Regulation of PKD2 channel function by TACAN

Abstract

Autosomal dominant polycystic kidney disease is caused by mutations in the membrane receptor PKD1 or the cation channel PKD2. TACAN (also termed TMEM120A), recently reported as an ion channel in neurons for mechanosensing and pain sensing, is also distributed in diverse non‐neuronal tissues, such as kidney, heart and intestine, suggesting its involvement in other functions. In this study, we found that TACAN is in a complex with PKD2 in native renal cell lines. Using the two‐electrode voltage clamp in Xenopus oocytes, we found that TACAN inhibits the channel activity of PKD2 gain‐of‐function mutant F604P. TACAN fragments containing the first and last transmembrane domains interacted with the PKD2 C‐ and N‐terminal fragments, respectively. The TACAN N‐terminus acted as a blocking peptide, and TACAN inhibited the function of PKD2 by the binding of PKD2 with TACAN. By patch clamping in mammalian cells, we found that TACAN inhibits both the single‐channel conductance and the open probability of PKD2 and mutant F604P. PKD2 co‐expressed with TACAN, but not PKD2 alone, exhibited pressure sensitivity. Furthermore, we found that TACAN aggravates PKD2‐dependent tail curvature and pronephric cysts in larval zebrafish. In summary, this study revealed that TACAN acts as a PKD2 inhibitor and mediates mechanosensitivity of the PKD2–TACAN channel complex. Key points TACAN inhibits the function of PKD2 in vitro and in vivo. TACAN N‐terminal S1‐containing fragment T160X interacts with the PKD2 C‐terminal fragment N580–L700, and its C‐terminal S6‐containing fragment L296–D343 interacts with the PKD2 N‐terminal A594X. TACAN inhibits the function of the PKD2 channel by physical interaction. The complex of PKD2 with TACAN, but not PKD2 alone, confers mechanosensitivity.

Regulation of PKD2 channel by TACAN: how does it link to cystogenesis in autosomal dominant polycystic kidney disease?

“…PKD2 is a non-selective ion channel that is permeable to divalent cations and monovalent ions (Brill & Ehrlich, 2020;Chebib et al, 2015). Using extracellular solutions containing 100 mM Na + , Li + , K + , or non-permeant N-methyl-d-glucamine, Liu et al (2022) investigated whether TACAN affects the ion selectivity of F604P. The finding suggested that despite TACAN inhibiting the channel activity of F604P, it does not affect the ion selectivity of F604P.…”

“…In terms of mechanism, the regulation of PKD2 channel function was previously reported to involve multiple factors such as the localization of PKD2, the interaction with other channels, and post-translational modification (Brill & Ehrlich, 2020;Chebib et al, 2015). Liu et al (2022) showed that TACAN-PKD2 physical association is critical in the functional regulation of PKD2 by TACAN. TACAN interacts with PKD2 in the cilia and plasma membrane, supported by PKD2-TACAN colocalization with the cilia marker Arl13b.…”

“…PKD2-KD in zebrafish causes hyperproliferation of kidney epithelia leading to pronephric cyst formation. Liu et al (2022) used CRISPR/Cas9 to generate PKD2-KD in larval fish. The combination of PKD2-KD and TACAN overexpression increased the number of pronephric cysts and the severity of tail curling.…”

“…Numerous studies have extensively characterized that PKD2 interacts with PKD1 forming a Ca 2+ -sensitive heterotetrameric channel, and dysregulation of this complex causes cystogenesis. Therefore, the study by Liu et al (2022) has led us to ask whether blocking peptides such as K135X can stabilize the PKD1-PKD2 complex and reduce cystogenesis.…”

“…Furthermore, the poor correlation between genotype and phenotype in ADPKD indicates the presence of modulating factors in PKD1/PKD2 signalling and cystogenesis. A study by Liu et al (2022) in a recent issue of The Journal of Physiology reported that transmembrane protein 120A (TACAN) is a novel regulator of the PKD2 channel. The study reported that TACAN physically interacts with PKD2, inhibits PKD2 channel activity and increases pronephric cysts in PKD2-knockdown (KD) zebrafish.…”