Analysis for transcriptional regulation of the BCL6 gene

BCL6基因重排在人类b细胞淋巴瘤中经常被发现，这是由于涉及3q27带的互惠染色体易位的结果。染色体断裂优先发生在含有BCL6基因第一外显子和内含子的3kb区域内。最近的报告显示，在这个有限区域内的内部缺失或点突变在b细胞淋巴瘤中也很常见。这些观察结果表明，BCL6基因的第一个外显子-内含子边界区域的结构改变，一个假定的调控区域，可能是b细胞淋巴瘤发展的关键事件。为了进一步了解BCL6在淋巴瘤中失调控表达的机制，我们研究了该区域在BCL6基因转录调控中的生理功能。通过使用b细胞系Raji进行荧光素酶报告基因检测，我们发现了两个负调控BCL6表达的区域。一个区域被指定为ES，位于第一个外显子+472和+543之间，另一个区域被指定为IS，位于第一个内含子的+783和+918之间。在ES区发现了BCL6蛋白自身结合的一致核苷酸序列。随后的电泳迁移率转移分析显示BCL6与ES区域的实际结合。用BCL6表达载体共转染实验表明，BCL6基因的转录部分受BCL6基因产物的负反馈调控。另一个负调控区域IS已被证明具有消音器活性。IS区完全包括在b细胞淋巴瘤中通常缺失的区域，以及在正常和肿瘤b细胞中发现体细胞超突变的部分。电泳迁移位移分析表明，特异性结合该内含子沉默元件的核蛋白在几种造血细胞系中表达。综上所述，已确定的BCL6基因区域包含负调控元件，这些区域的结构改变可能在b细胞淋巴瘤中BCL6基因的失调控表达中发挥潜在作用。少

Rearrangements of the BCL6 gene have been frequently found in human B-cell lymphomas, as a result of reciprocal chromosomal translocation involving band 3q27. Chromosomal breaks preferentially occur within a 3-kb region containing the first exon and intron of thh BCL6 gene. Recent reports revealed that internal deletions or point mutations within this limited region are also common in B-cell lymphomas. These observations suggest that the structural alteration of the first exon-intron boundary region of the BCL6 gene, a putative regulatory region, may be crucial event in the development of B-cell lymphomas. To further understand the mechanism of the deregulated expression of BCL6 in lymphomas, we investigated the physiological function of this region in transcriptional regulation of the BCL6 gene.Through luciferase reporter assay using B-cell line Raji, we have identified two regions that negatively regulate BCL6 expression. One region designated as ES located within the first exon betw … More een nucleotides +472 and +543, and the other region designated as IS between +783 and +918 of the first intron. Consensus nucleotide sequence for a binding of BCL6 protein itself was found within the ES region. Subsequent electrophoretic mobility shift assay revealed an actual binding of BCL6 to the ES region. Co-transfection experiment using a BCL6 expression vector showed that transcription of the BCL6 gene was partly regulated by a negative feedback of the BCL6 gene product.Another negative regulatory region IS has been shown to have a silencer activity. The IS region is entirely included in the regions commonly deleted in B-cell lymphomas as well as in the parts where somatic hypermutations are found in both normal and neoplastic B-cells. Electrophoretic mobility shift assay showed that the nuclear proteins that specifically bind to this intronic silencer element are expressed in several hematopoietic cell lines.Taken together, the identified regions of the BCL6 gene contain negative regulatory elements and the structural alterations of these regions have potential roles in the deregulated expression of the BCL6 gene in B-cell lymphomas. Less