The Role of the IRF4-NOTCH2 Interplay in B-Cell Development and Malignancy

B淋巴细胞的发育受到主要转录调控因子的协调表达的严格控制。由于基因改变，这些调节因子的异常表达可以破坏有序的b细胞发育并促进致癌转化。转录因子干扰素调节因子-4 （IRF4）已被确定为B细胞慢性淋巴细胞白血病（CLL）的潜在肿瘤抑制因子，慢性淋巴细胞白血病是一种静止成熟B细胞的恶性肿瘤。为了了解IRF4在B细胞中的功能，宿主实验室最近获得了IRF4控制淋巴组织内成熟B细胞迁移和归巢特性的证据。因此，已经观察到体内irf4基因的诱导缺失导致irf4缺陷B细胞在边缘区淋巴微环境中积累。值得注意的是，NOTCH2信号在irf4缺陷的B细胞中被发现过度激活，并且通过治疗性单克隆抗体抑制NOTCH2信号导致边缘区快速解体。这些结果可能与CLL相关，因为已发表的证据表明NOTCH2在CLL肿瘤细胞中具有组成性活性。潜在的假设是，IRF4和NOTCH2建立的转录网络平衡的改变可能会破坏B细胞的正常迁移和归巢特性，从而通过在支持生存的淋巴样微环境中异常定位转化的B细胞，从而促进淋巴瘤的发生。在这里，我建议阐明IRF4调控NOTCH2在B细胞中的激活的分子机制。此外，我将通过对转录靶点进行全基因组鉴定，确定irf4缺陷B细胞中NOTCH2控制的生物学程序。最后，我将在模拟CLL增殖中心微环境的体外实验中研究notch2抑制抗体对CLL细胞表型和功能的影响。阐明IRF4和NOTCH2在正常b细胞生理学中的功能相互作用及其在恶性肿瘤中的破坏，有可能为开发针对CLL和脾边缘区b细胞淋巴瘤的创新治疗策略提供基础，其中NOTCH2过度激活与肿瘤促进作用有关。

The development of B lymphocytes is tightly controlled by the coordinated expression of master transcriptional regulators. Aberrant expression of these regulators due to genetic alterations can disrupt ordered B-cell development and contribute to oncogenic transformation. The transcription factor interferon regulatory factor-4 (IRF4) has been identified as a potential tumor suppressor in B-cell chronic lymphocytic leukemia (CLL), a malignancy of quiescent mature B cells. Towards understanding the function of IRF4 in B cells, the host laboratory has recently obtained evidence that IRF4 controls the migration and homing properties of mature B cells within the lymphoid tissues. Thus, it has been observed that the inducible deletion of the irf4 gene in vivo led to an accumulation of IRF4-deficient B cells in the lymphoid microenvironment of the marginal zone. Notably, NOTCH2 signaling was found to be hyperactivated in IRF4-deficient B cells, and inhibition of NOTCH2 signaling by a therapeutic monoclonal antibody led to a rapid disintegration of the marginal zone. These results are likely to be relevant for CLL, since published evidence suggests that NOTCH2 is constitutively active in CLL tumor cells. The underlying hypothesis is that alterations in the balance of the transcriptional network established by IRF4 and NOTCH2 may disrupt the normal migration and homing properties of B cells and thereby contribute to lymphomagenesis by aberrantly positioning transformed B cells in a lymphoid microenvironment that supports survival.Here I propose to elucidate the molecular mechanism by which IRF4 regulates NOTCH2 activation in B cells. In addition, I will determine the biological program controlled by NOTCH2 in IRF4-deficient B cells by performing a genome-wide identification of transcriptional targets. Finally, I will investigate the effects of a NOTCH2-inhibitory antibody on CLL cell phenotype and function in in vitro assays that mimic the CLL proliferation center microenvironment. Elucidating the functional interplay between IRF4 and NOTCH2 in normal B-cell physiology and its disruption in malignancy has the potential to provide the basis for developing innovative therapeutic strategies targeted at CLL and splenic marginal zone B-cell lymphoma, where NOTCH2 hyperactivation has been associated with tumor-promoting roles.