Double-Stranded RNA Adenosine Deaminases Enhance Expression of Human Immunodeficiency Virus Type 1 Proteins

Abstract

ADARs (adenosine deaminases that act on double-stranded RNA) are RNA editing enzymes that catalyze a change from adenosine to inosine, which is then recognized as guanosine by translational machinery. We demonstrate here that overexpression of ADARs but not of an ADAR mutant lacking editing activity could upregulate human immunodeficiency virus type 1 (HIV-1) structural protein expression and viral production. Knockdown of ADAR1 by RNA silencing inhibited HIV-1 production. Viral RNA harvested from transfected ADAR1-knocked-down cells showed a decrease in the level of unspliced RNA transcripts. Overexpression of ADAR1 induced editing at a specific site in the env gene, and a mutant with the edited sequence was expressed more efficiently than the wild-type viral genome. These data suggested the role of ADAR in modulation of HIV-1 replication. Our data demonstrate a novel mechanism in which HIV-1 employs host RNA modification machinery for posttranscriptional regulation of viral protein expression.Human immunodeficiency virus (HIV) uses many host cellular machineries for its replication. Posttranscriptional modifications of the HIV type 1 (HIV-1) RNA, i.e., alternative splicing, capping, and poly(A) synthesis of the viral pre-mRNA, have been well described (15). However, the process of RNA editing, another subtle type of pre-mRNA modification, is still not well defined, and its role in HIV-1 replication is in doubt.RNA editing was found to be an important process in regulating gene expression in many eukaryotes and viruses. In hepatitis D virus, the process of RNA editing has been well studied (reviewed in reference 3). A-to-I editing converts a stop codon into a Trp codon, providing envelope protein for virion assembly (4, 25). In the hepatitis C replicon, ADAR1 was shown to abolish replication through editing (33). Hypermutation by RNA editing was found in measles virus mRNA. It is speculated that this process leads to persistence of the virus (5). The editing has also been found in other viruses, such as parainfluenza virus 3 (9), mumps virus (22), and Ebola virus (28).Evidence of RNA editing in HIV-1 has also been demonstrated. Edited adenosine in the (transactivating response region) (TAR) when the virus is injected into Xenopus oocytes has been reported (31), though the functional consequences of this conversion are not known. It is hypothesized that the phenomenon caused a change in the secondary structure of TAR, which may affect transcription and translation of the viral RNA. Base modification of A to G and C to U has also been shown in the HIV-1 transcript (1). The modification was proposed to play a role in modulation of viral gene expression.There are many data suggesting that RNA editing might be involved in HIV-1 gene expression. ADARs are the RNA editing enzymes of interested that may be involved in modulation of HIV-1 expression. It was demonstrated that mouse ADAR1 but not ADAR2 is upregulated in lymphocytes in response to inflammation (34). In this study, we demonstrated that ADARs could enhance H...

ADAR1 Interacts with PKR during Human Immunodeficiency Virus Infection of Lymphocytes and Contributes to Viral Replication

“…4C and 5D). A similar activity was recently observed in an independent study and showed that the deaminase function was responsible for this increased HIV production (45). However, we observed similar results with our Dcat mutant and ADAR1-p150 in the absence of PKR, which does not support the same conclusion (Fig.…”

“…It was suggested recently that the overexpression of ADAR1 or ADAR2, another member of the ADAR family, increases HIV production in the absence of PKR transfection, and this activity was ascribed to the deaminase function (45). To determine if this was also the case in our assay, we verified the activity of our constructs in the absence of transfected PKR (Fig.…”

“…A previous study showed that an siRNA against ADAR1-p150 only (siA) decreased the long form of the protein and decreased VSV production correlated with increased PKR activation (35). Another study showed that an siRNA against both ADAR1-p150 and ADAR1-p110 decreased HIV expression but was not correlated with PKR activation (45). To further determine the role of ADAR1 in HIV replication, we used siA and an siRNA targeting both forms (si4; Qiagen), and we analyzed their effect on viral expression and production (Fig.…”

Adenosine Deaminase Acting on RNA 1 (ADAR1) Suppresses the Induction of Interferon by Measles Virus

“…Similarly, with vesicular stomatitis virus, ADAR1 was found to be proviral in both mouse embryonic fibroblasts and HeLa cells by suppressing the activation of PKR phosphorylation (25,34). Several independent reports concluded that ADAR1 was proviral and increased HIV replication (11,14,40). Furthermore, in a screening of ϳ380 ISGs by overexpression, ADAR1 was identified as one of a few ISG products that significantly enhanced the replication of multiple viruses, including HIV, West Nile virus, Venezuelan equine encephalitis virus, and yellow fever virus (50).…”

Mouse models for Aicardi–Goutières syndrome provide clues to the molecular pathogenesis of systemic autoimmunity

“…Thus, TREX1 serves to hide HIV from the innate immune system. ADAR1 was reported to promote HIV replication [69,70]; however, anti-retroviral effects of ADAR1 were demonstrated in a recent study [71]. SAMHD1 potently suppresses HIV replication in noncycling human cells by degrading dNTPs and reducing their concentration below a threshold required for viral reverse transcription [25,26,[72][73][74].…”