The Early Gene hhi1 Reactivates Heliothis zea Nudivirus 1 in Latently Infected Cells

Abstract

Heliothis zea nudivirus 1 (HzNV-1), previously known as Hz-1 virus, is an insect virus able to establish both productive and latent infections in several lepidopteran insect cells. Here, we have cloned and characterized one of the HzNV-1 early genes, hhi1, which maps to the HindIII-I fragment of the viral genome. During the productive viral infection, a 6.2-kb hhi1 transcript was detectable as early as 0.5 h postinfection (hpi). The level of transcript reached a maximum at 2 hpi and gradually decreased after 4 hpi. The transcript was not detectable during the latent phase of viral infection. Upon cycloheximide treatment, much higher levels of hhi1 transcript were detected throughout the productive viral infection cycle, suggesting that newly synthesized proteins are not needed for the expression of hhi1. Nevertheless, viral coinfection can further stimulate the expression of transfected hhi1 promoter in a plasmid. Transient hhi1 expression in latently infected cells resulted in a significant increase in virus titer and viral DNA propagation, suggesting that hhi1 plays a critical role in viral reactivation. Additional experiments showed that six early genes, which possibly function in transcription or DNA replication, were activated in the latent cells upon hhi1 transfection. Among these six genes, orf90 and orf121 expression could be induced by hhi1 alone without the need for other viral genes. Our discovery should be useful for future mechanistic study of the switches of latent/productive HzNV-1 viral infections.

Paleozoic origin of insect large dsDNA viruses

“…1), for which the highest genome content similarities (six unique genes) have been found (27). HzNV is able to develop particular infection strategies such as having a tropism for gonadal cells (31) and the establishment of latent infections (32). Both of these mechanisms could have been instrumental for the evolution of bracoviruses.…”

Nudivirus Genomics and Phylogeny

“…In the HzNV-1 transcripts, the early gene hhi1 (HzNV-1 HindIII fragment 1 gene) contains 270 nucleotides (nts) of 5' untranslated region (UTR) which, together with its upstream 62 bps, compose hhi1 early promoter (Wu et al 2008, Wu et al 2010; the HzNV-1 late gene p34 (ORF79) possesses 16 and 17 nts of 5' UTR, respectively, differing by 1 nt, and both 5' UTRs overlap with the identified 9 bp late promoter motif of the p34 (Guttieri and Burand 1996); as for the HzNV-1 late gene p51 (ORF64), the major late transcriptional initiation site is at −205 bp relative to the translational start codon and seven minor late start sites locate at various positions upstream of this primary site (Guttieri and Burand 2001). The putative www.intechopen.com polyadenylation signals (AATAAA) downstream of the stop codon of the p34 and p51 were found Burand 1996, Guttieri and.…”

Heliothis zea Nudivirus 1 Gene hhi1 Induces Apoptosis Which Is Blocked by the Hz-iap2 Gene and a Noncoding Gene, pag1

“…Such transactivation is due to the function of ie1 and p35 genes of this heterologous virus (50). We have reported before that hhi1 can serve as a transcriptional activator and is involved in viral reactivation from latently infected cells (50,51). Also, during latent viral infection, only one transcript derived from persistency-associated gene 1 (pag1) was detectable.…”

“…The HzNV-1 virus has a relatively broad host range and has been reported to productively and latently infect many insect cell lines (4,14,24,31,34,35,40). Previously, we found that more than 100 transcripts are produced during productive HzNV-1 virus infection (6); during this phase of infection, a gene located on the HzNV-1 HindIII-I fragment (hhi1) was found to generate an abundant 6.2-kb transcript within 0.5 h postinfection (hpi) (50,51). In contrast to the expression pattern of many early genes of baculovirus, the expression of hhi1 requires the assistance of HzNV-1 viral infection (51).…”

“…Previously, we found that more than 100 transcripts are produced during productive HzNV-1 virus infection (6); during this phase of infection, a gene located on the HzNV-1 HindIII-I fragment (hhi1) was found to generate an abundant 6.2-kb transcript within 0.5 h postinfection (hpi) (50,51). In contrast to the expression pattern of many early genes of baculovirus, the expression of hhi1 requires the assistance of HzNV-1 viral infection (51). In another experiment, we showed that hhi1 expression also can be transactivated by Autographa californica multiple nucleopolyhedrovirus (AcMNPV).…”