The majority of human papillomavirus (HPV) types cause cutaneous and mucosal disease. Persistent infection with high-risk HPV types is the primary risk factor for the development of cervical cancer. The ability of the virus to persist is contributed to by numerous immune evasion mechanisms. We previously demonstrated that the HPV type 16 (HPV16) E6 protein, down-regulates epithelial (E)-cadherin expression and that the associated Langerhans cells (LC) depletion may contribute to impaired immune recognition by the host.
The aims of this study were firstly to establish if E6 down-regulation of E-cadherin is conserved amongst all HPV types, secondly to determine if the reduced E-cadherin expression correlates with reduced LC density in HPV-infected tissues, thirdly, to identify a region of E6 responsible in E-cadherin regulation and fourthly to establish if down-regulation of cell surface E-cadherin also occurs in another DNA tumour virus, adenovirus (Ad).
E6 protein from a range of HPV types representing the α, β and γ genera was expressed in HCT116 cells and the effect on cell surface E-cadherin expression was measured by flow cytometry. In addition, a series of tissues infected with HPV types representative of HPV of α, β, [nu] and γ genera were stained to confirm E-cadherin regulation in vivo and to determine the functional significance of E-cadherin expression in relation to LC localisation. In order to identify the region of the E6 protein that was important for E-cadherin regulation, a series of HPV16 E6 mutants were tested for their ability to regulate E-cadherin. Finally, the effects of Ad on cell surface E-cadherin were examined by measuring E-cadherin expression in Ad infected HCT116 cells.
E6 down-regulation of E-cadherin was conserved in α, [nu] and γ genera but was lost in β-HPV types, correlating with the ability of the virus to persist. In vivo analysis of patient tissues confirmed this pattern of E-cadherin regulation by E6 types and showed a direct association between loss of E-cadherin and LC depletion, suggesting that E-cadherin regulation by E6 is the cause of depletion of LC in infected tissue. Mutational analysis of HPV16 E6 led to the identification of a putative E-cadherin regulatory region with a conserved motif, H/L/V-[phi]-X-X-X-X-R. A potential mechanism used by E6 to regulate cell surface E-cadherin involved down-regulation of p21[waf1/cip1] (p21) via a p53-independent pathway. Finally, study of Ad showed a similar ability of the virus to regulate E-cadherin, indicating conservation in another DNA tumour virus.
This research shows that E-cadherin regulation by E6 is directly associated with LC depletion and viral persistence. The data presented here suggest that LC depletion by HPV is widely conserved in HPV types that cause persistent disease. E-cadherin regulation contributes to this effect through a specific regulatory region of the protein and manipulation of levels of cellular p21. These data may provide a foundation for the development of therapeutics for HPV that aim to overcome immune evasion by the virus.
| Identifer | oai:union.ndltd.org:ADTP/217725 |
| Date | January 2007 |
| Creators | Leong, Cheng-Mee, n/a |
| Publisher | University of Otago. Department of Microbiology & Immunology |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | http://policy01.otago.ac.nz/policies/FMPro?-db=policies.fm&-format=viewpolicy.html&-lay=viewpolicy&-sortfield=Title&Type=Academic&-recid=33025&-find), Copyright Cheng-Mee Leong |
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