Screening of drugs to counteract human papillomavirus 16 E6 repression of E-cadherin expression

Abstract

Persistent infections with certain high-risk human papillomavirus (HPV) types such as 16 and 18 can result in the development of cervical cancer. Neither of the two prophylactic vaccines against HPV16 and 18 that are in current use have any therapeutic efficacy for prevalent HPV infections. Ablative therapy is widely used for the treatment of HPV cervical dysplasia however disease recurrence is a widely recognized problem. Thus there is a continuing need for therapeutic approaches for the treatment of HPV infections. The HPV16 E6 viral oncoprotein represses surface expression of the cellular adhesion molecule, E-cadherin. Reduced E-cadherin expression on HPV-infected keratinocytes is associated with lowered numbers of antigen-presenting Langerhans cells in the infected epidermis, potentially reducing immune surveillance for HPV. Four chemicals reported to up-regulate E-cadherin were screened for their ability to counteract E6 repression of surface E-cadherin. 5-Aza-2'-deoxycytidine (AzaDC), a DNA methyltransferase inhibitor, and Indole-3-carbinol (I3C), reported to increase E-cadherin through a p21(Waf1/Cip1)-dependent mechanism, had low cytotoxicity and increased or restored E-cadherin expression and adhesive function in HPV16 E6 expressing HCT116 cells. Doxorubicin, also known to induce p21(Waf1/Cip1), increased E-cadherin in E6 expressing cells but had some associated cytotoxicity. Tamoxifen, which can restore adhesive function of surface E-cadherin, was ineffective in counteracting E6 repression of E-cadherin. AzaDC and I3C both show potential to restore antigen-presenting cells to HPV infected skin by antagonizing E6 repression of E-cadherin, thereby counteracting an important immune evasion mechanism of HPV16 and reinstating immune function at the infected site.

Transcriptional Repression of E-Cadherin by Human Papillomavirus Type 16 E6

“…1B). We have previously shown that HPV16 E6 expression (transiently) in an immortalized keratinocyte cell line, HaCaT, reduces surface E-cadherin expression by around half [14] and that surface E-cadherin expression is similarly reduced in HCT116 cells stably expressing E6 [18]. HCT116 cells are widely used to study E-cadherin regulation [19]–[21] being intact in the major E-cadherin repressor pathways such as E-box-mediated repression [20] and having low levels of promoter methylation [22].…”

Modulation of antigen presenting cell functions during chronic HPV infection

“…However, human KCs transfected with HPV8 E7 protein exhibited decreased CCL20 expression by preventing binding of C/EBP to the CCL20 promoter [67] , suggesting a possible mechanism for HPV oncoprotein interference with KC-derived CCL20, which attracts LCs. Similarly, lower E-cadherin expression on HPV-infected KCs is correlated with cervical lesion severity [59] , [68] , [69] and reduced numbers of LCs in HPV-infected epidermis [60] , [70] . In vitro , inhibition of HPV16 E6 and E7 oncoproteins restored E-cadherin expression and LC adhesion to KCs [69] , [70] .…”

“…Similarly, lower E-cadherin expression on HPV-infected KCs is correlated with cervical lesion severity [59] , [68] , [69] and reduced numbers of LCs in HPV-infected epidermis [60] , [70] . In vitro , inhibition of HPV16 E6 and E7 oncoproteins restored E-cadherin expression and LC adhesion to KCs [69] , [70] . Together, these data imply that recruitment and localization of DCs to HPV-infected epithelia may hamper accessibility of HPV proteins to APCs and this may in part contribute to failure to generate effective anti-HPV CTL responses.…”

Papillomavirus E6 oncoproteins

“…High-risk E6s are capable of activating NF-κB (D’Costa et al, 2012; Havard et al, 2005; James et al, 2006b; Nees et al, 2001; Yuan et al, 2005). The mechanism is not entirely clear although there is evidence that it may interact with the PDZ binding motif (James et al, 2006b).…”