The transcription factor CREMτ and cAMP regulate the activity of the Na,K‐ATPase α4 isoform promoter

The catalytic α subunit of the Na,K‐ATPase exists as multiple isoforms (α1, α2, α3 and α4) that are expressed in a tissue specific manner. The α4 isoform exhibits the most limited pattern of expression, and is restricted to male germ cells. Activity of α4 is essential for sperm function, and the protein is up‐regulated during spermatogenesis. At present, the mechanisms involved in α4 expression are unknown. The present study addressed the transcriptional control of α4 gene expression. We describe that a 5′ untranslated region of the α4 gene (designated −339/+480 based on the α4 transcription initiation site) has promoter activity in luciferase reporter assays. Computer analysis of this promoter region revealed consensus sites for the cAMP Response Element Modulator (CREM). Accordingly, dibutyryl cAMP (db‐cAMP) and CREMτ, a testis specific splice variant of CREM were able to activate the α4 promoter driven expression of luciferase in HEK 293T, JEG‐3 and GC‐1 cells. Further characterization of the effect of db‐cAMP and ectopic CREMτ expression on deleted constructs of the α4 promoter (−339/+80, and +25/+480), and on the −339/+480 region carrying mutations in the CRE sites showed that db‐cAMP and CREMτ required the CRE motif located 263bp upstream the transcription initiation site to elicit their effect. EMSA experiments confirmed the CRE sequence as a bonafide CREMτ binding site. These results constitute the first demonstration of the transcriptional control of α4 gene expression by cAMP and by CREMτ, a transcription factor essential for male germ cell gene expression [Supported by NIH grant HD043044‐01].