RESUMO
Wnt signalling, which is transduced through beta-catenin/TCF4, maintains the undifferentiated state of intestinal crypt progenitor cells. Mutational activation of the pathway initiates the adenomacarcinoma sequence. Whereas all other differentiated epithelial cells migrate from the crypt onto the villus, Paneth cells home towards the source of Wnt signals--that is, the crypt bottom. Here, we show that expression of a Paneth gene programme is critically dependent on TCF4 in embryonic intestine. Moreover, conditional deletion of the Wnt receptor Frizzled-5 abrogates expression of these genes in Paneth cells in the adult intestine. Conversely, adenomas in Apc-mutant mice and colorectal cancers in humans inappropriately express these Paneth-cell genes. These observations imply that Wnt signals in the crypt can separately drive a stem-cell/progenitor gene programme and a Paneth-cell maturation programme. In intestinal cancer, both gene programmes are activated simultaneously.
Assuntos
Peptídeos e Proteínas de Sinalização Intercelular/fisiologia , Intestino Delgado/citologia , Celulas de Paneth/fisiologia , Transdução de Sinais/fisiologia , Animais , Cromatina/imunologia , Regulação da Expressão Gênica/fisiologia , Humanos , Imuno-Histoquímica , Hibridização In Situ , Peptídeos e Proteínas de Sinalização Intercelular/genética , Intestino Delgado/embriologia , Intestino Delgado/ultraestrutura , Camundongos , Camundongos Knockout , Análise de Sequência com Séries de Oligonucleotídeos/métodos , Celulas de Paneth/citologia , Celulas de Paneth/ultraestrutura , Proteínas WntRESUMO
Truncated Notch receptors have transforming activity in vitro and in vivo. However, the role of wild-type Notch signaling in neoplastic transformation remains unclear. Ras signaling is deregulated in a large fraction of human malignancies and is a major target for the development of novel cancer treatments. We show that oncogenic Ras activates Notch signaling and that wild-type Notch-1 is necessary to maintain the neoplastic phenotype in Ras-transformed human cells in vitro and in vivo. Oncogenic Ras increases levels and activity of the intracellular form of wild-type Notch-1, and upregulates Notch ligand Delta-1 and also presenilin-1, a protein involved in Notch processing, through a p38-mediated pathway. These observations place Notch signaling among key downstream effectors of oncogenic Ras and suggest that it might be a novel therapeutic target.
Assuntos
Transformação Celular Neoplásica/genética , Proteínas de Membrana/metabolismo , Receptores de Superfície Celular , Transdução de Sinais/genética , Fatores de Transcrição , Proteínas ras/metabolismo , Animais , Neoplasias da Mama/genética , Neoplasias da Mama/metabolismo , Células Cultivadas , Regulação para Baixo , Feminino , Regulação Neoplásica da Expressão Gênica/genética , Humanos , Peptídeos e Proteínas de Sinalização Intracelular , Proteínas de Membrana/genética , Camundongos , Camundongos SCID , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Fenótipo , Presenilina-1 , Receptor Notch1 , Regulação para Cima , Neoplasias do Colo do Útero/genética , Neoplasias do Colo do Útero/metabolismo , Proteínas Quinases p38 Ativadas por Mitógeno , Proteínas ras/genéticaRESUMO
Most sporadic colorectal cancers are initiated by activating Wnt pathway mutations, characterized by the stabilization of beta-catenin and constitutive transcription by the beta-catenin/T cell factor-4 (Tcf-4) complex. EphB guidance receptors are Tcf4 target genes that control intestinal epithelial architecture through repulsive interactions with Ephrin-B ligands. Here we show that, although Wnt signalling remains constitutively active, most human colorectal cancers lose expression of EphB at the adenoma-carcinoma transition. Loss of EphB expression strongly correlates with degree of malignancy. Furthermore, reduction of EphB activity accelerates tumorigenesis in the colon and rectum of Apc(Min/+) mice, and results in the formation of aggressive adenocarcinomas. Our data demonstrate that loss of EphB expression represents a critical step in colorectal cancer progression.
Assuntos
Neoplasias Colorretais/metabolismo , Neoplasias Colorretais/patologia , Receptores da Família Eph/metabolismo , Adenoma/metabolismo , Adenoma/patologia , Animais , Linhagem Celular Tumoral , Progressão da Doença , Regulação para Baixo , Regulação Neoplásica da Expressão Gênica , Genes APC , Genes Dominantes/genética , Humanos , Peptídeos e Proteínas de Sinalização Intercelular/metabolismo , Camundongos , Camundongos Transgênicos , Mutação/genética , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Receptores da Família Eph/deficiência , Receptores da Família Eph/genética , Transdução de Sinais , Proteínas WntRESUMO
The genes encoding tyrosine kinase receptors EphB2 and EphB3 are beta-catenin and Tcf4 target genes in colorectal cancer (CRC) and in normal intestinal cells. In the intestinal epithelium, EphB signaling controls the positioning of cell types along the crypt-villus axis. In CRC, EphB activity suppresses tumor progression beyond the earliest stages. Here we show that EphB receptors compartmentalize the expansion of CRC cells through a mechanism dependent on E-cadherin-mediated adhesion. We demonstrate that EphB-mediated compartmentalization restricts the spreading of EphB-expressing tumor cells into ephrin-B1-positive territories in vitro and in vivo. Our results indicate that CRC cells must silence EphB expression to avoid repulsive interactions imposed by normal ephrin-B1-expressing intestinal cells at the onset of tumorigenesis.
Assuntos
Neoplasias Colorretais/metabolismo , Neoplasias Colorretais/prevenção & controle , Efrina-B1/metabolismo , Regulação Neoplásica da Expressão Gênica , Adenoma/metabolismo , Adenoma/patologia , Adenoma/prevenção & controle , Animais , Linhagem Celular Tumoral , Neoplasias Colorretais/patologia , Progressão da Doença , Efrina-B1/antagonistas & inibidores , Efrina-B1/genética , Feminino , Genes APC/fisiologia , Humanos , Mucosa Intestinal/metabolismo , Mucosa Intestinal/patologia , Neoplasias Intestinais/metabolismo , Neoplasias Intestinais/patologia , Neoplasias Intestinais/prevenção & controle , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , RNA Mensageiro/antagonistas & inibidores , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , Receptores da Família Eph/antagonistas & inibidores , Receptores da Família Eph/genética , Receptores da Família Eph/metabolismo , Transdução de Sinais , Frações Subcelulares , Fatores de Transcrição TCF/metabolismo , Proteína 2 Semelhante ao Fator 7 de Transcrição , beta Catenina/metabolismoRESUMO
Little is known about the signaling mechanisms that determine the highly regular patterning of the intestinal epithelium into crypts and villi. With the use of mouse models, we show that bone morphogenetic protein (BMP)-4 expression occurs exclusively in the intravillus mesenchyme. Villus epithelial cells respond to the BMP signal. Inhibition of BMP signaling by transgenic expression of noggin results in the formation of numerous ectopic crypt units perpendicular to the crypt-villus axis. These changes phenocopy the intestinal histopathology of patients with the cancer predisposition syndrome juvenile polyposis (JP), including the frequent occurrence of intraepithelial neoplasia. Many JP cases are known to harbor mutations in BMP pathway genes. These data indicate that intestinal BMP signaling represses de novo crypt formation and polyp growth.