RESUMO
High-risk human papillomaviruses (HR-HPVs) are the causative agents of cervical cancer, and they are also associated with a subset of head and neck squamous cell carcinomas. In addition, HPVs have also been postulated in the development of non-melanoma skin cancers (NMSC). In these cancers, the oncogene E6 is best known for its ability to inactivate the tumor suppressor p53 protein. Interestingly, in transgenic mice for HPV16 E6 (K14E6), it was reported that E6 alone induced epithelial hyperplasia and delay in differentiation in skin epidermis independently of p53 inactivation. Transforming growth factor ß (TGFß) is an important regulator of cell growth/differentiation and apoptosis, and this pathway is often lost during tumorigenesis. Ultraviolet radiation B (UVB) exposure activates diverse cellular responses, including DNA damage and apoptosis. In this study, we investigated whether the E6 oncogene alone or in combination with UVB dysregulate some components of the TGFß pathway in the epidermis of K14E6 mice. We used 8-day-old K14E6 and non-transgenic mice irradiated and unirradiated with a single dose of UVB. We found that the E6 oncogene and UVB irradiation impair the TGFß pathway in epidermis of K14E6 mice by downregulation of the TGFß type II receptor (TßRII). This loss of TßRII prevents downstream activation of Smad2 and target genes as p15, an important regulator of cell cycle progression. In summary, the TGFß signalling in cells of the epidermis is downregulated in our mouse model by both the E6 oncoprotein and the UVB irradiation.
Assuntos
Epiderme/efeitos da radiação , Proteínas Oncogênicas Virais/genética , Proteínas Repressoras/genética , Transdução de Sinais/genética , Transdução de Sinais/efeitos da radiação , Fator de Crescimento Transformador beta/genética , Fator de Crescimento Transformador beta/efeitos da radiação , Raios Ultravioleta , Animais , Apoptose/efeitos da radiação , Dano ao DNA/efeitos da radiação , Modelos Animais de Doenças , Relação Dose-Resposta à Radiação , Regulação para Baixo/genética , Regulação para Baixo/efeitos da radiação , Epiderme/metabolismo , Epiderme/patologia , Camundongos , Camundongos Transgênicos , Proteínas Oncogênicas Virais/metabolismo , Fosforilação , Proteínas Repressoras/metabolismo , Proteína Smad2 , Fator de Crescimento Transformador beta/metabolismo , Proteína Supressora de Tumor p53/genética , Proteína Supressora de Tumor p53/metabolismo , Proteína Supressora de Tumor p53/efeitos da radiaçãoRESUMO
We have studied the expression of the tight junction proteins (TJ) occludin, claudin-1 and ZO-2 in the epidermis of female mice. We observed a peak of expression of these proteins at postnatal day 7 and a decrease in 6 week-old mice to values similar to those found in newborn animals. We explored if the expression of the E6 oncoprotein from high-risk human papilloma virus type 16 (HPV16) in the skin of transgenic female mice (K14E6), altered TJ protein expression in a manner sensitive to ovarian hormones. We observed that in ovariectomized mice E6 up-regulates the expression of occludin and ZO-2 in the epidermis and that this effect was canceled by 17ß-estradiol. Progesterone instead induced occludin and ZO-2 over-expression. However, the decreased expression of occludin and ZO-2 induced by 17ß-estradiol in the epidermis was not overturned by E6 or progesterone. In addition, we employed MDCK cells transfected with E6, and observed that ZO-2 delocalizes from TJs and accumulates in the cell nuclei due to a decrease in the turnover rate of the protein. These results reinforce the view of 17ß-estradiol and E6 as risk factors for the development of cancer through effects on expression and mislocalization of TJ proteins.