Kyo S, Tam A, Laimins L A
Department of Microbiology-Immunology, Northwestern University, Chicago, Illinois 60611, USA.
Virology. 1995 Aug 1;211(1):184-97. doi: 10.1006/viro.1995.1390.
Transcription of human papillomaviruses (HPV) is regulated by enhancer sequences located in the upstream regulatory region. The factors regulating expression of one of the high risk genital HPV types, HPV 31b, were investigated using transient expression and protein binding assays. A region of 262 base pairs in length was identified as the minimal functional enhancer and a series of five protected binding sites were observed by footprint analyses. Electrophoretic mobility shift assays demonstrated that AP1, Oct-1, as well as three novel factors bound these sequences. Mutational analyses indicated that AP1 synergistically activated the HPV31b enhancer together with either of two novel factors. One of these novel factors bound a sequence similar to an NF1 site but was distinct from NF-1. The second factor bound sequences bearing similarity to KRF-1 binding sites which have previously been characterized in HPV 18. Competition binding assays demonstrated that this factor was not identical to KRF-1. Additional studies implicated Oct-1 as a negative regulator of HPV 31b expression as mutation of Oct-1 binding sequences resulted in an increase in viral expression. None of the factors observed to be important for HPV 31b enhancer activity was found exclusively in epithelial cells and instead were detected in a variety of cell types. Of these factors, AP1 binding correlated most strongly with enhancer function in a variety of cell types, implicating it as a principal regulator of HPV expression. Variations in the constituents of the AP1 complex that bind the HPV 31b enhancer were also observed in different cell types, suggesting that changes in the distribution of jun proteins may play a significant role in determining the tropism of HPV. These results indicate that AP1 may be a common regulator for various HPV types and that it contributes to enhancer specificity. In addition, a set of novel factors, which may be specific for each HPV type, act synergistically with AP1 for full activation of the enhancer.
人乳头瘤病毒（HPV）的转录受位于上游调控区的增强子序列调控。利用瞬时表达和蛋白质结合试验，对调控高危型生殖器HPV之一的HPV 31b表达的因子进行了研究。一个长度为262个碱基对的区域被确定为最小功能增强子，通过足迹分析观察到一系列五个受保护的结合位点。电泳迁移率变动分析表明，AP1、Oct-1以及三个新因子结合这些序列。突变分析表明，AP1与两个新因子之一协同激活HPV31b增强子。其中一个新因子结合了一个与NF1位点相似的序列，但与NF-1不同。第二个因子结合了与先前在HPV 18中鉴定的KRF-1结合位点相似的序列。竞争结合试验表明，该因子与KRF-1不同。进一步的研究表明，Oct-1作为HPV 31b表达的负调控因子，因为Oct-1结合序列的突变导致病毒表达增加。在HPV 31b增强子活性中观察到的重要因子没有一个仅在上皮细胞中发现，而是在多种细胞类型中检测到。在这些因子中，AP1结合在多种细胞类型中与增强子功能的相关性最强，表明它是HPV表达的主要调节因子。在不同细胞类型中也观察到结合HPV 31b增强子的AP1复合物成分的变化，这表明jun蛋白分布的变化可能在决定HPV的嗜性方面起重要作用。这些结果表明，AP1可能是各种HPV类型的共同调节因子，并且它有助于增强子特异性。此外，一组可能对每种HPV类型特异的新因子与AP1协同作用，以完全激活增强子。
