The epithelial sodium channel (ENaC) is involved in the tightly-regulated absorption of sodium across the epithelia lining the aldosterone-sensitive distal nephron (ASDN), critically important for maintaining total body sodium content and thus the long term control of arterial blood pressure. ENaC activity depends, in part, on the number of channels resident at the apical membrane of the epithelia and this involves a balance between insertion and retrieval processes [1]. Preliminary data [2] revealed that the proteasomal inhibitors MG132 and bortezomib could stimulate ENaC-mediated Na+ transport by ~3 fold in mCCDcl1 cells, a mammalian model of principal cells from the ASDN [3]. This stimulatory effect is likely mediated by increased serum and glucocorticoid inducible kinase 1 (SGK1) activity [4], thought to stimulate ENaC by reducing channel retrieval. The aim of this study was to clarify the molecular mechanisms underpinning ENaC stimulation by proteasomal inhibitors. ENaC-mediated Na+ transport was quantified by measuring amiloride-sensitive short circuit current (ISC) across monolayers of mCCDcl1 cells mounted in Ussing chambers. The surface abundance of β-ENaC was monitored by Western blot analysis of cell lysates following a biotinylation assay. The activity of SGK1 was monitored by Western blot analysis of a downstream target n-myc downstream-regulated gene 1, NDRG1. Data are shown as mean ± SEM, statistical significance was assessed using a Student’s unpaired t-test. The time-course and magnitude of ENaC stimulation by proteasomal inhibitors was similar to the 2.0 ± 0.2 fold (n = 5, p < 0.001) stimulation seen with aldosterone (3nM, 3h). Following treatment with MG132, SGK1 activity was increased as shown by a ~3 fold increase in NDRG1 phosphorylation [4]. Inhibiting SGK1 activity, using GSK650394 (10µM), abolished the stimulation of amiloride-sensitive ISC caused by MG132 (n = 6, p < 0.001) or by aldosterone (n = 5, p < 0.001). Interestingly, the abundance of the mature glycosylated form of β-ENaC at the apical surface of mCCDcl1 cells increased by 1.9 ± 0.2 fold with MG132 (n = 5, p < 0.01) and 4.1 ± 1.4 with aldosterone (n = 6, p < 0.001). This was associated with a decrease in the less glycosylated form of β-ENaC, indicating a shift in glycosylation status of β-ENaC rather than an overall increase in subunit abundance. Inhibiting SGK1 activity prevented this shift in glycosylation. Together these data suggest that proteasomal inhibitors stimulate ENaC activity by preventing the breakdown of SGK1 thus mimicking the stimulation of ENaC activity by aldosterone, which acts by upregulating transcription of SGK1.