HPV-16/18 E6-Induced APOBEC3B Upregulation Promotes Proliferation of Cervical Cancer Cells by Epigenetically Regulating Cyclin D1

Oncogenic high-risk human papillomavirus (HR-HPV) infection causes a majority of cases of cervical cancer and pre-cancerous cervical lesions. However, the mechanisms underlying the direct evolution from HPV-16/18-infected epithelium to cervical intraepithelial neoplasia (CIN) III, which can progress to cervical cancer, remain poorly identified. Here, we performed RNA-seq after laser capture microdissection, and found that APOBEC3B was upregulated in cervical cancer specimens compared with CIN III after HPV-16/18 infection. Furthermore, immunohistochemical analysis confirmed that high levels of APOBEC3B were correlated with lymph node metastasis in cervical cancer. Subsequent experiments revealed that HPV-16 E6 could upregulate APOBEC3B through direct binding to the promoter of APOBEC3B in cervical cancer cells. Silencing of APOBEC3B by stable shRNA-mediated knockdown reduced the proliferative capacity of Caski and HeLa cells in vitro and in vivo, but had only a small effect on the migration and invasion of two cervical cancer cell lines. Finally, we identified the changes in gene expression following APOBEC3B silencing in Caski cells by microarray, demonstrating a biological link between APOBEC3B and CCND1 in cervical cancer cells. Importantly, through methyl-capture sequencing (MS) and pyrosequencing, APOBEC3B was found to affect the levels of the downstream protein Cyclin D1 (which is encoded by the CCND1 gene) through hypomethylation of the CCND1 promoter. In conclusion, our study supports a novel function of HPV-16 E6-induced APOBEC3B upregulation, in promoting proliferation of cervical cancer cells by epigenetically regulating Cyclin D1. Thus, APOBEC3B may be a potential therapeutic target in human cervical cancer.