Human Herpesvirus 6A (HHV-6A) and HHV-6B Alter E2F1/Rb Pathways and E2F1 Localization and Cause Cell Cycle Arrest in Infected T Cells

Abstract

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. Additionally, the effect of viral infections on E2F1/Rb interactions has been analyzed for different viruses, concentrating on cell division, which is essential for viral replication. In the present study, we monitored E2F1-Rb interactions during human herpesvirus 6A ( Human herpesvirus 6A (HHV-6A) and HHV-6B were initially isolated from peripheral blood mononuclear cells of immunologically deprived AIDS patients and patients with lymphoproliferative disorders (42, 58). They were recognized as distinct viruses by employing restriction enzyme analyses, antigenicity, and epidemiology (1, 60). Together with HHV-7, they constitute the group of roseoloviruses, a subgroup of the betaherpesvirus subfamily, possessing a colinear gene arrangement (54, 64). HHV-6A, HHV-6B, and HHV-7 associations with diseases have been reviewed recently (24, 37). Both HHV-6A and HHV-6B variants use CD46 as a receptor (59) to gain entry into various types of cells. They replicate productively in cultured CD4 ϩ T cells but also are known to have central nervous system involvement, as reviewed previously (24, 37). HHV-6B infects the majority of children by the age of 2, causing either asymptomatic infections or roseola infantum, characterized by high fever and skin rash. The virus can be isolated from peripheral blood mononuclear cells of the sick children (78, 79). In more rare cases, HHV-6 and HHV-7 infections were reported to cause seizures, convulsions, and encephalopathy (6,49,66,70,77,78,80,82,84). Furthermore, HHV-6B strains were found to be activated from latency in bone marrow, kidney, liver, and other transplantations (9,25,41,55,65,74,81,(83)(84)(85)(86)(87)(88). Of interest is our previous study (55), in which HHV-6B reactivation was prophylactically inhibited by ganciclovir treatment at the onset of transplantation. There is no acute disease currently known to be caused by HHV-6A. Viral isolates were implicated in the aggravation of symptoms of chronic fatigue syndrome and also in a subset of relapsing-remitting multiple sclerosis exacerbations. Recent studies have tested these associations (2-4, 14, 23, 34, 44, 56, 76).In the present paper, we describe the interaction of HHV-6A and HHV-6B with the host cell, concentrating on changes in E2F1/Rb pathways in infected SupT1 T cells. There are eight known members of the E2F family, which function to activate or repress the transcription of different combinations of genes, promoting or inhibiting cell cycle progression (18). The E2F1 transcription factor, originally identified as the cel...

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

“…(18,27). As shown here in HHV-6A infection of SupT1 T cells, there was pronounced up-regulation of E2F1 and DP1 proteins by 48 h.p.i.…”

“…It has been shown that human cytomegalovirus (HCMV) tegument protein pp71 induces Rb degradation (16) and that HCMV kinase protein UL97 phosphorylates Rb protein (17). We have shown (18) that the infection of SupT1 T cells with HHV-6A was associated with cellcycle arrest at the G2/M phase. Such arrest might be advantageous for viral replication and the production of the typical HHV-6 cytopathic effect, consisting of multiple fused infected cells.…”

“…Protein extracts were prepared as described (18). The antibodies used in Western blotting are described in SI Materials and Methods.…”

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

“…The SupT1 CD4 ϩ human T cells (37) were obtained from the National Institutes of Health AIDS Research and Reference reagent program. The viruses were propagated in SupT1 cells as described before (38). The virus with the short DR is infectious both by cell-to-cell and cell-free propagation.…”

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

“…The isolates were propagated initially in activated PBLs and CBMCs and then in continuous T-cell lines, including HSB-2, J-JHAN, SupT1, Molt-3, and MT-4 (11,45). The U1102 strain isolated by Downing and colleagues (12) was contributed to our laboratory by Robert Honess and was propagated first in activated PBLs and CBMCs (11,18,36,45) and then in J-JHAN and SupT1 T cells (4,30). To answer the question with regard to the origin of the short DRs and their structure, we have compared earlier viral HHV-6A passages with the currently propagated virus and the HHV-6A BAC clones.…”