Suppression of Stromal Interferon Signaling by Human Papillomavirus 16

Abstract

Human papillomaviruses (HPVs) infect squamous epithelia and cause several important cancers. Immune evasion is critical for viral persistence. Fibroblasts in the stromal microenvironment provide growth signals and cytokines that are required for proper epithelial differentiation, maintenance, and immune responses and are critical in the development of many cancers. In this study, we examined the role of epithelial-stromal interactions in the HPV16 life cycle using organotypic (raft) cultures as a model. Rafts were created using uninfected human foreskin keratinocytes (HFKs) and HFKs containing either wild-type HPV16 or HPV16 with a stop mutation to prevent the expression of the viral oncogene E5. Microarray analysis revealed significant changes in gene expression patterns in the stroma in response to HPV16, some of which were E5 dependent. Interferon (IFN)-stimulated genes (ISGs) and extracellular matrix remodeling genes were suppressed, the most prominent pathways affected. STAT1, IFNAR1, IRF3, and IRF7 were knocked down in stromal fibroblasts using lentiviral short hairpin RNA (shRNA) transduction. HPV late gene expression and viral copy number in the epithelium were increased when the stromal IFN pathway was disrupted, indicating that the stroma helps control the late phase of the HPV life cycle in the epithelium. Increased late gene expression correlated with increased late keratinocyte differentiation but not decreased IFN signaling in the epithelium. These studies show HPV16 has a paracrine effect on stromal innate immunity, reveal a new role for E5 as a stromal innate immune suppressor, and suggest that stromal IFN signaling may influence keratinocyte differentiation. IMPORTANCE The persistence of high-risk human papillomavirus (HPV) infections is the key risk factor for developing HPV-associated cancers. The ability of HPV to evade host immunity is a critical component of its ability to persist. The environment surrounding a tumor is increasingly understood to be critical in cancer development, including immune evasion. Our studies show that HPV can suppress the expression of immune-related genes in neighboring fibroblasts in a three-dimensional (3D) model of human epithelium. This finding is significant, because it indicates that HPV can control innate immunity not only in the infected cell but also in the microenvironment. In addition, the ability of HPV to regulate stromal gene expression depends in part on the viral oncogene E5, revealing a new function for this protein as an immune evasion factor.

High-Risk Human Papillomavirus and Epstein–Barr Virus Coinfection: A Potential Role in Head and Neck Carcinogenesis

“…Additionally, E6 can decrease the expression of IFN-α [ 171 ]. A role was also reported for HPV16 E5 in the suppression of stromal Type I IFNs signaling, which involved the function of IRF3 and IRF7 [ 172 ]. The capacity of HR-HPVs to inhibit the expression of IFN-stimulated genes (ISG), such as IFIT1, MX1, STAT1, RIG-I, and MDA5, consequently impairing the production of IFN-β and IFN-λ, has previously been reported [ 173 ].…”

Manipulation of JAK/STAT Signalling by High-Risk HPVs: Potential Therapeutic Targets for HPV-Associated Malignancies

“…Recently, the HPV E5 oncoprotein has also been shown to contribute to the impairment of IFNκ signalling. Using a HPV16 mutant which results in the loss of E5 expression, the downregulation of STAT1 and downstream ISG expression in HPV-containing keratinocytes was shown to be E5-dependent [135,136]. The authors demonstrated that this is dependent on E5-mediated methylation of the IFNK promoter, which is driven by activation of EGFR signalling [136].…”

Human papillomavirus associated cervical lesion: pathogenesis and therapeutic interventions

“…Meanwhile, E6 binds to IRF3, suppressing its transcriptional activity, and it can also disrupt JAK–STAT activation by binding to Tyk2 81,84 . HPV16 E5 has been observed to suppress the IFN signal in both infected cells and stromal microenvironment 85 . This suppression potentially involves EGFR and TGFBR2 signaling pathways 86 …”