The role of DDX3 in human papillomavirus-infected lung tumorigenesis

Our genome-wide analysis showed that a putative gene DDX3 located at Xp11.4 had higher prevalent with loss of heterozygosity (LOH) in HPV-infected lung tumors than in HPV-uninfected lung tumors. Real-time PCR data showed that DDX3 mRNA expression levels in HPV-infected lung tumors was markedly lower than in HPV-uninfected lung tumors. These results suggest that DDX3 alteration could play an important role in HPV-infected lung tumorigenesis. Our recent study further indicated that p21 transcription was synergistically suppressed by E6-DDX3 pathway to promote lung cancer cell growth and patients with lower DDX3 expression had shorter relapse free survival (RFS) than those with higher DDX3 expression. This result reflects the possibility that DDX3 could promote lung tumor local recurrence and distant metastasis after surgical resection to lead patients with a worse prognosis. In this three-year project, we will conduct the following specific aims to explore the role of DDX3 in HPV-infected lung progression and metastasis: Aim 1. To explore whether DDX3 reduction by E6 could promote tumor metastasis via DDX3-MDM2-Slug pathway. We hypothesized that deregulation of DDX3 by E6 may reduce E-cadherin expression via the p53-MDM2-Slug pathway, which is known to be involved in the deregulation of E-cadherin. Cell in vitro and tumor in vivo experiments will be conducted to verify the hypothesis. Aim 2. To explore whether INFβ transcription suppressed by DDX3 reduction could enhance HPV viral load via reduction of virus clearance. DDX3 has been shown to be essential for IRF3-dependent transcription and contribute to IFNβ induction. We hypothesize that DDX3 reduction may decrease INFβ expression to promote tumor aggressiveness via the genome instability by HPV persistent infection. HPV infection efficacy and its viral load will be examined in a co-cultured cell models to test whether INFβ could be responsible for HPV infection and whether the oncogenic potential of the cells with HPV persistent infection will be examined by cell in vitro and animal in vivo, and Aim 3. To explore whether DDX3 restored by p53 stabilizing small molecules could reduce tumor aggressiveness and whether DDX3 reduction could promote the resistance to cisplatin via increased antiapototic gene expression. p53 has been shown to directly upregulate DDX3 expression. We will expect that p53 stabilized by nutlin or proteasomal inhibitors (Bortezomib) may restore DDX3 expression and subsequently to reduce tumor aggressive and resistance to cisplatin. The hypothesis will be examined in cell and animal models. Additionally, microarray analysis will be conducted to indentify which gene could be responsible for cisplatin resistance in E6-reduced DDX3 lung cancer cells, and which signaling pathway may be involved in the candidate gene regulation. The inhibitor of the signaling pathway will be combined with cisplatin to reduce the resistance to cisplatin in lung cancer cells with DDX3 reduction. Collectively, these results obtained from this proposal will be helpful to understand the underlying molecular mechanisms of DDX3 on tumor aggressiveness, HPV persistent infection, and cisplatin resistance in HPV-infected lung tumorigenesis, and expect to address a reliable strategy to improve patients’ outcome and life quality.