Inhibition of prostasin expression by TGF-β1 in renal epithelial cells

Abstract

Background. Prostasin has been shown to be involved in the regulation of sodium handling in the kidney. TGF-β1 has been demonstrated to suppress αENaC expression and sodium uptake. Therefore, we hypothesized that TGF-β1 may regulate prostasin expression to modulate sodium reabsorption in the kidney. Methods. To determine if TGF-β1 has an effect on prostasin expression, we isolated 2.9 kb of the rat prostasin promoter, and measured its transcriptional activity with a luciferase assay in mouse cortical collecting duct cell line (M-1). The effect of TGF-β1 on the mRNA and protein abundance of prostasin, and amiloride-sensitive 22Na uptake was determined. Results. Treatment of M-1 cells with 20 ng/mL of TGF-β1 for 24 hours significantly decreased the promoter activity by 50 ± 1%, and the inhibitory effect was dose dependent over the range of 0.1 to 20 ng/mL. We identified a 50 bp region (-410 to -360) containing c-Rel-like sequence in prostasin promoter that is responsible for the TGF-β1-mediated inhibition, and found that TGF-β1 increases IκBα expression in M-1 cells. TGF-β1 reduced endogenous prostasin mRNA and protein expression in M-1 cells by 50 ± 12% and 44 ± 12%, respectively, and the amiloride-sensitive 22Na uptake by 35.9 ± 4.8%. Conclusion. Our findings indicate the possibility that TGF-β1 transcriptionally inhibits prostasin expression by the induction of IκBα and the subsequent inhibition of NF-κB/Rel activity in M-1 cells, and also suggest the possibility that TGF-β1 might inhibit sodium reabsorption through a reduction in prostasin expression and subsequent inhibition of ENaC activity.