Viral Gene Expression Patterns in Human Herpesvirus 6B-Infected T Cells

Abstract

Herpesvirus gene expression is divided into immediate-early (IE) or ␣ genes, early (E) or ␤ genes, and late (L) or ␥ genes on the basis of temporal expression and dependency on other gene products. By using real-time PCR, we have investigated the expression of 35 human herpesvirus 6B (HHV-6B) genes in T cells infected by strain PL-1. Kinetic analysis and dependency on de novo protein synthesis and viral DNA polymerase activity suggest that the HHV-6B genes segregate into six separate kinetic groups. The genes expressed early (groups I and II) and late (groups V and VI) corresponded well with IE and L genes, whereas the intermediate groups III and IV contained E and L genes. Although HHV-6B has characteristics similar to those of other roseoloviruses in its overall gene regulation, we detected three B-variant-specific IE genes. Moreover, genes that were independent of de novo protein synthesis clustered in an area of the viral genome that has the lowest identity to the HHV-6A variant. The organization of IE genes in an area of the genome that differs from that of HHV-6A underscores the distinct differences between HHV-6B and HHV-6A and may provide a basis for further molecular and immunological analyses to elucidate their different biological behaviors.In the mid-and late 1980s human herpesvirus 6A (HHV-6A) and HHV-6B were discovered and subsequently named as variants of 20,32,34). Although they share approximately 90% nucleotide sequence identity (13, 18), the accumulating biological, genetic, and epidemiological data suggest that these viruses have independent biological functions (13,18,34,37,38). Whereas little is known about the disease potential of HHV-6A, HHV-6B is the causative agent of the childhood disease exanthem subitum, characterized by a few days of high fever followed by a rash appearing with fever subsidence (34, 39). Thus, the frequency of HHV-6B seropositive individuals reaches almost 100% in early childhood (7, 10), but late primary infection may provoke a mononucleosislike disease similar to human cytomegalovirus (HCMV) mononucleosis. In addition, HHV-6B is thought to be involved in a number of other conditions, including encephalitis and neoplasia (2, 3).HHV-6B displays primarily tropism for T cells and monocytes (22,24). The virus enters the cells in part via binding to the ubiquitously expressed glycoprotein CD46 (33), but additional cellular proteins involved in virus entry still remain to be discovered (6, 33). As with other herpesviruses, HHV-6 establishes latency following the primary infection. In addition to its tropism for mononuclear cells, HHV-6 is highly neurotropic and may also reside in astrocytes within the central nervous system (8, 15), and it remains to be determined which cells harbor the majority of the latent virus (21, 23). Of clinical significance, HHV-6 is an important pathogen when reactivated in immunocompromised hosts, such as patients with AIDS, leukemia, lymphoma, and solid organ or bone marrow transplants (3).The entire genomes of HHV-6B strains Z29 and HST have...

Microarray-based determination of the lytic cascade of human herpesvirus 6B

“…Transcripts derived from 12 of the 41 genomic regions tested were detected in the CHX-treated sample. Detection of B7, U79 and G91/B8 (which corresponds to the 59 untranslated region of U90) under IE conditions is in agreement with previously published data (Oster & Hollsberg, 2002;Schiewe et al, 1994;Taniguchi et al, 2000). Several previously unclassified transcripts including B2, U85, G86/90.2 and G86/ 90.3 were also detected under IE conditions.…”

“…The late cluster consisted of genes expressed only at times after 24 h p.i. Among this group of genes, U11, U22, U23, U47 and U100 have been described previously as L genes (French et al, 1999;Mirandola et al, 1998;Oster & Hollsberg, 2002).Although these data showed good agreement with the known temporal order of many HHV-6 genes, the kinetics of some remained poorly defined, especially for the early cluster, which contains a mixture of IE and E genes. To better define the transitions between IE-to-E and E-to-L genes, viral gene expression in cells treated with CHX (protein synthesis inhibitor) and PAA (DNA synthesis inhibitor) was analysed for the classification of IE and E/L genes, respectively.…”

“…The late cluster consisted of genes expressed only at times after 24 h p.i. Among this group of genes, U11, U22, U23, U47 and U100 have been described previously as L genes (French et al, 1999;Mirandola et al, 1998;Oster & Hollsberg, 2002).…”

“…Transcription of genes in the delayed-early cluster peaked between 12 and 24 h p.i. and involved two known E genes, U51 and U69 (Menotti et al, 1999;Oster & Hollsberg, 2002), together with genes proposed to be involved in DNA replication, such as U27 and U28 (Pellett & Dominguez, 2001). The late cluster consisted of genes expressed only at times after 24 h p.i.…”

Human herpesvirus 6 infections after liver transplantation

“…The virus then replicates, assembles, and exits the infected cell to infect other cells. The first proteins synthesized during viral replication are the immediate-early (IE) proteins [16] . It was recently reported that two proteins, IE1 and IE2, distinguish the variants, HHV-6A and HHV-6B, respectively (L. Flamand, abstract 3-2, 6th International Conference on HHV6 & 7, 2008).…”