The role of b-catenin/Tcf-1 signaling in T-cell leukemia/lymphoma

描述(申请人提供)：基因组不稳定是癌症的固有特征，也是肿瘤进展和治疗抵抗的根本原因。然而，导致基因组不稳定的确切分子机制仍不清楚。在这里，我们提供了证据，Tcf-1，Wnt信号通路的T细胞特异性DNA结合蛋白，介导了基因组完整性的维持，并且这一功能被导致染色体不稳定的T细胞淋巴瘤的？-catenin所拮抗，这些T细胞淋巴瘤有反复的致癌易位。在这方面，我的实验室在识别促进基因组不稳定的分子过程方面取得了重大进展。β-连环蛋白和Tcf-1在T细胞发育的多个阶段都有重要作用，我们已经证明，放松对-连环蛋白的调控会导致淋巴瘤。淋巴肿瘤的发生严格依赖于RAG和c-Myc，并且需要TCR信号。淋巴瘤有反复的RAG诱导的TCR？/Myc易位。小鼠模型的这些特性在几个方面与人类白血病有关。在人类T细胞白血病中也发现了相同的易位。在基因组不稳定的T细胞白血病/淋巴瘤中已检测到β-catenin突变和Wnt信号的激活，并且已知通过有条件地切除Pten或表达活性Akt而产生的淋巴瘤具有依赖于-catenin信号的TCR？/Myc易位。我们的初步CHIP-SEQ分析表明，Tcf-1与RAG2重组酶共占据共同的DNA位点。这是一个特别有趣的观察，因为我们还发现DNA修复组件与？-catenin竞争与Tcf-1的结合，这导致RAG诱导的DNA DSB的修复改变。基于这些发现，我们提出了一个模型，通过该模型，解除调控的连环蛋白活性改变了Tcf-1结合位点附近的染色质景观，并改变了修复和重组蛋白的相对局部可获得性。同时，与TCR信号的协同作用增强了持续断裂的选定基因座之间的拓扑接近，从而导致染色体易位。我们的研究旨在阐明与人类疾病相关的癌症模型中致癌易位的控制规则和分子成分。在第一个目的中，我们将检验假设-连环蛋白/Tcf-1以及重组和DNA修复组件参与共同的染色质重塑复合体，该复合体介导了基因组完整性的维持。在第二个目的中，我们将检验这样的假设，即在具有稳定的连环蛋白TCR信号的胸腺细胞中，能够使DNA受损位点的拓扑接近，从而使得经常性的非法重组成为可能。这项拟议的研究将确定导致癌症中非法DNA重组和基因组不稳定的分子机制，这些机制与解除连环蛋白的调控有关。

DESCRIPTION (provided by applicant): Genomic instability is an inherent characteristic of cancer and is the underlying reason for tumor progression as well as resistance to therapy. However, the precise molecular mechanisms causing genomic instability remain unclear. Here we provide evidence that Tcf-1 the T-cell specific DNA binding protein of the Wnt signaling pathway mediates maintenance of genomic integrity and that this function is antagonized by ¿-catenin leading to chromosomally unstable T-cell lymphomas that have recurrent oncogenic translocations. In this regard my lab has made significant progress in identifying molecular processes that promote genomic instability. Both ¿-catenin and Tcf-1 have essential functions at multiple stages of T-cell development and we have shown that deregulation of ¿-catenin causes lymphomas. Lymphomagenesis is strictly RAG and c-Myc- dependent and requires TCR signaling. The lymphomas have recurrent RAG induced TCR¿/Myc translocations. These properties of the mouse model are relevant to human leukemia in several ways. Identical translocations have been seen in human T-cell leukemia. Mutations in ¿-catenin and activation of Wnt signaling have been detected in genomically unstable T-cell leukemia/lymphoma, and it is known that lymphomas generated by conditional ablation of Pten or expression of active Akt have TCR¿/Myc translocations that depend on ¿-catenin signaling. Our preliminary ChIP-seq analyses show that Tcf-1 co- occupies common DNA sites with the RAG2 recombinase. This is a particularly intriguing observation since we also found that DNA repair components compete with ¿-catenin for binding to Tcf-1 and this results in altered repair of RAG induced DNA DSBs. Based on these findings we propose a model by which deregulated ¿- catenin activity changes the chromatin landscape near Tcf-1 binding sites and alters the relative local availabilities of repair and recombination proteins. Simultaneously, synergy with TCR signaling enhances topological proximity of select loci that have sustained breaks, leading to chromosomal translocation. Our studies are designed to elucidate governing rules and molecular components responsible for oncogenic translocations in a cancer model relevant for human disease. In the first aim we will test the hypothesis that ¿-catenin/Tcf-1 and the recombination and DNA repair components participate in common chromatin remodeling complexes that mediate maintenance of genome integrity. In the second aim we will test the hypothesis that in thymocytes with stabilized ¿-catenin TCR signaling enables topological proximity of DNA damaged loci, thus enabling recurrent illegitimate recombinations. The proposed research will define molecular mechanisms responsible for illegitimate DNA recombination and genomic instability in cancers that are causatively associated with deregulation of ¿-catenin.