ADAR1 function affects HPV replication and is associated to recurrent human papillomavirus-induced dysplasia in HIV coinfected individuals

Abstract

Infection by human papillomavirus (HPV) alters the microenvironment of keratinocytes as a mechanism to evade the immune system. A-to-I editing by ADAR1 has been reported to regulate innate immunity in response to viral infections. Here, we evaluated the role of ADAR1 in HPV infection in vitro and in vivo. Innate immune activation was characterized in human keratinocyte cell lines constitutively infected or not with HPV. ADAR1 knockdown induced an innate immune response through enhanced expression of RIG-I-like receptors (RLR) signaling cascade, over-production of type-I IFNs and pro-inflammatory cytokines. ADAR1 knockdown enhanced expression of HPV proteins, a process dependent on innate immune function as no A-to-I editing could be identified in HPV transcripts. A genetic association studywas performed in a cohort of HPV/HIV infected individuals followed for a median of 6 years (range 0.1-24). We identified the low frequency haplotype AACCAT significantly associated with recurrent HPV dysplasia, suggesting a role of ADAR1 in the outcome of HPV infection in HIV+ individuals. In summary, our results suggest that ADAR1-mediated innate immune activation may influence HPV disease outcome, therefore indicating that modification of innate immune effectors regulated by ADAR1 could be a therapeutic strategy against HPV infection.HPV is a small non-enveloped double-stranded DNA virus that infects keratinocytes. Most HPV infections clear spontaneously, however, persistent HPV infection is strongly associated with risk of several cancers including cervical, laryngeal, esophageal and anal cancer 1 . In immunosuppressed individuals there is a higher rate of cervical and anal HPV infections 2 . HPV infection favors HIV acquisition, and HIV-infected individuals encompass a heavier burden of HPV-induced dysplasia and cancer due to progressive immune suppression and impaired cell-mediated immunity. Persistent HPV infections are strong determinants of anal high-grade squamous intraepithelial lesions (HSIL) 3 .Innate immune responses are characterized by production of a complex network of cytokines that effectively activate cellular immune cells 4 . Pattern recognition receptors (PRRs) include the RNA-binding helicase family of RIG-I-like receptors (RLR: RIG-I and MDA5), and the family of Toll-like receptors (TLR). In response to viral infections, produced type I interferons (IFN) activate the Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling pathway, which, in turn, induces the expression of additional interferon signaling

A20 (TNFAIP3) alleviates viral myocarditis through ADAR1/miR-1a-3p-dependent regulation

“…ADAR1 prevents autoimmunity during viral infection by blocking canonical antiviral pathways including RIG-I-like receptor, PKR, and oligoadenylate synthetase-RNase L [ 28 ]. Studies have demonstrated that ADAR1 is implicated in the replication of various viruses such as Zika virus [ 29 ], hepatitis B virus [ 30 ] and human papillomavirus [ 31 ]. ADAR1 functions as a mammalian RNA-editing enzyme that converts selected adenosine residuals to inosine in the double-stranded regions of RNA transcripts (dsRNA) [ 32 ].…”

Adenosine Deaminases Acting on RNA (ADARs) and Viral Infections

“…Ubiquitination of RIG-I mediated by the ubiquitin ligase tripartite motif-containing 25 (TRIM25) promotes dsRNA signaling to produce type I IFN; the HPV16 E6 oncoprotein targets TRIM25 to impair this signaling (121). ADAR1 regulates the expression of HPV proteins in keratinocyte cells (SiHa) in which the HPV16 genome is integrated (122,123). ADAR1 knock-down upregulates HPV mRNA and protein (E1 and E7) expression.…”

“…No A-to-I editing, however, is observed in HPV transcripts. It is postulated that downregulation of ADAR1 overcomes innate immune check-point blockade, thus facilitating enhanced viral expression (122). Furthermore, a genetic association between ADAR1 and HPV-induced dysplasia recurrence in HPV/human immunodeficiency virus (HIV) coinfected individuals has been observed using ADAR1 haplotype analysis, although the contribution of HIV infection was not excluded (122).…”

The impact of RNA modifications on the biology of DNA virus infection

“…HPV has evolved mechanisms to evade the host immune responses by altering the expression of pattern recognition receptors and suppression of interferon responses ( Bordignon et al, 2017 ). Pujantell et al (2019) , investigated the role of ADAR1 in innate immune signaling and antiviral responses upon HPV infection. Knockdown of ADAR1 in HPV16 genome integrated keratinocytes (SiHa) led to increased expression of RIG-I and MDA5, as well as IFNB, CXCL10 and transcriptional factor IRF7.…”

“…Furthermore, depletion of ADAR1 increased the expression of viral proteins E1 and E7 in SiHa cells. A-to-I editing within HPV RNAs has not been identified, and thus the regulation of viral gene expression by ADAR1 is independent of deamination of viral transcripts ( Pujantell et al, 2019 ). Collectively this work suggests that ADAR1 regulates innate immune responses to modulate viral gene expression in HPV infection.…”