Department of Microbiology-Immunology, Northwestern University, Feinberg School of Medicine, Chicago, IL 60611, USA.
Department of Gynecologic Oncology, Women's Hospital, Zhejiang University School of Medicine, Hangzhou, Zhejiang, 310006, China.
Oncogene. 2019 Apr;38(17):3274-3287. doi: 10.1038/s41388-018-0633-1. Epub 2019 Jan 10.
High-risk human papillomaviruses (HPVs) constitutively activate ataxia telangiectasia mutated (ATM) and ataxia telangiectasia- and Rad3-related (ATR) DNA damage repair pathways for viral genome amplification. HPVs activate these pathways through the immune regulator STAT-5. For the ATR pathway, STAT-5 increases expression of the topoisomerase IIβ-binding protein 1 (TopBP1), a scaffold protein that binds ATR and recruits it to sites of DNA damage. TopBP1 also acts as a transcriptional regulator, and we investigated how this activity influenced the HPV life cycle. We determined that TopBP1 levels are increased in cervical intraepithelial neoplasias as well as cervical carcinomas, consistent with studies in HPV-positive cell lines. Suppression of TopBP1 by shRNAs impairs HPV genome amplification and activation of the ATR pathway but does not affect the total levels of ATR and CHK1. In contrast, knockdown reduces the expression of other DNA damage factors such as RAD51 and Mre11 but not BRCA2 or NBS1. Interestingly, TopBP1 positively regulates the expression of E2F1, a TopBP1-binding partner, and p73 in HPV-positive cells in contrast to its effects in other cell types. TopBP1 transcriptional activity is regulated by AKT, and treatment with AKT inhibitors suppresses expression of E2F1 and p73 without interfering with ATR signaling. Importantly, the levels of p73 are elevated in HPV-positive cells and its knockdown impairs HPV genome amplification. This demonstrates that p73, like p63 and p53, is an important regulator of the HPV life cycle that is controlled by the transcriptional activating properties of the multifunctional TopBP1 protein.
高危型人乳头瘤病毒 (HPV) 持续激活共济失调毛细血管扩张突变 (ATM) 和共济失调毛细血管扩张症和 Rad3 相关 (ATR) DNA 损伤修复途径，以进行病毒基因组扩增。HPV 通过免疫调节剂 STAT-5 激活这些途径。对于 ATR 途径，STAT-5 增加了拓扑异构酶 IIβ 结合蛋白 1 (TopBP1) 的表达，TopBP1 是一种支架蛋白，可与 ATR 结合并将其募集到 DNA 损伤部位。TopBP1 还作为转录调节剂发挥作用，我们研究了这种活性如何影响 HPV 生命周期。我们发现 TopBP1 水平在宫颈上皮内瘤变以及宫颈癌中增加，与 HPV 阳性细胞系中的研究一致。通过 shRNA 抑制 TopBP1 会损害 HPV 基因组扩增和 ATR 途径的激活，但不影响 ATR 和 CHK1 的总水平。相比之下，敲低会降低其他 DNA 损伤因子的表达，如 RAD51 和 Mre11，但不影响 BRCA2 或 NBS1。有趣的是，与其他细胞类型相比，TopBP1 在 HPV 阳性细胞中正向调节 E2F1（TopBP1 结合伙伴）和 p73 的表达。TopBP1 的转录活性受 AKT 调节，AKT 抑制剂的处理抑制 E2F1 和 p73 的表达，而不干扰 ATR 信号。重要的是，p73 在 HPV 阳性细胞中的水平升高，其敲低会损害 HPV 基因组扩增。这表明 p73 与 p63 和 p53 一样，是 HPV 生命周期的重要调节剂，受多功能 TopBP1 蛋白的转录激活特性控制。
