The C-Terminal Region Mesd Peptide Mimics Full-Length Mesd and Acts as an Inhibitor of Wnt/β-Catenin Signaling in Cancer Cells

Abstract

While Mesd was discovered as a specialized molecular endoplasmic reticulum chaperone for the Wnt co-receptors LRP5 and LRP6, recombinant Mesd protein is able to bind to mature LRP5 and LRP6 on the cell surface and acts as a universal antagonist of LRP5/6 modulators. In our previous study, we found that the C-terminal region of Mesd, which is absent in sequences from invertebrates, is necessary and sufficient for binding to mature LRP6 on the cell surface. In the present studies, we further characterized the interaction between the C-terminal region Mesd peptide and LRP5/6. We found that Mesd C-terminal region-derived peptides block Mesd binding to LRP5 at the cell surface too. We also showed that there are two LRP5/6 binding sites within Mesd C-terminal region which contain several positively charged residues. Moreover, we demonstrated that the Mesd C-terminal region peptide, like the full-length Mesd protein, blocked Wnt 3A- and Rspodin1-induced Wnt/β-catenin signaling in LRP5- and LRP6- expressing cells, suppressed Wnt/β-catenin signaling in human breast HS578T cells and prostate cancer PC-3 cells, and inhibited cancer cell proliferation, although the full-length Mesd protein is more potent than its peptide. Finally, we found that treatment of the full-length Mesd protein and its C-terminal region peptide significantly increased chemotherapy agent Adriamycin-induced cytotoxicity in HS578T and PC-3 cells. Together, our results suggest that Mesd C-terminal region constitutes the major LRP5/6-binding domain, and that Mesd protein and its C-terminal region peptide have a potential therapeutic value in cancer.

Salinomycin Suppresses LRP6 Expression and Inhibits Both Wnt/β‐catenin and mTORC1 Signaling in Breast and Prostate Cancer Cells

“…In addition, small molecule LRP6 inhibitors were able to inhibit human breast and prostate cancer cell proliferation [Lu et al, 2011b, 2012, 2014], and LRP6 antibodies antagonized Wnt1- and Wnt3-induced Wnt/β-catenin signaling and suppressed the growth of allografted tumor cells derived from MMTV-Wnt1 and MMTV-Wnt3 tumors [Ettenberg et al, 2010; Gong et al, 2010]. Moreover, the recombinant Mesd protein and its C-terminal region peptide, two universal inhibitors of LRP6, markedly inhibited Wnt/β-catenin signaling in prostate and breast cancer cells, leading to inhibition of cancer cell proliferation in vitro and tumor growth in vivo [Liu et al, 2010; Lu et al, 2010; Lin et al, 2011, 2013]. In the present study, we demonstrated that salinomycin is a potent inhibitor of Wnt/β-catenin signaling by suppressing LRP6 expression in prostate and breast cancer cells.…”

Mesd extrinsically promotes phagocytosis by retinal pigment epithelial cells

“…In conjunction with Frizzled, LRP5/6 are coreceptors for canonical Wnt signaling. Besides its function as a molecular chaperon, Mesd is also capable of binding to mature LRP5/6 on cell surface (Li et al, 2005), thereby inhibiting Wnt/β-catenin signaling (Hsieh et al, 2003; Lin et al, 2013; Lu et al, 2010). …”

“…6a) is consistent with the previous report that Mesd is not a secretory protein (Li et al, 2005). Although Mesd was reported to bind to and inhibit LRP5/6 on cell surface (Li et al, 2005; Lin et al, 2013; Lu et al, 2010), the lack of the extracellular expression raises a question of how Mesd may access to LRP5/6 on cell surface and inhibit their function.…”

“…LRPs play diverse roles in cell signaling and endocytosis (Li et al, 2000; Schneider and Nimpf, 2003). Mesd was reported to bind to LRP5/6 on cell surface, competitively block the binding of Wnt ligands to LRP5/6 and inhibit Wnt/β-catenin signaling (Li et al, 2005; Lin et al, 2013; Lu et al, 2010). However, it is unclear how Mesd strictly expressed in the ER may regulate LRP5/6 on cell surface (Li et al, 2005).…”

Rottlerin induces Wnt co-receptor LRP6 degradation and suppresses both Wnt/β-catenin and mTORC1 signaling in prostate and breast cancer cells

“…Moreover, small molecule LRP6 inhibitors were able to inhibit human breast and prostate cancer cell proliferation [20, 21]. We recently demonstrated that the recombinant Mesd protein and its C-terminal region peptide, two universal inhibitors of LRP6, markedly inhibited Wnt/β-catenin signaling in prostate and breast cancer cells, and suppressed cancer cell proliferation in vitro and tumor growth in vivo [41–43]. In the present study, we demonstrated for the first time that rottlerin is a potent inhibitor of Wnt/β-catenin signaling by inducing LRP6 degradation in prostate and breast cancer cells.…”