The role of human papillomavirus type 16 E6/E7 oncoproteins in cervical epithelial-mesenchymal transition and carcinogenesis

Abstract

Cervical cancer is the most common malignancy in females worldwide. This study investigated the prevalence of the E6/E7 oncoproteins of human papillomavirus (HPV) type 16, which are important in fibroblast growth factor (FGF) 2- and 4-induced epithelial-mesenchymal transition (EMT) and cervical tumorigenesis. We investigated the functional interaction between HPV16 E6/E7-transfected Cx cells (CxWJ cells) and treatment with FGF2 and 4, according to the expression of α-smooth muscle actin (α-SMA), vimentin and E-cadherin protein as well as cell growth and invasive ability. The results showed the upregulation of α-SMA and vimentin and the downregulation of E-cadherin protein expression in CxWJ cells. HPV16 E6/E7 infection partially repressed proliferation, but not the invasive ability of FGF2 or FGF4 stimulation in cervical cancer cells (CxWJ cells). These data provide evidence of a functional interaction between HPV16 E6/E7 and FGFs 2 and 4, suggesting that cooperative stimulation of HPV E6/E7 and FGFs activated in human cervical cancer cells is required to completely overcome the oncogenic function associated with the development of cervical epithelial-mesenchymal transition and tumorigenesis.

Figure 1

Microscope analysis and expression of EMT cell markers. (A) Morphology of cell lines (Epi, Cx and CxWJ) as observed by microscope. (B) EMT cell markers (E-cadherin, α-SMA and vimentin) were determined using western blotting. EMT, epithelial-mesenchymal transition; α-SMA, α-smooth muscle actin; Str, stroma; Epi, epithelial cells.

Figure 2

Proliferation effects of transfection with HPV16 E6/7 and FGF ligands in cervical cancer cells (Cx and CxWJ). (A) Number of cells, and (B) MTS assay were used to determine the proliferation of cervical cancer cells. Data were shown as the mean (±SEM) of at least three separate experiments. Statistical analysis was performed via a t-test, with significance set at ^*P<0.05 for the control group (0 ng/ml) and ^%,&P<0.05 for the Cx cell group. FGF, fibroblast growth factor; SF, serum-free.

Figure 3

Effects of FGF and HPV16 E6/7 transfection on the invasive ability of cervical cancer cells. (A and C) Cx cells and (B and D) CxWJ cells were evaluated for invasive ability following culturing with FGFs 2 and 4 for 48 h. Cells treated with serum-free (SF) medium were used as the control. Data were presented as the mean (±SEM) of at least three separate experiments. Statistical analysis was determined using the t-test, with significance set at ^&P<0.05 for the SF control group, ^#P<0.05 for the Cx cells group and ^%P<0.05 for the 10 ng/ml group. FGF, fibroblast growth factor.