Loss of adenomatous polyposis coli gene function disrupts thymic development

Abstract

Loss of the adenomatous polyposis coli (APC) protein is a common initiating event in colon cancer. Here we show that thymocyte-specific loss of APC deregulated β-catenin signaling and suppressed Notch-dependent transcription. These events promoted the proliferation of cells of the double-negative 3 and 4 stages and reduced rearrangements between the variable, diversity and joining regions of the gene encoding T cell receptor (TCR) β, encouraging developmental progression of aberrant thymocytes lacking pre-TCR and αβ TCR. Simultaneously, the loss of APC prolonged the mitotic metaphase-to-anaphase checkpoint and impaired chromosome segregation, blocking development beyond the double-negative 4 stage. The result was extensive thymic atrophy and increased frequencies of thymocytes with chromosomal abnormalities. Thus, loss of APC in immature thymocytes has consequences distinct from those of deregulation of β-catenin signaling and is essential for T cell differentiation.Adenomatous polyposis coli (APC) is a tumor suppressor whose loss is intimately linked with colon cancer. APC is an essential component of the Wnt signaling pathway and is required for the formation of a cytoplasmic complex containing β-catenin, the kinase GSK-3β and axin. In this complex, β-catenin is phosphorylated by GSK-3β and is 'tagged' for degradation 1 . When Wnt signaling is activated by the binding of Wnt soluble proteins to frizzled receptors, this complex is disrupted and nonphosphorylated β-catenin is stabilized. The non-phospholylated β-catenin binds to the Tcf-Lef family of transcription factors and activates Wnt-dependent gene transcription by providing a transcription activation domain to the complex 1 .Correspondence should be addressed to F.G. (fgounari@tufts-nemc.org) or K.K. (khashayarsha_khazaie@dfci.harvard.edu). COMPETING INTERESTS STATEMENTThe authors declare that they have no competing financial interests.Supplementary information is available on the Nature Immunology website. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptMost human colorectal tumors contain mutations in APC, although in rare instances those with an intact APC contain activating mutations of the gene encoding β-catenin that alter the functionally important phosphorylation sites [2][3][4] . The APC mutations result in truncated proteins that lack all axin-binding motifs and a variable number of the 20-amino acid repeats that are associated with down-regulation of intracellular β-catenin [5][6][7] . Those findings led to the idea that the main tumor-suppressing function of APC resides in its capacity to properly regulate intracellular β-catenin 2,3,8 . However, APC encodes a multifunctional protein that participates in several cellular processes, including cell adhesion and migration, signal transduction, microtubule assembly and chromosome segregation. In dividing cells, APC is localized at the kinetochore and interacts with the microtubule end-binding protein EB1 as well as the cell cycle checkpoint proteins...

Dual roles for adenomatous polyposis coli in regulating retinoic acid biosynthesis and Wnt during ocular development

“…For example, recent studies using mice show that loss of Apc impairs T cell differentiation during thymus development. These defects were not fully recapitulated by introduction of stabilized ␤-catenin (35). In addition, Dang et al (36) demonstrated that APC and cdx2 regulate Kruppel-like factor 4, which suppresses proliferation in a ␤-cateninindependent manner.…”

Tumor progression in Apc1638N mice with Exo1 and Fen1 deficiencies

“…This reduction in immunity is substantiated by the existence of documented immune phenotypes in mouse models with mutations in either Apc or Exo1. Apc 1638N mice undergo lymphocyte depletion (Coletta et al, 2004;Gounari et al, 2005), and have defects in cellular immunity. Bardwell et al (2004) have demonstrated that Exo1/dex six mice have deficiency in somatic hypermutation and class switching in B lymphocytes.…”

Sonic hedgehog negatively regulates pre-TCR–induced differentiation by a Gli2-dependent mechanism

“…During fetal thymocyte development, TCR␤ expression is not necessary for transition from DN3 to DN4 and the majority of the DN4 population do not express icTCR␤ until E17.5. 27 We therefore measured TCR␤ gene rearrangement using a Q-PCR assay, 28 using 5Ј primers to V␤8.2 and V␤5.1 and a 3Ј primer to J␤2.7 ( Figure 2C). We did not detect a statistically significant reduction in either V␤8.2 to J␤2.7 or V␤5.1 to J␤2.7 rearrangement in the Gli2 Ϫ/Ϫ DN cells, relative to WT, suggesting that the reduction in icTCR␤ staining in the DN4 population was most likely the consequence of delayed progression of thymocyte development.…”

“…28 Cell sorting DN1-4 populations were sorted, using anti-CD25 FITC , -CD4/8 PE , and -CD44 Cychrome . Staining with anti-CD4 PE and -CD8 Cychrome allowed sorting of DP and SPs, on MoFlo (Cytomation, Fort Collins, CO).…”