Induction of tumor suppressor p16INK4A by human papillomavirus 16 E7 oncoprotein

描述(申请人提供)：高危人乳头瘤病毒(HPV)感染与多种癌症有关，包括口咽癌、宫颈癌、外阴癌、阴道癌、肛门癌和阴道癌。超过99%的宫颈癌是年轻女性癌症死亡的最常见原因，与高危HPV感染有关。虽然有针对两种最常见的导致高危HPV的癌症的有效疫苗，但这些疫苗只能预防新的感染。出于这个原因，致力于HPV研究以开发有效的治疗方法对于治疗受影响的个人至关重要，这是本提案工作的最终目标。由于E7癌蛋白的表达，高危HPV16型感染导致肿瘤抑制基因p16INK4A的诱导。正常情况下，p16INK4A蛋白抑制细胞周期蛋白依赖性激酶(CDK)4/6，导致视网膜母细胞瘤肿瘤抑制因子pRb的低磷酸化形式积聚，从而导致细胞衰老；然而，HPV16阳性细胞继续增殖，因为HPVE7蛋白也通过结合和降解pRb来逆转衰老。这一建议试图通过确定由E7导致致癌应激和p16INK4A诱导的细胞通路来弥合知识上的差距。众所周知，E7的表达导致组蛋白3赖氨酸27(H3K27)去甲基酶KDM6B的诱导，该酶去除了包括p16INK4A在内的多梳抑制基因上的抑制三甲基化标记。移除单个抑制标记并不一定会使基因转录活跃，目前尚不清楚E7的表达是否会改变组蛋白标记的核心集，当多梳抑制基因被激活时，组蛋白标记的核心集需要改变。这项建议的第二个目标是使用p16INK4A启动子作为多梳抑制下的模型基因来阐明这些变化，因为p16INK4A是HPV相关癌症的生物标记物，是触发癌基因诱导衰老的重要肿瘤抑制因子。此外，我们的实验室已经证明，表达E7的细胞在表观上被重新编程，并对p16INK4A和KDM6B的表达“上瘾”，并且有望用KDM6B的小分子抑制剂进行的初步研究表明，表达E7的细胞的增殖/存活减少。因此，识别其他调节p16INK4A表达的表观遗传因素可能会为其他潜在的治疗方式提供深入的见解，这些治疗方式可以进行测试。由于其他几种癌症的p16INK4A水平也升高，这些结果可能适用于其他非HPV相关癌症的治疗。

DESCRIPTION (provided by applicant): High-risk human papillomavirus (HPV) infections are associated with a variety of carcinomas including oropharyngeal, cervical, vulvar, vaginal, anal, and penile cancers. Over 99% of cervical cancers, which are the most common cause of cancer death in young women, are associated with high-risk HPV infections. Although there are effective vaccines against the two most common cancer causing high-risk HPV types, the vaccines only protect against new infections. For this reason, efforts into HPV research to develop effective therapies are critical to treat effected individuals, which is the ultimate goal f the work in this proposal. High-risk HPV type 16 infection results in the induction of the tumor suppressor p16INK4A as a consequence of the expression of the E7 oncoprotein. Normally, the p16INK4A protein inhibits cyclin dependent kinases (CDK) 4/6 leading to an accumulation of the hypophosphorylated form of the retinoblastoma tumor suppressor pRB which results in cellular senescence; however, HPV16 positive cells continue to proliferate since the HPV E7 protein also subverts senescence through the binding and degradation of pRB. This proposal seeks to bridge the gap in knowledge by determining cellular pathways that are dysregulated by E7 leading to oncogenic stress and induction of p16INK4A. It is known that E7 expression results in the induction of the histone 3 lysine 27 (H3K27) demethylase KDM6B, which removes repressive trimethylation marks on polycomb repressed genes including p16INK4A. Removal of a single repressive mark does not necessarily render a gene transcriptionally active, and it is unknown if E7 expression changes the core set of histone marks that need to be altered when a polycomb repressed gene is activated. The second goal of this proposal is to elucidate these changes using the p16INK4A promoter as a model gene under polycomb repression because p16INK4A serves as a biomarker for HPV- associated cancers and is an important tumor suppressor that triggers oncogene-induced senescence. Moreover, our lab has demonstrated that E7 expressing cells are epigenetically reprogrammed and become "addicted" to expression of p16INK4A and KDM6B and promising preliminary investigations with a small molecule inhibitor of KDM6B demonstrate decreased proliferation/survival of E7 expressing cells. Therefore, identification of other epigenetic factors that regulate p16INK4A expression may provide insight into additional potential therapeutic modalities that can be tested. As several other cancers also have increased levels of p16INK4A, these results may be applicable to the treatment of other non-HPV associated cancers.