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The early phase of the stimulatory action of aldosterone on sodium reabsorption in tight epithelia involves hormone-regulated genes that remain to be identified. Using a subtractive hybridization technique on isolated renal cortical collecting ducts from rats injected with a physiological dose of aldosterone, we have identified an early response cDNA highly homologous to human and murine NDRG2 (N-Myc downstream regulated gene 2), which consists of four isoforms and belongs to a new family of differentiation-related genes. NDRG2 mRNA was expressed in classical aldosterone target epithelia, and in the kidney, it was specifically located in the collecting duct, the site of aldosterone-regulated sodium absorption. NDRG2 mRNA was increased within 45 min by aldosterone in the kidney and distal colon, whereas it was unaffected in the heart. In the RCCD2 collecting duct cell line, NDRG2 mRNA was enhanced as early as 15 min after aldosterone addition by transcription-dependent effects. NDRG2 was induced by aldosterone concentrations as low as 10(-9) M, and a maximal effect was observed at 10(-8) M. In contrast, the glucocorticoid dexamethasone was ineffective in NDRG2 expression, whereas the glucocorticoid-regulated gene sgk was induced. Taken together, these results indicate that NDRG2 regulation by aldosterone is an early mineralocorticoid-specific effect. Interestingly, NDRG2 is homologous to Drosophila MESK2, a component of the Ras pathway, suggesting that activation of the Ras cascade may play a significant role in mineralocorticoid signaling.

Long-term effects of arginine vasopressin (AVP) in the kidney involve the transcription of unidentified genes. By subtractive hybridization experiments performed on the RCCD(1) cortical collecting duct cell line, we identified calcyclin as an early AVP-induced gene (1 h). Calcyclin is a calcium-binding protein involved in the transduction of intracellular signals. In the kidney, calcyclin was localized at the mRNA level in the glomerulus, all along the collecting duct, and in the epithelium lining the papilla. In RCCD(1) cells and in m-IMCD(3) inner medullary collecting duct cells, calcyclin was evidenced in the cytoplasm. Calcyclin mRNA levels were progressively increased by AVP treatment in RCCD(1) (1.7-fold at 4 h) and m-IMCD(3) (2-fold at 7.5 h) cells. In RCCD(1) cells, calcyclin protein levels were increased by 4 h of AVP treatment. In vivo, treatment of genetically vasopressin-deficient Brattleboro rats with AVP for 4 days induced an increase in both calcyclin and aquaporin-2 mRNA expression. Finally, introduction of anti-calcyclin antibodies into RCCD(1) cells by permeabilizing the plasma membrane prevented the long-term (but not short-term) increase in short-circuit current induced by AVP. Taken together, these results suggest that calcyclin is an early vasopressin-induced gene that participates in the late phase of the hormone response in transepithelial ion transport.