Specific short hairpin RNA-mediated inhibition of viral DNA packaging of human cytomegalovirus

Insights into the Transcriptome of Human Cytomegalovirus: A Comprehensive Review

Human cytomegalovirus (HCMV) is a widespread pathogen that poses significant risks to immunocompromised individuals. Its genome spans over 230 kbp and potentially encodes over 200 open-reading frames. The HCMV transcriptome consists of various types of RNAs, including messenger RNAs (mRNAs), long non-coding RNAs (lncRNAs), circular RNAs (circRNAs), and microRNAs (miRNAs), with emerging insights into their biological functions. HCMV mRNAs are involved in crucial viral processes, such as viral replication, transcription, and translation regulation, as well as immune modulation and other effects on host cells. Additionally, four lncRNAs (RNA1.2, RNA2.7, RNA4.9, and RNA5.0) have been identified in HCMV, which play important roles in lytic replication like bypassing acute antiviral responses, promoting cell movement and viral spread, and maintaining HCMV latency. CircRNAs have gained attention for their important and diverse biological functions, including association with different diseases, acting as microRNA sponges, regulating parental gene expression, and serving as translation templates. Remarkably, HCMV encodes miRNAs which play critical roles in silencing human genes and other functions. This review gives an overview of human cytomegalovirus and current research on the HCMV transcriptome during lytic and latent infection.

The KSHV portal protein ORF43 is essential for the production of infectious viral particles

Herpesvirus capsid assembly involves cleavage and packaging of the viral genome. The Kaposi's sarcoma-associated herpesvirus (KSHV) open reading frame 43 (orf43) encodes a putative portal protein. The portal complex functions as a gate through which DNA is packaged into the preformed procapsids, and is injected into the cell nucleus upon infection. The amino acid sequence of the portal proteins is conserved among herpesviruses. Here, we generated an antiserum to ORF43 and determined late expression kinetics of ORF43 along with its nuclear localization. We generated a recombinant KSHV mutant, which fails to express ORF43 (BAC16-ORF43-null). Assembled capsids were observed upon lytic induction of this virus; however, the released virions lacked viral DNA and thus could not establish infection. Ectopic expression of ORF43 rescued the ability to produce infectious particles. ORF43 antiserum and the recombinant ORF43-null virus can provide an experimental system for further studies of the portal functions and its interactions.

An update on the management and prevention of cytomegalovirus infection following allogeneic hematopoietic stem cell transplantation

ABSTRACT 

A significant progress has been made in deciphering critical aspects of the biology and immunology of CMV infection in the allogeneic stem cell transplantation setting. Genetic traits predisposing to active CMV infection and CMV end-organ disease have begun to be delineated. Reliable molecular assays for CMV DNA load quantitation in body fluids have been developed. Elucidation of immune mechanisms affording control of CMV infection will help to improve the management of active CMV infection. Finally, the advent of new CMV-specific antivirals and promising vaccine prototypes as well as the development of fine procedures for large-scale ex vivo generation of functional CMV-specific T cells for adoptive T cell transfer therapies will certainly minimize the negative impact of CMV on survival in these patients.

Decrease of murine cytomegalovirus-induced retinitis by intravenous delivery of immediate early protein-3-specific siRNA

PURPOSE

Retinitis induced by both human and murine cytomegaloviruses following immunosuppression is characterized by progressive loss of retinal architecture, due to necrosis of virus-infected cells as well as widespread apoptosis of uninfected bystander cells. Because small inhibitory RNA molecules (siRNA) can reduce murine cytomegalovirus (MCMV) gene expression and thereby inhibit virus replication in vitro, we tested siRNAs directed against MCMV immediate early protein-3 (IE-3) to determine if MCMV-induced retinitis could be alleviated in vivo.

METHODS

Immunosuppressed Balb/c mice (2.0 mg methylprednisolone acetate every 3 days beginning on day -2) were infected with 5 × 10(3) pfu of the K181 strain of MCMV via the supraciliary route. At day 2 post infection, mice were treated with various doses of IE-3-specific siRNA ranging from 0.1 nmol to 10 nmol, in a volume of 20 μL PBS via tail vein injection. Injected eyes were collected at various times post inoculation and subjected to plaque assay for virus titer, MCMV antigen staining, H&E staining, TUNEL assay, and Western blot for MCMV IE-3 protein.

RESULTS

Small but significant amounts of fluorescently labeled IE-3-specific siRNA localized to the RPE layer 48 hours after intravenous injection. IE-3-specific siRNA significantly reduced virus titers at all concentrations tested (ranging from 0.1 nmol to 10 nmol), but the most potent effect of siRNA was observed at a dose of 1 nmol. We also observed that IE-3-specific siRNA produced a substantial decrease in MCMV titers and a substantial reduction in bystander cell apoptosis over the time course of virus infection.

CONCLUSIONS

Systemic administration of IE-3-specific siRNA could alleviate MCMV retinitis by inhibiting virus replication and subsequent death of uninfected retinal cells.

Inhibition of human cytomegalovirus DNA replication by small interfering RNAs targeted to UL49

Human cytomegalovirus (HCMV) is a ubiquitous virus. Although the infection in healthy children and adults is usually asymptomatic, in immunocompromised individuals and newborns it is a significant cause of morbidity and mortality. UL49, an essential gene of HCMV, is highly conserved among various HCMV strains. The expression of UL49 is correlated with the production of virions. When UL49 is inhibited in the HCMV, the production of virions is reduced severely. In this study, RNA interference was applied to further investigate the roles of UL49 in viral replication. Two effective small interfering RNAs against UL49 were selected. Silencing of UL49 in HCMV-infected human foreskin fibroblast cells reduced the transcription levels of early and late genes, but not immediate-early ones. In addition, the viral DNA content was significantly reduced. This is the first time to uncover the role of UL49 in viral DNA synthesis, which indicates that UL49 might play an important role in this period. So the down-regulation of UL49 mRNA using RNAi might be a potential clinical therapy against the virus.

RNA interference-mediated targeting of human cytomegalovirus immediate-early or early gene products inhibits viral replication with differential effects on cellular functions

Viral drug toxicity, resistance, and an increasing immunosuppressed population warrant continued research into new avenues for limiting diseases associated with human cytomegalovirus (HCMV). In this study, a small interfering RNA (siRNA), siX3, was designed to target coding sequences within shared exon 3 of UL123 and UL122 transcripts encoding IE1 and IE2 immediate-early proteins of HCMV. Pretreatment of cells with siX3 reduced the levels of viral protein expression, DNA replication, and progeny virus production compared to control siRNA. Two siRNAs against UL54 and overlapping transcripts (UL55-57) were compared to siX3 in HCMV infection and were also found to be effective at inhibiting HCMV replication. Further investigation into the effects of the siRNAs on viral replication showed that pretreatment with each of the siRNAs resulted in an inhibition in the formation of mature replication compartments. The ability of these siRNAs to prevent or reduce certain cytopathic effects associated with HCMV infection was also examined. Infected cells pretreated with siX3, but not siUL54, retained promyelocytic leukemia (PML) protein in cellular PML bodies, an essential component of this host intrinsic antiviral defense. DNA damage response proteins, which are localized in nuclear viral replication compartments, were reduced in the siX3- and siUL54-treated cells. siX3, but not siUL54, prevented DNA damage response signaling early after infection. Therapeutic efficacy was demonstrated by treating cells with siRNAs after HCMV replication had commenced. Together, these findings suggest that siRNAs targeting exon 3 of the major IE genes or the UL54-57 transcripts be further studied for their potential development into anti-HCMV therapeutics.

The effect of murine cytomegalovirus IE-3 specific shRNA is dependent on intragenic target site due to multiple transcription initiation sites

BACKGROUND

Murine cytomegalovirus (MCMV) is closely related to human cytomegalovirus (HCMV) which is responsible for a variety of diseases, including retinitis, in immunocompromised individuals. Small inhibitory RNA molecules directed against essential viral regulatory genes may prove clinically useful.

METHODS

Small hairpin RNAs (shRNAs) directed against the essential MCMV immediate early-3 gene (IE-3) were designed and tested in vitro at m.o.i.'s of 2 and 0.2 to determine if virus replication could be inhibited.

RESULTS

At m.o.i. = 2, a MCMV IE-3 specific shRNA specific for sequences at the beginning of exon 5 inhibited virus replication with a maximum decrease in virus titer of approximately two logs at day 5 p.i. Surprisingly, however, at m.o.i. = 0.2, the same shRNA enhanced virus replication. In the latter case, the main IE-3 product observed in infected cells was not the expected 88 kd full length IE-3 protein observed at high m.o.i. but rather a truncated 45 kd form of this protein. Rapid analysis of 5' cDNA ends (5' RACE) indicated that substantial differences exist in the transcript profile produced by the IE-3 gene at low and high m.o.i. early after infection and that multiple transcripts are produced under both conditions. One such transcript, which originated in exon 5 of the IE-3 gene, was located outside the region targeted by our shRNA and was the major transcript produced at low m.o.i. Targeting of this exon 5 transcript with a second shRNA resulted in inhibition of virus replication at both low and high m.o.i.

CONCLUSIONS

These studies indicate that IE-3 has a complex transcriptional profile and that shRNA targeting of this and other viral regulatory genes which produce multiple transcripts may have unexpected effects on virus replication.

Short hairpin RNAs specific to human cytomegalovirus terminase subunit pUL89 prevent viral maturation

BACKGROUND

In order to define the role of the human cytomegalovirus (HCMV) small terminase subunit pUL89, analysis by RNA interference was applied.

METHODS

Cell lines expressing pUL89-specific short hairpin RNAs (shRNAs) were constructed by transduction of shRNAs via infection with retroviral vectors. These cell lines were infected with HCMV AD169 and were analysed for pUL89 expression, viral yield, plaque reduction, amount of viral DNA and particle formation.

RESULTS

After infection of the cell lines with HCMV, the expression of pUL89 was reduced by up to 86% for shRNA_A and 84% for shRNA_B at the later time points of infection. Cell lines expressing shRNA_C and the control had no effect on the pUL89 expression level. In addition, the inhibitory effect corresponded to a decrease in viral growth kinetics, viral DNA and plaque formation. Analysis by electron microscopy demonstrated that infection of cells expressing pUL89-specific shRNA_A and shRNA_B resulted in a complete inhibition of viral particle formation.

CONCLUSIONS

HCMV is a serious life-threatening opportunistic pathogen in immunocompromised patients. Because of multiple problems caused by the current available drugs, development of new strategies are needed. Our data clearly demonstrate that pUL89-specific shRNAs mediated the inhibition of formation of replicative infectious particles and therefore represent a new promising mechanism for antiviral therapy against HCMV infection.

Adenovirus-mediated shRNA interference against porcine circovirus type 2 replication both in vitro and in vivo

Porcine circovirus type 2 (PCV2) is the primary causative agent of an emerging swine disease, postweaning multisystemic wasting syndrome (PMWS), which is responsible for the heavy economic losses in stockbreeding. There are no specific antiviral drugs for treatment of the virus infection. We have now constructed two recombinant adenoviruses expressing short-hairpin RNAs (shRNAs) directed against either ORF1 (rAdS1) or ORF2 (rAdS2) of PCV2 and measured the inhibition of PCV2 replication. The results showed that delivery of these shRNAs by recombinant adenovirus into PK15 cells could induce a significant inhibition of viral RNA and DNA replication and protein synthesis level in cells subsequently infected with PCV2. The antiviral effect was dose-dependent and could sustain at least for 120h and the inhibition of virus replication could be significantly strengthened by combination of rAdS1 with rAdS2. Mice injected with shRNA before PCV2 infection showed substantial and low level of PCV2 DNA replication in the spleen during the period of 21-28 days post-PCV2 infection. These results indicated that shRNAs generated by adenovirus could sufficiently and continuously inhibit PCV2 infection in vitro as well as in vivo. The adenovirus based shRNA targeting ORF1 and ORF2 of PCV2 might be a new potential alternative strategy for controlling PCV2 infection.