Gating of the polycystin ion channel signaling complex in neurons and kidney cells

Abstract

Mutations in either polycystin-2 (PC2) or polycystin-1 (PC1) proteins cause severe, potentially lethal, kidney disorders and multiple extrarenal (including brain) disease phenotypes. PC2, a member of the transient receptor potential channel superfamily, and PC1, an orphan membrane receptor of largely unknown function, are thought to be part of a common signaling pathway. Here, we show that in rat sympathetic neurons and kidney cells, coassembly of full-length PC1 with PC2 forms a plasmalemmal ion channel signaling complex in which PC1 stimulation simultaneously activates PC2 ion channels and Gi/o-proteins. PC2 activation occurs through a structural rearrangement of PC1, independent of G-protein activation. Thus, PC1 acts as a prototypical membrane receptor that concordantly regulates PC2 channels and G-proteins, a bimodal mechanism that may account for the multifunctional roles of polycystin proteins in fundamental cellular processes of various cell types.

Cell biology of polycystin-2

“…Activation through PKD1-Following up on the work of Hanaoka et al [29], Delmas et al [35] confirmed that PKD1 promoted the targeting of PKD2 to the plasma membrane. Moreover, they showed that addition of a monoclonal antibody (MR3) against a portion of the extracellular domain of PKD1 (amino acid residues 2938 -2956), which is in close proximity to a domain homologous to the receptor for egg jelly (REJ) further augmented the activity of the PKD1/ PKD2 complex.…”

“…It allowed non-selective passing of cations, with slightly higher selectivity for Ca 2+ over Na + and K + , but higher conductance in K + [34]. However, the high single channel conductance (100-200 pS) [24,31,35] in combination with the relatively high open probability (~20-40%) [24,31,35] did not correlate well with the moderate amplitude of whole cell currents (several hundreds pA at -100 mV) in cells overexpressing PKD2 [35,36]. This, along with the observation that the vast amount of PKD2 was in the ER [25] raised the question of whether PKD2 alone or even in combination with PKD1 could actually form a functional channel in the plasma membrane.…”

“…It is now accepted that PKD2 can function at the plasma membrane, but its activity there is under complex regulation involving shuttling between ER and plasma membrane, protein-protein interactions, and modes of activation. Specifically, it has been shown that the amount of PKD2 in the plasma membrane is dynamically regulated by interacting proteins (PKD1 [29,35], Polycystin-2 interactor, Golgi-and ER-associated protein-14 (PIGEA-14) [37]), posttranslational modifications (serine phosphorylation by casein kinase 2 (CK2) [38] and glycogen synthase kinase 3 (GSK3) [39]), interaction with other channel subunits in the plasma membrane (PKD1 [29,35,[40][41][42], TRPC1 [11], TRPV4 [43]) (Fig. 2), and finally, activation secondary to cell surface receptor activation (epidermal growth factor receptor (EGFR) [36]).…”

“…Deletion studies identified a cluster of acidic residues in the Cterminal cytosolic tail of PKD2 that was responsible for the retention of the protein in the ER [25]. Interestingly, the pathogenic mutant PKD2(742X) which lacked the ER retention signal was forwarded to the plasma membrane and displayed constitutive channel activity [35,44]. However, according to Hanaoka et al this mutant did not display channel activity [29].…”

“…The reasons for these discrepancies are unknown. It is also interesting to note that addition of the MR3 antibody, which recognized a different region in the extracellular domain of PKD1 from the region recognized by p96521 (amino acid residues 866-882), resulted in an increase in PKD2 activity through PKD1-mediated gating [35]. Although it could be possible that antibody binding to different epitopes in the extracellular domain of PKD1 could result in activation or inhibition, it would be interesting to test whether addition of MR3 in kidney epithelia cells could fail to induce an additional increase in response to fluid flow.…”