Endocrine Abstracts

Aldosterone stimulates the rapid phosphorylation and activation of PKD1 in a murine renal cortical collecting duct cell line (M1-CCD), through the transactivation of the epidermal growth factor receptor (EGFR). PKD1 belongs to a family of serine/threonine kinases known to be important modulators of subcellular trafficking. The epithelial sodium channel ENaC is a major effector of aldosterone action in the kidney and plays a crucial role in the maintenance of whole body sodium homeostasis. In the distal nephron, the α subunit of ENaC is under transcriptional control of the ligand-bound mineralocorticoid receptor (MR), while β and γ are constitutively expressed. Using siRNA-mediated stable knockdown of PKD1 in M1-CCD cells, we examined the role of PKD1 in the regulation of ENaC activity. Aldosterone treatment (10 nM) resulted in an increase in the amiloride-sensitive transepithelial current (I_TE) from 1±0.21 μA/cm² to 7±0.86 μA/cm² (n=8, P< 0.005) in wild-type (WT) cells within 24 h, an effect which was inhibited in the PKD1-suppressed cells. Furthermore, using immunocytochemistry and confocal microscopy, we observed an increase in ENaCα expression in WT cells treated with aldosterone for 24 h, and this response was absent in PKD1 knockdown cells. Aldosterone stimulated the apical membrane insertion of constitutively expressed ENaCβ in WT cells, whereas no effect was observed in PKD1-suppressed cells. In conclusion, PKD1 plays a central role in the aldosterone-mediated regulation of ENaC activity, through both transcriptional control and subcellular trafficking.