Host Response to Polyomavirus Infection Is Modulated by RNA Adenosine Deaminase ADAR1 but Not by ADAR2

Abstract

Adenosine deaminases acting on RNA (ADARs) catalyze the C-6 deamination of adenosine (A) to produce inosine (I), which behaves as guanine (G), thereby altering base pairing in RNAs with double-stranded character. Two genes, adar1 and adar2, are known to encode enzymatically active ADARs in mammalian cells. Furthermore, two size forms of ADAR1 are expressed by alternative promoter usage, a short (p110) nuclear form that is constitutively made and a long (p150) form that is interferon inducible and present in both the cytoplasm and nucleus. ADAR2 is also a constitutively expressed nuclear protein. Extensive A-to-G substitution has been described in mouse polyomavirus (PyV) RNA isolated late times after infection, suggesting modification by ADAR. To test the role of ADAR in PyV infection, we used genetically null mouse embryo fibroblast cells deficient in either ADAR1 or ADAR2. The single-cycle yields and growth kinetics of PyV were comparable between adar1 ؊/؊ and adar2 ؊/؊ genetic null fibroblast cells. While large T antigen was expressed to higher levels in adar1 ؊/؊ cells than adar2 ؊/؊ cells, less difference was seen in VP1 protein expression levels between the two knockout MEFs. However, virus-induced cell killing was greatly enhanced in PyV-infected adar1 ؊/؊ cells compared to that of adar2 ؊/؊ cells. Complementation with p110 protected cells from PyVinduced cytotoxicity. UV-irradiated PyV did not display any enhanced cytopathic effect in adar1 ؊/؊ cells. Reovirus and vesicular stomatitis virus single-cycle yields were comparable between adar1 ؊/؊ and adar2 ؊/؊ cells, and neither reovirus nor VSV showed enhanced cytotoxicity in adar1 ؊/؊ -infected cells. These results suggest that ADAR1 plays a virus-selective role in the host response to infection.

RNA Editing—Systemic Relevance and Clue to Disease Mechanisms?

“…RNA and DNA binding of ADAR1 have been attributed to Z-DNA binding domains, which might confer target site specificity of editing of viral RNA templates (Brown et al, 2000) and, thus, play a virus selective role in the host response to infection (George and Samuel, 2011). When ADAR1 or ADAR2 is incubated with double-stranded RNA (dsRNA; >20 bp), about 50% of the adenosine residues will be edited in a promiscuous fashion (Bass and Weintraub, 1987; Nishikura et al, 1991).…”

Protein kinase PKR and RNA adenosine deaminase ADAR1: new roles for old players as modulators of the interferon response

“…Some of these predictions have been tested, either by ADAR1 loss of function or overexpression strategies. Depletion of ADAR1 by knockdown in human cells or by genetic knockout in mouse MEFs leads to enhanced apoptosis and cell cytotoxicity following infection with a number of different viruses of the Paramyxoviridae families and the DNA virus, polyoma [41,68,76]. In the case of MV, growth of both wild-type and V ko mutant virus are reduced in ADAR1 deficient cells compared to ADAR1 sufficient cells [68].…”

“…The p150 isoform of ADAR1 has emerged as an important component in the host response to infection by a number of RNA viruses that replicate either in the cytoplasm or nucleus [27,41,68], whereas the p110 isoform plays a role for some DNA viruses that replicate in the nucleus [76]. A common theme is that the presence of ADAR1 correlates with a cell protective response, and in some cases even enhances virus replication.…”

Editing of Cellular Self-RNAs by Adenosine Deaminase ADAR1 Suppresses Innate Immune Stress Responses

“…Western Immunoblot Analysis-Western blotting was carried out, as described previously (27,43), using whole-cell extracts (48). Primary antibodies used were as follows: rabbit monoclonal anti-ADAR1 (Santa Cruz Biotechnology, catalog no.…”