Bouvard V, Storey A, Pim D, Banks L
International Centre for Genetic Engineering and Biotechnology, Trieste, Italy.
EMBO J. 1994 Nov 15;13(22):5451-9. doi: 10.1002/j.1460-2075.1994.tb06880.x.
The major regulator of papillomavirus transcription is encoded by the viral E2 gene. The E2 gene has been well characterized in bovine papillomavirus (BPV) where it encodes at least three different polypeptides which differentially affect viral gene expression. In human papillomaviruses (HPVs) the E2 gene product is much less well characterized. In this study we have analysed the mechanism of action of the HPV-16, HPV-18 and BPV-1 E2 proteins in cervical keratinocytes. We show that the full length HPV E2 protein acts as a potent transcriptional activator of viral gene expression in both normal and immortalized keratinocytes. In contrast, the BPV-1 E2 protein produces transcriptional repression under identical conditions. A cDNA encoding the C-terminal half of the HPV-16 E2 protein in these assays weakly repressed viral gene expression. Further, co-transfection of this cDNA with the full length clone progressively abolishes the activation in trans by the full length HPV E2 protein. Gel retardation assays have defined a number of protein complexes between the long and short forms of E2 but with no evidence for preferential DNA binding. These results define two distinct activities for the HPV-16 E2 protein, indicate functional differences with the BPV E2 protein and suggest that splicing of the HPV E2 mRNA is a critical mechanism for controlling viral gene expression.
乳头瘤病毒转录的主要调节因子由病毒E2基因编码。E2基因在牛乳头瘤病毒（BPV）中已得到充分表征，它编码至少三种不同的多肽，这些多肽对病毒基因表达有不同影响。在人乳头瘤病毒（HPV）中，E2基因产物的特征则了解得少得多。在本研究中，我们分析了HPV-16、HPV-18和BPV-1 E2蛋白在宫颈角质形成细胞中的作用机制。我们发现，全长HPV E2蛋白在正常和永生化角质形成细胞中均作为病毒基因表达的强效转录激活因子。相比之下，BPV-1 E2蛋白在相同条件下产生转录抑制作用。在这些实验中，编码HPV-16 E2蛋白C端一半的cDNA对病毒基因表达有微弱的抑制作用。此外，将该cDNA与全长克隆共转染会逐渐消除全长HPV E2蛋白的反式激活作用。凝胶阻滞分析确定了E2长、短形式之间的多种蛋白复合物，但没有证据表明存在优先DNA结合。这些结果确定了HPV-16 E2蛋白的两种不同活性，表明其与BPV E2蛋白存在功能差异，并提示HPV E2 mRNA的剪接是控制病毒基因表达的关键机制。
