RESUMO
Activation of the Wnt/ß-catenin pathway occurs in the vast majority of colorectal cancers. However, the outcome of the disease varies markedly from individual to individual, even within the same tumor stage. This heterogeneity is governed to a great extent by the genetic make-up of individual tumors and the combination of oncogenic mutations. In order to express throughout the intestinal epithelium a degradation-resistant ß-catenin (Ctnnb1), which lacks the first 131 amino acids, we inserted an epitope-tagged ΔN(1-131)-ß-catenin-encoding cDNA as a knock-in transgene into the endogenous gpA33 gene locus in mice. The resulting gpA33(ΔN-Bcat) mice showed an increase in the constitutive Wnt/ß-catenin pathway activation that shifts the cell fate towards the Paneth cell lineage in pre-malignant intestinal epithelium. Furthermore, 19% of all heterozygous and 37% of all homozygous gpA33(ΔN-Bcat) mice spontaneously developed aberrant crypt foci and adenomatous polyps, at frequencies and latencies akin to those observed in sporadic colon cancer in humans. Consistent with this, the Wnt target genes, MMP7 and Tenascin-C, which are most highly expressed in benign human adenomas and early tumor stages, were upregulated in pre-malignant tissue of gpA33(ΔN-Bcat) mice, but those Wnt target genes associated with excessive proliferation (i.e. Cdnn1, myc) were not. We also detected diminished expression of membrane-associated α-catenin and increased intestinal permeability in gpA33(ΔN-Bcat) mice in challenge conditions, providing a potential explanation for the observed mild chronic intestinal inflammation and increased susceptibility to azoxymethane and mutant Apc-dependent tumorigenesis. Collectively, our data indicate that epithelial expression of ΔN(1-131)-ß-catenin in the intestine creates an inflammatory microenvironment and co-operates with other mutations in the Wnt/ß-catenin pathway to facilitate and promote tumorigenesis.
Assuntos
Pólipos Adenomatosos/genética , Transformação Celular Neoplásica/genética , Colo , Neoplasias do Colo/genética , Pólipos do Colo/genética , Mutação , Via de Sinalização Wnt/genética , beta Catenina/genética , Pólipos Adenomatosos/induzido quimicamente , Pólipos Adenomatosos/metabolismo , Pólipos Adenomatosos/patologia , Animais , Azoximetano , Transformação Celular Neoplásica/metabolismo , Transformação Celular Neoplásica/patologia , Colite/genética , Colite/metabolismo , Colite/patologia , Colo/metabolismo , Colo/patologia , Neoplasias do Colo/induzido quimicamente , Neoplasias do Colo/metabolismo , Neoplasias do Colo/patologia , Pólipos do Colo/induzido quimicamente , Pólipos do Colo/metabolismo , Pólipos do Colo/patologia , Citocinas/genética , Citocinas/metabolismo , Regulação Neoplásica da Expressão Gênica , Genes APC , Predisposição Genética para Doença , Heterozigoto , Homozigoto , Humanos , Metaloproteinase 7 da Matriz/genética , Metaloproteinase 7 da Matriz/metabolismo , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Estadiamento de Neoplasias , Neovascularização Patológica , Celulas de Paneth/metabolismo , Celulas de Paneth/patologia , Fenótipo , Tenascina/genética , Tenascina/metabolismo , Microambiente Tumoral , beta Catenina/metabolismoRESUMO
BACKGROUND AND AIM: Our previous study of Helicobacter pylori-induced apoptosis showed the involvement of Bcl-2 family proteins and cytochrome c release from mitochondria. Here, we examine the release of other factors from mitochondria, such as apoptosis-inducing factor (AIF), and upstream events involving caspase-8 and Bid. METHODS: Human gastric adenocarcinoma (AGS) cells were incubated with a cagA-positive H. pylori strain for 0, 3, 6, and 24 hours and either total protein or cytoplasmic, nuclear, and mitochondrial membrane fractions were collected. RESULTS: Proteins were immunoblotted for AIF, Bid, polyadenosine ribose polymerase (PARP), caspase-8, and beta-catenin. H. pylori activated caspase-8, caused PARP cleavage, and attenuated mitochondrial membrane potential. A time-dependent decrease in beta-catenin protein expression was detected in cytoplasmic and nuclear extracts, coupled with a decrease in beta-actin. An increase in the cytoplasmic pool of AIF was seen as early as 3 hours after H. pylori exposure, and a concomitant increase was seen in nuclear AIF levels up to 6 hours. A band corresponding to full-length Bid was seen in both the cytoplasmic and the nuclear fractions of controls, but not after H. pylori exposure. Active AIF staining was markedly increased in gastric mucosa from infected persons, compared to uninfected controls. CONCLUSION: H. pylori might trigger apoptosis in AGS cells via interaction with death receptors in the plasma membrane, leading to the cleavage of procaspase-8, release of cytochrome c and AIF from mitochondria, and activation of subsequent downstream apoptotic events, as reported previously for chlorophyllin. This is consistent with AIF activation that was found in the gastric mucosa of humans infected with H. pylori. Hence, the balance between apoptosis and proliferation in these cells may be altered in response to injury caused by H. pylori infection, leading to an increased risk of cancer.