Regulation of Na+/H+ exchanger gene expression. Role of a novel poly(dA.dT) element in regulation of the NHE1 promoter

In this study we examine regulation of expression of the Na+/H+ exchanger promoter in L6 and NIH 3T3 cells. We have identified a highly conserved poly(dA dT)-rich region that appears to be important in regulation of expression of the NHE1 gene. Deletion or mutation of this region results in dramatic decreases in promoter activity in both L6 and NIH 3T3 cells. In addition, DNase I footprinting experiments demonstrated that this region is protected by nuclear extracts from both cell types, and gel mobility shift assays showed that a protein or proteins specifically binds to the poly(dA dT)-rich element. Using Southwestern blotting, we determined that a 33-kDa protein binds to the poly(dA dT)-containing region. Mutations that abolished protein binding to this element diminished activity of the promoter. Insertion of the poly(dA dT)-rich element into a plasmid containing the SV40 promoter demonstrated that this element can also enhance the activity of a foreign promoter. Together, the results we have presented here show that the poly(dA dT)-rich region is important in regulation of NHE1 expression in different cell types.