APOBEC3在HPV-16感染抑制和病毒整合中的机制研究

Apolipoprotein B mRNA-editing catalytic polypeptide3 (APOBEC3) are a family of proteins, including A3A, B, C, DE, F, G and H. APOBEC3 proteins (A3s) are antiviral factors that counteract various viruses such as HIV and HBV by inducing cytidine (C)-to-uracil (U) mutation in viral DNA and inhibiting reverse transcription, but little is known in HPV. We have shown that A3G and A3A hypermutate HPV-16 circular DNA in W12 cells. W12 cells were established from HPV-16(+) CINI lesions, carrying circular HPV viral DNAs but not integration form in nuclei. However, the consequences of A3s caused hypermutation are not demonstrated yet. HPV persistent infection and virial-host integration have been proved to associate with tumorgenesis, especially in cervical cancer as well as head and neck cancer. In cervical cancer, more than 90% showed HPV infection. Although epidemiological investigation showed correlation between HPV infection and tumorgenesis, a number of question are still unclear, such as host immunity clearance HPV and the viral-host integration. A3s caused HPV viral DNA hypermutation may disrupt viral replication. Therefore, A3s may cause HPV suppression. In another hand, circular HPV viral DNA maybe linearized by A3s caused hypermutation and DNA repair system. Rather than circular viral DNA, linearized DNA is more suitable for viral-host integration. Moreover, recent studies have shown that A3s can induce genomic instability. Taken together, we speculate that A3s may play important role in HPV suppression and integration. Our preliminary results showed that A3s mutational signature was found in E2 region of HPV-16(+) clinical samples. In addition, A3s apparently disrupt HPV infectivity in HPV-16 pesudovirion system, while deaminase dead mutant A3s exhibit weaker activity. Using pesudovirion model, we also found physical interaction between A3s and L1 protein, which is capsid protein of HPV virion. To further explore our hypothesis, we will carry out a variety of experiment techniques, including gene transfection, 3DPCR, gene interference, DNA sequencing, HPV pesudovirion system as well as clinical specimen analysis. Our study not only will clarify the mechanism of A3s against HPV, but also further discuss the potential role of A3s in viral-host integration progression.

胞嘧啶脱氨酶APOBEC3家族（A3s）包括A3A、B、C、DE、F、G和H。近年来A3s突变并抑制病毒的作用机制已有报道，但在HPV中还有待探讨。在高危型HPV诱导相关肿瘤过程中，持续感染和病毒整合是重要原因。基于申请人在国际上首次报道A3G和A3A突变HPV-16环状DNA的结果，本项目旨在讨论A3s诱导的突变在病毒感染和整合中的后续作用。预实验表明：（1）在临床标本中，A3s特征性突变存在于HPV-16病毒基因组；（2）A3G和A3A可抑制HPV-16假病毒的感染；（3）过表达A3A上调γH2AX表达水平，暗示其影响基因组稳定性。本项目拟利用HPV假病毒、基因转染、沉默等方法，深入探讨A3G和A3A抑制HPV-16假病毒感染的机制，阐述A3G和A3A在病毒整合中的作用，分析A3s成员表达概况与病毒和宫颈癌瘤变分期的相关性。该项目将丰富A3s家族的抗病毒谱，为病毒整合提供新的理论方向。

背景：胞嘧啶脱氨酶APOBEC3家族(A3s)包括A3A、B、C、DE、F、G和H。近年来A3s突变并抑制病毒的作用机制已有报道,但在HPV中近年来报道较少。持续感染和病毒整合是高危型HPV诱导相关肿瘤过程中重要因素，但是否A3s参与HPV的持续感染和病毒整合未有明确报道。内容：基于申请人既往在国际上首次报道A3G和A3A突变HPV-16环状DNA的结果 ,本项目讨论了A3s诱导的突变在HPV病毒感染和整合中的后续作用。更重要的是发现和揭示A3s在致癌病毒HPV诱导相关肿瘤发生发展中起到的关键作用。重要结果和数据：研究结果显示：1）体外实验的HPV假病毒实验模型中，A3A过表达可以明显降低HPV假病毒的感染能力。A3A过表达明显抑制假病毒包裹的报告质粒的拷贝数。2）利用临床收集的HPV阳性的低级别瘤变（L-SIL）和高级别瘤变（H-SIL）的宫颈脱落细胞，发现H-SIL中的HPV突变要多于L-SIL样品。而相同标本中，TP53基因的突变却没有差别。3）在HPV阳性的口咽癌标本中，发现了HPV病毒基因存在大量的A3s相关的突变。A3s的表达量与在HPV阳性标本中明显高于HPV阴性的标本。还发现，A3s的表达量与HPV的整合状态呈正相关。4）利用TCGA数据库分析,发现口腔癌中FHIT的表达低于癌旁正常组织。更重要的是, 在高表达FHIT的标本中,A3A的表达是显著降低的。通过分析TCGA数据库中502个口腔癌外显子测序数据,我们发现,FHIT低表达,A3A高表达组中突变量显著高于A3A低表达组。进一步分析突变偏好性,发现T/GpC占65%左右,特别是TpC占40%。科学意义：首先A3s抑制假病毒的结果可以为抗HPV病毒感染的治疗提供一种新的思路和科学依据。另外，无论是宫颈L-SIL、H-SIL还是HPV阳性的口咽癌中的研究结果都进一步说明了A3s在HPV持续感染以及病毒整合中的关键作用和意义。最后，在口腔癌中结果标明，A3s可能是预测口腔癌预后及疾病发展的一个新的生物学标志物。