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Abstract: SA-OR089

Polycystin 1 Acts as an Atypical Adhesion G-Protein-Coupled Receptor (GPCR) That Responds to Non-Canonical WNT Signals and Inhibits GSK3?

Session Information

Category: Genetic Diseases of the Kidneys

  • 1001 Genetic Diseases of the Kidneys: Cystic

Authors

  • Gresko, Nikolay P., Yale University School of Medicine, New Haven, Connecticut, United States
  • Caplan, Michael J., Yale University School of Medicine, New Haven, Connecticut, United States
  • Mistry, Kavita, Yale University, New Haven, Connecticut, United States
  • Merrick, David, University of Pennsylvania, Philadelphia, Pennsylvania, United States
Background

A recent study demonstrates that polycystin-1 (PC1) serves as a receptor for Wnt ligands. We find that PC1 responds to Wnt9b by shedding its 350kD N-terminal fragment (NTF), which bears a striking resemblance to the activation mechanism of an adhesion GPCR (aGPCR). For aGPCRs, NTF removal liberates a short peptide sequence near the GPS cleavage site called stachel, which then interacts with an internal binding site and engages a G protein signalling cascade.

Methods

Biosensor kinase assay, western blot, morpholino in zebra fish

Results

We find that Wnt9b induces a PC1-dependent phosphorylation and inhibition of the GSK3β kinase through the RhoA GTPase-ROCK kinase pathway. Expression of a “constitutively active” aGPCR form of PC1 that lacks its NTF (NTF PHS) leads to profound suppression of GSK3β activity that is dependent upon Gα13, RhoA and ROCK. Furthermore, a form of the NTF PHS that lacks the putative “stachel” peptide (NTF PH) is unable to inhibit GSK3β kinase, indicating the importance of “stachel” peptide for the active participation of PC1 in this signalling pathway. Interestingly, GSK3β is an important negative regulator of the HIPPO/non-canonical Wnt signalling target TAZ(WWTR1), lack of which leads to the development of severe renal cysts. Furthermore, recent data show that pharmacological inhibition of GSK3β is beneficial in mouse models of ADPKD. We find that exogenous expression of an active form of TAZ in PC1 null cells or in PKD1a/b morphant zebrafish suppresses the development of relevant phenotypes. We also demonstrate that pharmacological inhibition of GSK3β leads to accumulation of the TAZ protein and to reduced cystogenesis in a 3D matrigel assay employing PC1 null cells. TAZ abundance and activity have been shown to be upregulated through the non-canonical Wnt signalling pathway. We find that HEK293 cells that express PC1 and PC2 respond to Wnt9b treatment by significantly increasing TAZ abundance as compared to the wild type HEK293 cells treated in the same manner.

Conclusion

Taken together, our data suggest that PC1 can act as an aGPCR-like receptor for non-canonical Wnt ligands and that it participates in a novel signalling pathway by linking non-canonical Wnt ligands to the GSK3β-dependent regulation of TAZ, a multifaceted signalling molecule whose absence is sufficient to induce renal cystic disease.

Funding

  • NIDDK Support