Heterogeneous response for a mammalian hepadnavirus infection to acyclovir: Drug-arrested intermediates of minus-strand viral DNA synthesis are enveloped and secreted from infected cells as virion-like particles

Abstract

Three woodchucks infected persistently with the woodchuck hepatitis virus (WHV) were treated with acyclovir (ACV) to investigate the effect of inhibiting viral DNA synthesis upon the replication of an orthohepadnavirus in vivo. Normal viraemia was reduced during the treatment period in all three animals, but each responded with a distinct serum phenotype. In the most provocative case, the profile of the WHV DNAs in both the liver and serum provided a simple and novel description of the orthohepadnaviral infection for this ACV protocol. The pre-drug viraemia was rapidly cleared from the serum and replaced by virion-like particles containing predominantly minus-strand WHV DNAs. These serum DNA species had the character of replicative intermediates arrested in their elongation by ACV-mediated chain termination and were contained in particles with a buoyant density in CsCl essentially identical with virions. However, in infected hepatocytes, initiation of reverse transcription within newly formed core particles was not inhibited by the ACV treatment. Instead, an heterogeneous array of minus-strand DNAs were synthesised, each presumed to be truncated by the incorporation of one molecule of ACV monophosphate. An approximately normal level of core particles was present in the liver of this woodchuck after 26 days of the ACV protocol; excess drug-arrested nucleocapsids were steadily removed throughout the dosing period upon their envelopment and secretion as virion-like particles into the circulation. These data suggest that plus-strand DNA synthesis may not be absolutely required prior to secretion of virus from the infected cell.

Reduced Secretion of Virions and Hepatitis B Virus (HBV) Surface Antigen of a Naturally Occurring HBV Variant Correlates with the Accumulation of the Small S Envelope Protein in the Endoplasmic Reticulum and Golgi Apparatus

“…In contrast to the established dogma of preferential virion secretion of mature genome for wild-type (WT) hepadnaviruses (17,33,40,44,47,48), the 97L mutation results in secretion of virions containing an immature genome into the medium and is characterized by excessive amounts of minus-strand DNA (47,48). Even though the immature secretion phenotype has been observed with woodchuck and snowgoose hepadnaviruses (7,42), it has not been reported with human patients. This may be due to the presence of naturally occurring compensatory mutations for 97L in the core protein at positions 5 (11) or 130 (49), both changing a highly conserved proline to threonine.…”

Replication Advantage and Host Factor-Independent Phenotypes Attributable to a Common Naturally Occurring Capsid Mutation (I97L) in Human Hepatitis B Virus

“…We further reported that this immature secretion phenotype can be rescued intramolecularly by a proline-tothreonine mutation at amino acid 130 (P130T) in the core protein (72) or intermolecularly by an alanine-to-phenylalanine mutation at amino acid 119 (A119F) in the large envelope protein (37). An immature secretion-like phenomenon was also observed in vivo in animal models (9,63). Although the immature secretion phenomenon of mutant 97L can be observed in both the adr and ayw subtypes, the mutation occurs frequently in subtype adr (1,5,14,15,16,17,21,29,33,61,64,65) but rarely in subtype ayw (40,41,48).…”

Coexistence of Two Distinct Secretion Mutations (P5T and I97L) in Hepatitis B Virus Core Produces a Wild-Type Pattern of Secretion

“…Although an immature secretion-like phenotype has also been found to occur in vivo in woodchuck and snow goose hepadnaviruses (4,26), it is puzzling that it has not been found so far in natural infection in humans (F. M. Suk, M. H. Lin, and C. Shih, unpublished results). Furthermore, it remains unclear whether an immature secretion phenotype can still be observed in the genetic context of naturally occurring variants, which often contain multiple mutations throughout the genome.…”