Polycystin-1 acts as an atypical adhesion GPCR that responds to novel Wnt signaling and mechanical stimuli

Mutations in the genes encoding Polycystin-1 and 2 cause autosomal dominant polycystic kidney disease (ADPKD). These proteins cellular functions and the mechanisms through which their absence causes disease are unknown. We find that the behavior of the 11 transmembrane domain polycystin-1 protein resembles that of an adhesion G protein-coupled receptor when activated by Wnt ligands. Exposure to Wnt ligands causes shedding of the polycystin-1 N terminal region, exposing a tethered agonist that activates G protein-dependent functions of the membrane-associated C terminal fragment. Activated polycystin-1 communicates through G13 to activate RhoA, leading in turn to the ROCK-dependent phosphorylation and inactivation of GSK3{beta}. Activated polycystin-1 traffics out of the primary cilium through an arrestin-dependent mechanism, and arrestin involvement is required for signaling to occur. These data elaborate a function for polycystin-1 that is structurally non-canonical and that is directly connected to pathways whose perturbation results in cystic disease. SummaryThe polycystin-1 protein can activate a signaling pathway resembling those employed by non-canonical adhesion G protein coupled receptors, which is induced by Wnt9b binding and which leads to leads to inhibition of the GSK3{beta} kinase and removal of polycystin-1 from the primary cilium. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=109 SRC="FIGDIR/small/655326v1_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1b32dc1org.highwire.dtl.DTLVardef@80ee43org.highwire.dtl.DTLVardef@9aa441org.highwire.dtl.DTLVardef@95ceb1_HPS_FORMAT_FIGEXP M_FIG Graphical Abstract PC1 resides at baseline in the primary cilium. PC1 behaves as an aGPCR that responds to Wnt9b and to flow-induced ATP release by departing from the cilium and initiating the inhibition of GSK3. The schematic diagram presents a model that integrates the findings presented here. Wnt9b binding to the PC1 NTF leads to shedding of the NTF, exposing the tethered agonist to activate the PC1 receptor-mediated signaling cascade, which involves triggering G13 binding and the subsequent nucleotide exchange and GTP-loading of RhoA. GTP-bound RhoA stimulates the kinase activity of ROCK, which phosphorylates and inhibits GSK3. C_FIG