Simone Spaderna

Invasion and Metastasis in Colorectal Cancer: Epithelial-Mesenchymal Transition, Mesenchymal-Epithelial Transition, Stem Cells and β-Catenin

Invasion by colorectal carcinomas is characterized by an epithelial-mesenchymal transition (EMT)-like dedifferentiation of the tumor cells. However, a redifferentiation towards an epithelial phenotype, resembling a mesenchymal-epithelial transition, is detectable in metastases. This indicates that malignant progression is based on dynamic processes, which cannot be explained solely by irreversible genetic alterations, but must be additionally regulated by the tumor environment. The main oncoprotein in colorectal cancer is the Wnt pathway effector β-catenin, which is overexpressed due to mutations in the APC tumor suppressor in most cases. EMT of the tumor cells is associated with a nuclear accumulation of the transcriptional activator β-catenin, which is reversed in metastases. Nuclear β-catenin is involved in two fundamental processes in embryonic development: EMT and stem cell formation. Accumulating data demonstrate that aberrant nuclear expression of β-catenin can also confer these two abilities to tumor cells, thereby driving malignant tumor progression.

Expression of L1-CAM and ADAM10 in human colon cancer cells induces metastasis.

L1-CAM, a neuronal cell adhesion receptor, is also expressed in a variety of cancer cells. Recent studies identified L1-CAM as a target gene of beta-catenin-T-cell factor (TCF) signaling expressed at the invasive front of human colon cancer tissue. We found that L1-CAM expression in colon cancer cells lacking L1-CAM confers metastatic capacity, and mice injected in their spleen with such cells form liver metastases. We identified ADAM10, a metalloproteinase that cleaves the L1-CAM extracellular domain, as a novel target gene of beta-catenin-TCF signaling. ADAM10 overexpression in colon cancer cells displaying endogenous L1-CAM enhanced L1-CAM cleavage and induced liver metastasis, and ADAM10 also enhanced metastasis in colon cancer cells stably transfected with L1-CAM. DNA microarray analysis of genes induced by L1-CAM in colon cancer cells identified a cluster of genes also elevated in a large set of human colon carcinoma tissue samples. Expression of these genes in normal colon epithelium was low. These results indicate that there is a gene program induced by L1-CAM in colon cancer cells that is also present in colorectal cancer tissue and suggest that L1-CAM can serve as target for colon cancer therapy.

β-Catenin activates a coordinated expression of the proinvasive factors laminin-5 γ2 chain and MT1-MMP in colorectal carcinomas

In colorectal carcinomas, loss‐of‐function mutations of the adenomatous polyposis coli (APC) tumor suppressor gene lead to a nuclear accumulation of the oncogenic transcriptional activator β‐catenin, predominantly at the invasive front within the tumor host interface. Various identified genes activated by β‐catenin are associated with tumor invasion. One prerequisite for malignant tumor invasion is the ability of tumor cells to migrate. We recently described the γ2 chain of laminin as another β‐catenin target gene. Fragments of the laminin γ2 chain, resulting from cleavage by the membrane type 1 matrix metalloproteinase (MT1‐MMP), are strong inducers of epithelial cell migration. We here show a coordinated expression of nuclear β‐catenin, its target gene and MT1‐MMP substrate laminin γ2 chain, as well as MT1‐MMP in tumor cells at invasive regions of colorectal carcinomas. We further demonstrate that MT1‐MMP expression is regulated by β‐catenin/TCF through a TCF binding site in its promoter. These results suggest that nuclear β‐catenin activates the coordinated expression of the interacting proinvasive proteins laminin γ2 chain and MT1‐MMP, thereby leading to a promigratory activity at the invasive front of colorectal cancers. This further supports an important role of β‐catenin for invasion and metastasis of colorectal carcinomas.

Down-Regulation of the Homeodomain Factor Cdx2 in Colorectal Cancer by Collagen Type I: An Active Role for the Tumor Environment in Malignant Tumor Progression

The homeobox transcription factor Cdx2 specifies intestinal development and homeostasis and is considered a tumor suppressor in colorectal carcinogenesis. However, Cdx2 mutations are rarely found. Invasion of colorectal cancer is characterized by a transient loss of differentiation and nuclear accumulation of the oncoprotein β-catenin in budding tumor cells. Strikingly, this is reversed in growing metastases, indicating that tumor progression is a dynamic process that is not only driven by genetic alterations but also regulated by the tumor environment. Here we describe a transient loss of Cdx2 in budding tumor cells at the tumor host interface, and reexpression of Cdx2 in metastases. Cell culture experiments show that collagen type I, through β1 integrin signaling, triggers a transient transcriptional down-regulation of Cdx2 and its intestine-specific target gene sucrase isomaltase, associated with a loss of differentiation. These data indicate an active role for the tumor environment in malignant tumor progression.

Evidence for acid-induced loss of Cdx2 expression in duodenal gastric metaplasia

Gastric metaplasia in the duodenum (GMD) is characterized by transdifferentiation of intestinal epithelial cells into gastric foveolar cells within the duodenal mucosa. GMD is often associated with duodenal ulceration. Higher duodenal acidity due to increased gastric acid output into the duodenum has been implicated in the development of GMD. Intestinal development and homeostasis are controlled by the homeobox transcription factor Cdx2, which is considered to be the master regulator of intestinal differentiation. Using immunohistochemistry, the present study shows that GMD is associated with loss of expression of Cdx2 and its target gene product sucrase‐isomaltase. Quantitative RT‐PCR experiments using the intestinal cell line Caco2 revealed that Cdx2 and sucrase‐isomaltase were down‐regulated and gastric mucins MUC5AC and MUC6 were up‐regulated under acidic culture conditions. Thus, it is suggested that increased acid exposure leads to GMD by impairing the transcription of Cdx2 and subsequently that of its intestine‐specific target genes. Copyright

List of Speakers and Titles

Session 2: EMT in Development Chair Donald F. Newgreen (Melbourne) Regulation of Epithelial-Mesenchymal Cell Transformation in the Embryonic Chick Heart Runyan RB, Shoemaker S, Person A, Berkompas J, Scholz M, Mercado-Pimental M, Doyle SE, Stanislaw S (Tucson, Ariz.) Neural Epithelial-Mesenchymal Transitions: Many Ways to the Same End Newgreen D, Lewis S, Minichiello J, Farlie P (Melbourne) Intravital Imaging of Neural Crest Cells Kulesa PM (Kansas City, Mo.) Regulation of Neural Crest Formation by Sox2, Slug and BMP4 Wakamatsu Y, Endo Y, Sakai D, Osumi N (Sendai) Transforming Growth Factor3 (TGF 3) Upregulates Lymphoid Enhancing Factor-1 (LEF-1) Gene to Induce Epithelial-Mesenchymal Transformation (EMT) during Mouse Palate Development Nawshad A, Hay ED (Boston, Mass.)