Thatikunta P, Raj G V, Kundu M, Khalili K, Amini S
Center for Neurovirology, Allegheny University of the Health Sciences, Philadelphia, Pennsylvania 19107, USA.
Oncogene. 1997 Jun 19;14(24):2959-69. doi: 10.1038/sj.onc.1201129.
The cell type specificity of the regulation of expression of the potent growth inhibitory cytokine transforming growth factor-beta (TGF-beta), prompted our analyses of the regulation of TGF-beta1 gene expression in glial cells by viral and cellular oncoproteins. We have shown that SV40 T-antigen diminished TGF-beta1 expression in glial cells and this repression was dependent on the ability of T-antigen to interact with the tumor suppressor protein, pRb, and two structurally related proteins, p107 and p130. The cellular transcription factor E2F-1, which is a downstream effector of T-antigen, was unable to influence expression from the TGF-beta1 promoter by itself. Interestingly, E2F-1 could overcome viral T-antigen-mediated repression of the TGF-beta1 promoter, suggesting potential feedback loop between TGF-beta and E2F in virally transformed glial cells. Using deletion analyses, we have mapped two E2F-1-responsive regions on the TGF-beta1 promoter: a T-antigen-dependent negative regulatory sequence (TdNRS) between -323 and -175, and a T-antigen-independent positive regulatory sequence (TiPRS) between -34 and +10 on the TGF-beta1 promoter. Further examination of TiPRS revealed the presence of a functional E2F binding site. Interestingly, the amino terminus of E2F-1 was required for its activation of TGF-beta1 expression, as mutations in that domain abolished the ability of E2F-1 to increase TGF-beta1 expression. These data suggest that yet-uncharacterized interaction between the amino terminus of E2F-1 and cellular proteins regulates TGF-beta1 expression. The mechanism for E2F-1-mediated T-antigen-dependent regulation of TGF-beta1 expression from TdNRS awaits further characterization.
强效生长抑制细胞因子转化生长因子-β（TGF-β）表达调控的细胞类型特异性，促使我们分析病毒和细胞癌蛋白对神经胶质细胞中TGF-β1基因表达的调控。我们已经表明，SV40 T抗原可降低神经胶质细胞中TGF-β1的表达，这种抑制作用取决于T抗原与肿瘤抑制蛋白pRb以及两种结构相关蛋白p107和p130相互作用的能力。细胞转录因子E2F-1是T抗原的下游效应物，其自身无法影响TGF-β1启动子的表达。有趣的是，E2F-1可以克服病毒T抗原介导的TGF-β1启动子抑制作用，这表明在病毒转化的神经胶质细胞中TGF-β和E2F之间可能存在反馈环。通过缺失分析，我们在TGF-β1启动子上定位了两个E2F-1反应区域：-323至-175之间的T抗原依赖性负调控序列（TdNRS），以及TGF-β1启动子上-34至+10之间的T抗原非依赖性正调控序列（TiPRS）。对TiPRS的进一步研究发现了一个功能性E2F结合位点。有趣的是，E2F-1的氨基末端是其激活TGF-β1表达所必需的，因为该结构域中的突变消除了E2F-1增加TGF-β1表达的能力。这些数据表明，E2F-1氨基末端与细胞蛋白之间尚未明确的相互作用调节了TGF-β1的表达。E2F-1介导的从TdNRS对TGF-β1表达的T抗原依赖性调控机制有待进一步阐明。
