Estrogen attenuates the growth of human papillomavirus positive epithelial cells

Abstract

12Human papillomaviruses (HPVs) are small, double-stranded DNA viruses that are 13 significant risk factors in the development of cancer, and HPV accounts for 14 approximately 5% of all worldwide cancers. Recent studies using data from The Cancer 15 Genome Atlas (TCGA) have demonstrated that elevated levels of estrogen receptor 16 alpha (ERα) are associated with improved survival in oropharyngeal cancers, and these 17 elevated receptor levels were linked with human papillomavirus positive cancers 18 (HPV+cancers). There has been a dramatic increase in HPV-related head and neck 19 squamous cell carcinomas (HPV+HNSCCs) over the last two decades and therapeutic 20 options for this ongoing health crisis are a priority; currently there are no anti-viral 21 therapeutics available for combating HPV+cancers. During our own TGCA studies on 22 head and neck cancer we had also discovered the overexpression of ERα in 23 HPV+cancers. Here we demonstrate that 17β-estradiol (estrogen) attenuates the 24 growth/cell viability of HPV+cancers in vitro, but not HPV negative cancer cells. In 25 addition, N/Tert-1 cells (foreskin keratinocytes immortalized with hTERT) containing 26 HPV16 have elevated levels of ERα and growth sensitivity following estrogen treatment 27 when compared with parental N/Tert-1. Finally, we demonstrate that there are 28 potentially two mechanisms contributing to the attenuation of HPV+ cell growth following 29 estrogen treatment. First, estrogen represses the viral transcriptional long control region 30 (LCR) downregulating early gene expression, including E6/E7. Second, expression of 31 E6 and E7 by themselves sensitizes cells to estrogen. Overall our results support the 32 recent proposal that estrogen could be exploited therapeutically for the treatment of 33 HPV positive oral cancers.34 3 Importance 35Human papillomaviruses cause around 5% of all human cancers, yet there are no 36 specific anti-viral therapeutic approaches available for combating these cancers. These 37 cancers are currently treated with standard chemo-radiation therapy (CRT). Specific 38 anti-viral reagents are desperately required, particularly for HPV+HNSCC whose 39 incidence is increasing and for which there are no diagnostic tools available for 40 combating this disease. Using data from The Cancer Genome Atlas (TCGA) ourselves 41 and others determined that the estrogen receptor α (ERα) is overexpressed in 42 HPV+HNSCC, and that elevated levels are associated with an improved disease 43 outcome. This has led to the proposal that estrogen treatment could be a novel 44 therapeutic approach for combating HPV+cancers. Here we demonstrate that estrogen 45 attenuates the growth of HPV+epithelial cells using multiple mechanisms, supporting 46 the idea that estrogen has potential as a therapeutic agent for the treatment of 47 65 correlates with increased survival in HPV+HNSCC(20, 21). These reports suggest ERα 66 as a diagnostic marker but also raise the possibility of using estrogen as a therapeutic 67 for the treatment of HPV+HNSCC. In...