转录因子FOXO1在经典霍奇金淋巴瘤中的抑癌机制

The B cell receptor (BCR) signaling is essential for survival of mature B cells as well as most non-Hodgkin lymphomas (NHL). Lack of BCR signaling induces apoptosis in B cells and NHL. It has been shown that activation of PI3K pathway or deletion of its target FOXO1 rescue B cells lacking BCR efficiently. The FOXO1 transcription factor promotes expression of B cell specific genes and facilitates B cell differentiation. We found that, normal B cell subsets and NHL express FOXO1 at a high level; in contrast, most classical Hodgkin lymphoma (cHL) primary cases and cell lines which do not have eligible BCR show very low or no expression of FOXO1; which we demonstrated is attributable to multiple mechanisms, including loss of genomic locus of FOXO1, constitutive activity of PI3K-AKT/PKB and MAPK/ERK kinases and up-regulation of microRNAs miR-96, miR-182, and miR-183. Ectopic expression of FOXO1 induced apoptosis in cHL cell lines and blocked proliferation. Microarray analysis revealed target genes of FOXO1 in cHL,including CD30 and PRDM1/BLIMP1 that are important for survival and the peculiar phenotype of cHL. In the current study, we propose to uncover the mechanisms of tumor suppression by FOXO1 in cHL, and to validate whether FOXO1 has any impact on activity of PI3K and NF-κB, to elucidate the mechanisms of regulation of CD30 and PRDM1 by FOXO1. We believe our study will shed more light on the molecular biology of cHL, and may provide therapeutic opportunities for the disease.

缺乏BCR信号导致成熟B淋巴细胞和绝大多数非霍奇金淋巴瘤（NHL）发生凋亡。激活PI3K通路或敲除其下游基因FOXO1可代替BCR信号，使细胞免于凋亡。FOXO1调控B细胞特异基因的表达，促进B细胞的分化。申请人前期发现，相比正常B细胞和NHL，FOXO1在缺乏BCR信号的经典霍奇金淋巴瘤（cHL）中表达最低；其低表达与染色体位点缺失、PI3K和ERK的高活性、microRNA高表达有关；导入FOXO1后，cHL细胞生长减缓并发生凋亡；Microarray揭示了FOXO1的靶基因，包括与cHL淋巴瘤细胞存活和特殊表型有关的CD30、BLIMP1等。本课题拟在前期工作的基础上，利用细胞系深入机制研究，阐明FOXO1的抑癌机制，及其对PI3K和NF-κB活性的影响、和对CD30、BLIMP1的调控机制。本课题研究结果不仅有助于从分子水平揭示cHL发病机理，而且可为cHL个性化治疗提供参考。

以往的研究表明，缺乏BCR信号导致成熟B淋巴细胞和绝大多数非霍奇金淋巴瘤（NHL）发生凋亡。激活PI3K通路或敲除其下游基因FOXO1可代替BCR信号，使细胞免于凋亡。FOXO1调控B细胞特异基因的表达，促进B细胞的分化。本课题通过研究证明，相比正常B细胞和NHL，FOXO1在缺乏BCR信号的经典霍奇金淋巴瘤（cHL）中表达最低；其低表达与染色体位点缺失、PI3K和ERK的高活性、microRNA高表达有关；导入FOXO1后，cHL细胞生长减缓并发生凋亡；Microarray揭示了FOXO1的靶基因，包括与cHL淋巴瘤细胞存活和特殊表型有关的CD30、BLIMP1等。本课题结果提示：1）cHL细胞中，FOXO1参与了经典靶基因的调控，如THFSF8、MYC、BCL6等。2）本课题证明E2A在cHL起到抑癌基因的作用。E2A能激活BIK表达，从而抑制cHL细胞生长。且E2A也参与经典靶基因调控，如NOTCH1、CDKN1A等。.此外，我们研究了与cHL及其类似的PMBL。我们发现FOXO1在PMBL表达低下，过表达FOXO1，MedB-1（PMBL细胞系）生长受抑，发生细胞周期阻滞，并诱导凋亡。亦为抑癌基因作用。且这一作用于MYC、JAK2相互调控相关。