Approximately 15% of human cancers are attributed to viruses. Numerous studies have shown that high-risk human polyomaviruses (HR-HPV) and Merkel cell polyomavirus (MCPyV) are two human tumor viruses associated with anogenetal and oropharyngeal cancers, and with Merkel cell carcinoma, respectively. MCPyV has been found in HR-HPV positive anogenetal and oropharyngeal tumors, suggesting that MCPyV can act as a co-factor in HR-HPV induced oncogenesis. This prompted us to investigate whether the oncoproteins large T-antigen (LT) and small antigen (sT) of MCPyV could affect the transcriptional activity HPV16 and HPV18 and vice versa whether HPV16 and HPV18 E6 and E7 oncoproteins affected the expression of MCPyV LT and sT. Reciprocal stimulation of these viral oncoproteinscould enhance the oncogenic processes triggered by these tumor viruses. Transient co-transfection studies using a luciferase reporter plasmid with the long control region of HPV16 or HPV18, or the early or late promoter of MCPyV and expression plasmids for LT and sT, or E6 and E7, respectively were performed in the HPV-negative cervical cancer cell line C33A, in the keratinocyte cell line HaCaT, and in the oral squamous cell carcinoma cell line HSC-3. Transfections were also performed with deletion mutants of all these promoters and with mutants of all four oncoproteins. Finally, the effect of E6 and E7 on LT and sT expression in the MCPyV-positive Merkel cell carcinoma cell line WaGa and the effect of LT and sT on the expression of E6 and E7 was monitored by Western blotting. LT and sT stimulated the transcriptional activity of the HPV16 and HPV18 LCR and v.v. E6 and E7 potentiated the MCPyV early and late promoter in all cell lines. Induction by E6 and E7 was p53- and pRb-independent, and transactivation by LT did not require DNA binding, nuclear localization and HSC70/pRb interaction, whereas sT stimulated the HPV16/18 LCR activity in a PP2A- and DnaJ-independent manner. These results indicate that the co-infection of MCPyV may act as a co-factor in the initiation and/or progression of HPV-induced cancers.

中文翻译：

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默克尔细胞多瘤病毒和高危人乳头瘤病毒启动子活性的相互反式激活及其癌蛋白的表达增加

大约 15% 的人类癌症是由病毒引起的。大量研究表明，高危人类多瘤病毒 (HR-HPV) 和默克尔细胞多瘤病毒 (MCPyV) 是两种分别与肛门生殖癌和口咽癌以及默克尔细胞癌相关的人类肿瘤病毒。已在 HR-HPV 阳性肛门生殖器和口咽肿瘤中发现 MCPyV，这表明 MCPyV 可以作为 HR-HPV 诱导的肿瘤发生的辅助因子。这促使我们研究 MCPyV 的癌蛋白大 T 抗原 (LT) 和小抗原 (sT) 是否会影响 HPV16 和 HPV18 的转录活性，反之亦然，HPV16 和 HPV18 E6 和 E7 癌蛋白是否会影响 MCPyV LT 和 sT 的表达. 这些病毒癌蛋白的相互刺激可以增强由这些肿瘤病毒引发的致癌过程。瞬时共转染研究使用荧光素酶报告质粒与 HPV16 或 HPV18 的长控制区，或 MCPyV 的早期或晚期启动子以及 LT 和 sT，或 E6 和 E7 的表达质粒，分别在 HPV 阴性宫颈癌中进行癌细胞系 C33A、角质形成细胞系 HaCaT 和口腔鳞状细胞癌细胞系 HSC-3。还用所有这些启动子的缺失突变体和所有四种癌蛋白的突变体进行转染。最后，通过Western印迹监测E6和E7对MCPyV阳性Merkel细胞癌细胞系WaGa中LT和sT表达的影响以及LT和sT对E6和E7表达的影响。LT 和 sT 刺激 HPV16 和 HPV18 LCR 和 vv 的转录活性 E6 和 E7 在所有细胞系中增强了 MCPyV 早期和晚期启动子。E6 和 E7 的诱导不依赖于 p53 和 pRb，LT 的反式激活不需要 DNA 结合、核定位和 HSC70/pRb 相互作用，而 sT 以不依赖 PP2A 和 DnaJ 的方式刺激 HPV16/18 LCR 活性。这些结果表明，MCPyV 的共感染可能是 HPV 诱导的癌症发生和/或进展的辅助因素。