Molecular genetics and targeted therapy of WNT-related human diseases (Review)

Abstract

Canonical WNT signaling through Frizzled and LRP5/6 receptors is transduced to the WNT/β-catenin and WNT/stabilization of proteins (STOP) signaling cascades to regulate cell fate and proliferation, whereas non-canonical WNT signaling through Frizzled or ROR receptors is transduced to the WNT/planar cell polarity (PCP), WNT/G protein-coupled receptor (GPCR) and WNT/receptor tyrosine kinase (RTK) signaling cascades to regulate cytoskeletal dynamics and directional cell movement. WNT/β-catenin signaling cascade crosstalks with RTK/SRK and GPCR-cAMP-PKA signaling cascades to regulate β-catenin phosphorylation and β-catenin-dependent transcription. Germline mutations in WNT signaling molecules cause hereditary colorectal cancer, bone diseases, exudative vitreoretinopathy, intellectual disability syndrome and PCP-related diseases. APC or CTNNB1 mutations in colorectal, endometrial and prostate cancers activate the WNT/β-catenin signaling cascade. RNF43, ZNRF3, RSPO2 or RSPO3 alterations in breast, colorectal, gastric, pancreatic and other cancers activate the WNT/β-catenin, WNT/STOP and other WNT signaling cascades. ROR1 upregulation in B-cell leukemia and solid tumors and ROR2 upregulation in melanoma induce invasion, metastasis and therapeutic resistance through Rho-ROCK, Rac-JNK, PI3K-AKT and YAP signaling activation. WNT signaling in cancer, stromal and immune cells dynamically orchestrate immune evasion and antitumor immunity in a cell context-dependent manner. Porcupine (PORCN), RSPO3, WNT2B, FZD5, FZD10, ROR1, tankyrase and β-catenin are targets of anti-WNT signaling therapy, and ETC-159, LGK974, OMP-18R5 (vantictumab), OMP-54F28 (ipafricept), OMP-131R10 (rosmantuzumab), PRI-724 and UC-961 (cirmtuzumab) are in clinical trials for cancer patients. Different classes of anti-WNT signaling therapeutics are necessary for the treatment of APC/CTNNB1-, RNF43/ZNRF3/RSPO2/RSPO3- and ROR1-types of human cancers. By contrast, Dickkopf-related protein 1 (DKK1), SOST and glycogen synthase kinase 3β (GSK3β) are targets of pro-WNT signaling therapy, and anti-DKK1 (BHQ880 and DKN-01) and anti-SOST (blosozumab, BPS804 and romosozumab) monoclonal antibodies are being tested in clinical trials for cancer patients and osteoporotic post-menopausal women. WNT-targeting therapeutics have also been applied as reagents for in vitro stem-cell processing in the field of regenerative medicine.

Figure 1

Overview of WNT signaling cascades. Canonical WNT signaling through Frizzled and LRP5/6 receptors promotes β-catenin-dependent transcription of CCND1, FZD7, MYC and other genes (WNT/β-catenin signaling) and β-catenin-independent stabilization of FOXM1, NRF2 (NFE2L2), YAP and other proteins (WNT/STOP signaling). Non-canonical WNT signaling through Frizzled or ROR receptors activates DVL-dependent Rho-ROCK and Rac-JNK cascades (WNT/PCP signaling), G protein-dependent calcineurin-NFAT, CAMK2-NLK and PKC cascades (WNT/GPCR signaling) and RTK-dependent PI3K-AKT and YAP/TAZ cascades (WNT/RTK signaling). Context-dependent WNT signaling through canonical and non-canonical signaling cascades regulates cell fate and proliferation, tissue or tumor microenvironment and whole-body homeostasis. GPCR, G protein-coupled receptor; PCP, planar cell polarity; RTK, receptor tyrosine kinase; STOP, stabilization of proteins.

Figure 2

WNT signaling dysregulation in cancer and non-cancerous diseases. Canonical WNT/β-catenin signaling cascade is aberrantly activated in hereditary colorectal cancer and various types of sporadic cancers owing to genetic alterations in the APC, AXIN2, CTNNB1, RNF43, RSPO2 and RSPO3 genes, and also in hereditary osteoblastic diseases owing to SOST and LRP5 mutations (red boxes). The WNT/β-catenin signaling cascade is downergulated in intellectual disability syndrome owing to CTNNB1 loss-of-function mutations, in familial exudative vitreoretinopathy owing to loss-of-function mutations in the FZD4 and LRP5 genes and in osteoporosis-associated syndromes owing to LRP5, LRP6 and WNT1 loss-of-function mutations (open box). By contrast, non-canonical WNT/RTK signaling cascade is aberrantly activated in B-cell leukemia and solid tumors as a result of ROR1 upregulation (blue box). Non-canonical WNT/PCP signaling cascade is dysregulated in PCP-related hereditary diseases, such as autism, epilepsy, neural tube defects and Robinow syndrome owing to mutations in the CELSR1, DVL1, DVL2, DVL3, FZD6, PRICKLE1, PRICKLE2, ROR2, VANGL1, VANGL2 and WNT5A genes (open boxes). Genetic alterations in the WNT signaling molecules affect multiple WNT signaling cascades. For example, RNF43, RSPO2 and RSPO3 alterations activate WNT/β-catenin and other WNT signaling cascades, whereas loss-of-function LRP5 mutations inactivate the WNT/β-catenin signaling cascade and reciprocally activate the WNT/PCP signaling cascade. PCP, planar cell polarity; RTK, receptor tyrosine kinase.

Figure 3

β-catenin at the crossroad of WNT, tyrosine kinase and GPCR-cAMP-PKA signaling cascades. WNT/β-catenin signaling activation induces stabilization and nuclear translocation of β-catenin and upregulation of β-catenin-TCF/LEF target genes. By contrast, activation of BCR-ABL, FLT3, KIT, SRC or RET tyrosine kinases and GPCR-mediated PKA activation induce β-catenin phosphorylation at Y654 and S675, respectively, which also promotes nuclear translocation of β-catenin and β-catenin-dependent transcription. FSHR (275), GLP1R (276), MC1R (277), PTGER2/EP2 (278,279), PTGER4/EP4 (278,280) and PTH1R (281) are GPCRs that are reported to induce cAMP-dependent PKA activation and subsequent β-catenin activation. AXIN2, CCND1, DKK1, FGF20, FZD7, JAG1, MYC, NEUROD1 and NOTUM are representative targets of the WNT/β-catenin signaling cascade; however, β-catenin target genes are context-dependently upregulated owing to additional transcriptional regulation by the tyrosine kinase and PKA signaling cascades. GPCR, G protein-coupled receptor; PKA, protein kinase A, DKK1, Dickkopf-related protein 1.

Figure 4

Mutations, downstream signaling and therapeutics of WNT-related human cancers. (Left) Loss-of-function APC mutations and gain-of-function CTNNB1 mutations in human cancers, such as colorectal cancer, breast cancer and uterine cancer (uterine corpus endometrial carcinoma), lead to ligand-independent activation of the WNT/β-catenin signaling cascade, which can be treated with β-catenin inhibitors in preclinical model animal experiments. (Middle) Loss-of-function RNF43 or ZNRF3 mutations, RSPO2/3 fusions and RSPO3 upregulation in colorectal cancer, breast cancer, pancreatic cancer and other cancers activate the WNT/β-catenin signaling cascade as well as β-catenin-independent WNT signaling cascades, such as WNT/STOP and WNT/PCP signaling cascades. This type of cancers can be treated with anti-FZD5 mAb, anti-RSPO3 mAb or PORCN inhibitors. (Right) ROR1 upregulation in B-cell leukemia and solid tumors gives rise to WNT/PCP and WNT/RTK signaling activation, which can be treated with anti-ROR1 mAb, anti-ROR1 × anti-CD3 bispecific antibodies, ROR1 inhibitor and ROR1 CAR-T cells. PCP, planar cell polarity; ALL, acute lymphoblastic leukemia; CAR-T, chimeric antigen receptor-modified T cells; CLL, chronic lymphocytic leukemia; GoF, gain-of-function; LoF, loss-of-function; mAb, monoclonal antibody; Mut, mutation; RTK, receptor tyrosine kinase; STOP, stabilization of proteins; PORCN, porcupine.

Figure 5

Context-dependent WNT signaling and immune evasion. Cancer cells and CAFs dictate accumulation of M2-TAMs, MDSCs and regulatory T (Treg) cells in the tumor environment to give rise to immune evasion through clearance or functional inhibition of CD8⁺ effector T cells and NK cells. WNT/β-catenin signaling activation in DCs can enhance immune evasion through Treg accumulation in the tumor microenvironment, whereas DKK1-induced WNT/β-catenin signaling inhibition in cancer cells or the tumor microenvironment can also enhance immune evasion through MDSC accumulation and NK clearance. Anti-WNT signaling therapy using PORCN inhibitor, tankyrase inhibitor or β-catenin inhibitor may be applicable for the treatment of immune evasion induced by WNT/β-catenin signaling activation. By contrast, pro-WNT signaling therapy using an anti-DKK1 monoclonal antibody may be applicable for the treatment of immune evasion associated with DKK1 upregulation. As WNT signaling cascades are involved in context-dependent immune evasion and antitumor immunity, precise immune monitoring and comprehensive understanding of WNT-dependent immune regulation are necessary to apply WNT-targeted therapy for cancer patients with immune evasion. CAFs, cancer-associated fibroblasts; M2-TAMs, M2-type tumor associated macrophages; NK, natural killer; DCs, dendritic cells; MDSCs, myeloid-derived suppressor cells; PORCN, porcupine; DKK1, Dickkopf-related protein 1.