RNA Exosome Complex Regulates Stability of the Hepatitis B Virus X-mRNA Transcript in a Non-stop-mediated (NSD) RNA Quality Control Mechanism

• Published in: The Journal of biological chemistry 2016-07, Vol.291 (31), p.15958-15974
• Main Authors: Aly, Hussein H., Suzuki, Junya, Watashi, Koichi, Chayama, Kazuaki, Hoshino, Shin-ichi, Hijikata, Makoto, Kato, Takanobu, Wakita, Takaji
• Format: Article
• Language: English
• Subjects: Codon, Initiator - genetics; Codon, Initiator - metabolism; DNA Helicases - genetics; DNA Helicases - metabolism; exosome complex; Exosome Multienzyme Ribonuclease Complex - genetics; Exosome Multienzyme Ribonuclease Complex - metabolism; HBS1L; Hep G2 Cells; hepatitis B virus (HBV, Hep B); Hepatitis B virus - genetics; Hepatitis B virus - metabolism; Humans; Microbiology; Non-Stop mediated RNA Decay (NSD); RNA degradation; RNA Exosome; RNA helicase; RNA Stability; RNA, Messenger - genetics; RNA, Messenger - metabolism; RNA, Viral - genetics; RNA, Viral - metabolism; RNA-binding protein; SKIV2L; Trans-Activators - biosynthesis; Trans-Activators - genetics; Viral Regulatory and Accessory Proteins; virus restriction factor
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M116.724641

Hepatitis B virus (HBV) is a stealth virus, minimally inducing the interferon system required for efficient induction of both innate and adaptive immune responses. However, 90% of acutely infected adults can clear the virus, suggesting the presence of other, interferon-independent pathways leading to viral clearance. Given the known ability of helicases to bind viral nucleic acids, we performed a functional screening assay to identify helicases that regulate HBV replication. We identified the superkiller viralicidic activity 2-like (SKIV2L) RNA helicase (a homolog of the Saccharomyces cerevisiae Ski2 protein) on the basis of its direct and preferential interaction with HBV X-mRNA. This interaction was essential for HBV X-mRNA degradation at the RNA exosome. The degradation of HBV X-mRNA at the RNA exosome was also mediated by HBS1L (HBS1-like translational GTPase) protein, a known component of the host RNA quality control system. We found that the redundant HBV-precore translation initiation site present at the 3′-end of HBV X-mRNA (3′ precore) is translationally active. The initiation of translation from this site without a proper stop codon was identified by the non-stop-mediated RNA decay mechanism leading to its degradation. Although 3′ precore is present in the five main HBV-RNA transcripts, only X-mRNA lacks the presence of an upstream start codons for large, middle, and small (L, M, and S) HBV surface proteins. These upstream codons are in-frame with 3′ precore translation initiation site, blocking its translation from the other HBV-mRNA transcripts. To our knowledge, this is the first demonstration of the anti-viral function of the non-stop-mediated RNA decay mechanism.