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This article belongs to the Special Issue Targeting Wnt Signaling in Cancer: Opportunities Abound If We Can Avoid the Sword of Damocles., [Simple Summary]: The Wnt/β-catenin signaling pathway is aberrantly activated in most colorectal cancers and less frequently in a variety of other solid neoplasias. Many epidemiological and experimental studies and some clinical trials suggest an anticancer action of vitamin D, mainly against colorectal cancer. The aim of this review was to analyze the literature supporting the interference of Wnt/β-catenin signaling by the active vitamin D metabolite 1α,25-dihydroxyvitamin D3. We discuss the molecular mechanisms of this antagonism in colorectal cancer and other cancer types. Additionally, we summarize the available data indicating a reciprocal inhibition of vitamin D action by the activated Wnt/β-catenin pathway. Thus, a complex mutual antagonism between Wnt/β-catenin signaling and the vitamin D system seems to be at the root of many solid cancers., Abnormal activation of the Wnt/β-catenin pathway is common in many types of solid cancers. Likewise, a large proportion of cancer patients have vitamin D deficiency. In line with these observations, Wnt/β-catenin signaling and 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3), the active vitamin D metabolite, usually have opposite effects on cancer cell proliferation and phenotype. In recent years, an increasing number of studies performed in a variety of cancer types have revealed a complex crosstalk between Wnt/β-catenin signaling and 1,25(OH)2D3. Here we review the mechanisms by which 1,25(OH)2D3 inhibits Wnt/β-catenin signaling and, conversely, how the activated Wnt/β-catenin pathway may abrogate vitamin D action. The available data suggest that interaction between Wnt/β-catenin signaling and the vitamin D system is at the crossroads in solid cancers and may have therapeutic applications., The work in the authors’ laboratory is funded by the Agencia Estatal de Investigación (PID2019-104867RB-I00/AEI/10.13039/501100011033), the Agencia Estatal de Investigación—Fondo Europeo de Desarrollo Regional (SAF2016-76377-R, MINECO/AEI/FEDER, EU), the Ministerio de Economía y Competitividad (SAF2017-90604-REDT/NuRCaMeIn), and the Instituto de Salud Carlos III—Fondo Europeo de Desarrollo Regional (CIBERONC; CB16/12/00273).

Colorectal cancer results from the malignant transformation of colonic epithelial cells. Stromal fibroblasts are the main component of the tumour microenvironment, and play an important role in the progression of this and other neoplasias. Wnt/β-catenin signalling is essential for colon homeostasis, but aberrant, constitutive activation of this pathway is a hallmark of colorectal cancer. Here we present the first transcriptomic study on the effect of a Wnt factor on human colonic myofibroblasts. Wnt3A regulates the expression of 1,136 genes, of which 662 are upregulated and 474 are downregulated in CCD-18Co cells. A set of genes encoding inhibitors of the Wnt/β-catenin pathway stand out among those induced by Wnt3A, which suggests that there is a feedback inhibitory mechanism. We also show that the PKP2 gene encoding the desmosomal protein Plakophilin-2 is a novel direct transcriptional target of Wnt/β-catenin in normal and colon cancer-associated fibroblasts. PKP2 is induced by β-catenin/TCF through three binding sites in the gene promoter and one additional binding site located in an enhancer 20 kb upstream from the transcription start site. Moreover, Plakophilin-2 antagonizes Wnt/β-catenin transcriptional activity in HEK-293T cells, which suggests that it may act as an intracellular inhibitor of the Wnt/β-catenin pathway. Our results demonstrate that stromal fibroblasts respond to canonical Wnt signalling and that Plakophilin-2 plays a role in the feedback control of this effect suggesting that the response to Wnt factors in the stroma may modulate Wnt activity in the tumour cells.

The Wnt/β-catenin signalling pathway is essential for intestinal epithelium homeostasis, but its aberrant activation is a hallmark of colorectal cancer (CRC). Several studies indicate that the bioactive vitamin D metabolite 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3) inhibits proliferation and promotes epithelial differentiation of colon carcinoma cells in part through antagonism of the Wnt/β-catenin pathway. It is now accepted that stromal fibroblasts are crucial in healthy and pathologic intestine: pericryptal myofibroblasts are constituents of the stem cell niche and cancer-associated fibroblasts (CAFs) contribute to CRC progression. However, studies on the combined action of 1,25(OH)2D3 and Wnt factors in colon fibroblasts are lacking. Here we show by global transcriptomic studies that 1,25(OH)2D3 and Wnt3A have profound, additive, partially overlapping effects on the gene expression profile of CCD-18Co human colon myofibroblasts. Moreover, 1,25(OH)2D3 and Wnt3A inhibit CCD-18Co cell proliferation and migration, while 1,25(OH)2D3 reduces, but Wnt3A increases, their capacity to contract collagen gels (a marker of fibroblast activation). These data were largely confirmed in patient-derived primary colon normal fibroblasts and CAFs, and in fibroblasts from other origins. Our results indicate that 1,25(OH)2D3 and Wnt3A are strong regulators of colon fibroblast biology and contribute to a better knowledge of intestinal homeostasis and stromal fibroblast action in CRC., We thank IdiPAZ Biobank (PT13/0010/0003, Plataforma de Apoyo a la Investigación en Ciencias y Tecnologías de la Salud en la Red de Biobancos 2013) for providing clinical samples, Javier Pérez for the artwork, and Lucille Banham for her assistance in the preparation of the English manuscript. The work in the authors’ laboratories is supported by the Spanish Ministerio de Ciencia, Innovación y Universidades - Fondo Europeo de Desarrollo Regional (FEDER) (SAF2016-76377-R, SAF2017-90604-REDT), Consejo Superior de Investigaciones Científicas (201820I058), and Instituto de Salud Carlos III - FEDER (CIBERONC, CB16/12/00273; CIBERES, CB15/00037).

Summary Aryl hydrocarbon receptor (AhR) deficiency alters tissue homeostasis. However, how AhR regulates organ maturation and differentiation remains mostly unknown. Liver differentiation entails a polyploidization process fundamental for cell growth, metabolism, and stress responses. Here, we report that AhR regulates polyploidization during the preweaning-to-adult mouse liver maturation. Preweaning AhR-null (AhR−/−) livers had smaller hepatocytes, hypercellularity, altered cell cycle regulation, and enhanced proliferation. Those phenotypes persisted in adult AhR−/− mice and correlated with compromised polyploidy, predominance of diploid hepatocytes, and enlarged centrosomes. Phosphatidylinositol-3-phosphate kinase (PI3K), extracellular signal-regulated kinase (ERK), and Wnt/β-catenin signaling remained upregulated from preweaning to adult AhR-null liver, likely increasing mammalian target of rapamycin (mTOR) activation. Metabolomics revealed the deregulation of mitochondrial oxidative phosphorylation intermediates succinate and fumarate in AhR−/− liver. Consistently, PI3K, ERK, and Wnt/β-catenin inhibition partially rescued polyploidy in AhR−/− mice. Thus, AhR may integrate survival, proliferation, and metabolism for liver polyploidization. Since tumor cells tend to be polyploid, AhR modulation could have therapeutic value in the liver., Graphical Abstract, Highlights • AhR is required for liver polyploidization during preweaning-to-adult transition • INS-R/PI3K/AKT, ERK, Wnt/β-Cat and mTOR are downregulated during liver polyploidization • Reduced polyploidy relates with enhanced mitochondrial metabolism in AhR-null liver • Understanding how AhR modulates polyploidy may provide strategies against cancer, Developmental Biology; Cancer Systems Biology; Metabolomics

Colon cancer is one of the most frequent and lethal neoplasias and the first to be associated with vitamin D deficiency. Many epidemiological studies indicate a protective effect of vitamin D on colon cancer. This is supported by preclinical studies using vitamin D, 1,25(OH)2D3 or analogues in cultured cells and experimental animals. These compounds regulate colon carcinoma cell gene expression, survival, differentiation, proliferation and invasion and inhibit angiogenesis and metastasis during colon cancer progression. Remarkably, in animal and in vitro models vitamin D compounds inhibit the Wnt/β-catenin signaling pathway, whose aberrant activation initiates and maintains colon cancer. Moreover, recent data show that 1,25(OH)2D3 protects against colon cancer acting also on tumor stromal fibroblasts. However, clinical data are scarce and inconclusive, and a definitive answer about the role of vitamin D compounds in the prevention and treatment of colon cancer requires new, large, well-designed clinical trials.

et al., SPROUTY-2 (SPRY2) is a modulator of tyrosine kinase receptor signaling with receptor- and cell type-dependent inhibitory or enhancing effects. Studies on the action of SPRY2 in major cancers are conflicting and its role remains unclear. Here we have dissected SPRY2 action in human colon cancer. Global transcriptomic analyses show that SPRY2 downregulates genes encoding tight junction proteins such as claudin-7 and occludin and other cell-to-cell and cell-to-matrix adhesion molecules in human SW480-ADH colon carcinoma cells. Moreover, SPRY2 represses LLGL2/HUGL2, PATJ1/INADL and ST14, main regulators of the polarized epithelial phenotype, and ESRP1, an epithelial-to-mesenchymal transition (EMT) inhibitor. A key action of SPRY2 is the upregulation of the major EMT inducer ZEB1, as these effects are reversed by ZEB1 knock-down by means of RNA interference. Consistently, we found an inverse correlation between the expression level of claudin-7 and those of SPRY2 and ZEB1 in human colon tumors. Mechanistically, ZEB1 upregulation by SPRY2 results from the combined induction of ETS1 transcription factor and the repression of microRNAs (miR-200 family, miR-150) that target ZEB1 RNA. Moreover, SPRY2 increased AKT activation by epidermal growth factor, whereas AKT and also Src inhibition reduced the induction of ZEB1. Altogether, these data suggest that AKT and Src are implicated in SPRY2 action. Collectively, these results show a tumorigenic role of SPRY2 in colon cancer that is based on the dysregulation of tight junction and epithelial polarity master genes via upregulation of ZEB1. The dissection of the mechanism of action of SPRY2 in colon cancer cells is important to understand the upregulation of this gene in a subset of patients with this neoplasia that have poor prognosis., This study was supported by the Ministerio de Economía y Competitividad of Spain and Fondo Europeo de Desarrollo Regional (FEDER) (grant SAF2013-43468-R to AM, SAF2011-29530 to FXR); FEDER-Instituto de Salud Carlos III (RD12/0036/0021 to AM and JMR, RD12/0036/0034 to FXR, RD12/0036/0016 to MS, RD12/0036/0012 to HGP, RD06/0020/0003, PS09/00562 and PI13/00703 to JMR); Comunidad de Madrid (S2010/BMD-2344 Colomics2 to AM); Fundación Científica de la Asociación Española contra el Cáncer (to JMR); US Department of Defense (CA093471 and CA110602 to EH); National Institutes of Health/National Cancer Institute (1R01CA155234-01 to EH); National Institutes of Health/National Institute of Arthritis and Musculoskeletal and Skin Diseases (1R21AR062239-01 to EH); and the Melanoma Research Alliance (to EH).

This work is licensed under a Creative Commons Attribution 4.0 International License., The role of DICKKOPF (DKK)-1 in human cancer is controversial. DKK-1 behaves as an inhibitor of the canonical Wnt/β-catenin signaling pathway acting at the plasma membrane, although several studies have proposed effects that are independent of the inhibition of β-catenin transcriptional activity, in some cases mediated by the activation of c-Jun N-terminal kinase (JNK). Recently, a proportion of DKK-1 protein has been found within the nucleus of human intestinal epithelial cells following an apical-to-basal crypt decreasing gradient, and in that of colon carcinoma cells. Moreover, we show here that in the human mammary gland DKK-1 is also present within the nucleus of many differentiated luminal epithelial cells and in that of a small proportion of myoepithelial cells. Nuclear DKK-1 binds to actively transcribed chromatin and regulates the expression of specific genes, some of which are involved in cell proliferation, survival and stemness, and in the defense against xenobiotics. This may explain the finding that while DKK-1 is downregulated more rapidly in the nucleus than in the cytosol during colon carcinoma progression, its expression remains high in a percentage of patients who do not respond to chemotherapy. Available data suggest that the accumulation of DKK-1 in the nucleus of colon carcinoma cells depends on signals from the surrounding tumor microenvironment., Work in authors' laboratories is supported by grants from Ministerio de Economía y Competitividad of Spain-Fondo Europeo de Desarrollo Regional (FEDER) (SAF2013-43468-R), Comunidad de Madrid (S2010/BMD-2344 Colomics2), and FEDER-Instituto de Salud Carlos III (RD12/0036/0021; RD12/0036/0051, PT13/0010/0012 and PI12/01552).

et al., [Aims]: Nuclear factor (erythroid-derived 2)-like 2 (NRF2) is a master regulator of oxidant and xenobiotic metabolism, but it is unknown how it is regulated to provide basal expression of this defense system. Here, we studied the putative connection between NRF2 and the canonical WNT pathway, which modulates hepatocyte metabolism. [Results]: WNT-3A increased the levels of NRF2 and its transcriptional signature in mouse hepatocytes and HEK293T cells. The use of short interfering RNAs in hepatocytes and mouse embryonic fibroblasts which are deficient in the redox sensor Kelch-like ECH-associated protein 1 (KEAP1) indicated that WNT-3A activates NRF2 in a β-Catenin- and KEAP1-independent manner. WNT-3A stabilized NRF2 by preventing its GSK-3-dependent phosphorylation and subsequent SCF/β-TrCP-dependent ubiquitination and proteasomal degradation. Axin1 and NRF2 were physically associated in a protein complex that was regulated by WNT-3A, involving the central region of Axin1 and the Neh4/Neh5 domains of NRF2. Axin1 knockdown increased NRF2 protein levels, while Axin1 stabilization with Tankyrase inhibitors blocked WNT/NRF2 signaling. The relevance of this novel pathway was assessed in mice with a conditional deletion of Axin1 in the liver, which showed upregulation of the NRF2 signature in hepatocytes and disruption of liver zonation of antioxidant metabolism. [Innovation]: NRF2 takes part in a protein complex with Axin1 that is regulated by the canonical WNT pathway. This new WNT-NRF2 axis controls the antioxidant metabolism of hepatocytes. [Conclusion]: These results uncover the participation of NRF2 in a WNT-regulated signalosome that participates in basal maintenance of hepatic antioxidant metabolism., This work was funded by SAF2013-43271-R of the Spanish Ministry of Economy and Competitiveness.

This work is licensed under a Creative Commons Attribution 3.0 License.-- et al., Sporadic colorectal cancer (CRC) insurgence and progression depend on the activation of Wnt/β-catenin signaling. Dickkopf (DKK)-1 is an extracellular inhibitor of Wnt/β-catenin signaling that also has undefined β-catenin-independent actions. Here we report for the first time that a proportion of DKK-1 locates within the nucleus of healthy small intestine and colon mucosa, and of CRC cells at specific chromatin sites of active transcription. Moreover, we show that DKK-1 regulates several cancerrelated genes including the cancer stem cell marker aldehyde dehydrogenase 1A1 (ALDH1A1) and Ral-binding protein 1-associated Eps domain-containing 2 (REPS2), which are involved in detoxification of chemotherapeutic agents. Nuclear DKK-1 expression is lost along CRC progression; however, it remains high in a subset (15%) of CRC patients (n = 699) and associates with decreased progression-free survival (PFS) after chemotherapy administration and overall survival (OS) [adjusted HR, 1.65; 95% confidence interval (CI), 1.23-2.21; P = 0.002)]. Overexpression of ALDH1A1 antiand REPS2 associates with nuclear DKK-1 expression in tumors and correlates with decreased OS (P = 0.001 and 0.014) and PFS. In summary, our findings demonstrate a novel location of DKK-1 within the cell nucleus and support a role of nuclear DKK-1 as a predictive biomarker of chemoresistance in colorectal cancer., This work was supported by grants from the Ministerio de Economía y Competitividad of Spain and Fondo Europeo de Desarrollo Regional (FEDER) (SAF2013-43468-R, A.M.; BFU2010-19659, J.M.G-S.; SAF2010-19256, B.J.; SAF2011-23089, C.L-O.), Comunidad de Madrid (S2010/BMD-2344 Colomics2, A.M., F.R. and J.M.G-S.) and FEDER-Instituto de Salud Carlos III (RD12/0036/0021, A.M.; RD12/0036/0051, PT13/0010/0012 and PI12/01552, F.R.; ProteoRed Networked Proteomics Platform, F.C.).