Differential modulation of polycystin-2 gain-of-function channels by cysteine-reactive compounds, amphiphilic substances, and S4-S5 linker mutations.

Polycystin-2 (PC2) mutations are responsible for ∼15% of cases of autosomal-dominant polycystic kidney disease (ADPKD). PC2 belongs to the transient receptor potential ion channel family and can function as a homotetrameric nonselective cation channel. Little is known about its gating mechanism, and no specific PC2 activators or inhibitors have been identified. In this study, we performed a comparative electrophysiological analysis of two well-established gain-of-function PC2 constructs, PC2 F604P and PC2 L677A N681A, expressed in Xenopus laevis oocytes. Interestingly, PC2 F604P, but not PC2 L677A N681A, could be inhibited by several membrane-permeable cysteine-reactive compounds. In contrast, positively charged cysteine-reactive compounds had no inhibitory effect. Thus, the inhibitory effect probably involves covalent modification of intracellular cysteine residues. Consistent with this, site-directed mutagenesis revealed a critical functional role of the free cysteine residue C593, localized in the intracellular S4-S5 linker of PC2 F604P. Moreover, the ion channel function of PC2 F604P was disturbed by S4-S5 linker mutations flanking C593. Interestingly, several structurally unrelated amphiphilic substances mimicked the inhibitory effect of membrane-permeable cysteine-reactive compounds on PC2 F604P without affecting PC2 L677A N681A. Collectively, our data suggest a critical role of the S4-S5 linker and the plasma membrane lipid environment in F604P-triggered PC2 gating. Finally, we demonstrated that the ADPKD-associated mutation located within the S4-S5 linker (N580K) completely abolished or significantly reduced currents mediated by PC2 F604P or PC2 L677A N681A, respectively. These findings provide new insights into molecular mechanisms involved in PC2 gating.