Low-density lipoprotein receptor-related protein 6 is a novel coreceptor of protease-activated receptor-2 in the dynamics of cancer-associated β-catenin stabilization

Protease-activated receptor-2 (PAR(2)) plays a central role in cancer; however, the molecular machinery of PAR(2)-instigated tumors remains to be elucidated. We show that PAR(2) is a potent inducer of β-catenin stabilization, a core process in cancer biology, leading to its transcriptional activity. Novel association of low-density lipoprotein-related protein 6 (LRP6), a known coreceptor of Frizzleds (Fz), with PAR(2) takes place following PAR(2) activation. The association between PAR(2) and LRP6 was demonstrated employing co-immunoprecipitation, bioluminescence resonance energy transfer (BRET), and confocal microscopy analysis. The association was further supported by ZDOCK protein-protein server. PAR(2)-LRP6 interaction promotes rapid phosphorylation of LRP6, which results in the recruitment of Axin. Confocal microscopy of PAR(2)-driven mammary gland tumors in vivo, as well as in vitro confirms the association between PAR(2) and LRP6. Indeed, shRNA silencing of LRP6 potently inhibits PAR(2)-induced β-catenin stabilization, demonstrating its critical role in the induced path. We have previously shown a novel link between protease-activated receptor-1 (PAR(1)) and β-catenin stabilization, both in a transgenic (tg) mouse model with overexpression of human PAR(1) (hPar1) in the mammary glands, and in cancer epithelial cell lines. Unlike in PAR(1)-G(α13) axis, both G(α12) and G(α13) are equally involved in PAR(2)-induced β-catenin stabilization. Disheveled (DVL) is translocated to the cell nucleus through the DVL-PDZ domain. Collectively, our data demonstrate a novel PAR(2)-LRP6-Axin interaction as a key axis of PAR(2)-induced β-catenin stabilization in cancer. This newly described axis enhances our understanding of cancer biology, and opens new avenues for future development of anti-cancer therapies.