HUMAN PAPILLOMAVIRUS TYPE-11 E2 PROTEINS REPRESS THE HOMOLOGOUS E6 PROMOTER BY INTERFERING WITH THE BINDING OF HOST TRANSCRIPTION FACTORS TO ADJACENT ELEMENTS
HUMAN PAPILLOMAVIRUS TYPE-11 E2 PROTEINS REPRESS THE HOMOLOGOUS E6 PROMOTER BY INTERFERING WITH THE BINDING OF HOST TRANSCRIPTION FACTORS TO ADJACENT ELEMENTS
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DOI：
10.1128/jvi.68.2.1115-1127.1994
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发表时间：
1994-02-01
影响因子：
5.4
通讯作者：
CHOW, LT
中科院分区：
文献类型：
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作者：
DONG, G;BROKER, TR;CHOW, LT
人乳头瘤病毒(HPVs)E6启动子对下生殖道和上呼吸道上皮细胞的营养作用在体外受同源和异源乳头瘤病毒E2蛋白调控，这些蛋白结合到一个共同的反应序列(E2-RS)ACCN(6)GGT。当在上皮细胞系中检测到HPV-11型(HPV-11)的表达时，缺乏全长E2蛋白的氨基末端反式激活结构域的HPV-11E2-C蛋白总是抑制同源病毒E6启动子。相反，当新的构成增强子(CE)CE II被删除时，不仅基础启动子的活性大大降低，而且它进一步被完整的HPV-11 E2蛋白抑制(M.T.Chin，T.R.Broker和L.T.Chow，J.Virol。63：2967-2976，)。在这里，我们证明了，当从更强的替代启动子表达时，HPV-11 E2蛋白有效地抑制E6启动子，而不管CE II。通过对HPV-11 E2-RS的四个高度保守的拷贝和邻近的增强子-启动子元件的系统突变分析，我们表明最上游的启动子-启动子-远端的E2-RS拷贝1在E6启动子调控中没有明显的作用。同源HPV-11E2蛋白的抑制是通过三个E2-RS启动子-近端拷贝中的每一个来实现的，但CE II的存在取消了全长E2蛋白对E2-RS拷贝2的抑制作用。当两个(对于E2)或三个(对于E2-C)启动子-近端拷贝的E2-RS发生突变时，抑制作用就会减轻。我们特别证明了在E2-RS 3处施加抑制是由于宿主转录因子SP1或Sp1样蛋白与位于串联的E2蛋白结合位点3和4上游1个核苷酸的非共有序列AGGAGG的结合。在相邻的Sp1和E2-RS 3位点之间插入3个碱基允许Sp1和E2蛋白结合，同时解除了E2-RS 3介导的抑制。类似的突变分析表明，与上游E2-RS2附近的GT-1基序结合的蛋白质有助于在CE II存在的情况下消除E2蛋白的抑制。本文讨论了这些结果在病毒感染周期和病毒致癌过程中的意义。
The E6 promoter of human papillomaviruses (HPVs) trophic for epithelia of the lower genital tract and the upper respiratory tract is regulated in vitro by homologous and heterologous papillomaviral E2 proteins that bind to a consensus responsive sequence (E2-RS) ACCN(6)GGT. When HPV type 11 (HPV-11) expression is examined in epithelial cell lines, the HPV-11 E2-C protein, which lacks the amino-terminal transactivating domain of the full-length E2 protein, invariably represses the homologous viral E6 promoter. In contrast, when the novel constitutive enhancer (CE) CE II is deleted, not only is the basal promoter activity much reduced, it is further repressed by the intact HPV-11 E2 protein (M. T. Chin, T. R. Broker, and L. T. Chow, J. Virol. 63:2967-2976, 1989). Here, we demonstrate that, when expressed from a stronger surrogate promoter, the HPV-11 E2 protein represses the E6 promoter effectively, regardless of CE II. By performing systematic mutational analyses of the four highly conserved copies of the HPV-11 E2-RS and of the adjacent enhancer-promoter elements, we show that the furthest upstream, promoter-distal E2-RS copy 1 plays no apparent role in E6 promoter regulation. Repression by the homologous HPV-11 E2 proteins is mediated through each of the three promoter-proximal copies of the E2-RS, but the presence of CE II abrogates the full-length E2 protein repression exerted at E2-RS copy 2. Repression is alleviated when the two (for E2) or three (for E2-C) promoter-proximal copies of E2-RS are mutated. We specifically demonstrate that repression exerted at E2-RS 3 is due to preclusion of binding of the host transcription factor Spl or Sp1-like proteins to a nonconsensus sequence AGGAGG located 1 bp upstream of the tandem E2 protein binding sites 3 and 4. A 3-bp insertion between the adjacent Sp1 and E2-RS 3 sites permits both Sp1 and E2 proteins to bind, with a concomitant relief of E2-RS 3-mediated repression. Similar mutational analyses show that proteins that bind to the GT-1 motif near the upstream E2-RS 2 help abrogate repression by the E2 protein in the presence of CE II. The implications of these results with respect to the viral infectious cycle and during viral oncogenesis are discussed.