Epigenetic Control of HPV-associated Oral Carcinogenesis

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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.