GLUCOCORTICOIDS REGULATE THE TRANSCRIPTION OF NA+-K+-ATPASE GENES IN THE INFANT RAT-KIDNEY

Glucocorticoids modulate the maturation of Na+-K+-ATPase mRNA in a tissue- and age-dependent manner. In this study, we report the effect of glucocorticoids on Na+-K+-ATPase gene transcription in the infant rat kidney. Ten-day-old rats were treated with one intraperitoneal injection of betamethasone. In glucocorticoid-treated rats, there was a significant increase in renal cortical alpha(1)- and beta(1)-mRNAs (3.08 +/- 0.34- and 4.06 +/- 0.10-fold). Pretreatment with cycloheximide, an inhibitor of protein synthesis, did not abolish the increase in alpha(1)- and beta(1)-mRNA after glucocorticoids. The alpha(1)- and beta(1)-gene transcription rates were significantly increased in nuclei isolated from kidneys of glucocorticoid-treated rat (2.16 +/- 0.05- and 3.12 +/- 0.50-fold). Interaction between nuclear proteins and Na+-K+-ATPase alpha(1)-promoter was studied by gel retardation assay. Nuclear protein from glucocorticoid-treated rats retarded a fragment of alpha(1)-promoter that includes a half-consensus glucocorticoid response element (GRE) at position -750 bp but did not retard a fragment including a half-consensus GRE at position -481. Retardation of alpha(1)-promoter was inhibited by incubation with molar excess of GRE or with a monoclonal antibody against glucocorticoid receptor. We conclude that in the infant kidney, glucocorticoids directly stimulate the transcription of alpha(1)-and beta(1)-Na+-K+-ATPase subunits. It is likely that the binding of glucocorticoid receptor to alpha(1)-Na+-K+-ATPase promoter requires the presence of an auxiliary factor.