Cleavage of N-terminus of polycystin-1 increases calcium permeability of polycystin-1/2 receptor channel complexes
Runping Wang, Danish Idrees, Mohammad Amir, Biswajit Padhy, Jian Xie, Chou-Long Huang
Runping Wang, Danish Idrees, Mohammad Amir, Biswajit Padhy, Jian Xie, Chou-Long Huang
View: Text | PDF
Research Article Cell biology Nephrology

Cleavage of N-terminus of polycystin-1 increases calcium permeability of polycystin-1/2 receptor channel complexes

Abstract

Mutations on genes encoding polycystin-1 (PC1) and PC2 cause autosomal-dominant polycystic kidney disease. How these 2 proteins work together to exert anticystogenesis remains elusive. PC1 resembles adhesion G-protein coupled receptors and undergoes autocleavage in the extracellular N-terminus to expose a hidden “stalk” region, which is hypothesized to act as a “tethered agonist.” Here, we show that WT PC1 and PC2 formed functional heteromeric channel complexes in Xenopus oocytes with different biophysical properties from PC2 homomeric channels. Deletion of PC1 N-terminus, which exposed the stalk, increased calcium permeability in PC1/PC2 heteromers that required the presence of stalk. Extracellular application of synthetic stalk peptide increased calcium permeation in stalkless PC1/PC2. Application of Wnt9B protein increased calcium permeability in PC1/PC2 but not in heteromers containing cleavage-resistant mutant PC1. Wnt9B interacted with N-terminal leucine-rich repeat (LRR) of PC1. Pretreatment with LRR blunted the increase in calcium permeability by Wnt9B. Thus, PC1 and PC2 form receptor-channel complexes that is activated by exposure of the stalk region following ligand binding to the PC1 N-terminus. The stalk peptide acts as a tethered agonist to activate PC1/PC2 by affecting ion selectivity of the complexes.

Authors

Runping Wang, Danish Idrees, Mohammad Amir, Biswajit Padhy, Jian Xie, Chou-Long Huang

×

Figure 10

Working model for Wnt9B action of heteromeric PC1/PC2 channel.

Options: View larger image (or click on image) Download as PowerPoint
Working model for Wnt9B action of heteromeric PC1/PC2 channel. PC1 conta...
PC1 contains 11 transmembrane (TM) domains, while PC2 has 6. The last 6 TMs of PC1, together with PC2, form heteromeric channels. Autocleavage of PC1 at GPS site produces NTF and CTF (right panel; the region CTF is marked by dotted lines). The cleaved NTF remains noncovalently attached to the heteromeric CTF/PC2 channels. The complexes exist on cell or ciliary membrane. Normally, PC1/PC2 heteromers preferentially conduct monovalent cations K+ and Na+ over Ca2+. Secreted Wnt9B and other unidentified potential ligands (labeled X) bind to the complex extracellularly facilitating the release of NTF. This process exposes the hidden stalk peptide, which act as a tethered agonist to increase the Ca2+ permeability of heteromers. How stalk peptide does this remains unknown, it may involve interaction with the TOP domain, which in turn interacts with the pore loop (PL) of PC1 (depicted by red arrows), as suggested recently by Pawnikar et al. (26, 27). Notably, the C-terminal tail of PC1 (PC1-CTT), located immediately downstream of the pore, likely influence ion permeation (depicted by arrowed red broken line). Only the TOP domain of PC1 is illustrated in the model. Shear stress may promote detachment of the noncovalently bound NTF under certain conditions (48), though this is not sufficient by itself in our experimental setting, where oocytes were subject to continuous shaking on a platform shaker for 7 days after mRNA injection.