Rna Editing in the Genomic Rna of Hepatitis Delta Virus by Host Cytidine and Adenosine Deaminases: Impact on Viral Evolution

Hepatitis delta virus (HDV) is a human pathogen that consists of a 1.7-kb circular negative-sense RNA genome and uses a unique replication strategy that redirects host RNA polymerase(s) to transcribe viral RNA. However, similar to many RNA viruses encoding viral RNA polymerases, HDV exhibits high genetic heterogeneity. Three known mechanisms for generating genetic diversity in HDV are host RNA polymerase-involved incorporation errors and homologous RNA recombination as well as host ADAR1 (adenosine deaminase that acts on RNA 1)-catalyzed amber/W RNA editing. The latter leads to the production of large form of the delta antigen (HDAg) and is required for virion assembly. The most prevalent type of editing involves a base change from adenosine to inosine (A-to-I), mediated by ADAR family. A second involves deamination of cytidine to uridine (C-to-U), mediated by APOBEC [apolipoprotein B (apoB) mRNA editing catalytic subunit] family. Whole-genome sequence analyses of cultured cells transfected with a HDV sequence indicated that, in addition to the well-documented amber/W editing, three potential RNA editing events occurring at nt 1375 (potential C-to-U APOBEC editing site in the HDV genomic RNA; leads a R-to-Q amino acid substitution at residue 75 of HDAg and refers to as R/Q-75 RNA editing) and nt 218/219 (potential ADAR editing sites in the HDV genomic and antigenomic RNA, respectively) were identified. The biological significance and the crucial trans factors/cis-elements in the regulation of the newly identified RNA editing events will be elucidated. Based on the analyses of the sequence/structure surrounding the novel RNA editing sites, a hypothesis is proposed that a random single base change generated during HDV RNA synthesis could serve as an “initiator” for the subsequent efficient multiple site-specific RNA editing events performed by members of host cytidine and adenosine deaminases. Host RNA polymerase-driven RNA recombination between two HDV edited/mutated genomes further amplifies the genetic heterogeneity of HDV. Taken together, studies in this grant proposal will expand our knowledge of the functional attributes of C-to-U and A-to-I RNA editing in viral life cycle and viral evolution. SPECIFIC AIMS 1. Roles of ADAR1 and APOBEC1/A1CF in the newly identified HDV RNA editing 2. Biological functions of R/Q-75 RNA editing 3. Identification of the “initiator” for the novel HDV RNA editing 4. Molecular regulations for the novel HDV RNA editing

Project ID:PC10607-0342
External Project ID:MOST106-2320-B182-008