EIF4E is a critical regulator of human papillomavirus (HPV)-immortalized cervical epithelial (H8) cell growth induced by nicotine

Abstract

Tobacco smoke is known as a cofactor in the development of cervical precancer and cancer caused by human papillomavirus (HPV). The main component in cigarette smoke, nicotine, can be concentrated more strongly in cervical mucus than in blood and it has been implicated as a cocarcinogen that promotes a serial of cancers development through multiple prosurvival pathways. Although the mechanisms of nicotine-induced cell proliferation have been well studied in some epithelial cells, the molecular mechanism of its action in cervical epithelial cells is still unclear. The aims of this study were to investigate the detailed mechanism by which nicotine could induce cervical cancer growth. We found that nicotine simultaneously activates AKT/mTOR pathway in HPV-immortalized cervical epithelial (H8) cell line, followed by elevation of 4EBP1/eIF4E axis expression and its translational activity with dose-dependent and time-dependent manners. Besides, nicotine decreases eIF4E-4EBP1 binding activity in H8 cell line, which is associated with increased expression of phospho-4EBP1 at threonine 70. We therefore chose to evaluate whether this effect on eIF4E was involved in nicotine-induced proliferation. Remarkably, eIF4E knockdown by small interfering RNA diminishes its translation activity to the downstream targets including c-Myc, VEGF, CyclinD1 and Bcl-2. What is more, eIF4E knockdown inhibits cellular growth and colony formation after nicotine treatment. Note as well that eIF4E-specific siRNA could also suppress cell proliferation by decelerating the G0/G1-S transition of H8 cell treated with nicotine. Taken together, it can be concluded that nicotine promotes H8 cell proliferation by activating AKT/mTOR pathway, as well as 4EBP1/eIF4E axis and its translational activity. Furthermore, phosphorylation of 4EBP1 induced by nicotine has been shown to cause dissociation of 4EBP1/eIF4E and eIF4E may serve as a promising determinant of nicotine activity in vitro.