Varied assembly and RNA editing efficiencies between genotypes I and II hepatitis D virus and their implications

Abstract

The mechanisms that link genotypes of hepatitis D virus (HDV) with clinical outcomes have not yet been elucidated. Genotypic variations are unevenly distributed along the sequences of hepatitis delta antigens (HDAgs). Of these variations, the packaging signal at the Cterminus has a divergence of 74% between genotypes I and II. In this report, we address the issue of whether these high variations between genotypes affect assembly efficiency of HDV particles and editing efficiency of RNA. Viral package systems of transfection with expression plasmids of hepatitis B surface antigen and HDAgs or whole genomes of HDV consistently indicate that the package efficiency of genotype I HDV is higher than that of genotype II. Segment swapping of large-form HDAg indicates that the C-terminal 19-residue region plays a key role for the varied assembly efficiencies. Also, the editing efficiency of genotype I HDV is higher than that of genotype II. The nucleotide and structural changes surrounding the editing site may explain why genotype II HDV has a low RNA editing efficiency. The findings of in vitro assembly systems were further supported by the observations that patients infected with genotype II had significantly lower alanine transaminase (ALT) levels, more favorable outcomes (P < .05), and a trend to have lower serum HDV RNA levels as compared with those infected with genotype I HDV (P ‫؍‬ .094). Coinfection or superinfection of HBV with HDV may cause severe liver diseases in humans. 3-8 An HDV viral particle is composed of HBsAg, a single-strand circular 1.7-kb RNA, and 2 forms of hepatitis delta antigen (HDAg). 9,10 HDV replicates through a rolling-circle mechanism involving RNA-directed RNA synthesis of genomic RNA and its complement, antigenomic RNA. 9,10 During the replication cycle of HDV, RNA editing at adenosine 1,012 (amber/W site) in antigenomic RNA allows the synthesis of 2 forms of HDAg from a single open reading frame. 11-13 The largeform HDAg (HDAg-L) is identical to the small-form (HDAg-S) except for a 19-amino acid extension at the C-terminus. 9,10 The Cxxx motif in this C-terminal extension is essential for isoprenylation, a function required for the package of HDV. 14 Both HDAg-S and HDAg-L form oligomers 15 and interact with viral RNA. 16,17 HDAg-L plays a crucial role in the assembly of HDV and suppresses viral replication, 18-20 whereas HDAg-S plays the opposite role in transactivating the replication of HDV RNA. 21,22 In addition to fulminant hepatitis or rapidly progressive chronic active hepatitis, HDV infection may also run a subclinical course. 8,23 Factors associated with different outcomes are still unclear. Persistent replication of HDV and/or HBV have been reported to be associated with active liver diseases. 8,24 There are 3 genotypes of HDV. 25 Genotype III HDV, prevalent in northern South America, has been associated with a severe form of hepatitis. 25 Whereas genotype II HDV, isolated from Japan and Taiwan, 26-29 is more frequently associated with a less aggressive disease as compared wi...

Roles of Carboxyl-Terminal and Farnesylated Residues in the Functions of the Large Hepatitis Delta Antigen

“…In general, genotype 3 appears to be associated with the most severe disease course, while genotype 2 seems to be associated the least severe outcomes (6,7,13). A previous study comparing the efficiency of HDAg-L incorporation into VLPs for genotypes 1 and 2, but not genotype 3, proposed a direct correlation between the low assembly efficiency of HDV genotype 2 and its low virulence relative to genotype 1 (13).…”

“…Among the three distinct HDV genotypes that have been identified, significant differences in the severity of disease observed in infected patients have been reported (6,7,13). In general, genotype 3 appears to be associated with the most severe disease course, while genotype 2 seems to be associated the least severe outcomes (6,7,13).…”

“…1A). Previously, it was shown that assembly of genotype 2 HDV particles proceeds less efficiently that that of genotype 1 HDV particles, and it was hypothesized that the relatively low assembly efficiency associated with genotype 2 could account for its milder disease phenotype (13).…”

Molecular interactions between hepatitis B virus and delta virus

“…Although an association between HDV-1/HBV-A and -D and HDV-3/HBV-F and -A has been observed, independent investigations suggest that the co-infections are mainly representative of common genotypes of each of the viruses in certain geographical areas and not specific for distinct HBV or HDV genotypes [13][14][15] . Studies indicate that HDV genotype 2 is associated with a less aggressive disease compared to genotype 1 which has been attributed to the higher packaging efficiency of genotype 1 than that of genotype 2 [16,17] . Moreover, a variation in the packaging efficiency has been observed among different isolates of the same genotype, which reflects the critical role of this length in HDAg interactions with HBsAg.…”

“…Moreover, a variation in the packaging efficiency has been observed among different isolates of the same genotype, which reflects the critical role of this length in HDAg interactions with HBsAg. It has been reported that the hydrophobic nature of the L-HDAg C-terminal domain provided by C211-farnesylation as well as the number of hydrophobic residues of the packaging signal (which differs among HDV genotypes) enhance HDV interactions with surface proteins of HBV and therefore the packaging efficiency [17] .…”