Activities of E6 Protein of Human Papillomavirus 16 Asian Variant on miR-21 Up-regulation and Expression of Human Immune Response Genes

Abstract

<b>Background:</b> Variants of human papillomavirus (HPV) show more oncogenicity than do prototypes. TheHPV16 Asian variant (HPV16As) plays a major role in cervical cancer of Asian populations. Some amino acidchanges in the E6 protein of HPV16 variants affect E6 functions such as p53 interaction and host immunesurveillance. This study aimed to investigate activities of HPV16As E6 protein on modulation of expressionof miRNA-21 as well as interferon regulatory factors (IRFs) 1, 3, 7 and c-fos. Materials and <br/><b>Methods</b>: Vectorsexpressing E6 protein of HPV16As (E6D25E) or HPV16 prototype (E6Pro) were constructed and transfected intoC33A cells. HCK1T cells expressing E6D25E or E6Pro were established by transducing retrovirus-containingE6D25E or 16E6Pro. The E6AP-binding activity of E6 and proliferation of the transfected C33A cells weredetermined. MiR-21 and mRNA of interesting genes were detected in the transfected C33A cells and/or theHCK1T cells, with or without treatment by culture medium from HeLa cells (HeLa-CM). <br/><b>Results</b>: E6D25Eshowed binding activity with E6AP similar to that of E6Pro. Interestingly, E6D25E showed a higher activity ofmiR-21 induction than did E6Pro in C33A cells expressing E6 protein. This result was similar to the HCK1Tcells expressing E6 protein, with HeLa-CM treatment. The miR-21 up-regulation significantly corresponded toits target expression. Different levels of expression of IRFs were also observed in the HCK1T cells expressing E6protein. Interestingly, when treated with HeLa-CM, IRFs 1, 3 and 7 as well as c-fos were significantly suppressedin the HCK1T cells expressing E6D25E, whereas those in the HCK1T cells expressing E6Pro were induced. Asimilar situation was seen for IFN-α and IFN-β. <br/><b>Conclusions</b>: E6D25E of the HPV16As variant differed fromthe E6 prototype in its activities on epigenetic modulation and immune surveillance and this might be a keyfactor for the important role of this variant in cervical cancer progression.