Human Herpesvirus 6A Exhibits Restrictive Propagation with Limited Activation of the Protein Kinase R-eIF2α Stress Pathway.

The eIF2α protein plays a critical role in the regulation of translation. The production of double-stranded RNA (dsRNA) during viral replication can activate protein kinase R (PKR), which phosphorylates eIF2α, leading to inhibition of the initial step of translation. Many viruses have evolved gene products targeting the PKR-eIF2a pathway, indicating its importance in antiviral defense.

Roseoloviruses manipulate host cell cycle.

During lytic infections HHV-6A and HHV-6B disrupt E2F1-Rb complexes by Rb degradation, releasing E2F1 and driving the infected cells toward the S-phase. Whereas upon infection E2F1 and its cofactor DP1 were up-regulated, additional E2F responsive genes were expressed differentially in various cells. E2F binding sites were identified in promoters of several HHV-6 genes, including the U27 and U79 associated with viral DNA replication, revealing high dependence on the binding site and the effect of the E2F1 transcription factor.

Human herpesvirus 6 (HHV-6) alters E2F1/Rb pathways and utilizes the E2F1 transcription factor to express viral genes.

E2F transcription factors play pivotal roles in controlling the expression of genes involved in cell-cycle progression. Different viruses affect E2F1/retinoblastoma (Rb) interactions by diverse mechanisms releasing E2F1 from its suppressor Rb, enabling viral replication. We show that in T cells infected with human herpesvirus 6A (HHV-6A), the E2F1 protein and its cofactor DP1 increased, whereas the Rb protein underwent massive degradation without hyperphosphorylation at three sites known to control E2F/Rb association.

Classification of HHV-6A and HHV-6B as distinct viruses.

Shortly after the discovery of human herpesvirus 6 (HHV-6), two distinct variants, HHV-6A and HHV-6B, were identified. In 2012, the International Committee on Taxonomy of Viruses (ICTV) classified HHV-6A and HHV-6B as separate viruses. This review outlines several of the documented epidemiological, biological, and immunological distinctions between HHV-6A and HHV-6B, which support the ICTV classification.

The DR1 and DR6 first exons of human herpesvirus 6A are not required for virus replication in culture and are deleted in virus stocks that replicate well in T-cell lines.

Human herpesvirus 6A (HHV-6A) and HHV-6B are lymphotropic viruses which replicate in cultured activated cord blood mononuclear cells (CBMCs) and in T-cell lines. Viral genomes are composed of 143-kb unique (U) sequences flanked by approximately 8- to 10-kb left and right direct repeats, DR(L) and DR(R). We have recently cloned HHV-6A (U1102) into bacterial artificial chromosome (BAC) vectors, employing DNA replicative intermediates.

Cloning human herpes virus 6A genome into bacterial artificial chromosomes and study of DNA replication intermediates.

Cloning of large viral genomes into bacterial artificial chromosomes (BACs) facilitates analyses of viral functions and molecular mutagenesis. Previous derivations of viral BACs involved laborious recombinations within infected cells. We describe a single-step production of viral BACs by direct cloning of unit length genomes, derived from circular or head-to-tail concatemeric DNA replication intermediates.

Human herpesvirus 6A (HHV-6A) and HHV-6B alter E2F1/Rb pathways and E2F1 localization and cause cell cycle arrest in infected T cells.

E2F transcription factors play pivotal roles in controlling the expression of genes involved in cell viability as well as genes involved in cell death. E2F1 is an important constituent of this protein family, which thus far contains eight members. The interaction of E2F1 with its major regulator, retinoblastoma protein (Rb), has been studied extensively in the past two decades, concentrating on the role of E2F1 in transcriptional regulation and the role of Rb in cell replication and cancer formation.

Characterization of the lymphotropic amplicons-6 and tamplicon-7 vectors derived from HHV-6 and HHV-7.

Amplicon-6 and Tamplicon-7 are novel non-integrating vectors derived from the lymphotropic Human Herpesviruses 6 and 7 (HHV-6 and HHV-7). In the presence of helper viruses the amplicon vectors replicate to yield packaged defective genomes of size approximately 150 kb and consisting of multiple repeat units containing (i) the oriLyt DNA replication origin (ii) the pac-1 and pac-2 cleavage and packaging signals (iii) bacterial plasmid DNA sequences (iv) the chosen transgene(s). Employing CD46 as a receptor HHV-6 gains entry into varied cells, including lymphocytes and dendritic cells, whereas HHV-7 employs the CD4 receptor to target CD4+ cells.

The history of the HSV amplicon: from naturally occurring defective genomes to engineered amplicon vectors.

We have derived the HSV amplicon vector in 1981/1982 after elaborate experience with "defective viruses", arising spontaneously in viral stocks propagated at high multiplicities of infection (m.o.i.

The herpes simplex virus type 1 vhs-UL41 gene secures viral replication by temporarily evading apoptotic cellular response to infection: Vhs-UL41 activity might require interactions with elements of cellular mRNA degradation machinery.

We have previously shown that herpes simplex virus type 1 (HSV-1) infection is associated with early destabilization/degradation of infected cell mRNAs and consequent shutoff of host protein synthesis by the activity of the virion-associated host shutoff (vhs) UL41 protein. Wild-type (wt) virus destabilized/degraded the housekeeping beta-actin and alpha-tubulin mRNAs as well host stress functions, like the heat shock 70 protein induced postinfection. vhs mutants did not degrade the mRNAs.

Use of amplicon-6 vectors derived from human herpesvirus 6 for efficient expression of membrane-associated and -secreted proteins in T cells.

The composite amplicon-6 vectors, which are derived from human herpesvirus 6 (HHV-6), can target hematopoietic cells. In the presence of the respective helper viruses, the amplicons are replicated by the rolling circle mechanism, yielding defective genomes of overall size 135 to 150 kb, composed of multiple repeats of units, containing the viral DNA replication origin, packaging signals, and the selected transgene(s). We report the use of amplicon-6 vectors designed for transgene expression in T cells.