Vitamin D Receptor Deficiency Enhances Wnt/β-Catenin Signaling and Tumor Burden in Colon Cancer

Aberrant activation of the Wnt/β-catenin pathway is critical for the initiation and progression of most colon cancers. This activation provokes the accumulation of nuclear β-catenin and the induction of its target genes. Apcmin/+ mice are the most commonly used model for colon cancer. They harbor a mutated Apc allele and develop intestinal adenomas and carcinomas during the first months of life. This phenotype is caused by the mutation of the second Apc allele and the consequent accumulation of nuclear β-catenin in the affected cells. Here we describe that vitamin D receptor (VDR) is a crucial modulator of nuclear β-catenin levels in colon cancer in vivo. By appropriate breeding of Apcmin/+ mice and Vdr+/− mice we have generated animals expressing a mutated Apc allele and two, one, or none Vdr wild type alleles. Lack of Vdr increased the number of colonic Aberrant Crypt Foci (ACF) but not that of adenomas or carcinomas in either small intestine or colon. Importantly, colon ACF and tumors of Apcmin/+Vdr-/- mice had increased nuclear β-catenin and the tumors reached a larger size than those of Apcmin/+Vdr+/+. Both ACF and carcinomas in Apcmin/+Vdr-/- mice showed higher expression of β-catenin/TCF target genes. In line with this, VDR knock-down in cultured human colon cancer cells enhanced β-catenin nuclear content and target gene expression. Consistently, VDR depletion abrogated the capacity of 1,25(OH)2D3 to promote the relocation of β-catenin from the nucleus to the plasma membrane and to inhibit β-catenin/TCF target genes. In conclusion, VDR controls the level of nuclear β-catenin in colon cancer cells and can therefore attenuate the impact of oncogenic mutations that activate the Wnt/β-catenin pathway

RhoA–ROCK and p38MAPK-MSK1 mediate vitamin D effects on gene expression, phenotype, and Wnt pathway in colon cancer cells

The active vitamin D metabolite 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) inhibits proliferation and promotes differentiation of colon cancer cells through the activation of vitamin D receptor (VDR), a transcription factor of the nuclear receptor superfamily. Additionally, 1,25(OH)2D3 has several nongenomic effects of uncertain relevance. We show that 1,25(OH)2D3 induces a transcription-independent Ca2+ influx and activation of RhoA–Rho-associated coiled kinase (ROCK). This requires VDR and is followed by activation of the p38 mitogen-activated protein kinase (p38MAPK) and mitogen- and stress-activated kinase 1 (MSK1). As shown by the use of chemical inhibitors, dominant-negative mutants and small interfering RNA, RhoA–ROCK, and p38MAPK-MSK1 activation is necessary for the induction of CDH1/E-cadherin, CYP24, and other genes and of an adhesive phenotype by 1,25(OH)2D3. RhoA–ROCK and MSK1 are also required for the inhibition of Wnt–β-catenin pathway and cell proliferation. Thus, the action of 1,25(OH)2D3 on colon carcinoma cells depends on the dual action of VDR as a transcription factor and a nongenomic activator of RhoA–ROCK and p38MAPK-MSK1

Autolysosomal β-catenin degradation regulates Wnt-autophagy-p62 crosstalk

The Wnt/β-catenin signalling and autophagy pathways each play important roles during development, adult tissue homeostasis and tumorigenesis. Here we identify the Wnt/β-catenin signalling pathway as a negative regulator of both basal and stress-induced autophagy. Manipulation of β-catenin expression levels in vitro and in vivo revealed that β-catenin suppresses autophagosome formation and directly represses p62/SQSTM1 (encoding the autophagy adaptor p62) via TCF4. Furthermore, we show that during nutrient deprivation β-catenin is selectively degraded via the formation of a β-catenin-LC3 complex, attenuating β-catenin/TCF-driven transcription and proliferation to favour adaptation during metabolic stress. Formation of the β-catenin-LC3 complex is mediated by a W/YXXI/L motif and LC3-interacting region (LIR) in β-catenin, which is required for interaction with LC3 and non-proteasomal degradation of β-catenin. Thus, Wnt/β-catenin represses autophagy and p62 expression, while β-catenin is itself targeted for autophagic clearance in autolysosomes upon autophagy induction. These findings reveal a regulatory feedback mechanism that place β-catenin at a key cellular integration point coordinating proliferation with autophagy, with implications for targeting these pathways for cancer therapy. © 2013 European Molecular Biology Organization

Vitamina D y cáncer de colon: identificación de genes diana y mecanismo de regulación de CDH1/E-cadherina

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid. Facultad de Medicina. Departamento de Bioquímica. Fecha de lectura: 15-11-200

Lrig1: a new master regulator of epithelial stem cells

The intestine represents the most vigorously renewing, adult epithelial tissue that makes maintenance of its homeostasis a delicate balance between proliferation, cell cycle arrest, migration, differentiation, and cell death. These processes are precisely controlled by a network of developmental signalling cascades, which include Wnt, Notch, BMP/TGF beta, and Hedgehog pathways. A new, elegant study by Wong et al (2012) now adds Lrig1 as a key player in the control of intestinal homeostasis. As for epidermal stem cells, Lrig1 limits the size of the intestinal progenitor compartment by dampening EGF/ErbB-triggered stem cell expansion

Complex metastatic niches: already a target for therapy?

Metastatic spread is an inefficient process which requires generation of supportive microenvironments in which cancer cells can survive, proliferate and escape from immune attack. These niches are induced by systemic and locally produced factors and establish a tumor-supportive and immune suppressive environment which is molecularly and functionally different from the niche at the primary site. Tumor dormancy may result if the niche is not sufficiently supportive/protective. Co-evolution of cancer cells and the surrounding microenvironment creates a large number of such dynamic niches, and we are just beginning to elucidate the complexity of these interactions and their tissue-specific differences. We will discuss exciting possibilities but also challenges which are immanent when trying to target these stromal responses for diagnosis and therapy

β-Catenin confers resistance to PI3K and AKT inhibitors and subverts FOXO3a to promote metastasis in colon cancer

El pdf del artículo es la versión pre-print.-- et al.The Wnt-β-catenin and PI3K-AKT-FOXO3a pathways have a central role in cancer. AKT phosporylates FOXO3a, relocating it from the cell nucleus to the cytoplasm, an effect that is reversed by PI3K and AKT inhibitors. Simultaneous hyperactivation of the Wnt-β-catenin pathway and inhibition of PI3K-AKT signaling promote nuclear accumulation of β-catenin and FOXO3a, respectively, promoting cell scattering and metastasis by regulating a defined set of target genes. Indeed, the anti-tumoral AKT inhibitor API-2 promotes nuclear FOXO3a accumulation and metastasis of cells with high nuclear β-catenin content. Nuclear b-catenin confers resistance to the FOXO3a-mediated apoptosis induced by PI3K and AKT inhibitors in patient-derived primary cultures and in corresponding xenograft tumors in mice. This resistance is reversed by XAV-939, an inhibitor of Wnt-β-catenin signaling. In the presence of high nuclear β-catenin content, activation of FOXO3a by PI3K or AKT inhibitors makes it behave as a metastasis inductor rather than a proapoptotic tumor suppressor. We show that it is possible to evaluate the β-catenin status of patients' carcinomas and the response of patient-derived cells to target-directed drugs that accumulate FOXO3a in the nucleus before deciding on a course of treatment. We propose that this evaluation could be essential to the provision of a safer and more effective personalized treatment. © 2012 Nature America, Inc. All rights reserved.Experiments were supported by a VHIO starting grant and grants from Fondo de Investigaciones Sanitarias–Instituto de Salud Carlos III (ISCIII) (FIS-PI081356, RETICC-RD06/0020/0075 and RETICC-RD06/0020/0009), and Plan Nacional de Biomedicina, Ministerio de Ciencia e Innovación (SAF-18302). S.P.T. was supported by a Fundació Olga Torres Fellowship, I.P. was funded by the Fundación Científica de la Asociación Española Contra el Cancer (AECC), and H.G.P. was supported by the Miguel Servet Program, ISCIII.Peer Reviewe

Nuclear receptors: Genomic and non-genomic effects converge

The nuclear receptor superfamily mediates the regulatory activities of many hormones, nutrients and metabolites on the homeostasis and physiology of cells and tissues. Classically, ligand binding induced the ability of nuclear receptors to modulate the transcription rate of target genes (genomic effects), which led to consider them as ligand-activated transcription factors. Later, rapid actions of nuclear receptor ligands were reported that did not involve changes in gene expression. These (non-genomic) effects have been attributed in some cases to receptors different to those mediating gene transcription but most evidences indicate that they result from the activity of a population of nuclear receptor molecules acting outside the cell nucleus. Recent studies on estrogen and vitamin D, and their receptors (ERα/β, VDR) support now the idea that non-genomic and genomic effects may integrate in a unique mode of action of nuclear receptor ligands, in which the non-genomic effects constitute signaling pathways required for the effects at the genome level. Here, we will discuss these novel findings and also those indicating transcriptional regulation through ligand-dependent and -independent crosstalk of nuclear receptors with β-catenin or VDR-interacting repressor (VDIR). ©2009 Landes Bioscience.The work in authors’ laboratory is supported by Grants of the Ministerio de Ciencia e Innovación of Spain (SAF2007-60341, ISCIII-RETIC RD06/0020/0009), Comunidad de Madrid (S-GEN-0266/2006) and the European Union (MRTN-CT-2005-019496, NucSys).Peer Reviewe