Abstract: TH-PO0031
Salt-Inducible Kinase Inhibition Bypasses Vasopressin Signaling to Induce Aquaporin-2 Expression
Session Information
- Fluid, Electrolyte, and Acid-Base Disorders: Basic Research
October 22, 2026 | Location: Exhibit Hall A, Convention Center
Abstract Time: 10:00 AM - 12:00 PM
Category: Fluid, Electrolytes, and Acid-Base Disorders
- 1101 Fluid, Electrolyte, and Acid-Base Disorders: Basic
Authors
- Raghuram, Viswanathan, National Heart Lung and Blood Institute Division of Intramural Research, Bethesda, Maryland, United States
- Khan, Shaza, National Heart Lung and Blood Institute Division of Intramural Research, Bethesda, Maryland, United States
- Murillo-de-Ozores, Adrian Rafael, National Heart Lung and Blood Institute Division of Intramural Research, Bethesda, Maryland, United States
- Knepper, Mark A., National Heart Lung and Blood Institute Division of Intramural Research, Bethesda, Maryland, United States
Background
Vasopressin regulates water homeostasis by promoting aquaporin-2 (AQP2) expression and trafficking in collecting duct principal cells. Impaired vasopressin signaling results in defective urine concentration, as observed in nephrogenic diabetes insipidus (NDI). Salt-inducible kinases (SIKs), members of the AMPK-related kinase family, are phosphorylated and inhibited by protein kinase A (PKA) downstream of vasopressin. In prior studies using PKA-deficient collecting duct cells, we identified SIKs as candidate downstream effectors of vasopressin signaling, motivating investigation of their role in AQP2 regulation. We hypothesized that inhibition of SIKs may contribute to vasopressin-mediated regulation of AQP2 expression.
Methods
Filter-grown, polarized mpkCCD cells were treated with desmopressin and/or SIK inhibitors. AQP2 expression assessed by immunoblotting, cAMP levels were measured and RNA-seq was performed.
Results
We examined the effects of two structurally distinct SIK inhibitors (SK-124 and MR22) in mpkCCD collecting duct cells. Both decreased phosphorylation of histone deacetylases (HDACs) at known SIK target sites, consistent with on-target SIK inhibition. SIK inhibition increased AQP2 protein abundance in the absence of vasopressin. This effect persisted in the presence of the V2 receptor antagonist tolvaptan and occurred without detectable increases in intracellular cAMP. Furthermore, SIK inhibitors increased AQP2 abundance in PKA-deficient cells, indicating that this effect is independent of canonical cAMP–PKA signaling. RNA-seq analysis demonstrated upregulation of multiple vasopressin-responsive transcripts, including Aqp2. Consistent with a transcriptional mechanism, SIK inhibition increased nuclear localization of CRTC1, a coactivator of CREB. Notably, SIK inhibitors failed to increase AQP2 protein abundance in CREB1/CREM/ATF1–deficient cells, demonstrating dependence on CREB-family transcription factors.
Conclusion
These findings identify SIK inhibition as a vasopressin-independent mechanism that increases AQP2 expression via a CRTC–CREB–dependent pathway. Our results support a model in which SIKs function as a regulatory node downstream of PKA and suggest that pharmacologic inhibition of SIKs can bypass upstream vasopressin signaling to promote AQP2 expression. Targeting SIKs may represent a potential therapeutic strategy for vasopressin-resistance disorders, including NDI.
Funding
- Other U.S. Government Support