Epithelial Smad4 Deletion Up-Regulates Inflammation and Promotes Inflammation-Associated Cancer.

Background & Aims: Chronic inflammation is a predisposing condition for colorectal cancer. Many studies to date have focused on proinflammatory signaling pathways in the colon. Understanding the mechanisms that suppress inflammation, particularly in epithelial cells, is critical for developing therapeutic interventions. Here, we explored the roles of transforming growth factor ß (TGFß) family signaling through SMAD4 in colonic epithelial cells. Methods: The Smad4 gene was deleted specifically in adult murine intestinal epithelium. Colitis was induced by 3 rounds of dextran sodium sulfate in drinking water, after which mice were observed for up to 3 months. Nontransformed mouse colonocyte cell lines and colonoid cultures and human colorectal cancer cell lines were analyzed for responses to TGFß1 and bone morphogenetic protein 2. Results: Dextran sodium sulfate treatment was sufficient to drive carcinogenesis in mice lacking colonic Smad4 expression, with resulting tumors bearing striking resemblance to human colitis-associated carcinoma. Loss of SMAD4 protein was observed in 48% of human colitis-associated carcinoma samples as compared with 19% of sporadic colorectal carcinomas. Loss of Smad4 increased the expression of inflammatory mediators within nontransformed mouse colon epithelial cells in vivo. In vitro analysis of mouse and human colonic epithelial cell lines and organoids indicated that much of this regulation was cell autonomous. Furthermore, TGFß signaling inhibited the epithelial inflammatory response to proinflammatory cytokines. Conclusions: TGFß suppresses the expression of proinflammatory genes in the colon epithelium, and loss of its downstream mediator, SMAD4, is sufficient to initiate inflammation-driven colon cancer. Transcript profiling: GSE100082.

Evaluation of frozen tissue-derived prognostic gene expression signatures in FFPE colorectal cancer samples.

Defining molecular features that can predict the recurrence of colorectal cancer (CRC) for stage II-III patients remains challenging in cancer research. Most available clinical samples are Formalin-Fixed, Paraffin-Embedded (FFPE). NanoString nCounter® and Affymetrix GeneChip® Human Transcriptome Array 2.0 (HTA) are the two platforms marketed for high-throughput gene expression profiling for FFPE samples. In this study, to evaluate the gene expression of frozen tissue-derived prognostic signatures in FFPE CRC samples, we evaluated the expression of 516 genes from published frozen tissue-derived prognostic signatures in 42 FFPE CRC samples measured by both platforms. Based on HTA platform-derived data, we identified both gene (99 individual genes, FDR < 0.05) and gene set (four of the six reported multi-gene signatures with sufficient information for evaluation, P < 0.05) expression differences associated with survival outcomes. Using nCounter platform-derived data, one of the six multi-gene signatures (P < 0.05) but no individual gene was associated with survival outcomes. Our study indicated that sufficiently high quality RNA could be obtained from FFPE tumor tissues to detect frozen tissue-derived prognostic gene expression signatures for CRC patients.

Comparison of Nanostring nCounter® Data on FFPE Colon Cancer Samples and Affymetrix Microarray Data on Matched Frozen Tissues.

The prognosis of colorectal cancer (CRC) stage II and III patients remains a challenge due to the difficulties of finding robust biomarkers suitable for testing clinical samples. The majority of published gene signatures of CRC have been generated on fresh frozen colorectal tissues. Because collection of frozen tissue is not practical for routine surgical pathology practice, a clinical test that improves prognostic capabilities beyond standard pathological staging of colon cancer will need to be designed for formalin-fixed paraffin-embedded (FFPE) tissues. The NanoString nCounter® platform is a gene expression analysis tool developed for use with FFPE-derived samples. We designed a custom nCounter® codeset based on elements from multiple published fresh frozen tissue microarray-based prognostic gene signatures for colon cancer, and we used this platform to systematically compare gene expression data from FFPE with matched microarray array data from frozen tissues. Our results show moderate correlation of gene expression between two platforms and discovery of a small subset of genes as candidate biomarkers for colon cancer prognosis that are detectable and quantifiable in FFPE tissue sections.

The Applicability of a Human Immunohistochemical Panel to Mouse Models of Hepatocellular Neoplasia.

Various immunohistochemical panels are used as aids to distinguish between primary hepatocellular malignancies and metastatic tumors and between benign lesions and carcinomas. We compared the immunohistochemical spectrum of hepatocellular lesions in mice with that of human hepatocellular carcinoma (HCC). Specifically, we compared the staining parameters of 128 murine foci of cellular alteration (FCA) and tumors (adenoma and HCC) from archival tissue blocks of 3 transgenic mouse models (LFABP-cyclin D1, Alb1-TGFß1, and LFABP-cyclin D1 × Alb1-TGFß1) with those of archival human HCC (n = 5). Antibodies were chosen according to their published performance and characterization in human hepatocellular tumor diagnosis and included: arginase 1 (Arg1), ß-catenin, glutamine synthetase (GS), glypican 3, hepatocyte paraffin 1 (HepPar1), and cytokeratin 19 (CK19). GS was the single best immunostain for identifying hepatocellular tumors in mice, with 100% positive staining. Data showed a trend toward loss of normal function (staining) with Arg1, with a higher percentage of positive staining in FCA than in adenomas and HCC. All FCA lacked murine ß-catenin nuclear translocation, which was present in 2 of the 7 adenomas and 22 of the 96 HCC tested. HepPar1 staining was lower than anticipated, except in trabecular HCC (16 of 22 samples were positive). Glyp3 stained very lightly, and only scattered CK19-positive cells were noted (4 of 44 cases of mouse trabecular HCC). Thus, GS appears to be the most useful marker for identifying neoplasia in the transgenic mouse models we tested and should be included in immunohistochemistry assessing hepatocellular neoplasia development.

Small molecule/ML327 mediated transcriptional de-repression of E-cadherin and inhibition of epithelial-to-mesenchymal transition.

Transcriptional repression of E-cadherin is a hallmark of Epithelial-to-Mesenchymal Transition (EMT) and is associated with cancer cell invasion and metastasis. Understanding the mechanisms underlying E-cadherin repression during EMT may provide insights into the development of novel targeted therapeutics for cancer. Here, we report on the chemical probe, ML327, which de-represses E-cadherin transcription, partially reverses EMT, and inhibits cancer cell invasiveness and tumor cell migration in vitro and in vivo. Induction of E-cadherin mRNA expression by ML327 treatment does not require de novo protein synthesis. RNA sequencing analysis revealed that ML327 treatment significantly alters expression of over 2,500 genes within three hours in the presence of the translational inhibitor, cycloheximide. Network analysis reveals Hepatocyte Nuclear Factor 4-alpha (HNF4α) as the most significant upstream transcriptional regulator of multiple genes whose expressions were altered by ML327 treatment. Further, small interfering RNA-mediated depletion of HNF4α markedly attenuates the E-cadherin expression response to ML327. In summary, ML327 represents a valuable tool to understand mechanisms of EMT and may provide the basis for a novel targeted therapeutic strategy for carcinomas.

Linking patient outcome to high throughput protein expression data identifies novel regulators of colorectal adenocarcinoma aggressiveness.

A key question in cancer systems biology is how to use molecular data to predict the biological behavior of tumors from individual patients. While genomics data have been heavily used, protein signaling data are more directly connected to biological phenotype and might predict cancer phenotypes such as invasion, metastasis, and patient survival. In this study, we mined publicly available data for colorectal adenocarcinoma from the Cancer Genome Atlas and identified protein expression and signaling changes that are statistically associated with patient outcome. Our analysis identified a number of known and potentially new regulators of colorectal cancer. High levels of insulin growth factor binding protein 2 (IGFBP2) were associated with both recurrence and death, and this was validated by immunohistochemical staining of a tissue microarray for a secondary patient dataset. Interestingly, GATA binding protein 3 (GATA3) was the protein most frequently associated with death in our analysis, and GATA3 expression was significantly decreased in tumor samples from stage I-II deceased patients. Experimental studies using engineered colon cancer cell lines show that exogenous expression of GATA3 decreases three-dimensional colony growth and invasiveness of colon cancer cells but does not affect two-dimensional proliferation. These findings suggest that protein data are useful for biomarker discovery and identify GATA3 as a regulator of colorectal cancer  aggressiveness.

Nuclear factor of activated T-cell activity is associated with metastatic capacity in colon cancer.

Metastatic recurrence is the leading cause of cancer-related deaths in patients with colorectal carcinoma. To capture the molecular underpinnings for metastasis and tumor progression, we performed integrative network analysis on 11 independent human colorectal cancer gene expression datasets and applied expression data from an immunocompetent mouse model of metastasis as an additional filter for this biologic process. In silico analysis of one metastasis-related coexpression module predicted nuclear factor of activated T-cell (NFAT) transcription factors as potential regulators for the module. Cells selected for invasiveness and metastatic capability expressed higher levels of NFATc1 as compared with poorly metastatic and less invasive parental cells. We found that inhibition of NFATc1 in human and mouse colon cancer cells resulted in decreased invasiveness in culture and downregulation of metastasis-related network genes. Overexpression of NFATc1 significantly increased the metastatic potential of colon cancer cells, whereas inhibition of NFATc1 reduced metastasis growth in an immunocompetent mouse model. Finally, we found that an 8-gene signature comprising genes upregulated by NFATc1 significantly correlated with worse clinical outcomes in stage II and III colorectal cancer patients. Thus, NFATc1 regulates colon cancer cell behavior and its transcriptional targets constitute a novel, biologically anchored gene expression signature for the identification of colon cancers with high risk of metastatic recurrence.

Transforming growth factor ß regulates P-body formation through induction of the mRNA decay factor tristetraprolin.

Transforming growth factor ß (TGF-ß) is a potent growth regulator and tumor suppressor in normal intestinal epithelium. Likewise, epithelial cell growth is controlled by rapid decay of growth-related mRNAs mediated through 3' untranslated region (UTR) AU-rich element (ARE) motifs. We demonstrate that treatment of nontransformed intestinal epithelial cells with TGF-ß inhibited ARE-mRNA expression. This effect of TGF-ß was promoted through increased assembly of cytoplasmic RNA processing (P) bodies where ARE-mRNA localization was observed. P-body formation was dependent on TGF-ß/Smad signaling, as Smad3 deletion abrogated P-body formation. In concert with increased P-body formation, TGF-ß induced expression of the ARE-binding protein tristetraprolin (TTP), which colocalized to P bodies. TTP expression was necessary for TGF-ß-dependent P-body formation and promoted growth inhibition by TGF-ß. The significance of this was observed in vivo, where colonic epithelium deficient in TGF-ß/Smad signaling or TTP expression showed attenuated P-body levels. These results provide new insight into TGF-ß's antiproliferative properties and identify TGF-ß as a novel mRNA stability regulator in intestinal epithelium through its ability to promote TTP expression and subsequent P-body formation.

Deciphering genomic alterations in colorectal cancer through transcriptional subtype-based network analysis.

Both transcriptional subtype and signaling network analyses have proved useful in cancer genomics research. However, these two approaches are usually applied in isolation in existing studies. We reason that deciphering genomic alterations based on cancer transcriptional subtypes may help reveal subtype-specific driver networks and provide insights for the development of personalized therapeutic strategies. In this study, we defined transcriptional subtypes for colorectal cancer (CRC) and identified driver networks/pathways for each subtype. Applying consensus clustering to a patient cohort with 1173 samples identified three transcriptional subtypes, which were validated in an independent cohort with 485 samples. The three subtypes were characterized by different transcriptional programs related to normal adult colon, early colon embryonic development, and epithelial mesenchymal transition, respectively. They also showed statistically different clinical outcomes. For each subtype, we mapped somatic mutation and copy number variation data onto an integrated signaling network and identified subtype-specific driver networks using a random walk-based strategy. We found that genomic alterations in the Wnt signaling pathway were common among all three subtypes; however, unique combinations of pathway alterations including Wnt, VEGF and Notch drove distinct molecular and clinical phenotypes in different CRC subtypes. Our results provide a coherent and integrated picture of human CRC that links genomic alterations to molecular and clinical consequences, and which provides insights for the development of personalized therapeutic strategies for different CRC subtypes.

Four jointed box 1 promotes angiogenesis and is associated with poor patient survival in colorectal carcinoma.

Angiogenesis, the recruitment and re-configuration of pre-existing vasculature, is essential for tumor growth and metastasis. Increased tumor vascularization often correlates with poor patient outcomes in a broad spectrum of carcinomas. We identified four jointed box 1 (FJX1) as a candidate regulator of tumor angiogenesis in colorectal cancer. FJX1 mRNA and protein are upregulated in human colorectal tumor epithelium as compared with normal epithelium and colorectal adenomas, and high expression of FJX1 is associated with poor patient prognosis. FJX1 mRNA expression in colorectal cancer tissues is significantly correlated with changes in known angiogenesis genes. Augmented expression of FJX1 in colon cancer cells promotes growth of xenografts in athymic mice and is associated with increased tumor cell proliferation and vascularization. Furthermore, FJX1 null mice develop significantly fewer colonic polyps than wild-type littermates after combined dextran sodium sulfate (DSS) and azoxymethane (AOM) treatment. In vitro, conditioned media from FJX1 expressing cells promoted endothelial cell capillary tube formation in a HIF1-α dependent manner. Taken together our results support the conclusion that FJX1 is a novel regulator of tumor progression, due in part, to its effect on tumor vascularization.

Smad4-mediated signaling inhibits intestinal neoplasia by inhibiting expression of ß-catenin.

BACKGROUND & AIMS: Mutational inactivation of adenomatous polyposis coli (APC) is an early event in colorectal cancer (CRC) progression that affects the stability and increases the activity of ß-catenin, a mediator of Wnt signaling. Progression of CRC also involves inactivation of signaling via transforming growth factor ß and bone morphogenetic protein (BMP), which are tumor suppressors. However, the interactions between these pathways are not clear. We investigated the effects of loss of the transcription factor Smad4 on levels of ß-catenin messenger RNA (mRNA) and Wnt signaling. METHODS: We used microarray analysis to associate levels of Smad4 and ß-catenin mRNA in colorectal tumor samples from 250 patients. We performed oligonucleotide-mediated knockdown of Smad4 in human embryonic kidney (HEK293T) and in HCT116 colon cancer cells and transgenically expressed Smad4 in SW480 colon cancer cells. We analyzed adenomas from (APC(Δ1638/+)) and (APC(Δ1638/+)) × (K19Cre(ERT2)Smad4(lox/lox)) mice by using laser capture microdissection. RESULTS: In human CRC samples, reduced levels of Smad4 correlated with increased levels of ß-catenin mRNA. In Smad4-depleted cell lines, levels of ß-catenin mRNA and Wnt signaling increased. Inhibition of BMP or depletion of Smad4 in HEK293T cells increased binding of RNA polymerase II to the ß-catenin gene. Expression of Smad4 in SW480 cells reduced Wnt signaling and levels of ß-catenin mRNA. In mice with heterozygous disruption of Apc(APC(Δ1638/+)), Smad4-deficient intestinal adenomas had increased levels of ß-catenin mRNA and expression of Wnt target genes compared with adenomas from APC(Δ1638/+) mice that expressed Smad4. CONCLUSIONS: Transcription of ß-catenin is inhibited by BMP signaling to Smad4. These findings provide important information about the interaction among transforming growth factor ß, BMP, and Wnt signaling pathways in progression of CRC.

A novel in vitro assay to assess phosphorylation of 3'-[(18)F]fluoro-3'-deoxythymidine.

PURPOSE: 3'-[(18)F]fluoro-3'-deoxythymidine ([(18)F]FLT) is phosphorylated by thymidine kinase 1 (TK-1), a cell cycle regulated enzyme. Appropriate use of [(18)F]FLT tracer requires validation of the TK-1 activity. Here, we report development of a novel phosphoryl-transfer assay to assess phosphorylation of [(18)F]FLT both in tumor cell lysates and tumor cells. PROCEDURES: The intrinsic F-18 radioactivity was used to quantify both substrate and phosphorylated products using a rapid thin layer chromatography method. Phosphorylation kinetics of [(18)F]FLT in SW480 and DiFi tumor cell lysates and cellular uptake were measured. RESULTS: The apparent Michaelis-Menten kinetic parameters for [(18)F]FLT are K(m) = 4.8 ± 0.3 µM and V(max) = 7.4 pmol min(-1) per 1 × 10(6) cells with ~2-fold higher TK-1 activity in DiFi versus SW480 lysates. CONCLUSIONS: The apparent K (m) of [(18)F]FLT was comparable to the value reported with purified recombinant TK-1. The uptake of [(18)F]FLT by SW480 cells is inhibited by nitrobenzylthioinosine or dipyridamole indicating that uptake is mediated predominantly by the equilibrative nucleoside transporters in these tumor cells.

Modeling tumor growth and treatment response based on quantitative imaging data.

We review current approaches to predicting tumor growth and treatment response that combine non-invasive imaging data with mathematical models of cancer progression, and propose some new directions for integrating quantitative imaging measurements with such numerical analyses. Historically, tumor modeling has been described by parameters that are measurable by invasive methods only or in isolated in vitro or ex vivo systems. This limits the practical usefulness of such models because it is not possible to test their predictions experimentally. Recent advances in three-dimensional magnetic resonance imaging, single photon emission computed tomography, and positron emission tomography techniques provide new opportunities to acquire measurements of relevant molecular and cellular features of tumors non-invasively and with high spatial resolution. Such data can be incorporated into mathematical models of tumors. We highlight some recent examples of this approach and identify several simple examples that allow for conventional mathematical models of tumor growth to be recast in terms of parameters that can be measured by imaging, thus raising the possibility of designing and constraining models that can be tested in clinical practice. It is our hope that this Perspective will stimulate further work in this evolving and exciting field.

Experimentally derived metastasis gene expression profile predicts recurrence and death in patients with colon cancer.

BACKGROUND & AIMS: Staging inadequately predicts metastatic risk in patients with colon cancer. We used a gene expression profile derived from invasive, murine colon cancer cells that were highly metastatic in an immunocompetent mouse model to identify patients with colon cancer at risk of recurrence. METHODS: This phase 1, exploratory biomarker study used 55 patients with colorectal cancer from Vanderbilt Medical Center (VMC) as the training dataset and 177 patients from the Moffitt Cancer Center as the independent dataset. The metastasis-associated gene expression profile developed from the mouse model was refined with comparative functional genomics in the VMC gene expression profiles to identify a 34-gene classifier associated with high risk of metastasis and death from colon cancer. A metastasis score derived from the biologically based classifier was tested in the Moffitt dataset. RESULTS: A high score was significantly associated with increased risk of metastasis and death from colon cancer across all pathologic stages and specifically in stage II and stage III patients. The metastasis score was shown to independently predict risk of cancer recurrence and death in univariate and multivariate models. For example, among stage III patients, a high score translated to increased relative risk of cancer recurrence (hazard ratio, 4.7; 95% confidence interval, 1.566-14.05). Furthermore, the metastasis score identified patients with stage III disease whose 5-year recurrence-free survival was >88% and for whom adjuvant chemotherapy did not increase survival time. CONCLUSION: A gene expression profile identified from an experimental model of colon cancer metastasis predicted cancer recurrence and death, independently of conventional measures, in patients with colon cancer.

Oncogenic Ras and transforming growth factor-beta synergistically regulate AU-rich element-containing mRNAs during epithelial to mesenchymal transition.

Colon cancer progression is characterized by activating mutations in Ras and by the emergence of the tumor-promoting effects of transforming growth factor-beta (TGF-beta) signaling. Ras-inducible rat intestinal epithelial cells (RIE:iRas) undergo a well-described epithelial to mesenchymal transition and invasive phenotype in response to H-RasV12 expression and TGF-beta treatment, modeling tumor progression. We characterized global gene expression profiles accompanying Ras-induced and TGF-beta-induced epithelial to mesenchymal transition in RIE:iRas cells by microarray analysis and found that the regulation of gene expression by the combined activation of Ras and TGF-beta signaling was associated with enrichment of a class of mRNAs containing 3' AU-rich element (ARE) motifs known to regulate mRNA stability. Regulation of ARE-containing mRNA transcripts was validated at the mRNA level, including genes important for tumor progression. Ras and TGF-beta synergistically increased the expression and mRNA stability of vascular endothelial growth factor (VEGF), a key regulator of tumor angiogenesis, in both RIE:iRas cells and an independent cell culture model (young adult mouse colonocyte). Expression profiling of human colorectal cancers (CRC) further revealed that many of these genes, including VEGF and PAI-1, were differentially expressed in stage IV human colon adenocarcinomas compared with adenomas. Furthermore, genes differentially expressed in CRC are also significantly enriched with ARE-containing transcripts. These studies show that oncogenic Ras and TGF-beta synergistically regulate genes containing AREs in cultured rodent intestinal epithelial cells and suggest that posttranscriptional regulation of gene expression is an important mechanism involved in cellular transformation and CRC tumor progression.

Variability of in situ proteomic profiling and implications for study design in colorectal tumors.

Knowledge of intrinsic tumor heterogeneity is vital for understanding of tumor progression mechanisms as well as for providing efficient treatments. In situ proteomic profiling of tumors is a powerful technology with potential to enhance our understanding of tumor biology, but sources of variability due to patient and tumor heterogeneity are poorly understood and are the topic of this investigation. Clarification of variability within case and between cases is also important for designing future studies. Direct protein profiling by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a sensitive and powerful technology for obtaining hundreds of protein expression peaks from a thin tissue section. By combining robotic microspotting and laser capture microdissection with MALDI MS, we acquired multiple spectra per case to evaluate inter- and intra-case variability in human colorectal tumor and murine cecal carcinoma. We detected 256 peaks from 164 samples of 111 patients, which consisted of 55 normal colorectal mucosal samples, 24 adenomas, 71 primary carcinomas, and 14 hepatic metastases. In addition, we detected 291 peptide/protein peaks from 34 orthotopically transplanted murine cecal carcinomas and 14 hepatic metastases. In human colorectal samples, we observed that proteomic profiling in adenomas was more homogeneous across patients than in normal mucosa specimens (p=0.0008), but primary carcinoma exhibited greater heterogeneity than normal mucosa and adenomas (both p<0.0001). Murine cecal carcinomas were homogeneous within and between carcinomas, while their hepatic metastases tended toward greater intra-tumor differences (p<0.0001). Inter- and intra-case variability was approximately equal for many protein peaks. Acquiring up to 5 subsamples per case could reduce the total number of cases required, but further reduction from additional subsampling was modest unless intra-case variability comprises a greater proportion of total variation (e.g. >70%). In summary, this study characterizes intra- and inter-case variability of high-throughput protein expression in colorectal tumors, and provides guidance for the sample numbers required for in situ proteomic studies.

Targeted imaging of colonic tumors in smad3-/- mice discriminates cancer and inflammation.

The peripheral benzodiazepine receptor (PBR) is a trans-mitochondrial membrane protein that modulates steroid biosynthesis. Recently, up-regulation and nuclear localization of PBR has been shown to be associated with colon, prostate, and breast cancer. PBR has been targeted by the exogenous synthetic ligand, PK11195, for various purposes including imaging. To capitalize on these observations, we developed a high-throughput, noninvasive, in vivo imaging approach to detect spontaneously arising colonic tumors in mice using a novel PBR-targeted molecular imaging agent (NIR-conPK11195). NIR-conPK11195 localized and was retained in colonic adenomas and carcinomas in Smad3(-/-) mice but not in non-neoplastic hamartomas or chronically inflamed colonic tissue. Using a fluorescence signal-to-noise ratio of > or =4-fold 13 h after injection of the agent, we detected colonic tumors with a sensitivity of 67% and a specificity of 86% in a cohort of 37 Smad3(-/-) mice and control littermates. Furthermore, using oral administration of dextran sulfate to induce colonic inflammation, we showed that the clearance profile of NIR-conPK11195 distinguished transient uptake in inflammatory tissue from longer term retention in tumors. Taken together, these results indicate that NIR-conPK11195 is a promising optical molecular imaging tool to rapidly screen for colonic tumors in mice and to discriminate inflammation from cancer.

Claudin-1 regulates cellular transformation and metastatic behavior in colon cancer.

Disruption of the cell-cell junction with concomitant changes in the expression of junctional proteins is a hallmark of cancer cell invasion and metastasis. The role of adherent junction proteins has been studied extensively in cancer, but the roles of tight junction (TJ) proteins are less well understood. Claudins are recently identified members of the tetraspanin family of proteins, which are integral to the structure and function of TJs. Recent studies show changes in expression/cellular localization of claudins during tumorigenesis; however, a causal relationship between claudin expression/localization and cancer has not been established. Here, we report an increased expression of claudin-1 in human primary colon carcinoma and metastasis and in cell lines derived from primary and metastatic tumors. We also report frequent nuclear localization of claudin-1 in these samples. Genetic manipulations of claudin-1 expression in colon cancer cell lines induced changes in cellular phenotype, with structural and functional changes in markers of epithelial-mesenchymal transition. Furthermore, we demonstrate that changes in claudin-1 expression have significant effects on growth of xenografted tumors and metastasis in athymic mice. We further provide data suggesting that the regulation of E-cadherin expression and beta-catenin/Tcf signaling is a possible mechanism underlying claudin-1-dependent changes.