Late temporal gene expression from the human cytomegalovirus pp28US (UL99) promoter when integrated into the host cell chromosome

Thioxothiazolo[3,4-a]quinazoline derivatives inhibit the human cytomegalovirus alkaline nuclease

Human cytomegalovirus (HCMV, human herpesvirus 5) is an opportunistic pathogen responsible for serious disease in immunocompromised patients. Current antiviral therapies rely predominantly on drugs interfering with viral DNA replication and packaging. However, the serious side effects of existing drugs and the emergence of drug resistance indicate the need for new targets for anti-HCMV therapy. One such target is the viral alkaline nuclease (AN), an enzyme highly conserved among the Herpesviridae. In this study, we validated the HCMV AN, encoded by the viral UL98 open reading frame, as a drug target by demonstrating that a UL98-deficient HCMV mutant is severely attenuated and shows a reduced ability to spread in cell culture. We established a fluorescence-based enzyme assay suitable for high-throughput screening and used it on a small-molecule compound library. The most promising hit, a thioxothiazolo[3,4-a]quinazoline derivative, blocked AN activity in vitro and inhibited HCMV replication in plaque reduction (PRA) and fluorescence reduction assays (FRA). Several derivatives of the hit compound were tested, some of which had similar or better inhibitory activities. The most potent derivative of hit scaffold A, compound AD-51, inhibited HCMV replication with a 50% effective concentrations (EC50) of 0.9 μM in the FRA and 1.1 μM in the PRA. AD-51 was also active against ganciclovir, foscarnet, and letermovir-resistant HCMVs. Moreover, it inhibited herpes simplex virus, Kaposi's sarcoma-associated herpesvirus, and murine CMV, a mouse virus serving as a model for HCMV. These results suggest that thioxothiazolo[3,4-a]quinazoline derivatives are a new class of herpesvirus inhibitors targeting the viral AN.

Features and Functions of the Conserved Herpesvirus Tegument Protein UL11 and Its Binding Partners

The herpesvirus UL11 protein is encoded by the UL11 gene and is a membrane-anchored protein with multiple functions. In the last stage of viral replication, UL11 participates in the secondary envelopment process. It also plays a key role in primary envelopment, the transportation of newly assembled viral particles through cytoplasmic vesicles, and virion egress from the cell. UL11 is an important accessory protein and sometimes cooperates with other proteins that participate in virus-induced cell fusion. Cell fusion is necessary for cell-to-cell transmissions. This review summarizes the latest literature and discusses the roles of UL11 in viral assembly, primary and secondary envelopment, and cell-to-cell transmission to obtain a better understanding of the UL11 protein in the life cycle of herpesviruses and to serve as a reference for studying other viruses. Additionally, some recently discovered characteristics of UL11 are summarized.

Whole-genome analysis of pseudorabies virus gene expression by real-time quantitative RT-PCR assay

Background

Pseudorabies virus (PRV), a neurotropic herpesvirus of pigs, serves as an excellent model system with which to investigate the herpesvirus life cycle both in cultured cells and in vivo. Real-time RT-PCR is a very sensitive, accurate and reproducible technique that can be used to detect very small amounts of RNA molecules, and it can therefore be applied for analysis of the expression of herpesvirus genes from the very early period of infection.

Results

In this study, we have developed and applied a quantitative reverse transcriptase-based real-time PCR technique in order to profile transcription from the whole genome of PRV after lytic infection in porcine kidney cells. We calculated the relative expression ratios in a novel way, which allowed us to compare different PRV genes with respect to their expression dynamics, and to divide the PRV genes into distinct kinetic classes. This is the first publication on the whole-genome analysis of the gene expression of an alpha-herpesvirus by qRT2-PCR. We additionally established the kinetic properties of uncharacterized PRV genes and revised or confirmed data on PRV genes earlier examined by traditional methods such as Northern blot analysis. Our investigations revealed that genes with the same expression properties form clusters on the PRV genome: nested overlapping genes belong in the same kinetic class, while most convergent genes belong in different kinetic classes. Further, we detected inverse relationships as concerns the expressions of EP0 and IE180 mRNAs and their antisense partners.

Conclusion

Most (if not all) PRV genes begin to be expressed from the onset of viral expression. No sharp boundary was found between the groups of early and late genes classified on the basis of their requirement for viral DNA synthesis. The expressions of the PRV genes were analyzed, categorized and compared by qRT2-PCR assay, with the average of the minimum cycle threshold used as a control for the calculation of a particular R value. In principle, this new calculation technique is applicable for the analysis of gene expression in all temporally changing genetic systems.

In vitro high-throughput screening assay for modulators of transcription

We developed a 96-well microtiter-plate high-throughput screening (HTS) assay for the detection of modulators of transcription. This HTS assay consists of three steps: (1) the in vitro transcription reaction; (2) modification and hybridization of RNA products; and (3) washing and quantification. During the first step, a DNA template containing the promoter of interest upstream of a cassette lacking guanosine residues in one of its strands (G-less cassette) is incubated with nuclear extract and the necessary cofactors/activators and substrates. During the second step, the in vitro synthesized transcripts are digested with RNase T1 and hybridized to two DNA oligonucleotides. One oligonucleotide is biotinylated for trapping of the RNA products to a streptavidin-coated plate, and the other is europium-labeled for detection by time-resolved fluorescence. We show that this assay is highly reproducible and robust, yielding results comparable to those obtained by standard methodologies employing radioactive nucleotide incorporation and gel electrophoresis while offering a very significant advantage in terms of throughput (>2000 assay points per operator per day). We demonstrate the usefulness of the assay for the discovery of small molecule inhibitors of transcription, and applications of this approach for the high-throughput discovery of transcriptional modulators are discussed.