E2 Proteins of High Risk Human Papillomaviruses Down-Modulate STING and IFN-κ Transcription in Keratinocytes

Abstract

In the early stages of human papillomavirus (HPV) infection, the viral proteins elicit specific immune responses that can participate to regression of ano-genital lesions. HPV E6 protein for instance can reduce type I interferon (IFN) including IFN-κ that is involved in immune evasion and HPV persistence. To evaluate the role of E2 protein in innate immunity in HPV16-associated cervical lesions, genome-wide expression profiling of human primary keratinocytes (HPK) transduced by HPV16 E2 was investigated using microarrays and innate immunity associated genes were specifically analyzed. The analyses showed that the expression of 779 genes was modulated by HPV16E2 and 92 of them were genes associated with innate immunity. Notably IFN-κ and STING were suppressed in HPK expressing the E2 proteins of HPV16 or HPV18 and the trans-activation amino-terminal domain of E2 was involved in the suppressive effect. The relationship between STING, IFN-κ and interferon stimulated genes (ISGs) in HPK was confirmed by gene silencing and real time PCR. The expression of STING and IFN-κ were further determined in clinical specimens by real time PCR. STING and IFN-κ were down-modulated in HPV positive low grade squamous intraepithelial lesions compared with HPV negative controls. This study demonstrates that E2 proteins of high risk HPV reduce STING and IFN-κ transcription and its downstream target genes that might be an immune evasion mechanism involved in HPV persistence and cervical cancer development.

Early Defensive Mechanisms against Human Papillomavirus Infection

“…This is the first report of a possible involvement of STING in HPV immunity. Furthermore, knockdown of STING moderately reduced IFN-expression in primary human KC, and both proteins were reduced in HPV-positive cervical tissue and CIN1 (60). IFN-downregulation in HPV-positive precursor lesions and cervical cancer has been observed before (64,65).…”

“…High-risk HPV oncoproteins are effective suppressors of ISG expression (58)(59)(60). The E6 and E7 oncoproteins from HPV16 and -31 inhibit both STAT1 (61), an essential mediator of IFN signaling, and PKR (40), which is increased by IFN-␣/␤/␥ to induce translation inhibition.…”

“…Sunthamala et al (60) reported that HPV16 E2 also suppresses many genes associated with innate immunity, including those for IFN-and stimulator of IFN genes (STING). Activation of STING by cytosolic DNA sensors induces type I IFN expression via Tank binding kinase 1 and IRF3.…”

Immunology of HPV Infection

“…A comparative analysis of ISG transcription in cells with complete 16, 18 and 31 genomes suggests that this is via the inhibition of the constitutive transcription of IFN-κ [21]. The HPV 16 and 18 E2 protein suppresses many genes associated with innate immunity and, in particular, the expression of STING and IFN-κ [22], the first report of a possible involvement of STING in HPV innate sensing. In contrast, hrE5 enhances IFN-β and IRF1 expression [23].…”

Epigenomics, Pharmacoepigenomics, and Personalized Medicine in Cervical Cancer

“…Studies have also shown that the oncoproteins encoded by high-risk HPV types such as E2, E6, and E7 target immune responsive genes, downregulate their expression facilitating immune eva-sion, persistent viral infection, and HPV persistence. E2 protein, via its transactivation amino-terminal domain, has shown to suppress IFN-κ and STING gene expression [113] .…”