Heckman Caroline A, Mehew John W, Boxer Linda M
Center for Molecular Biology in Medicine, Veterans Affairs Palo Alto Health Care System, Palo Alto, CA 94305, USA.
Oncogene. 2002 May 30;21(24):3898-908. doi: 10.1038/sj.onc.1205483.
The t(14;18) translocation, which is characteristic of follicular lymphoma, results in the overexpression of the bcl-2 gene dependent upon regulatory elements within the bcl-2 5' flanking region and the immunoglobulin heavy chain gene enhancers. Conflicting evidence exists on the effects of NF-kappaB expression on Bcl-2 levels in different cell types. Lymphoma cells with the t(14;18) translocation show high levels of nuclear NF-kappaB proteins. We observed decreased levels of endogenous Bcl-2 when the IkappaBalpha-super-repressor was expressed in a t(14;18) cell line. Deletion analysis of the bcl-2 promoter indicated that the repressive effect of the IkappaBalpha-super-repressor occurred through a region that contained no NF-kappaB consensus sequences. This highly active region contained a c-AMP response element (CRE) and several Sp1 binding sites. Chromatin immunoprecipitation assays with antibodies specific for the NF-kappaB and CREB/ATF family members, as well as Sp1, resulted in the isolation of this IkappaBalpha-super-repressor responsive region of the bcl-2 promoter. Mutation of the CRE and the two Sp1 sites in different combinations in bcl-2 reporter constructs resulted in the loss of bcl-2 promoter repression by the IkappaBalpha-super-repressor. We therefore conclude that the activation of bcl-2 by NF-kappaB in t(14;18) lymphoma cells is mediated through the CRE and Sp1 binding sites.
t(14;18)易位是滤泡性淋巴瘤的特征，它导致bcl-2基因的过表达，该过表达依赖于bcl-2 5'侧翼区域内的调控元件和免疫球蛋白重链基因增强子。关于NF-κB表达对不同细胞类型中Bcl-2水平的影响存在相互矛盾的证据。具有t(14;18)易位的淋巴瘤细胞显示出高水平的核NF-κB蛋白。当IkappaBalpha超级阻遏物在t(14;18)细胞系中表达时，我们观察到内源性Bcl-2水平降低。bcl-2启动子的缺失分析表明，IkappaBalpha超级阻遏物的抑制作用通过一个不包含NF-κB共有序列的区域发生。这个高活性区域包含一个c-AMP反应元件（CRE）和几个Sp1结合位点。用针对NF-κB和CREB/ATF家族成员以及Sp1的特异性抗体进行染色质免疫沉淀分析导致分离出bcl-2启动子的这个IkappaBalpha超级阻遏物反应区域。在bcl-2报告基因构建体中以不同组合对CRE和两个Sp1位点进行突变导致IkappaBalpha超级阻遏物对bcl-2启动子的抑制作用丧失。因此，我们得出结论，t(14;18)淋巴瘤细胞中NF-κB对bcl-2的激活是通过CRE和Sp1结合位点介导的。
