Transcriptional silencing by the Bcl-6 oncoprotein

描述（由申请人提供）：Bcl-6转录抑制因子是b细胞淋巴瘤中最常见的突变癌蛋白。大约50%的患者发生Bcl-6调控区的突变，导致Bcl-6的表达失调，从而导致分化受阻和细胞存活异常。Bcl-6的n端BTB/POZ结构域是其转录功能所必需的。通过x射线晶体学，我们发现Bcl-6 BTB结构域通过非保守的“侧槽”基序直接与它的协同抑制因子伴侣蛋白结合。互易表面由SMRT、N-CoR和BCoR共阻遏子中的短序列提供。这个“COW”基序的点突变导致体外和体内协同抑制因子与Bcl-6之间的物理和功能相互作用丧失。这可能与Bcl-6的主要功能相关，因为该蛋白介导转录抑制需要辅抑制因子相互作用。我们假设侧沟在Bcl-6依赖性抑制中起关键作用。因此，我们设计了肽抑制剂来阻止辅抑制因子与Bcl-6的相互作用。这些试剂将用于“有条件地敲除”SMRT/N-CoRJBCoR共抑制因子对Bcl-6沉默的贡献。这将使我们能够确定这些辅助抑制因子对Bcl-6的基因组和表观基因组转录机制的相对贡献。通过芯片上ChIP的高通量染色质结构分析和标准表达阵列的差异甲基化杂交可以获得这些结果。还需要通过对独立基因座的具体研究进行验证。最后，我们预测Bcl-6的侧沟阻断将抵消Bcl-6的致癌活性，并构成一种新的特异性b细胞淋巴瘤转录治疗方法。我们将在该疾病的临床前动物模型中评估侧沟阻断逆转b细胞淋巴瘤细胞恶性表型的能力，以及其改变病程的能力。总的来说，这些结果将揭示Bcl-6转录抑制作用机制的新颖和重要见解，并为b细胞淋巴瘤患者提供新的特异性分子治疗方式的基础。

DESCRIPTION (provided by applicant): The Bcl-6 transcriptional repressor is the most commonly mutated oncoprotein in B-cell lymphomas. Mutations of its regulatory regions occur in approximately 50% of patients, leading to deregulated expression of Bcl-6 with consequent differentiation block and aberrant cell survival. The N-terminal BTB/POZ domain of Bcl-6 is required for its transcriptional functions. By X-ray crystallography we found that the Bcl-6 BTB domain binds directly to its co-repressor partner proteins through a non-conserved "lateral groove" motif. The reciprocal surface is provided by a short sequence present in the SMRT, N-CoR and BCoR corepressors. Point mutations in this "COW' motif cause loss of physical and functional interactions between corepressors and Bcl-6 in vitro and in vivo. This could be of major functional relevance for Bcl-6, since corepressor interaction is required for this protein to mediate transcriptional repression. We hypothesize that the lateral groove plays a critical role in Bcl-6 dependent repression. Therefore, we designed peptide inhibitors that prevent co-repressor interaction with Bcl-6. These reagents will be used to "conditionally knock out" the contribution of the SMRT/N-CoRJBCoR co-repressors to silencing by Bcl-6. This will allow us to determine the relative contribution of these corepressors to the genomic and epigenomic transcriptional mechanisms of Bcl-6. Such results can be obtained by combining high-throughput chromatin structure analysis by ChIP on chip and differential methylation hybridization with standard expression arrays. Validation through specific studies on independent loci is also required. Finally, we predict that lateral groove blockade of Bcl-6 will counteract the oncogenic activity of Bcl-6 and constitutes a novel and specific transcription therapy approach for B-cell lymphomas. We will assess the ability of lateral groove blockade to reverse the malignant phenotype of B-cell lymphoma cells as well as its capacity to alter the course of disease in pre-clinical animal models of this disease. Collectively, these results will reveal novel and important insights into the mechanism of action of Bcl-6 transcriptional repression, as well as provide the basis for a novel and specific molecular therapeutic modality for patients with B-cell lymphomas.