Phosphorylation of ATF-1 enhances its DNA binding and transcription of the Na,K-ATPase alpha 1 subunit gene promoter.

Transcriptional activity of both ATF-1 and CREB is enhanced by protein phosphorylation. While enhancement has been attributed to an increase in binding affinity for a co-activator (CBP), induction of the DNA binding activity by phosphorylation is an open question. Using the Na,K-ATPase alpha1 subunit gene promoter, which has an asymmetrical ATF/CRE site, we analyzed the effect of phosphorylation on DNA binding activity of the ATF-1-CREB heterodimer. Dephosphorylation of the heterodimer in nuclear extracts reduced binding to the ATF/CRE site. Phosphorylation of ATF-1 at Ser63 enhanced its binding to the ATF/CRE site in both the homodimeric and heterodimeric forms. Transcription of the Na,K-ATPase alpha 1 subunit gene promoter was also stimulated by phosphorylated ATF-1 in vitro.