PMC:4925210 / 19052-23338 JSONTXT

{"project":"2_test","denotations":[{"id":"27214281-10858654-73835263","span":{"begin":609,"end":610},"obj":"10858654"},{"id":"27214281-10858654-73835263","span":{"begin":609,"end":610},"obj":"10858654"},{"id":"27214281-12771126-73835264","span":{"begin":612,"end":613},"obj":"12771126"},{"id":"27214281-12771126-73835264","span":{"begin":612,"end":613},"obj":"12771126"},{"id":"27214281-20660632-73835265","span":{"begin":615,"end":616},"obj":"20660632"},{"id":"27214281-20660632-73835265","span":{"begin":615,"end":616},"obj":"20660632"},{"id":"27214281-24767998-73835266","span":{"begin":1757,"end":1759},"obj":"24767998"},{"id":"27214281-24767998-73835266","span":{"begin":1757,"end":1759},"obj":"24767998"},{"id":"27214281-24767999-73835267","span":{"begin":1761,"end":1763},"obj":"24767999"},{"id":"27214281-24767999-73835267","span":{"begin":1761,"end":1763},"obj":"24767999"},{"id":"27214281-19543268-73835268","span":{"begin":2034,"end":2036},"obj":"19543268"},{"id":"27214281-19543268-73835268","span":{"begin":2034,"end":2036},"obj":"19543268"},{"id":"27214281-20843830-73835269","span":{"begin":2274,"end":2276},"obj":"20843830"},{"id":"27214281-20843830-73835269","span":{"begin":2274,"end":2276},"obj":"20843830"},{"id":"27214281-23143599-73835270","span":{"begin":2761,"end":2763},"obj":"23143599"},{"id":"27214281-23143599-73835270","span":{"begin":2761,"end":2763},"obj":"23143599"},{"id":"27214281-20660632-73835271","span":{"begin":3263,"end":3264},"obj":"20660632"},{"id":"27214281-20660632-73835271","span":{"begin":3263,"end":3264},"obj":"20660632"},{"id":"27214281-20858476-73835272","span":{"begin":3266,"end":3268},"obj":"20858476"},{"id":"27214281-20858476-73835272","span":{"begin":3266,"end":3268},"obj":"20858476"},{"id":"27214281-24767998-73835273","span":{"begin":4023,"end":4025},"obj":"24767998"},{"id":"27214281-24767998-73835273","span":{"begin":4023,"end":4025},"obj":"24767998"},{"id":"27214281-24767999-73835274","span":{"begin":4027,"end":4029},"obj":"24767999"},{"id":"27214281-24767999-73835274","span":{"begin":4027,"end":4029},"obj":"24767999"},{"id":"27214281-12062060-73835275","span":{"begin":4031,"end":4033},"obj":"12062060"},{"id":"27214281-12062060-73835275","span":{"begin":4031,"end":4033},"obj":"12062060"},{"id":"27214281-10655152-73835275","span":{"begin":4031,"end":4033},"obj":"10655152"},{"id":"27214281-10655152-73835275","span":{"begin":4031,"end":4033},"obj":"10655152"},{"id":"27214281-21865467-73835276","span":{"begin":4070,"end":4072},"obj":"21865467"},{"id":"27214281-21865467-73835276","span":{"begin":4070,"end":4072},"obj":"21865467"},{"id":"27214281-26245976-73835277","span":{"begin":4088,"end":4090},"obj":"26245976"},{"id":"27214281-26245976-73835277","span":{"begin":4088,"end":4090},"obj":"26245976"},{"id":"27214281-25043421-73835278","span":{"begin":4092,"end":4094},"obj":"25043421"},{"id":"27214281-25043421-73835278","span":{"begin":4092,"end":4094},"obj":"25043421"},{"id":"27214281-11689485-73835279","span":{"begin":4187,"end":4189},"obj":"11689485"},{"id":"27214281-11689485-73835279","span":{"begin":4187,"end":4189},"obj":"11689485"},{"id":"27214281-18321855-73835279","span":{"begin":4187,"end":4189},"obj":"18321855"},{"id":"27214281-18321855-73835279","span":{"begin":4187,"end":4189},"obj":"18321855"},{"id":"27214281-18652813-73835279","span":{"begin":4187,"end":4189},"obj":"18652813"},{"id":"27214281-18652813-73835279","span":{"begin":4187,"end":4189},"obj":"18652813"}],"text":"Discussion\nOur data provide evidence that the PKD1/TRPP2 channel complex can function as a ligand-activated channel. Our data support the possibility of a direct ligand/receptor interaction for several reasons. First, the PKD1/WNT interaction does not require cell surface receptors, as it can occur in the extracellular space in trans and also, using purified proteins. Second, PKD1 is unlikely to function as a FZD or RYK co-receptor or downstream of these receptors, because neither WNT9B nor PKD1/TRPP2 induced or mediated Ca2+ release from the ER, an effect associated with FZD or RYK receptor activation4, 6, 8. Third, clearing FZDs and LRP6 from the cell surface did not suppress WNT9B-or WNT3A-induced currents and heterologous expression of PKD1 and TRPP2 in Drosophila S2 cells, which lack endogenous FZD receptors, supported WNT9B-induced currents. Therefore, PKD1 is likely to function as a (co)receptor for WNT ligands to induce Ca2+ influx, independently of FZD receptors. The fact that WNT3A, a typical canonical WNT activated TRPP2, a Ca2+ permeable channel, suggests that WNT ligands could induce Ca2+ influx regardless of their ability to signal through β-catenin as long as they can bind to PKD1 and PKD1/TRPP2 is present in the target cell. This may represent a general property of WNTs and implies a broader effect of WNTs on Ca2+ signaling than previously thought. It may also help explain the strong influence of cell context on WNT signaling.\nWe show that TRPP2 plays an important role in directional cell migration of MEFs in response to WNT9B. This is consistent with recent studies showing an essential role of PKD1 and TRPP2 in directional cell migration in embryonic kidney and endothelial cells during lymphatic development11, 47, 48. Despite caveats, directed cell migration in cell culture has been used as a reliable surrogate assay for convergent extension during embryonic development11. Defective convergent extension was proposed to underlie cystogenesis in embryonic Pkd1 and Wnt9b mutant kidneys10, 11. Although our data do not contradict this idea, we do not believe that defective convergent extension is the sole cause of cystogenesis in ADPKD, as deletion of core components of PCP, such as Vangl2, show very mild cystic dilatation49. We rather propose that defective WNT-induced PKD1/TRPP2-mediated Ca2+ signaling can adversely affect multiple processes, including convergent extension. Such a combinatorial effect can contribute to cyst initiation/formation.\nExperiments in Xenopus embryos suggest that xPkd1 genetically interacts with xDvl2 in pronephric development. Overexpression of a dexamethasone-inducible, PCP-specific dominant negative form of xDvl2 in Xenopus embryos produces dilated and shortened tubules50, the same phenotype as the one modified by the combinatorial effects of xPkd1 and xDvl2. We also show that PKD1 physically interacts with DVL2 and a point mutation in the DEP domain of DVL2 renders it unable to interact with PKD1. However, DVLs are dispensable for WNT9B-induced channel activity. These data suggest that DVL proteins can function as downstream effectors of PKD1/TRPP2 in the embryonic kidney. DVLs have been shown to function downstream of WNT/Ca2+ signaling by an unknown mechanism8, 51. One possibility is that the physical interaction between PKD1 and DVLs may function to keep the two proteins in close proximity so that incoming Ca2+ could directly impinge on DVLs or immediate downstream effectors.\nWe show that several WNTs can bind to PKD1. These data suggest that PKD1/TRPP2 can mediate effects of other WNTs not only in the kidney but in other tissues where WNT/Ca2+ activity is present. This is supported by the ubiquitous expression of PKD1 and TRPP2 and the wider phenotypic spectrum caused by the homozygous deletions of Pkd1 or Pkd2 genes compared to the phenotypic spectrum of patients with autosomal dominant PKD. We speculate that renal (cystogenesis), cardiovascular (heterotaxy, defective septation, lymphatic development)47, 48, 52-54, hearing (inner ear architecture)55, hydrocephalus 56, 57 and skeletal defects (neural crest cell migration, spina bifida, osteoblast differentiation)58-60 in Pkd1- or Pkd2-null mice may represent bona fide defects of the WNT/Ca2+ signaling pathway."}