In vitro and in vivo modeling of helix-loop-helix protein-mediated reprogramming and malignanttransformation of lymphoid cells

癌性转化不仅表现为恶性细胞增殖能力增强和/或更高的细胞凋亡抗性，而且还表现为生理分化过程的破坏。因此，肿瘤细胞可以表现出谱系不忠甚至细胞重编程的特征，这可能会开辟另一种生长和生存途径。许多淋巴细胞恶性肿瘤表现出与这种重编程过程相一致的表型，经典霍奇金淋巴瘤（cHL）是最突出的例子：与起源于B细胞形成鲜明对比的是，cHL的恶性霍奇金/里德-斯特恩伯格（HRS）细胞几乎完全丧失了其B细胞特异性基因表达程序，并获得了其他造血谱系特有的基因表达。在我们之前的工作中，我们可以证明B细胞相关的螺旋-环-螺旋转录因子E2A被其拮抗剂ID2和ABF1的功能性抑制是这个重编程过程中的一个关键事件。在进一步的工作中，我们培育了Id2和Abf1转基因小鼠，它们表现出对B细胞分化的严重干扰，我们认为这是建立cHL体内模型的第一步。此外，我们已经证明B谱系不适当的信号通路的激活，如ltr驱动的髓系CSF1受体的表达，是HRS细胞生长和存活所必需的。在这些发现的基础上，我们计划在我们目前的提案中解决以下主题：I)我们将把Id2和Abf1转基因小鼠与携带关键cHL特异性致癌缺陷的小鼠品系杂交，这些缺陷驱动生长和存活，以促进cHL体内模型的产生。II)我们将分析谱系不合适基因在野生型环境和E2A活性降低的情况下诱导B细胞重编程和赋予B细胞受体（BCR）不依赖生存的能力和分子作用。III)我们将在体外和体内描述新发现的E2A靶基因在淋巴样细胞恶性转化中的作用。除了深入了解淋巴样细胞的（去）分化和转化过程外，我们的提案旨在确定治疗人类淋巴瘤的新治疗靶点，特别是越来越多的E2A活性改变的人类淋巴瘤。

Oncogenic transformation is not only characterized by an enhanced proliferative capacity and/or higher apoptosis resistance of malignant cells, but also by a disruption of the physiological differentiation process. As a consequence, tumor cells can display features of lineage infidelity or even cellular reprogramming that might open up alternative growth and survival pathways. A number of lymphoid malignancies display a phenotype that is in accordance with such a reprogramming process, with classical Hodgkin lymphoma (cHL) being the most prominent example: in striking contrast to their origin from B-cells, the malignant Hodgkin-/Reed-Sternberg (HRS) cells of cHL have almost completely lost their B cell-specific gene expression program and have acquired the expression of genes characteristic for other hematopoietic lineages. In our previous work, we could demonstrate that functional inhibition of the B cell-associated helix-loop-helix transcription factor E2A by its antagonists ID2 and ABF1 represents a key event in this reprogramming process. In further work, we have generated Id2 and Abf1 transgenic mice, which show a profound disturbance of B cell differentiation, a phenotype that we consider as a first step towards an in vivo model of cHL. In addition, we have demonstrated that activation of B lineage-inappropriate signaling pathways, such as the LTR-driven expression of the myeloid CSF1 receptor, are required for growth and survival of HRS cells. In an extension of these findings, we plan to address the following topics in our current proposal: I) We will cross Id2 and Abf1 transgenic mice with mouse strains that carry key cHL-specific oncogenic defects driving growth and survival to promote the generation of a cHL in vivo model. II) We will analyze the capacity and the molecular action of lineage-inappropriate genes to induce reprogramming of B cells and to confer B cell receptor (BCR)-independent survival in the wild-type setting and in the context of reduced E2A activity. III) We will characterize the role of newly identified E2A target genes for malignant transformation of lymphoid cells in vitro and in vivo. Apart from insights into the (de)-differentiation and transformation process of lymphoid cells, our proposal seeks to identify new therapeutic targets for the treatment of human lymphomas, in particular for the growing number of human lymphomas with altered E2A activity.