Estrogen contributes to non-pRb targeted HPV18 E7-caused cell proliferation and transformation

Almost all of cervical carcinoma arises as a result of persistent infection with high-risk human papillomaviruses (HPVS) where E7 oncogene plays an important role. In addition, estrogen is a confirmed cofactor in HPV related cervical carcinoma working synergistically with E7. There are two pathways involved in the E7 carcinogenesis of cervical cancer, the pRb-dependent and pRb-independent pathway. In this study we analyzed that whether estrogen contributes to high-risk HPV E7 in cervical carcinogenesis via pRb-independent pathway or not. E7^ΔRB, which can not bind to and degrade pRb protein, hence no transformation ability, worked synergistically with estrogen in cell proliferation and transformation. Estrogen combined with PTD-HPV18E7^ΔRB enhanced cell proliferation rate, induced genomic instability, including abnormal centrosome duplication and chromosomal instability, and exhibited malignant transformation with anchorage-independent growth. We also observed that, PTD-HPV18E7^ΔRB can interact with c-Jun and c-Myc proteins, but this interaction was limited to the estrogen-treated cells where c-Jun and c-Myc were expressed highly and no such interaction was observed in estrogen-untreated cells where c-Jun and c-Myc expression levels were low. In conclusion, estrogen can cooperate with E7 through a pRB-independent manner in cervical carcinogenesis. The functional interaction between E7 and c-Jun or between E7 and c-Myc could only be triggered when the c-Jun or c-Myc expression level reaches a certain threshold.