The heteromeric PC-1/PC-2 polycystin complex is activated by the PC-1 N-terminus

Abstract

Mutations in the polycystin proteins, PC-1 and PC-2, result in autosomal dominant polycystic kidney disease (ADPKD) and ultimately renal failure. PC-1 and PC-2 enrich on primary cilia, where they are thought to form a heteromeric ion channel complex. However, a functional understanding of the putative PC-1/PC-2 polycystin complex is lacking due to technical hurdles in reliably measuring its activity. Here, we successfully reconstitute the PC-1/PC-2 complex in the plasma membrane of mammalian cells and show that it functions as an outwardly rectifying channel. Using both reconstituted and ciliary polycystin channels, we further show that a soluble fragment generated from the N-terminal extracellular domain of PC-1 functions as an intrinsic agonist that is necessary and sufficient for channel activation. We thus propose that autoproteolytic cleavage of the N-terminus of PC-1, a hotspot for ADPKD mutations, produces a soluble ligand in vivo. These findings establish a mechanistic framework for understanding the role of PC-1/PC-2 heteromers in ADPKD and suggest new therapeutic strategies that would expand upon the limited symptomatic treatments currently available for this progressive, terminal disease.

Insights Into the Molecular Mechanisms of Polycystic Kidney Diseases

“…PС1 and PС2 modulate a variety of signaling pathways. The structure, function, and stoichiometry of the PC1/PC2 complex are widely discussed ( Wang et al, 2019b ; Woodward and Watnick, 2019 ; Ha et al, 2020 ). PC1 and PC2 can interact via their coiled-coil domains, forming a heteromeric complex (likely consisting of one PC1 and three PC2 subunits; Su et al, 2018 ).…”

A polycystin-2 protein with modified channel properties leads to an increased diameter of renal tubules and to renal cysts

“…An earlier publication reported that, in the oocyte expression system, polycystin-1 inhibited the activity of the polycystin-2 (F604P) mutant and altered the ion channel properties of another gain-of-function mutant protein, polycystin-2 (L677A/N681A) ( Wang et al, 2019 ). In contrast, a subsequent study in HEK 293 cells described a stimulatory effect of polycystin-1 on polycystin-2 (F604P), but not on wild-type polycystin-2 ( Ha et al, 2020 ). Moreover, it is still a matter of debate whether heteromeric complexes between polycystin-1 and polycystin-2 play an important physiological role because it has been shown that polycystin-2-dependent ion channel activity in primary cilia does not require the presence of polycystin-1 ( Liu et al, 2018 ).…”

A plasma membrane-localized polycystin-1/polycystin-2 complex in endothelial cells elicits vasodilation

“…In contrast, other studies demonstrated that a physical interaction between PC-1 and PC-2 is essential for these proteins to traffic to the cell surface and generate plasma membrane currents (25,(29)(30)(31)(43)(44)(45). It was essential to include an IgҠchain secretion sequence into recombinant PC-1 to induce its trafficking and associated PC-2 to the plasma membrane in HEK293 cells (45). We show that when both PC-1 and PC-2 are expressed, they readily traffic to the plasma membrane in endothelial cells.…”

“…Ciliary localization of PC-2 is necessary for flow-sensing in perinodal crown cells and left-right symmetry in mouse embryos (40). In contrast, other studies demonstrated that a physical interaction between PC-1 and PC-2 is essential for these proteins to traffic to the cell surface and generate plasma membrane currents (25,(29)(30)(31)(43)(44)(45). It was essential to include an IgҠchain secretion sequence into recombinant PC-1 to induce its trafficking and associated PC-2 to the plasma membrane in HEK293 cells (45).…”

“…The PC-1 extracellular N-terminus contains several putative adhesion-and ligand-binding sites that may confer mechanosensitivity (3,7,8). Recent evidence indicates that the C-type lectin domain located in the PC-1 N-terminus activates recombinant PC-1/PC-2 channels, providing one possible activation mechanism for flow (45). Conceivably, other mechanosensitive proteins, such as Piezo1 and GPR68, may also stimulate PC-1/PC-2-dependent currents in endothelial cells (53,54).…”