Study for the mechanism of lymphocyte development by Bach2 transcription factor and clinical analysis of Bach2 gene

转录因子Bach1和Bach2是BTB碱性区亮氨酸拉链(BZip)因子家族的成员，它们通过与Maf相关转录因子形成同源二聚体或异源二聚体，与12-O-十四酰佛波醇-13-乙酸酯(TPA)反应元件和相关的Maf识别元件(MAF-Recognition Element，MAF-Recognition Element)结合。在人类造血细胞系(12个髓系细胞系和16个淋巴细胞系)中，BACH2仅在部分B淋巴细胞系中大量表达。在不表达内源性BACH2的人Burkitt细胞系Raji中强制表达BACH2，导致克隆形成活性显著降低，表明BACH2具有抑制细胞增殖的作用。利用cDNA微阵列双色荧光杂交技术，对内源性BACH2型细胞株和BACH2型高表达亚系的表达谱进行了大规模比较，鉴定出具有抗凋亡活性的Bcl2同源物A1和…更多与IL-12(P40)同源的EBI3作为Bach2的靶基因。A1和EBI3在所有不表达BACH2的人B细胞系中都有表达。然而，在表达BACH2的B细胞系中未检测到表达。荧光素酶报告和凝胶延迟分析表明，人A1基因5‘端有反应元件。因此，Bach2可能参与了B细胞分化早期A1基因的抑制和B细胞凋亡的调控。通过荧光原位杂交，BACH2基因定位于染色体6q15。由于6号染色体长臂缺失(6q)是人类B细胞淋巴瘤最常见的染色体改变之一，我们检测了人类B细胞非霍奇金淋巴瘤(NHL)中BACH2基因的杂合性缺失(LOH)。在25例信息性病例中，5例(20%)有杂合性缺失。为了分析BACH2基因在这些淋巴瘤中的突变，我们检查了BACH2基因的结构，并确定了所有编码外显子的序列和外显子-内含子的边界。经直接测序分析，在存在BACH2基因杂合性缺失的f淋巴瘤标本中未发现突变。这些结果表明，BACH2在调节B细胞增殖方面起着重要作用，尽管BACH2功能缺失是否在B细胞肿瘤发生中的作用较小仍不清楚

The transcription factors Bach1 and Bach2, members of the BTB-basic region leucine zipper (bZip) factor family, bind to a 12-O-tetradecanoylphorbol-13-acetate (TPA)-responsive element and the related Maf-recognition element (MARE) by forming homodimers or heterodirners with Maf-related transcription factors. Among human hematopoietic cell lines (12 myeloid cell lines and 16 lymphocytic cell lines), BACH2 is expressed abundantly only in some B-lymphocytic cell lines. Enforced expression of BACH2 in a human Burkitt cell line, RAJI that does not express endogenous BACH2, resulted in marked reduction of clonogenic activity, indicating that BACH2 possesses an inhibitory effect on cell proliferation. A large-scale comparison of the expression profiles between a human B cell line without endogenous BACH2 expression and a BACH2-overexpressing subline, using two-color fluorescence hybridization of cDNA microarray, led to the identification of Bcl-2 homologue A1 with anti-apoptotic activity and … More EBI3 which is a homologue to IL-12 (p40) as target genes of Bach2. A1 and EBI3 were expressed in all human B-cell lines which do not express BACH2. However, no expression was detected in B-cell lines expressing BACH2. Luciferase reporter and gel retardation assays revealed the responsive elements in the 5' region of the human A1 gene. Hence Bach2 might be involved in repression of A1 gene at earlier stages of B-cell differentiation and control of B-cell apoptosis.By fluorescent in situ hybridization, the BACH2 gene was localized to chromosome 6q15. Because deletion of the long arm of chromosome 6 (6q) is one of the commonest chromosomal alterations in human B-cell lymphoma, we examined for the loss of heterozygosity (LOH) of the BACH2 gene in human B-cell non-Hodgkin's lymphomas (NHL). Among 25 informative cases, 5 (20 %) showed LOH. To analyze the mutations of BACH2 gene in these lymphomas, we examine the structure of the BACH2 gene and determined the sequences of the all coding exons and the exon-intron boundaries. By direct sequence analysis, no mutations were detected in the f lymphoma samples with the LOH of BACH2 gene. These results indicate that BACH2 plays important roles irregulation of B cell proliferation, although it remains still elusive whether loss of BACH2 function is involved in B-cell tumorigenesis Less