Abstract
Epigallocatechin-3-gallate (EGCG), the primary bioactive polyphenol in green tea, has been shown to inhibit the growth of human papilloma virus (HPV)-transformed keratinocytes. Here, we set out to examine the consequences of EGCG treatment on the growth of HPV18-immortalised foreskin keratinocytes (HFK-HPV18) and an authentic HPV18-positive vulvar intraepithelial neoplasia (VIN) clone, focusing on its ability to influence cell proliferation and differentiation and to impact on viral oncogene expression and virus replication. EGCG treatment was associated with degradation of the E6 and E7 oncoproteins and an upregulation of their associated tumour suppressor genes; consequently, keratinocyte proliferation was inhibited in both monolayer and organotypic raft culture. While EGCG exerted a profound effect on cell proliferation, it had little impact on keratinocyte differentiation. Expression of the late viral protein E4 was suppressed in the presence of EGCG, suggesting that EGCG was able to block productive viral replication in differentiating keratinocytes. Although EGCG did not alter the levels of E6 and E7 mRNA, it enhanced the turnover of the E6 and E7 proteins. The addition of MG132, a proteasome inhibitor, to EGCG-treated keratinocytes led to the accumulation of the E6/E7 proteins, showing that EGCG acts as an anti-viral, targeting the E6 and E7 proteins for proteasome-mediated degradation.
Highlights
Persistent infection with high-risk human papilloma virus (HR-HPV) strains is causally linked to the development of usual type vulvar intraepithelial neoplasia [1]
Using primary human foreskin keratinocytes stably infected with episomal forms of HPV18 and an authentic HPV18-positive cell line isolated from a primary vulvar intraepithelial neoplasia (VIN), we examined the effects of EGCG treatment on keratinocyte proliferation and differentiation in both monolayer and organotypic raft culture, focusing on the expression of the key viral oncoproteins E6 and E7
The cell models employed in this study included human foreskin keratinocytes (HFK)HPV18, an immortalised foreskin keratinocyte cell line containing episomal forms of both cell lines contained integrated forms of HPV16 precluding an assessment of the effects of EGCG on the HPV life cycle
Summary
Persistent infection with high-risk human papilloma virus (HR-HPV) strains is causally linked to the development of usual type vulvar intraepithelial neoplasia (uVIN) [1]. Novel alternatives to surgery have been investigated, for example, the use of the topical anti-viral Cidoforvir or the immune modular Imiquimod, but both have yielded variable results [8,9,10]. Towards this end, we have recently completed a Phase II randomised control trial (EPIVIN) evaluating the use of a novel topical therapeutic agent, Sinecathecin, in the treatment of women with uVIN and found that the treatment is safe and shows promise in inducing clinical resolution of uVIN and symptom improvement [11]
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