Wnt-β-catenin-T Cell Factor signaling is causally linked to c-myc dependent tumorigenesis in mouse and human colon epithelial cells. of thymocytes and PTC-209 intestinal epithelial cells is usually a direct consequence of the gene expression elicited by β-catenin expression in each tissue. We find that whereas intestinal cells induce genes that promote proliferation thymocytes induce expression of genes associated with OIS growth arrest and p53-dependent apoptosis. We correlate gene expression pattern with the role β-catenin plays in the development of each tissue and suggest that susceptibility of transformation by β-catenin is usually intimately related to its function during development. We propose that when oncogenes are used as signaling molecules safety nets in the form of OIS growth arrest and apoptosis are in place to prevent accidental transformation. (Min) mouse model. Min mice bear a heterozygous germ line mutation at codon 850 of the gene and consequently over-express endogenous β-catenin in all tissues25-27. Min mice develop adenomatous polyps28 and Fig. 1a). By contrast Min mice have small dramatically hypocellular thymuses (Fig. 1b c). We found that relative abundance of β-catenin protein levels was increased in Min thymocytes and gut compared to control (Fig. 1d). However the relative abundance of β-catenin protein levels was much higher in the gut compared to thymocytes from both control and Min mice (Fig. 1d). Accordingly we found that expression levels of Wnt target genes in the control gut were approximately two-fold higher than in the thymus (Fig. 1e). We also found that both Min thymocytes and Min gut polyps showed increased expression of target genes such as and (Fig. 1e) compared to control thymocytes and gut. These data demonstrate increased β-catenin dependent signaling in Min thymocytes but a failure to develop thymic lymphoma. Min mice are known to undergo loss of the wild-type allele in intestinal epithelium29. Therefore we assayed for the status of the alleles in Min thymocytes and found that in the Min thymocytes one allele was wild type and one allele was mutant (Fig. 1f). To determine if the lack of thymic lymphoma correlated with changes in cell death or proliferative status we stained ex-vivo thymocytes with AnnexinV and studied BrdU uptake in-vivo. We found that Min PTC-209 thymocytes had PTC-209 increased apoptosis (Fig. 1g) and reduced proliferation (Fig. 1h). Thus increased expression of β-catenin induces apoptosis and growth arrest in developing thymocytes which results in small hypocellular thymuses in Min mice. Figure 1 Min thymuses are hypocellular with enhanced apoptosis and impaired proliferation Thymocyte development is stalled in Min mice Thymocyte development is defined based on the expression of cell surface markers CD4 and CD8 with the most immature thymocytes lacking these markers. The immature CD4- and CD8-double negative (DN) thymocyte population can be further dissected into developing subsets using cell surface expression of c-kit and CD25 (ETP:c-kit+CD25?; DN2:c-kit+CD25+; DN3:c-kit-CD25+; DN4/pre-DP: c-kit-CD25?)30. We found that Min thymocytes were blocked at the DN4/pre-DP stage of development (Fig 2a-c). DN4/pre-DP Min thymocytes expressed intracellular T cell receptor β chain (TCRβIC) which identifies developmentally competent PTC-209 DN4 thymocytes (Fig. 2d). TCRα chain is expressed in DP thymocytes following TCRβ chain expression. We found that Min-pre-DP thymocytes did not express cell-surface TCRα (Fig. 2e). The lack of TCRα chain expression confirmed that these stalled thymocytes were attenuated in development at the pre-DP stage. Molecular features of developmentally stalled Min pre-DP Rabbit polyclonal to ATF1.ATF-1 a transcription factor that is a member of the leucine zipper family.Forms a homodimer or heterodimer with c-Jun and stimulates CRE-dependent transcription.. thymocytes showed a higher abundance of compared with control DN4 cells (Fig. 2f). These data demonstrate that stalled thymocytes had failed to extinguish pre-TCR signals (represented by higher expression of Egr proteins) and to induce transcription factor (Supplementary Fig. 2). These data shows that Min thymocytes share several features with CAT-Tg thymocytes and thereby demonstrate that thymic hypocellularity in Min mice was not a result of the intestinal tumors as intestinal cells do not over-express β-catenin in CAT-Tg mice and the intestine is healthy. Finally we note that even in Min mice adenoma count was comparable in mice with normal or low thymocyte count (60 ±3 and 68 ±4.