Regulation of WNK4 gene transcription in the kidneys

With-no-lysine (K) kinase-4 (WNK4) is a newly cloned kinase-encoding gene that plays a crucial role in the maintenance of electrolyte homeostasis. Mutations of WNK4 can cause pseudohypoaldosteronism type alpha, an autosomal dominant disease characterized by hyperkalemia, metabolic acidosis and hypertension. We explored the expression and regulatory mechanism of WNK4 in the human kidneys, which is a key regulator of blood pressure. Expression of WNK4 was determined by RT-PCR. Transcription initiation site and regulatory elements in the promoter region of WNK4 were systematically analyzed with a combined set of experimental and bioinformatic methods. Using 5'-RACE, we have determined the transcription initiation site. We identified a number of putative cis-acting elements by analysis of the promoter region with the TRANSFAC-TESS software; these were subsequently confirmed with an electrophoresis mobility shift assay. As confirmed by a CAT-ELISA reporter assay, the promoter region of WNK4 has a high level of transcriptional activity. Several hormones, in particular dexamethasone, can suppress the level of WNK4 mRNA. These results have shed light on the regulatory mechanism of WNK4 expression in kidneys, as well as the influence of various hormones on expression levels. This should prove useful for studies on the roles of WNK4 in the pathogenesis of hypertension.