Department of Biochemistry, College of Life Sciences, Nankai University, Tianjin, China.
Carcinogenesis. 2013 Apr;34(4):927-35. doi: 10.1093/carcin/bgs399. Epub 2013 Jan 5.
Hepatitis B X-interacting protein (HBXIP) is an important oncoprotein that plays critical role in the development of cancer. In this study, we report that HBXIP activates LIM-only protein 4 (LMO4), a transcriptional coregulatory protein, in promotion of cell proliferation. We observed that the messenger RNA (mRNA) expression levels of HBXIP were positively associated with those of LMO4 in clinical breast cancer tissues. We further identified that HBXIP upregulated LMO4 at the levels of promoter, mRNA and protein in MCF-7 and LM-MCF-7 breast cancer cell lines. The expression of cyclin D1 and cyclin E, downstream effectors of LMO4, could be upregulated by HBXIP through LMO4. Then, chromatin immunoprecipitation (ChIP) assay revealed that HBXIP was able to interact with the promoter region of LMO4. Electrophoretic mobility shift assay showed that HBXIP occupied the -237/-206 region of LMO4 promoter containing Sp1 binding element. The mutant of Sp1 binding site in the LMO4 promoter impeded the interaction of HBXIP with the promoter. Co-immunoprecipitation, ChIP and luciferase reporter gene assays showed that HBXIP activated LMO4 promoter through binding to Sp1. In function, flow cytometry, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, 5-ethynyl-2'-deoxyuridine (EdU) incorporation assays and animal transplantation assays demonstrated that HBXIP-enhanced cell proliferation of breast cancer through upregulating LMO4 in vitro and in vivo. Thus, we concluded that oncoprotein HBXIP is able to activate the transcriptional coregulatory protein LMO4 through transcription factor Sp1 in promotion of proliferation of breast cancer cells. HBXIP may serve as a driver gene to activate transcription in the development of cancer.
乙型肝炎病毒 X 交互蛋白 (HBXIP) 是一种重要的癌蛋白，在癌症的发展中起着关键作用。在这项研究中，我们报告 HBXIP 激活 LIM 仅蛋白 4 (LMO4)，一种转录共调节蛋白，促进细胞增殖。我们观察到 HBXIP 的信使 RNA (mRNA) 表达水平与临床乳腺癌组织中 LMO4 的表达水平呈正相关。我们进一步确定 HBXIP 在 MCF-7 和 LM-MCF-7 乳腺癌细胞系中上调 LMO4 的启动子、mRNA 和蛋白水平。LMO4 的下游效应子 cyclin D1 和 cyclin E 的表达可以通过 LMO4 被 HBXIP 上调。然后，染色质免疫沉淀 (ChIP) 实验表明 HBXIP 能够与 LMO4 的启动子区域相互作用。电泳迁移率变动分析显示 HBXIP 占据了含有 Sp1 结合元件的 LMO4 启动子的-237/-206 区域。LMO4 启动子中 Sp1 结合位点的突变阻止了 HBXIP 与启动子的相互作用。共免疫沉淀、ChIP 和荧光素酶报告基因实验表明，HBXIP 通过与 Sp1 结合激活 LMO4 启动子。在功能上，流式细胞术、3-(4,5-二甲基噻唑-2-基)-2,5-二苯基四氮唑溴盐、5-乙炔基-2'-脱氧尿苷 (EdU) 掺入实验和动物移植实验表明，HBXIP 通过在体外和体内上调 LMO4 增强乳腺癌细胞的增殖。因此，我们得出结论，癌蛋白 HBXIP 通过转录因子 Sp1 激活转录共调节蛋白 LMO4，促进乳腺癌细胞的增殖。HBXIP 可能作为驱动基因在癌症的发展中激活转录。
