Transcriptional features and transcript structure of UL145 in different strains of human cytomegalovirus

Cellular Cullin RING Ubiquitin Ligases: Druggable Host Dependency Factors of Cytomegaloviruses

Human cytomegalovirus (HCMV) is a ubiquitous betaherpesvirus that frequently causes morbidity and mortality in individuals with insufficient immunity, such as transplant recipients, AIDS patients, and congenitally infected newborns. Several antiviral drugs are approved to treat HCMV infections. However, resistant HCMV mutants can arise in patients receiving long-term therapy. Additionally, side effects and the risk to cause birth defects limit the use of currently approved antivirals against HCMV. Therefore, the identification of new drug targets is of clinical relevance. Recent work identified DNA-damage binding protein 1 (DDB1) and the family of the cellular cullin (Cul) RING ubiquitin (Ub) ligases (CRLs) as host-derived factors that are relevant for the replication of human and mouse cytomegaloviruses. The first-in-class CRL inhibitory compound Pevonedistat (also called MLN4924) is currently under investigation as an anti-tumor drug in several clinical trials. Cytomegaloviruses exploit CRLs to regulate the abundance of viral proteins, and to induce the proteasomal degradation of host restriction factors involved in innate and intrinsic immunity. Accordingly, pharmacological blockade of CRL activity diminishes viral replication in cell culture. In this review, we summarize the current knowledge concerning the relevance of DDB1 and CRLs during cytomegalovirus replication and discuss chances and drawbacks of CRL inhibitory drugs as potential antiviral treatment against HCMV.

Functional annotation of human cytomegalovirus gene products: an update

Human cytomegalovirus is an opportunistic double-stranded DNA virus with one of the largest viral genomes known. The 235 kB genome is divided in a unique long (UL) and a unique short (US) region which are flanked by terminal and internal repeats. The expression of HCMV genes is highly complex and involves the production of protein coding transcripts, polyadenylated long non-coding RNAs, polyadenylated anti-sense transcripts and a variety of non-polyadenylated RNAs such as microRNAs. Although the function of many of these transcripts is unknown, they are suggested to play a direct or regulatory role in the delicately orchestrated processes that ensure HCMV replication and life-long persistence. This review focuses on annotating the complete viral genome based on three sources of information. First, previous reviews were used as a template for the functional keywords to ensure continuity; second, the Uniprot database was used to further enrich the functional database; and finally, the literature was manually curated for novel functions of HCMV gene products. Novel discoveries were discussed in light of the viral life cycle. This functional annotation highlights still poorly understood regions of the genome but more importantly it can give insight in functional clusters and/or may be helpful in the analysis of future transcriptomics and proteomics studies.

Selective degradation of host MicroRNAs by an intergenic HCMV noncoding RNA accelerates virus production

Virulence of human cytomegalovirus (HCMV) clinical isolates correlates with carriage of a 15 kb segment in the UL/b' region of the viral genome, which is absent from attenuated strains. The mechanisms by which this segment contributes to HCMV virulence remain obscure. We observed that intergenic RNA sequences within the 15 kb segment function as a microRNA (miRNA) decay element (miRDE) and direct the selective, sequence-specific turnover of mature miR-17 and miR-20a encoded within the host miR-17-92 cluster. Unlike canonical miRNA-mRNA interactions, the miRNA-miRDE interactions did not repress miRDE expression. miRNA binding site mutations retargeted miRDE to other miR-17-92 cluster miRNAs, which are otherwise resistant to miRDE-mediated decay. miRDE function was required to accelerate virus production in the context of lytic HCMV infection. These results indicate a role for viral noncoding RNA in regulating cellular miRNAs during HCMV pathogenesis and suggest that noncoding RNAs may play a role in mature miRNA turnover.

Overlapping transcription structure of human cytomegalovirus UL140 and UL141 genes

Transcription of human cytomegalovirus UL/b' region has been studied extensively for some genes. In this study, transcripts of the UL140 and UL141, two of the UL/b' genes, were identified in late RNAs of three HCMV isolates using Northern blot hybridization, cDNA library screening and RACE-PCR. At least three transcripts with length of 2800, 2400 and 1700 nt, as well as a group of transcripts of about 1000-1300 nt, were found in this gene region with an accordant 3' ends. Among the transcripts, two initiated upstream of the start code of the UL140 gene and contained the UL140 and UL141 open reading frame (ORF), one initiated in the middle of the UL140 gene, and could encode short ORFs upstream of the UL141 ORF. A group of transcripts initiated upstream or downstream of the start code of the UL141 gene, and could encode 'nested' ORFs, including the UL141 ORF. These 'nested' ORFs possess different initiation sites but the same termination site as that of the UL141 ORF.

Transcription characteristics of the human cytomegalovirus UL13 gene

The human cytomegalovirus (HCMV) UL13 gene is located in the unique long (UL) region of its genome. The transcript structure of UL13 gene has not been investigated to date. By using cDNA library screening, northern blot, and rapid amplification of cDNA ends (RACE), the HCMV UL13 gene was demonstrated to be transcribed from the immediate early (IE) to the late (L) phase of infection, and at least one 1602-nt unspliced transcript was identified in the present study from three clinical isolates.

Human CMV transcripts: an overview

The human CMV (HCMV) genome consists of an approximately 230-kb dsDNA and is predicted to contain over 165 open reading frames. Although the entire sequence of the laboratory-adapted AD169 strain of HCMV was first available in 1991, the precise number and nature of viral genes and gene products are still unclear. Fewer than 100 predicted genes have been convincingly elucidated with respect to their expression patterns, transcript structure and transcription characteristics. The high gene number of HCMV creates a crowded genome with many overlapping transcriptional units. 3´- or 5´-coterminal overlapping polycistronic transcripts could use a common promoter element or a poly-A signal. 3´-coterminal monocistronic transcripts could encode 'nested' open reading frames, which possess different initiation but the same termination sites. As a virus with eukaryotic cells as the host, HCMV has the capacity to splice out introns during transcription. Major alternately spliced mRNA species of HCMV originate primarily, but not exclusively, from the immediate early gene regions. Alternate splicing patterns of the mRNAs could encode a number of gene products with different sizes. In recent years, some antisense and noncoding transcripts of HCMV have been reported. These RNAs probably have functions in genomic replication or the regulation of gene expression.