@article{mbs:/content/journal/jgv/10.1099/0022-1317-78-2-401, author = "Kyo, Satoru and Klumpp, David J. and Inoue, Masaki and Kanaya, Taro and Laimins, Laimonis A.", title = "Expression of AP1 during cellular differentiation determines human papillomavirus E6/E7 expression in stratified epithelial cells", journal= "Journal of General Virology", year = "1997", volume = "78", number = "2", pages = "401-411", doi = "https://doi.org/10.1099/0022-1317-78-2-401", url = "https://www.microbiologyresearch.org/content/journal/jgv/10.1099/0022-1317-78-2-401", publisher = "Microbiology Society", issn = "1465-2099", type = "Journal Article", abstract = "E6 and E7 oncoproteins of human papillomavirus (HPV) play significant roles in the pathogenesis of cervical cancer. However, the pattern of E6/E7 expression during the productive virus life cycle in differentiating epithelia of the uterine cervix remains unclear. In addition, little is known about the cellular factors regulating E6/E7 expression in differentiating epithelia. In the present study, using transient expression assays and DNA binding assays, we demonstrated that E6/E7 transcription is critically regulated by the cellular factor API, a Jun/Fos heterodimer complex. Immunohistochemical analyses of various uterine cervical lesions showed API expression in lower cell layers of normal cervix and low-grade cervical intraepithelial neoplasia (CIN), while it was detected throughout all layers in high-grade CIN and invasive cancer. In situ RNA-RNA hybridization analyses of organotypic raft culture specimens of an HPV-31-containing cell line revealed that E6/E7 transcripts were expressed in most cell layers, with reduced expression in differentiated cells. This pattern of HPV expression correlated with the pattern of API expression detected by immunohistochemical analyses. These findings suggest that E6/E7 expression in differentiating epithelia is dependent on AP1, which appears to be associated with proliferative activity of the cells. Since E6/E7 expression induces cell proliferation, co-expression of AP1 and E6/E7 in undifferentiated cell layers might create a positive regulatory loop, probably contributing to maintenance of initial HPV infection and subsequent activation in basal and suprabasal cell layers.", }