wild-type construct upon cotransfection with an HNF1alpha expression plasmid, while activity of the HNF1-mutated construct remained unaffected. Since liver AE2 is putatively involved in the biliary secretion of bicarbonate, HNF1alpha may have a role in increasing bicarbonate secretion in response to certain stimuli.