br MYD and TRIF were inhibited
MYD88 and TRIF, were inhibited, which could exacerbate HPV infection. Third, we found that ectopic Herboxidiene of YAPS127A in-
hibited the expression and activation of transcriptional factors that are critical for the production of type I IFNs, including IRF1, IRF3, and IRF7, resulting in decreases of IFNA1, IFNB1, and IFNE in hCerECs. These IFNs can activate intracellular anti-viral programs and play a key role in the development of innate and adaptive immune responses. Finally, we observed that the expression and activation of key components of the type I IFN pathway, including IFNAR2, JAK1, STAT1, and IRF9, were broadly inhibited by expression of YAPS127A in cervical epithelial cells. Inhibition the IFNAR2/JAK1/STAT1 signaling pathway resulted in massive downregulation of antiviral ISGs, including MX1, CH25H, and IFITMs (inhibitors of virus entry) and APOBEC3G, OAS1, ISG15, and IFI44L (suppressors of virus translation and replication). More important, the inhibition of innate antiviral pathways by YAP was confirmed in studies with the K14-YAPS127A transgenic mouse. Therefore, the present studies indicate that disruption of the Hippo pathway and subse-quent activation of YAP1 in the cervical epithelial may result in defective innate antiviral immunity, which may allow HPV to escape immune surveillance, leading to persistent HPV infec-tion. Consistent with this observation, two research groups in China recently reported that YAP1 negatively regulated the production of type I interferon by suppressing TBK1 activity (Zhang et al., 2017; Wang et al., 2017). In the Drosophila model, hyperactivation of Yorkie (YAP in mammals) also led to the decrease of antimicrobial peptides in adipose tissues, suggest-ing that YAP1 regulation of innate immunity is a conserved mechanism of pathological immune suppression (Liu et al., 2016). These data suggest that enhancing HPV infection may represent a new mechanism for YAP1 to control cervical cancer development.
Identification of the Hippo/YAP Pathway as a Major Player in Cervical Cancer Development Does Not Reduce the Importance of hrHPV in Cervical Tumorigenesis
Although our transgenic mouse model demonstrates that HPV infection is not a necessary event for the development of CVSCC, our present data, plus previous numerous reports, still support the notion that hrHPV infection, especially in vulnerable popula-tions, greatly increases the risk for cervical cancer. Therefore, identification of the Hippo/YAP pathway as a major player in cer-vical carcinogenesis does not reduce the importance of hrHPV in
the development of cervical cancer. Our data clearly indicate that hyperactivation of YAP1 increased viral infectivity and sup-pressed innate immunity, two events that greatly increase the susceptibility of cervical epithelial cells to HPV infection and facil-itate the establishment of persistent HPV infection in these cells. Although HPV alone is not sufficient to induce malignant transfor-mation of cervical epithelial cells, expression of HPV oncoproteins E6 and E7 leads to inactivation of critical tumor suppressors such as TP53 and RB1 in many types of cells (Dyson et al., 1989; Scheffner et al., 1990; White et al., 2016). Inactivation of TP53 and RB1 can lead to extension of cell life (via suppression of senescence) and even induce immortal phenotype in cervical epithelial cells (Liu et al., 2018), paving the way for malignant transformation of HPV-infected cells by an oncogenic signal (such as hyperactivation of YAP1). Moreover, we have shown that HPV can prevent proteinase-dependent degradation of YAP1 protein, which maintains high levels of YAP1 protein in HPV-infected cervical epithelial cells. Most important, we found that HPV E6 protein suppressed Hippo pathway in the cervical epithelial cells (He et al., 2015b). Clearly, HPV synergizes with hy-peractivated YAP1 to drive carcinogenesis of cervix. Introduction of HPV16 E6 and E7 oncoproteins significantly promoted cervical carcinogenesis of KRT14-YAPS127A cells, indicating that syner-getic function between YAP1 and HPV does exist during cervical tumorigenesis. Therefore, the current HPV vaccination program, which has been shown to be very effective in preventing selected types of HPV (Baldur-Felskov et al., 2014; Sankaranarayanan, 2015), may greatly reduce infection by HPV and carcinogenesis of the cervix in women in the near future.