Jung and Park Experimental & Molecular Medicine (2020) 52:183–191 https://doi.org/10.1038/s12276-020-0380-6 Experimental & Molecular Medicine REVIEW ARTICLE Open Access Wntsignalingincancer:therapeutictargetingof Wntsignalingbeyondβ-catenin and the destruction complex Youn-Sang Jung1 and Jae-Il Park 1,2,3 Abstract Wnt/β-catenin signaling is implicated in many physiological processes, including development, tissue homeostasis, and tissue regeneration. In human cancers, Wnt/β-catenin signaling is highly activated, which has led to the development of various Wnt signaling inhibitors for cancer therapies. Nonetheless, the blockade of Wnt signaling causes side effects such as impairment of tissue homeostasis and regeneration. Recently, several studies have identified cancer-specific Wnt signaling regulators. In this review, we discuss the Wnt inhibitors currently being used in clinical trials and suggest how additional cancer-specific regulators could be utilized to treat Wnt signaling-associated cancer. Introduction to target Wnt signaling for cancer therapies proposed Wnt signaling orchestrates various biological processes, from recent studies. 1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; such as cell proliferation, differentiation, organogenesis, – tissue regeneration, and tumorigenesis1 5. Classically, Wnt signaling and clinical trials in human cancers Wnt signaling is divided into β-catenin-dependent β-Catenin is a crucial signaling transducer in Wnt (canonical, Wnt/β-catenin pathway) and β-catenin-inde- signaling10,11.Theβ-catenin protein destruction com- pendent (noncanonical, Wnt/planar cell polarity [PCP] plex composed of adenomatous polyposis coli (APC), and calcium pathway) signaling6,7. Canonical Wnt sig- casein kinase 1 (CK1), glycogen synthase kinase 3α/β naling mainly regulates cell proliferation, and non- (GSK-3α/β), and AXIN1 tightly controls β-catenin via – canonical Wnt signaling controls cell polarity and phosphorylation-mediated proteolysis10,12 16. In this movement. However, this terminological distinction is section, we brieflydescribehowgeneticalterationsof unclear, and has been questions by studies proposing the Wnt signaling contribute to tumorigenesis and introduce involvement of both β-catenin-dependent and β-catenin- recent clinical trials that have aimed to inhibit Wnt independent Wnt signaling in tumorigenesis8. For signaling for cancer treatment. instance, APC and β-catenin are not only involved in cell proliferation but have also been linked to cell-to-cell The β-catenin destruction complex adhesion9. In this review, we will discuss an ongoing effort Colorectal cancer (CRC) is the representative of human to inhibit Wnt signaling and suggest potential approaches cancer caused by Wnt signaling hyperactivation17,18.CRC – displays a high mutation frequency in APC (~70%)19 21.In 1991, APC mutation was identified as the cause of heredi- Correspondence: Jae-Il Park ([email protected]) 1Department of Experimental Radiation Oncology, Division of Radiation tary colon cancer syndrome, also called familial adenoma- Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX tous polyposis22.APCformstheβ-catenin destruction 77030, USA 2 complex in association with CK1, AXIN1, and GSK-3 and Graduate School of Biomedical Sciences, The University of Texas MD 15,23,24 Anderson Cancer Center, Houston, TX 77030, USA interacts with β-catenin . This protein destruction Full list of author information is available at the end of the article. © The Author(s) 2020 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a linktotheCreativeCommons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Official journal of the Korean Society for Biochemistry and Molecular Biology Jung and Park Experimental & Molecular Medicine (2020) 52:183–191 184 complex downregulates β-catenin through phosphorylation and the stabilization/accumulation of β-catenin. Then, – and ubiquitin-mediated protein degradation10,12 16. Genetic β-catenin undergoes nuclear translocation and transacti- mutations causing the loss of function of the destruction vates Wnt target genes57. The secretion of WNT ligands complex or gain of function of β-catenin lead to nuclear mainly depends on acylation by Porcupine (PORCN)58,59. translocation of β-catenin, resulting in T-cell factor (TCF)4/ PORCN is a membrane-bound O-acyltransferase that β-catenin-mediated transactivation of Wnt target genes25,26. mediates the palmitoylation of WNT ligands to induce The Vogelstein group established a multistep tumorigenesis their secretion. In line with this observation, PORCN model of CRC. APC mutation is an early event that initiates shows increased genetic alterations in various human CRC adenoma27. CRC progression also requires additional cancers, including esophageal, ovarian, uterine, lung, and genetic alterations in KRAS, PI3K, TGF-β, SMAD4,and cervical cancers60. TP5327. Moreover, epigenetic silencing of negative reg- ulators of Wnt signaling was also frequently found in the Mutations in CTNNB1/β-catenin absence of APC mutations28,29. APC is a multifunctional Unlike CRC, in which the APC gene is frequently protein. In addition to its role in β-catenin degradation, mutated, the CTNNB1 gene encoding β-catenin is pre- – APC binds to actin and actin-regulating proteins30 33, dominantly mutated in hepatocellular carcinoma, endo- – which controls the interaction between E-cadherin and α-/ metrial cancer, and pancreatic cancer61 63. The CTNNB1/ β-catenin and various physiological processes, including β-catenin gene harbors 16 exons. β-Catenin is mainly – migration and chromosomal fidelity34 38. Importantly, composed of three domains (N-terminal [~150 aa], recent studies revealed that APC mutation is insufficient to armadillo repeat [12 copies; 550 aa], and C-terminal fully activate Wnt signaling. Furthermore, even if APC is [~100 aa]). The N-terminal domain contains the phos- mutated, mutant APC still negatively regulates β-catenin to phorylation sites for GSK3 and CK112,14,45,46, which some extent39,40, which will be discussed later. induces β-TrcP-mediated β-catenin degradation. The C- AXIN1 is a multidomain scaffolding protein that forms terminal domain is involved in transactivation of Wnt – the β-catenin destruction complex in association with target genes via TCF/LEF interactions25,64 66. The arma- APC, CK1, and GSK310,41,42. In human cancer, AXIN1 dillo repeat domain interacts with various proteins, mutations are scattered throughout the whole coding including E-cadherin, APC, AXIN1, and PYGOs/Pygo- sequence of the AXIN1 gene43,44, which results in dis- pus67,68. In human cancer, the phosphorylation sites (Ser/ assembly of the β-catenin destruction complex. As a Thr) in the N-terminal domain of CTNNB1/β-catenin are priming kinase, CK1 initially phosphorylates β-catenin mutational hotspots14,69,70, demonstrating that escape (Ser45), which induces the sequential phosphorylation of from destruction complex-mediated β-catenin protein β-catenin by GSK3. Subsequently, phosphorylated degradation is a key process for Wnt signaling-induced β-catenin is recognized and degraded by E3 ubiquitin tumorigenesis. – ligase (β-TrCP)10,12 16. GSK3 is a serine/threonine kinase that phosphorylates three serine/threonine residues of Therapeutic targeting of Wnt/β-catenin signaling β-catenin (Ser33, Ser37, and Thr41)45,46. Since GSK3 does To suppress WNT ligands or receptors for cancer not bind to β-catenin directly, AXIN1 and APC facilitate treatment, PORCN inhibitors, WNT ligand antagonists, the interaction of GSK3 with β-catenin47,48. Moreover, and FZD antagonists/monoclonal antibodies have been unphosphorylated AXIN1 shows a low binding affinity to examined in clinical trials of various Wnt signaling- β-catenin, which is increased by phosphorylation of associated human cancers (Table 1 and Fig. 1). AXIN1 via GSK3 kinase activity49,50. Low-density lipo- protein receptor-related protein 5/6 (LRP5/6) coreceptor (i) PORCN inhibitors is also phosphorylated by CK1 and GSK3, leading to the WNT974 (LGK974; NIH clinical trial numbers [clin- – recruitment of AXIN1 to the membrane51 53. icaltrials.gov]: NCT02278133, NCT01351103, and NCT02649530), ETC-1922159 (ETC-159; NCT02521844), WNT ligands and receptors RXC004 (NCT03447470), and CGX1321 (NCT02675946 Under physiological conditions, Wnt signaling is acti- and NCT03507998) are orally administered PORCN inhi- vated by the binding of secreted WNT ligands to LRP5/6 bitors that commonly bind to PORCN in the endoplasmic – coreceptors and frizzled (FZD) receptors54, which induces reticulum71 74. Therefore, PORCN inhibitors block the the recruitment of the protein destruction complex to the secretion of WNT ligands through inhibition of post- LRP receptors and the subsequent phosphorylation of the translational acylation of