Epigenetic Control of HPV-associated Oral Carcinogenesis

描述(由申请人提供)：本申请的长期目标是了解表观遗传机制如何控制高风险的人类乳头瘤病毒(HPV)相关的口腔癌发生。鳞状细胞癌(SCC)是口腔、口咽、头颈部最常见的恶性肿瘤。HPV16是一种嗜性于鳞状上皮的小DNA病毒，高危HPV16与口腔和口咽鳞状细胞癌(OSCC)的发生发展有关。更重要的是，HPV阳性口腔鳞癌的发病率在过去十年中在美国有所增加。高危HPV16表达两种主要的癌蛋白E6和E7。E6和E7(E6/E7)的结合使人类口腔角质形成细胞永生化，并促进肿瘤的发生。虽然在了解E6/E7介导的口腔鳞状细胞癌发生的分子调控方面取得了重大进展，但对于HPV感染和口腔角质形成细胞染色质动力学在口腔鳞癌发生发展中的相互作用知之甚少。组蛋白甲基化是一个重要的过程，与基因表达的激活和抑制有关，因此在细胞生长控制和肿瘤发生中起着关键作用。为了探索HPV相关口腔鳞癌的表观遗传学调控，我们系统地研究了组蛋白去甲基酶在表达E6/E7的口腔鳞癌细胞中的表达。有趣的是，我们发现E6/E7能有效抑制口腔鳞癌细胞中KDM5C(也称为SMCX)的表达。KDM5C是一种组蛋白去甲基酶，它能去除赖氨酸4(H3K4me3)上的三甲基化组蛋白H3。H3K4me3是一个激活标志，抑制KDM5C可以增加H3K4me3的水平，导致基因激活。作为基因表达谱的补充方法，我们的siRNA筛选已经确定组蛋白去甲基酶KDM4A通过移除H3K9me3在AP-1的表观遗传激活中发挥重要作用。以前，我们已经发现AP-1在口腔鳞癌的侵袭性生长中起着关键作用，而口腔鳞癌是原位癌向口腔鳞癌发展所必需的。AP-1除了控制E6/E7转录外，还在HPV介导的肿瘤发生中发挥重要作用。基于我们令人兴奋的初步研究，在这一新的应用中，我们的新假设是KDM5C和KDM4A通过修改H3K4me3和H3K9me3标记来表观遗传控制HPV阳性口腔鳞癌的发生和发展。为了检验我们的假设，本文提出了三个具体目标。目的1是确定高危HPV16E6/E7癌蛋白是否通过抑制KDM5C而对口腔鳞状细胞癌进行表观遗传学重新编程并促进口腔鳞癌的进展。目的2确定KDM4A是否通过AP-1在表观遗传学上促进E6/E7的表达。目的3确定E6/E7是否通过KDM4A激活AP-1，促进口腔鳞癌的发生发展。由于组蛋白去甲基酶是可以化学修饰的，KDM5C和KDM4A可能是专门控制HPV相关口腔鳞癌的新的治疗靶点。

DESCRIPTION (provided by applicant): The long-term objectives of this application are to understand how epigenetic mechanisms control the high-risk human papillomaviruses (HPV)-associated oral carcinogenesis. Squamous cell carcinoma (SCC) is the most common cancer arising in the oral cavity, oropharynx, head and neck. The high-risk HPV16, a small DNA virus having tropism for squamous epithelia, has been found to be associated with the development and progression of oral and oropharyngeal SCC (OSCC). More importantly, the incidence of HPV-positive OSCC has increased in the USA in the last decade. The high-risk HPV16 expresses two major oncoproteins, E6 and E7. The combination of E6 and E7 (E6/E7) potently immortalizes human oral keratinocytes and promotes oncogenesis. While significant progress has been made in understanding the molecular control of E6/E7-mediated OSCC development, little is known about the interplay between HPV infection and oral keratinocyte chromatin dynamics in OSCC development and progression. Histone methylation is an important process linked to the activation and repression of gene expression, thus playing a critical role in cell growth control and oncogenesis. To explore the epigenetic regulation of HPV-associated OSCC, we systemically profiled the expression of histone demethylases in E6/E7-expressing OSCC cells. Interestingly, we found that E6/E7 potently suppressed KDM5C (also known as SMCX) expression in OSCC cells. KDM5C is a histone demethylase which removes trimethylated histone H3 at lysine 4 (H3K4me3). H3K4me3 is an activation marker, and the inhibition of KDM5C can increase the levels of H3K4me3, leading to gene activation. As a complementary approach to gene expression profiling, our siRNA screening has identified that the histone demethylase KDM4A plays an important role in the epigenetic activation of AP-1 by removing H3K9me3. Previously, we have found that AP-1 plays a critical role in the invasive growth of OSCC which is required for the progression of carcinoma in situ to OSCC. In addition to control of E6/E7 transcription, AP-1 plays an essential role in HPV-mediated oncogenesis. Based on our exciting preliminary studies, in this new application, our novel hypothesis is that KDM5C and KDM4A epigenetically control development and progression of HPV-positive OSCC by modifying H3K4me3 and H3K9me3 marks. Three specific aims are proposed to test our hypothesis. Aim 1 is to determine whether the high-risk HPV16 E6/E7 oncoproteins epigenetically reprogram OSCCs and promote OSCC progression by inhibiting KDM5C. Aim 2 is to determine whether KDM4A epigenetically promotes E6/E7 expression through AP-1. Aim 3 is to determine whether E6/E7 activate AP-1 and promote OSCC development through KDM4A. Since histone demethylases are chemically modifiable, KDM5C and KDM4A might represent novel therapeutic targets for specifically controlling HPV-associated OSCC.