Human cytomegalovirus IE1 and IE2 proteins block apoptosis

The human cytomegalovirus-encoded chemokine receptor US28 induces caspase-dependent apoptosis

Viral subversion of apoptosis regulation plays an important role in the outcome of host/virus interactions. Although human cytomegalovirus (HCMV) encodes several immediate early (IE) antiapoptotic proteins (IE1, IE2, vMIA and vICA), no proapoptotic HCMV protein has yet been identified. Here we show that US28, a functional IE HCMV-encoded chemokine receptor, which may be involved in both viral dissemination and immune evasion, constitutively induces apoptosis in several cell types. In contrast, none of nine human cellular chemokine receptors, belonging to three different subfamilies, induced any significant level of apoptosis. US28-induced cell death involves caspase 10 and caspase 8 activation, but does not depend on the engagement of cell-surface death receptors of the tumour necrosis factor receptor/CD95 family. US28 cell-death induction is prevented by coexpression of C-FLIP, a protein that inhibits Fas-associated death domain protein (FADD)-mediated activation of caspase 10 and caspase 8, and by coexpression of the HCMV antiapoptotic protein IE1. The use of US28 mutants indicated that the DRY sequence of its third transmenbrane domain, required for constitutive G-protein signalling, and the US28 intracellular terminal domain required for constitutive US28 endocytosis, are each partially required for cell-death induction. Thus, in HCMV-infected cells, US28 may function either as a chemokine receptor, a phospholipase C activator, or a proapoptotic factor, depending on expression levels of HCMV and/or cellular antiapoptotic proteins.

Mouse cytomegalovirus M33 is necessary and sufficient in virus-induced vascular smooth muscle cell migration

Mouse cytomegalovirus (MCMV) encodes two potential seven-transmembrane-spanning proteins with homologies to cellular chemokine receptors, M33 and M78. While these virus-encoded chemokine receptors are necessary for the in vivo pathogenesis of MCMV, the function of these proteins is unknown. Since vascular smooth muscle cell (SMC) migration is of critical importance for the development of atherosclerosis and other vascular diseases, the ability of M33 to promote SMC motility was assessed. Similar to human CMV, MCMV induced the migration of mouse aortic SMCs but not mouse fibroblasts. To demonstrate whether M33 was required for MCMV-induced SMC migration, we employed interfering-RNA technology to specifically knock down M33 expression in the context of viral infection. The knockdown of M33 resulted in the specific reduction of M33 protein expression and ablation of MCMV-mediated SMC migration but failed to reduce viral growth in cultured cells. Adenovirus vector expression of M33 was sufficient to promote SMC migration, which was enhanced in the presence of recombinant mouse RANTES (mRANTES). In addition, M33 promoted the activation of Rac1 and extracellular signal-related kinase 1/2 upon stimulation with mRANTES. These findings demonstrate that mRANTES is a ligand for this chemokine receptor and that the activation of M33 occurs in a ligand-dependent manner. Thus, M33 is a functional homologue of US28 that is required for MCMV-induced vascular SMC migration.

Insights into viral transmission at the uterine-placental interface

During human gestation, viruses can cause intrauterine infections associated with pregnancy complications and fetal abnormalities. The ability of viruses to spread from the infected mother to the fetus arises from the architecture of the placenta, which anchors the fetus to the uterus. Placental cytotrophoblasts differentiate, assume an endothelial phenotype, breach uterine blood vessels and form a hybrid vasculature that amplifies the maternal blood supply for fetal development. Human cytomegalovirus - the major cause of congenital disease - infects the uterine wall and the adjacent placenta, suggesting adaptation for pathogen survival in this microenvironment. Infection of villus explants and differentiating and/or invading cytotrophoblasts offers an in vitro model for studying viruses associated with prenatal infections.

Immediate-early antigen expression and modulation of apoptosis after in vitro infection of polymorphonuclear leukocytes by human cytomegalovirus

Polymorphonuclear leukocytes (PMNL) are a major carrier of human cytomegalovirus (CMV) in viremic immunodepressed patients. We transmitted infectious virions and viral components to PMNL by coculturing these cells with infected human embryonic lung fibroblasts (HELF) or human umbilical vein endothelial cells (HUVEC). Quantitative time-course analysis of viral DNA and protein expression in PMNL, after functional separation from infected donor cells, indicated the initiation of viral cycling, with immediate-early protein expression. No viral replication or early or late gene expression was observed, but infected PMNL were able to infect naive fibroblasts more than 48 h after the end of co-culture. PMNL apoptosis was significantly delayed during co-culture with infected or uninfected HUVEC, and this phenomenon did not require contact between the two cell populations. The increased production of IL-8 in the same culture conditions that protect PMNL from apoptosis, associated with the reversion of this protection by inhibiting or depleting this factor in the culture media, targets this cytokine as a likely candidate for this protective effect. These data suggest that PMNL play a key role in virus dissemination in vivo, through their interactions with infected endothelial cells.

Role of tumor cell immune escape mechanisms in cytomegalovirus-mediated oncomodulation

It has been known for a long time that cytomegalovirus (CMV) has evolved mechanisms that allow the escape from the host immune surveillance. In the past, many efforts have been done to elucidate the molecular mechanisms underlying this virus-mediated immune escape and thus virus persistence. However, it is unknown, whether CMV may also impair immune responses directed against tumor cells. This might have severe consequences on tumor progression and may explain the growing evidence for CMV-mediated oncomodulation. This review summarizes recent work on CMV-mediated immune escape mechanisms of tumor cells and oncomodulation and proposes novel aspects that may be important for understanding the CMV-associated tumor progression.

Lack of association of cytomegalovirus with human brain tumors

Cytomegalovirus (CMV) is thought to possess oncogenic properties and has been linked with a number of human malignancies. CMV infection was recently described in association with malignant gliomas. The intent of the present study was to further investigate the reported association between CMV and malignant gliomas. Tissue from 22 brain tumors of various histologic types and grades, four normal brains, six breast carcinomas, six colon carcinomas, six lung carcinomas, and six sarcomas were evaluated for the presence of CMV by polymerase chain reaction (PCR), in situ hybridization, and immunohistochemical methods. None of the brain tumors or normal brain tissue tested demonstrated evidence of CMV pp65 or early nuclear proteins by immunohistochemistry. In addition, no CMV RNA or DNA was detected in these cases by in situ hybridization and PCR. None of the carcinomas or sarcomas evaluated were positive for CMV by immunohistochemistry, in situ hybridization, or PCR. The findings of the present study suggest that CMV is not significantly associated with brain tumors in humans.

Elimination of ie1 significantly attenuates murine cytomegalovirus virulence but does not alter replicative capacity in cell culture

The major immediate-early (MIE) genes of cytomegaloviruses (CMV) are broadly thought to be decisive regulators of lytic replication and reactivation from latency. To directly assess the role of the MIE protein IE1 during the infection of murine CMV (MCMV), we constructed an MCMV with exon 4 of the ie1 gene deleted. We found that, independent of the multiplicity of infection, the resulting recombinant virus, MCMVdie1, which fails to express the IE1 protein, was fully competent for early gene expression and replicated in different cultured cell types with identical kinetics to those of parental or revertant virus. Immunofluorescence microscopy studies revealed that MCMVdie1 was greatly impaired in its capacity to disrupt promyelocytic leukemia bodies in NIH 3T3 cells early after infection, a process that has been proposed to increase viral transcription efficiency. We examined MCMVdie1 in the murine model using both immunocompetent BALB/c and severe combined immunodeficient (SCID) mice. When MCMVdie1 was inoculated into these two types of mice, significantly lower viral titers were detected in infected organs than in those of the wild-type virus-infected animals. Moreover, the ie1-deficient MCMV exhibited a markedly reduced virulence. While all animals infected with 5 x 10(4) PFU of parental virus died by 30 days postinfection, SCID mice infected with a similar dose of MCMVdie1 did not succumb before 60 days postinfection. The in vivo defective growth phenotype of MCMVdie1 was abrogated upon rescue of ie1. These results demonstrate the significance of the ie1 gene for promoting an acute MCMV infection and virulence yet indicate that MCMV is able to grow in vivo, although impaired, in the absence of the ie1 gene.

Characterization of the elements and proteins responsible for interferon-stimulated gene induction by human cytomegalovirus

Human cytomegalovirus (HCMV) infection of human fibroblast cells activates a large number of interferon-stimulated genes (ISGs) in a viral envelope-cell membrane fusion-dependent mechanism. In this study, we identified two interferon response elements, the interferon-stimulated response element (ISRE) and the gamma interferon-activated site (GAS), which act as HCMV response sites (VRS). Gel mobility shift assays showed that cellular proteins form specific and identical complexes with ISRE and GAS elements, and the binding of these complexes to ISRE and GAS is stimulated by HCMV infection. Point mutations in the consensus sequences of ISRE and GAS completely abolished their activities in response to HCMV-mediated transactivation, as well as their abilities to interact with HCMV-activated VRS-binding proteins. Interferon regulatory factor 3 does not appear to be present in the VRS-binding complexes or to be involved directly in HCMV-mediated ISG activation. Using ProteinChip technology, four potential proteins were identified, ranging from 20 to 42 kDa, in the VRS-binding complexes. The data suggest that HCMV infection activates VRS-binding proteins, which then bind to the VRS and stimulate ISG expression.

Two gamma interferon-activated site-like elements in the human cytomegalovirus major immediate-early promoter/enhancer are important for viral replication

Human cytomegalovirus (HCMV) infection directly initiates a signal transduction pathway that leads to activation of a large number of cellular interferon-stimulated genes (ISGs). Our previous studies demonstrated that two interferon response elements, the interferon-stimulated response element and gamma interferon-activated site (GAS), in the ISG promoters serve as HCMV response sites (VRS). Interestingly, two GAS-like VRS elements (VRS1) were also present in the HCMV major immediate-early promoter-enhancer (MIEP/E). In this study, the importance of these VRS elements in viral replication was investigated. We demonstrate that the expression of the major IE genes, IE1 and IE2, is interferon inducible. To understand the biological significance of this signal transduction pathway in HCMV major IE expression, the two VRS1 in the MIEP/E were mutated. Mutant HCMVs in which the VRS elements were deleted or that contained point mutations grew dramatically more slowly than wild-type virus at a low multiplicity of infection (MOI). Insertion of wild-type VRS1 into the mutant viral genome rescued the slow growth phenotype. Furthermore, the expression levels of major IE RNAs and proteins were greatly reduced during infection with the VRS mutants at a low MOI. HCMV microarray analysis indicated that infection of host cells with the VRS mutant virus resulted in a global reduction in the expression of viral genes. Collectively, these data demonstrate that the two VRS elements in the MIEP/E are necessary for efficient viral gene expression and replication. This study suggests that although the HCMV-initiated signal transduction pathway results in induction of cellular antiviral genes, it also functions to stimulate viral major IE gene expression. This might be a new viral strategy in which the pathway is used to regulate gene expression and play a role in reactivation.

Cell death suppression by cytomegaloviruses

Cytomegaloviruses (CMVs), a subset of betaherpesviruses, employ multiple strategies to suppress apoptosis in infected cells and thus to delay their death. Human cytomegalovirus (HCMV) encodes at least two proteins that directly interfere with the apoptotic signaling pathways, viral inhibitor of caspase-8-induced apoptosis vICA (pUL36), and mitochondria-localized inhibitor of apoptosis vMIA (pUL37 x 1). vICA associates with pro-caspase-8 and appears to block its recruitment to the death-inducing signaling complex (DISC), a step preceding caspase-8 activation. vMIA binds and sequesters Bax at mitochondria, and interferes with BH3-only-death-factor/Bax-complex-mediated permeabilization of mitochondria. vMIA does not seem to either interact with Bak, a close structural and functional homologue of Bax, or to suppress Bak-mediated permeabilization of mitochondria and Bak-mediated apoptosis. All sequenced betaherpesviruses, including CMVs, encode close homologues of vICA, and those vICA homologues that have been tested, were found to be functional cell death suppressors. Overt sequence homologues of vMIA were found only in the genomes of primate CMVs, but recent observations made with murine CMV (MCMV) indicate that non-primate CMVs may also encode a cell death suppressor functionally resembling vMIA. The exact physiological roles and relative contributions of vMIA and vICA in suppressing death of CMV-infected cells in vivo have not been elucidated. There is strong evidence that the cell death suppressing function of vMIA is indispensable, and that vICA is dispensable for replication of HCMV. In addition to suppressed caspase-8 activation and sequestered Bax, CMV-infected cells display several other phenomena, less well characterized, that may diminish, directly or indirectly the extent of cell death.

The phosphorylation status of the serine-rich region of the human cytomegalovirus 86-kilodalton major immediate-early protein IE2/IEP86 affects temporal viral gene expression

The 86-kDa major immediate-early protein (IE2/IEP86) of human cytomegalovirus (HCMV) contains a serine-rich region (amino acids 258 to 275) with several consensus casein kinase II (CKII) sites. We performed extensive mutational analysis of this region, changing serines to alternating alanines and glycines. Mutation of the serines between amino acids 266 and 275 eliminated in vitro phosphorylation by CKII. In vitro CKII phosphorylation of the serines between amino acids 266 and 269 or between amino acids 271 and 275 inhibited the ability of IE2/IEP86 to bind to TATA-binding protein. Correspondingly, nonphosphorylatable mutants in these regions showed increased activation of specific HCMV gene promoters in transfection studies. Viruses containing mutations of the serines throughout the entire region (amino acids 258 to 275) or the second half (amino acids 266 to 275) of the region showed delayed expression of all viral proteins tested and, correspondingly, delayed growth compared to wild-type HCMV. Mutation of the serines in the first half of the serine-rich region (amino acids 258 to 264) or between amino acids 266 and 269 propagated very slowly and has not been further studied. In contrast, mutation of the serines between amino acids 271 and 275 resulted in accelerated virus growth and accelerated temporal expression of viral proteins. These results suggest that the serine-rich region is structurally complex, possibly affecting multiple functions of IE2/IEP86. The data show that the phosphorylation state of the serine-rich region, particularly between amino acids 271 and 275, modulates the temporal expression of viral genes.

The carboxyl-terminal region of human cytomegalovirus IE1491aa contains an acidic domain that plays a regulatory role and a chromatin-tethering domain that is dispensable during viral replication

The human cytomegalovirus major immediate-early (alpha) protein IE1(491aa) plays an important role in controlling viral gene expression at low multiplicities of infection. With a transient complementation assay, full-length IE1(491aa) enhanced the growth of ie1 mutant virus CR208 20-fold better than a deletion mutant lacking 71 carboxyl-terminal amino acids (IE1(1-420aa)). A 16-amino-acid domain between amino acids 476 and 491 was both necessary and sufficient for chromatin-tethering activity; however, this domain was completely dispensable for complementation of CR208 replication. The proximal 55-amino-acid acidic domain (amino acids 421 to 475) was found to be most important for function. A deletion mutant lacking only this domain retained chromatin-tethering activity but failed to complement mutant virus. Interestingly, serine phosphorylation (at amino acids 399, 402, 406, 423, 428, 431, 448, 451, and 455) was not required for complementation. These results show that IE1(491aa) is composed of at least two domains that support replication, a region located between amino acids 1 and 399 that complements ie1 mutant virus replication to low levels and an acidic domain between amino acids 421 and 479 that dramatically enhances complementation.

Human cytomegalovirus proteins encoded by UL37 exon 1 protect infected fibroblasts against virus-induced apoptosis and are required for efficient virus replication

Human cytomegalovirus (HCMV) strain AD169 mutants carrying transposon insertions or large deletions in UL37 exon 1 (UL37x1) were recovered from modified bacterial artificial chromosomes by reconstitution in human fibroblasts expressing the adenovirus anti-apoptotic protein E1B19K. UL37x1 mutant growth was severely compromised in normal fibroblasts, with minimal release of infectious progeny. Growth in E1B19K-expressing cells was restored, but did not reach wild-type levels. Normal fibroblasts infected by UL37x1 mutants underwent apoptosis spontaneously between 48 and 96 h after infection. Apoptosis was inhibited by treatment of cells with the broad-spectrum caspase inhibitor z-Val-Ala-Asp(OMe)-fluoromethylketone, resulting in substantially increased release of virus. Inhibition of viral DNA replication by phosphonoformate or ganciclovir also inhibited apoptosis, implying that death was triggered by late viral functions or by replication and packaging of the viral genome. Immunofluorescent staining showed that although viral proteins accumulated normally during delayed-early phase and viral DNA replication compartments formed, viral late proteins were detected only rarely, suggesting that spontaneous apoptosis occurs early in late phase. These results demonstrate that anti-apoptotic proteins encoded by HCMV UL37x1 [pUL37x1 (vMIA), gpUL37 and gpUL37(M)] prevent apoptosis that would otherwise be initiated by the replication programme of the virus and are required for efficient and sustainable virus replication.

ORF390 of white spot syndrome virus genome is identified as a novel anti-apoptosis gene

Apoptosis serves as an important defense strategy employed by host cells against viral invasion. Many viruses contain the anti-apoptotic genes to block the defense-by-death response of host cells. In this study, we tried to identify the putative anti-apoptotic genes in white spot syndrome virus (WSSV) genome. We confirmed that actinomycin D could induce apoptosis of shrimp primary cells. However, the apoptosis triggered by actinomycin D was inhibited by WSSV infection. As mutants of Autographa californica nucleopolyhedrovirus (AcMNPV), AcMNPVDelta35k/pol+ lacks a functional P35 gene undergoing apoptosis and its infection could induce Sf9 cell apoptosis. To identify the putative apoptotic suppressor gene of WSSV, overlapping cosmid clones representing the entire WSSV genome were individually cotransfected along with genome DNA of AcMNPVDeltaP35k/pol+. Using this marker rescue assay, a WSSV DNA fragment that was able to rescue AcMNPVDeltaP35k/pol+ infection in Sf9 cells was isolated. By further sequence analysis and rescue assay, the ORF390 was identified as a novel anti-apoptotic gene. The ORF displays two putative caspase9 cleavage sites LLVETDGPS, VKLEHDGSK, and a caspase3 cleavage site EEDEVDGVP. The ORF was cloned into the pIE1 vector and then the recombinant vector was transfected into Sf9 cells. The Sf9 cells did not show obvious characteristics of apoptosis when infected with AcMNPVDeltaP35k/pol+. And the transient expression of ORF390 allowed AcMNPVDeltaP35k/pol+ replication in Sf9 cells and resulted in the formation of polyhedra successfully. The results indicate that function of ORF390 in WSSV is a kind of apoptotic suppressor like P35 in AcMNPV.

Human cytomegalovirus immediate-early 1 protein facilitates viral replication by antagonizing histone deacetylation

The human cytomegalovirus 72-kDa immediate-early (IE)1 and 86-kDa IE2 proteins are expressed at the start of infection, and they are believed to exert much of their function through promiscuous transcriptional activation of viral and cellular gene expression. Here, we show that the impaired growth of an IE1-deficient mutant virus in human fibroblasts is efficiently rescued by histone deacetylase (HDAC) inhibitors of three distinct chemical classes. In the absence of IE1 expression, the viral major IE and UL44 early promoters exhibited decreased de novo acetylation of histone H4 during the early phase of infection, and the hypoacetylation correlated with reduced transcription and accumulation of the respective gene products. Consistent with these findings, IE1 interacts specifically with HDAC3 within infected cells. We also demonstrate an interaction between IE2 and HDAC3. We propose that the ability to modify chromatin is fundamental to transcriptional activation by IE1 and, likely, IE2 as well.

Cellular stress and signal transduction responses to human cytomegalovirus infection

Human cytomegalovirus (HCMV) receptor-ligand interactions and viral entry excite cellular responses such as receptor tyrosine kinase and mitogen-activated protein kinase signaling, cytoskeletal rearrangement, and the induction of transcription factors, prostaglandins, and cytokines. Bi-phasic stimulation of these pathways, excepting interferon, facilitates productive viral infection and likely contributes to viral pathogenesis.

Analysis of splice variants of the immediate-early 1 region of human cytomegalovirus

The major immediate-early (MIE) gene of human cytomegalovirus (HCMV) produces multiple mRNAs through differential splicing and polyadenylation. Reverse transcriptase PCR was used to characterize transcripts from exons 1, 2, 3, and 4 (immediate-early 1 [IE1]). The expected IE72 and IE19 mRNAs were detected, as well as two heretofore-uncharacterized transcripts designated IE17.5 and IE9. The IE72, IE19, and IE17.5 transcripts utilized the same 5'-splice site in exon 3. IE9 utilized a cryptic 5'-splice site within exon 3. The IE19, IE17.5, and IE9 transcripts all used different 3'-splice sites within exon 4. These spliced species occur in infected human foreskin fibroblast (HFF) cells, with accumulation kinetics similar to those of IE72 mRNA. IE19 and IE9 RNAs were much more abundant than IE17.5 RNA. Transfection of CV-1 cells with cDNAs resulted in IE19 and IE17.5 proteins detectable by antibodies to either N-terminal or C-terminal epitopes. No IE9 protein product has been detected. We have not been able to detect IE19, IE17.5, or IE9 proteins during infection of HFF, HEL, or U373MG cells. Failure to detect IE19 protein contrasts with a previous report (M. Shirakata, M. Terauchi, M. Ablikin, K. Imadome, K. Hirai, T. Aso, and Y. Yamanashi, J. Virol. 76:3158-3167, 2002) of IE19 protein expression in HCMV-infected HEL cells. Our analysis suggests that an N-terminal breakdown product of IE72 may be mistaken for IE19. Expression of IE19 or IE17.5 from its respective cDNA results in repression of viral gene expression in infected cells. We speculate that expression of these proteins during infection may be restricted to specific conditions or cell types.

SUMOylation of the human cytomegalovirus 72-kilodalton IE1 protein facilitates expression of the 86-kilodalton IE2 protein and promotes viral replication

The 72-kDa immediate-early 1 protein (IE1-72kDa) of human cytomegalovirus has been previously shown to be posttranslationally modified by covalent conjugation to the ubiquitin-related protein SUMO-1. Using an infectious bacterial artificial chromosome clone of human cytomegalovirus, we constructed a mutant virus (BADpmIE1-K450R) that is deficient for SUMOylation of IE1-72 kDa due to a single amino acid exchange in the SUMO-1 attachment site. Compared to wild-type virus, this mutant grew more slowly and generated a reduced yield in infected human fibroblasts, indicating that SUMO modification is required for the full activity of IE1-72 kDa. The lack of SUMOylation did not affect the intranuclear localization of IE1-72 kDa, including its ability to target to and disrupt PML bodies and to bind to mitotic chromatin. Likewise, SUMOylation-deficient IE1-72 kDa activated several viral promoters as efficiently as the wild-type protein. However, the failure to modify IE1-72 kDa resulted in substantially reduced levels of the IE2 transcript and its 86-kDa protein (IE2-86 kDa). These observations suggest that SUMO modification of IE1-72 kDa contributes to efficient HCMV replication by promoting the accumulation of IE2-86 kDa.

Latent Epstein-Barr virus (EBV) infection and cytomegalovirus (CMV) infection in synovial tissue of autoimmune chronic arthritis determined by RNA- and DNA-in situ hybridization

In rheumatoid arthritis (RA) viral triggers, especially Epstein-Barr virus (EBV) and cytomegalovirus (CMV), have been suggested. By PCR analysis DNA of several viruses among which EBV, CMV, and parvovirus B19 (B19) has been detected in RA synovial fluid and synovial tissue. In 63 synovial tissues of 29 rheumatoid arthritis (RA), 6 psoriatic arthritis (PsA), 26 reactive arthritis/synovitis (rA/S), and two normal synovial cases, we recently could demonstrate a high percentage of replicative B19 infection within the synovial tissue, being significantly more frequent in autoimmune arthritis. To further investigate the influence of synovial virus infections in rheumatoid arthritis, we now analyzed the same sample of synovial tissues for CMV and EBV infections by DNA-in situ hybridization (CMV), EBER1/2-RNA-in situ hybridization (EBV), and immunohistochemistry. A significant latent EBV infection of synovial lining cells, synovial fibroblasts, and/or infiltrating lymphocytes was identified in 5/29 (17.2 %) RA, 1/6 (16.7%) PsA, and to a much lower degree in 1/26 (3.8%) rA/S specimens. CMV-DNA was detected in 31% of RA, 3/6 (50%) of PsA, and 11.5% of rA/S. Immunohistochemical analysis of CMV early antigen revealed replicative CMV activity in 20.7% of RA and 2/6 (33.3%) of PsA specimens but not in reactive arthritis synovia. Comparative analysis of the EBV-, CMV-, and published B19-data demonstrated that relevant synovial virus infections in general and furthermore double or multiple infections are far more common in autoimmune arthritis than in rA/S. A triple virus infection was found solely in RA in 10.3% of cases. The evidence of increased synovial persistence of EBV, CMV, or B19 either alone or even more as coinciding infections may further reinforce the notion of a primary role of these viruses in autoimmune arthritis.

Evaluation of the host transcriptional response to human cytomegalovirus infection

Gene expression data from human cytomegalovirus (HCMV)-infected cells were analyzed using DNA-Chip Analyzer (dChip) followed by singular value decomposition (SVD) and compared with a previous analysis of the same data that employed GeneChip software and a fold change filtering approach. dChip and SVD analysis revealed two clusters of coexpressed human genes responding differently to HCMV infection: one containing some genes identified previously, and another that was largely unique to this analysis. Annotating these genes, we identified several functional categories important to host cell responses to HCMV infection. These categories included genes involved in transcriptional regulation, oncogenesis, and cell cycle regulation, which were more prevalent in cluster 1, and genes involved in immune system regulation, signal transduction, and cell adhesion, which were more prevalent in cluster 2. Within these categories, we found genes involved in the host response to HCMV infection (mainly in cluster 1), as well as genes targeted by HCMV’s immune evasion strategies (mainly in cluster 2). As the second group of genes identified by the dChip and SVD approach was statistically and biologically significant, our results point out the advantages of using different methods to analyze gene expression data.

Protein kinase B/Akt regulates coxsackievirus B3 replication through a mechanism which is not caspase dependent

The role of signaling pathways including the mitogen-activated protein kinases (MAPKs) and phosphatidylinositol 3-kinase (PI3K) during viral infection has gained much recent attention. Our laboratory reported on an important regulatory role for extracellular signal-regulated kinases (ERK1/2), subfamily members of the MAPKs, during coxsackievirus B3 (CVB3) infection. However, the role of the PI3K pathway in CVB3 infection has not been well characterized. CVB3 is the most common known viral infectant of heart muscle that directly injures and kills infected cardiac myocytes during the myocarditic process. In the present study, we investigated the role of protein kinase B (PKB) (also known as Akt), a general downstream mediator of survival signals through the PI3K cascade, in regulating CVB3 replication and virus-induced apoptosis in a well-established HeLa cell model. We have demonstrated that CVB3 infection leads to phosphorylation of PKB/Akt on both Ser-473 and Thr-308 residues through a PI3K-dependent mechanism. Transfection of HeLa cells with a dominant negative mutant of Akt1 or pretreatment of wild-type HeLa cells with the specific PI3K inhibitor LY294002 significantly suppresses viral RNA expression, as reflected in diminished viral capsid protein expression and viral release. Dominant negative Akt1 and LY294002 also increase apoptosis in infected cells, which can be reversed by addition of the general caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD.fmk). Interestingly, blocking of apoptosis by zVAD.fmk does not reverse the viral RNA translation blockade, indicating that the inhibitory effect of dominant negative Akt1 on viral protein expression is not caspase dependent. In addition, we showed that the attachment of virus to its receptor-coreceptor complex is not sufficient for PKB/Akt activation and that postentry viral replication is required for Akt phosphorylation. Taken together, these data illustrate a new and imperative role for Akt in CVB3 infection in HeLa cells and show that the PI3K/Akt signaling is beneficial to CVB3 replication.

Productive human herpesvirus 6 infection causes aberrant accumulation of p53 and prevents apoptosis

p53 plays an important role in tumour suppression in cells exposed to some genotoxic stresses. We found that the p53 protein level was increased in a variety of cell lines infected with human herpesvirus 6 (HHV-6). Because the elevation in p53 began very soon after infection (4 h) and did not occur with UV-inactivated virus infection, it appeared to require the expression of one or more viral immediate-early (IE) genes. To elucidate the mechanism of p53 induction, we investigated its regulation at the protein level. Pulse-chase analysis showed that the stability of p53 increased in HHV-6-infected cells. In addition, the ubiquitination of p53 decreased after infection, indicating that the stability of p53 was increased through deubiquitination. We showed by confocal microscopy that the additional p53 mainly localized to the cytoplasm and that p53 was retained in the cytoplasm even after UV irradiation, but that it translocated into the nucleus in mock-infected cells. Furthermore, DNA fragmentation analysis, a terminal deoxynucleotidyl transferase-mediated dUTP nick end-labelling (TUNEL) assay and annexin V staining showed that infected cells were resistant to UV-induced apoptosis. These results lead us to propose that HHV-6 has a mechanism for retaining p53 within the cytoplasm and protects the infected cells from apoptosis.

Viral Bcl-2 homologs and their role in virus replication and associated diseases

Cellular Bcl-2 family proteins regulate a critical step in the mammalian programmed cell death pathway by modulating mitochondrial permeability and function. Bcl-2 family proteins are also encoded by several large DNA viruses, including all known gamma herpesviruses, adenoviruses, and several other unrelated viruses. Viral Bcl-2 proteins can prevent cell death but often escape cellular regulatory mechanisms that govern their cellular counterparts. By evading the "altruistic" suicide of infected cells, viruses can ensure replication and propagation in the infected host, but sometimes in surprising ways. Many human cancers and other disorders are associated with viruses that encode Bcl-2 homologs. Here we consider the available mechanistic data for viral compared to cellular Bcl-2 protein function along with relevance to the virus life cycle and human disease states.

Oncomodulatory signals by regulatory proteins encoded by human cytomegalovirus: a novel role for viral infection in tumor progression

A high frequency of human cytomegalovirus (HCMV) genome and antigens in tumor samples of patients with different malignancies is now well documented, although the causative role for HCMV in the development of the neoplasias remains to be established. HCMV infection can modulate multiple cellular regulatory and signalling pathways in a manner similar to that of oncoproteins of small DNA tumor viruses such as human papilloma virus or adenoviruses. However, in contrast to these DNA tumor viruses, HCMV infection fails to transform susceptible normal human cells. There is now growing evidence that tumor cells with disrupted regulatory and signalling pathways enable HCMV to modulate their properties including stimulation of cell proliferation, survival, invasion, production of angiogenic factors, and immunogenic properties. In contrast to previously suggested "hit and run" transformation we suggest that persistence in tumor cells is essential for HCMV to fully express its oncomodulatory effects. These effects are observed particularly in persistent HCMV infection and are mediated mainly by activity of HCMV regulatory proteins. In persistently HCMV-infected tumor cell lines - a selection of novel, slowly growing virus variants with changes in coding sequences for virus regulatory proteins takes place. As a result, oncomodulatory effects of HCMV infection may lead to a shift to more malignant phenotype of tumor cells contributing to tumor progression.

Human cytomegalovirus and Epstein-Barr virus type 1 in periodontal abscesses

OBJECTIVES

Recent studies have linked herpesviruses to severe types of periodontal disease, but no information exists on their relationship to periodontal abscesses. The present study determined the presence of human cytomegalovirus (HCMV) and Epstein-Barr virus type 1 (EBV-1) in periodontal abscesses and the effect of treatment on the subgingival occurrence of these viruses.

MATERIAL AND METHODS

Eighteen adults with periodontal abscesses participated in the study. Subgingival samples were collected from each patient with sterile curettes from an abscess-affected site and a healthy control site. HCMV and EBV-1 were identified by polymerase chain reaction at the time of the abscess and at 4 months after surgical and systemic doxycycline therapy.

RESULTS

HCMV was detected in 66.7% of periodontal abscess sites and in 5.6% of healthy sites (P=0.002). EBV-1 occurred in 72.2% of abscess sites but not in any healthy site (P<0.001). HCMV and EBV-1 co-infection was identified in 55.6% of the abscess sites. Posttreatment, HCMV and EBV-1 were not found in any study site.

CONCLUSIONS

HCMV and EBV-1 genomes are commonly found in periodontal abscesses. These data favor a model in which a herpesvirus infection of the periodontium impairs the host defense and serves as a platform for the entrance of bacterial pathogens into gingival tissue with subsequent risk of abscess development.

HCMV infection: modulating the cell cycle and cell death

Human cytomegalovirus (HCMV) is a member of the Herpesviridae family and is recognized as a significant pathogen to certain subgroups of the human population. It has become apparent that HCMV manipulation of the host cell cycle as well as the immune response promotes the replication and propagation of the virus. The ability of HCMV to modulate components of the host immune system and the response to infection most likely contributes to the pathology associated with this virus. This review will address the mechanisms HCMV has adapted to modulate the cell cycle to promote viral replication as well as the different ways it can prevent the "death" of an infected cell.

Human cytomegalovirus (HCMV) IE1 plays role in resistance to apoptosis with etoposide in cancer cell line by Cdk2 accumulation

Human cytomegalovirus (HCMV) has many strategies to survive the attack of the host. HCMV infection of host cells induces cellular activation and disturbance of the cell cycle. It is possible that HCMV modulates the behavior of certain cancer cells that are susceptible to HCMV infection. This study was performed to identify the possible mechanism of resistance to apoptotic stimuli in some cancer cell lines by HCMV infection. HCMV-infected cancer cells showed resistance to apoptosis induced by the topoisomerase II inhibitor etoposide. UMG1-2, which constitutively expresses HCMV immediate-early protein-1 (IE1), had resistance to apoptosis induced by etoposide as compared with the parental cell line U373MG. Measurement of caspases activity with fluorogenic substrates in etoposide-treated U373MG and UMG1-2 cells and the direct activation of caspase-3 with peptides containing arginine-glycine-aspartate in U373MG and UMG1-2 cells revealed that the inhibition level of apoptosis by HCMV IE1 would be upstream of caspase-3 in the caspase cascade pathway. Cellular expression of Cdk2 was increased in UMG1- 2 after etoposide treatment while the expression of E2F-1 in UMG1-2 was decreased as compared with that in U373MG. The Cdk2 inhibitor, roscovitine, decreased the resistance to apoptosis on etoposide-treated UMG1-2. These results suggest that aberrant HCMV infection confers resistance to anticancer drugs on some cancer cells and protects cells from apoptosis, possibly due to the deregulation of cyclin-dependent kinase by HCMV immediate-early protein.

The role of viruses in cardiac allograft vasculopathy

Considerable evidence suggests a role for viruses in transplant arteriosclerosis (TA), including observational data, experimental models and therapeutic trials implicating human cytomegalovirus (HCMV) in the progression to TA. In pediatric heart transplant patients, adenoviral genome in endomyocardial biopsies (EMB) is an important predictor of TA and graft loss. During CMV viremia, EMBs from adult patients demonstrate endothelialitis and vascular smooth muscle cell proliferation. These changes are predictors of subsequent diffuse TA. HCMV immediate early proteins (IE-1 and IE-2) increase the constitutive expression of intercellular adhesion molecule-1 (ICAM-1) independent of other intracellular cytokines. Likewise, viral chemokines such as US28 have been implicated in vascular disease because of their ability to induce smooth muscle cell migration. Recent data suggests that CMV might accelerate TA through its ability to abrogate the vascular protective effects of the endothelium-derived nitric oxide system (eNOS). Confirmation of causality requires clinical trials demonstrating that antiviral agents such as ganciclovir inhibit TA. Such studies in patients though limited to retrospective analyses, suggest that ganciclovir prophylaxis early after heart transplantation reduces the risk of TA. These observations emphasize the need for randomized controlled clinical trials to confirm a causal role for CMV (and other viruses) in TA.

Characterization of vnr-13, the first alphaherpesvirus gene of the bcl-2 family

The Bcl-2 family, including antiapoptotic and proapoptotic members, plays key regulating roles in programmed cell death. We report the characterization of a new member of the bcl-2 family, encoded by herpesvirus of turkeys (HVT). The product of this gene shares 80% homology with Nr-13, an apoptosis inhibitor, which is overexpressed in avian cells transformed by the v-src oncogene. This new gene, that we propose to call vnr-13, is the first member of the bcl-2 family to be isolated among alpha-herpesviruses. Results from cells expressing the HVT-vnr-13 gene product show that the encoded protein inhibits apoptosis and also reduces the rate of cellular proliferation. Contrary to all bcl-2 homologues found in gamma-herpesvirus, which are intronless, vnr-13 has the same organization as the cellular nr-13 gene. Hence, the HVT vnr-13 gene may have been acquired from a reverse transcriptase product of an unspliced precursor RNA, or via direct recombination with the host chromosomal DNA.

Differential function and expression of the viral inhibitor of caspase 8-induced apoptosis (vICA) and the viral mitochondria-localized inhibitor of apoptosis (vMIA) cell death suppressors conserved in primate and rodent cytomegaloviruses

Human cytomegalovirus (CMV) genes UL36 and UL37 encode viral inhibitor of caspase-8-induced apoptosis (vICA) and viral mitochondria inhibitor of apoptosis (vMIA), respectively. Rhesus macaque CMV homologues, denoted Rh-vICA and Rh-vMIA, were identified and found to suppress apoptosis. One of these functions was conserved in MCMV, encoded by the M36 gene and denoted M-vICA. Conserved regions were compared to domains important to vICA- and vMIA-mediated cell death suppression. The conserved sequences of primate CMV vMIA homologues overlapped with the two known functional domains, providing further evidence supporting a crucial role of vMIA in cell death suppression. RNA blot analyses revealed that expression of murine and rhesus macaque CMV UL36 and UL37 homologues started early and continued through late times of infection. Murine CMV homologues were expressed with alpha (immediate early) kinetics, like human CMV UL36 and UL37, whereas rhesus macaque CMV homologues exhibited beta (delayed early) kinetics. Despite differences in organization and transcriptional regulation, this region appears to carry out a conserved role in cell death suppression. When viewed in light of sequence conservation, a functional vMIA homologue appears to be encoded by every primate CMV, whereas a functional vICA homologue appears to be encoded by all cytomegaloviruses for which sequence data are available.

Murine cytomegalovirus m41 open reading frame encodes a Golgi-localized antiapoptotic protein

Viruses have evolved various strategies to prevent premature apoptosis of infected host cells. Some of the viral genes mediating antiapoptotic functions have been identified by their homology to cellular genes, but others are structurally unrelated to genes of known function. In this study, we used a random, unbiased approach to identify such genes in the murine cytomegalovirus genome. From a library of random transposon insertion mutants, a mutant virus that caused premature cell death was isolated. The transposon was inserted within open reading frame m41. An independently constructed m41 deletion mutant showed the same phenotype, whereas deletion mutants lacking the adjacent genes m40 and M42 did not. Apoptosis occurred in different cell types, could be blocked by caspase inhibitors, and did not require p53. Within the murine cytomegalovirus genome, m41, m40, and m39 form a small cluster of genes of unknown function. They are homologous to r41, r40, and r39 of rat cytomegalovirus, but lack sequence homology to UL41, UL40, and UL37 exon 1 (UL37x1) which are located at the corresponding positions of the human cytomegalovirus genome. Unlike UL37x1 of human cytomegalovirus, which encodes a mitochondrion-localized inhibitor of apoptosis that is essential for virus replication, m41 encodes a protein that localizes to the Golgi apparatus. The murine cytomegalovirus m41 product is the first example of a Golgi-localized protein that prevents premature apoptosis and thus extends the life span of infected cells.

Varicella-zoster virus-infected human sensory neurons are resistant to apoptosis, yet human foreskin fibroblasts are susceptible: evidence for a cell-type-specific apoptotic response

The induction of apoptosis or programmed cell death in virus-infected cells is an important antiviral defense mechanism of the host, and some herpesviruses have evolved strategies to modulate apoptosis in order to enhance their survival and spread. In this study, we examined the ability of varicella-zoster virus (VZV) to induce apoptosis in primary human dorsal root ganglion neurons and primary human foreskin fibroblasts (HFFs). Three independent methods (annexin V, TUNEL [terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling] staining, and electron microscopy) were used to assess apoptosis in these cells on days 1, 2, and 4 postinoculation. By all three methods, apoptosis was readily detected in VZV-infected HFFs. In stark contrast, apoptosis was not detected during productive VZV infection of neurons. The low-passage clinical isolate Schenke and the tissue culture-adapted ROka strain both induced apoptosis in HFFs but not in neurons, suggesting that this cell-type-specific apoptotic phenotype was not VZV strain specific. These data show that the regulation of apoptosis differs markedly between HFFs and neurons during productive VZV infection. Inhibition of apoptosis during infection of neurons may play a significant role in the establishment, maintenance, and reactivation of latent infection by promoting survival of these postmitotic cells.

The human cytomegalovirus UL45 gene product is a late, virion-associated protein and influences virus growth at low multiplicities of infection

Human cytomegalovirus (HCMV) encodes a protein related to the large (R1) subunit of ribonucleotide reductase (RR), but does not encode the corresponding small (R2) subunit. The R1 homologue, UL45, lacks many catalytic residues, and its impact on deoxyribonucleotide (dNTP) production remains unknown. Here, UL45 is shown to accumulate at late stages of infection and to be a virion tegument protein. To study UL45 function in its genome context, UL45 was disrupted by transposon insertion. The UL45-knockout (UL45-KO) mutant exhibited a growth defect in fibroblasts at a low m.o.i. and also a cell-to-cell spread defect. This did not result from a reduced dNTP supply because dNTP pools were unchanged in resting cells infected with the mutant virus. Irrespective of UL45 expression, all cellular RR subunits - S-phase RR subunits, and the p53-dependent p53R2 - were induced by infection. p53R2 was targeted to the infected cell nucleus, suggesting that HCMV diverts a mechanism normally activated by DNA damage response. Cells infected with the UL45-KO mutant were moderately sensitized to Fas-induced apoptosis relative to those infected with the parental virus. Together with the report on the UL45-KO endotheliotropic HCMV mutant (Hahn et al., J Virol 76, 9551-9555, 2002), these data suggest that UL45 does not share the prominent antiapototic role attributed to the mouse cytomegalovirus homologue M45 (Brune et al., Science 291, 303-305, 2001).

Human cytomegalovirus proteins PP65 and IEP72 are targeted to distinct compartments in nuclei and nuclear matrices of infected human embryo fibroblasts

The cellular distribution of the human cytomegalovirus (HCMV)-specific UL83 phosphoprotein (pp65) and UL123 immediate-early protein (IEp72) in lytically infected human embryo fibroblasts was studied by means of indirect immunofluorescence and confocal microscopy. Both proteins were found to have a nuclear localization, but they were concentrated in different compartments within the nuclei. The pp65 was located predominantly in the nucleoli; this was already evident with the parental viral protein, which was targeted to the above nuclear compartment very soon after infection. The nucleolar localization of pp65 was also observed at later stages of the HCMV infectious cycle. After chromatin extraction (in the so-called in situ nuclear matrices), a significant portion of the pp65 remained associated with nucleoli within the first hour after infection, then gradually redistributed in a perinucleolar area, as well as throughout the nucleus, with a granular pattern. A quite different distribution was observed for IEp72 at very early stages after infection of human embryo fibroblasts with HCMV; indeed, this viral protein was found in bright foci, clearly observable in both non-extracted nuclei and in nuclear matrices. At later stages of infection, IEp72 became almost homogeneously distributed within the whole nucleus, while the foci increased in size and were more evenly spread; in several infected cells some of them lay within nucleoli. This peculiar nuclear distribution of IEp72 was preserved in nuclear matrices as well. The entire set of data is discussed in terms of the necessity of integration for HCMV-specific products into the pre-existing nuclear architecture, with the possibility of subsequent adaptation of nuclear compartments to fit the needs of the HCMV replicative cycle.

Prevalence of Human Herpesviruses in Patients with Aggressive Periodontitis

BACKGROUND

Recent studies have demonstrated that various human viruses, especially cytomegalovirus (HCMV) and Epstein-Barr virus type-1 (EBV-1), seem to play a part in the pathogenesis of human periodontitis. The aim of this investigation was to evaluate the subgingival presence of HCMV and EBV in patients with aggressive periodontitis (AgP) and healthy subjects and to examine the effect of treatment on the incidence of these viruses 3 months following surgery.

METHODS

A polymerase chain reaction (PCR) method determined the presence of HCMV and EBV-1. Subgingival plaque samples from 17 consecutive AgP patients and 16 healthy controls were collected. The following indices were measured: plaque index (PI), gingival index (GI), probing depths (PD), and clinical attachment loss (CAL). Clinical parameters were assessed pretherapy and at 3 months following surgical and antimicrobial therapy.

RESULTS

HCMV was detected in 64.7% of AgP patients but not detected in healthy subjects (P < 0.001) and EBV-1 in 70.6% of AgP patients and 6.3% of the healthy controls (P < 0.001). HCMV and EBV-1 coinfection was detected in 41.7% of AgP patients. A statistically significant decrease was found in all clinical parameters 3 months after treatment. There was a statistically significant decrease in HCMV and EBV-1 following therapy (P < 0.001; no HCMV; 1 patient with EBV-1).

CONCLUSIONS

These findings indicate that subgingival presence of EBV-1 HCMV is strongly associated with aggressive periodontitis, and coinfection with HCMV and EBV-1 appears to be particularly deleterious to periodontal health.

Human cytomegalovirus induces apoptosis in promonocyte THP-1 cells but not in promyeloid HL-60 cells

The effect of human cytomegalovirus (HCMV) infection on the viability of the cells in the monocyte/myeloid lineage was investigated. Two cell lines at different stages in the differentiation pathway, the less differentiated promyeloid HL-60 and the more differentiated promonocyte THP-1 cells, were used in this study. While the viability of THP-1 cells was significantly impaired by HCMV infection, the viability of HL-60 cells was not affected. The decrease in the viability of THP-1 cells appears to result from the increase in apoptosis following HCMV infection. Interestingly, HL-60 cells were more sensitive than THP-1 cells to the apoptotic effect of other apoptogenic agents such as ultraviolet irradiation and hydrogen peroxide. When HL-60 cells were induced to differentiate by treating cells with 12-O-tetradecanoyl-phorbol 13-acetate (TPA), HCMV infection induced an increase in apoptosis of the differentiated HL-60 cells by TPA. Therefore, HCMV-induced apoptosis in the cells of the myeloid/monocyte lineage appears to depend on the degree of cell differentiation.

The human cytomegalovirus

Human cytomegalovirus (HCMV), a betaherpesvirus, represents the major infectious cause of birth defects, as well as an important pathogen for immunocompromised individuals. The viral nucleocapsid containing a linear double-stranded DNA of 230 kb is surrounded by a proteinaceous tegument, which is itself enclosed by a loosely applied lipid bilayer. Expression of the HCMV genome is controlled by a cascade of transcriptional events that leads to the synthesis of three categories of viral proteins designated as immediate-early, early, and late. Clinical manifestations can be seen following primary infection, reinfection, or reactivation. About 10% of infants are infected by the age of 6 months following transmission from their mothers via the placenta, during delivery, or by breastfeeding. HCMV is a significant post-allograft pathogen and contributes to graft loss independently from graft rejection. Histopathologic examination of necropsy tissues demonstrates that the virus enters via the epithelium of the upper alimentary, respiratory, or genitourinary tracts. Hematogenous spreading is typically followed by infection of ductal epithelial cells. Infections are kept under control by the immune system. However, total HCMV clearance is rarely achieved, and the viral genome remains at selected sites in a latent state. Virological and molecular detection of HCMV, as well as serological demonstration of a specific immune response, are used for diagnosis. Treatment of HCMV infections is difficult because there are few options. The presently available drugs produced a significant clinical improvement, but suffer from poor oral bioavailability, low potency, development of resistance in clinical practice, and dose-limiting toxicities.

Characterization of the immediate-early 2 protein of human herpesvirus 6, a promiscuous transcriptional activator

In the present work we report the cloning of a full-length cDNA encoding the immediate-early (IE) 2 protein from human herpesvirus 6 (HHV-6) variant A (GS strain). The transcript is 4690 nucleotides long and composed of 5 exons. Translation initiation occurs within the third exon and proceeds to the end of U86. Kinetic studies indicate that the 5.5-kb IE2 mRNA is expressed under IE condition, within 2-4 h of infection. IE2 transcripts from both variants A and B are expressed under similar kinetics with IE2 transcripts accumulating up to 96 h postinfection. Although several large transcripts (>5.5 kb) hybridized with the IE2 probe, suggesting multiple transcription initiation sites, a single form of the IE2 protein, in excess of 200 kDa, was detected by Western blot. Within cells, the IE2 protein was detected (8-48 h) as intranuclear granules while at later time points (72-120 h), the IE2 protein coalesced into a few large immunoreactive patches. Transfection of cells with an IE2 expression vector (pBK-IE2A) failed to reproduce the patch-like distribution, suggesting that other viral proteins are necessary for this process to occur. Last, IE2 was found to behave as a promiscuous transcriptional activator. Cotransfection experiments in T cells indicate that IE2 can induce the transcription of a complex promoter, such as the HIV-LTR, as well as simpler promoters, whose expression is driven by a unique set of responsive elements (CRE, NFAT, NF-kB). Moreover, minimal promoters having a single TATA box or no defined eukaryotic regulatory elements were significantly activated by IE2, suggesting that IE2 is likely to play an important role in initiating the expression of several HHV-6 genes. In all, the work presented represents the first report on the successful cloning, expression, and functional characterization of the major regulatory IE2 gene/protein of HHV-6.

P53 facilitates degradation of human T-cell leukaemia virus type I Tax-binding protein through a proteasome-dependent pathway

Human T-cell leukaemia virus type 1 (HTLV-I), the aetiological agent of adult T-cell leukaemia (ATL) and tropical spastic paraparesis (TSP/HAM), transforms human T-cells in vivo and in vitro. The Tax protein of HTLV-I is essential for cellular transformation as well as viral and cellular gene transactivation. The interaction of Tax with cellular proteins is critical for these functions. We previously isolated and characterized a novel Tax-binding protein, TRX (TAX1BP2), by screening a Jurkat T-cell cDNA library. In the present study, we present evidence that the tumour suppressor p53 targets the TRX protein for proteasome degradation. Pulse-chase experiments revealed that p53 enhanced the degradation of TRX protein and reduced the half-life from 2.0 to 0.25 h. p53 mutants R248W and R273H enhance TRX degradation suggesting a transcriptionally independent mechanism. Both HTLV-I Tax and the proteasome-specific inhibitor MG132 inhibited p53-mediated TRX protein degradation. These results suggest that TRX degradation is mediated through activation of the proteasome protein degradation pathway independent of transcriptional function of p53. Our results provide the first experimental evidence that Tax inhibits transcription-dependent and independent functions of p53.

Strain variations in single amino acids of the 86-kilodalton human cytomegalovirus major immediate-early protein (IE2) affect its functional and biochemical properties: implications of dynamic protein conformation

The 86-kDa major immediate-early protein, IEP86 (IE2, IE2(579aa), or ppUL122a), from the Towne and AD169 strains of human cytomegalovirus show four amino acid variations, namely, R68Q, K455E, T541A, and seven consecutive serines beginning at position 258 in Towne and eight serines in AD169. A commonly utilized IEP86 cDNA expression clone (herein called the original cDNA) (E. Baracchini, E. Glezer, K. Fish, R. M. Stenberg, J. A. Nelson, and P. Ghazal, Virology 188:518-529, 1992) shows the Towne R68 and seven serines but contains the AD169 E455 and A541 plus two amino acid mutations, M242I and A463T. In transcriptional activation analyses using several promoters, the IEP86 produced by the original cDNA was 40 to 60% less active than wild-type (WT) Towne IEP86, whereas AD169 IEP86 was two to three times more active than WT Towne IEP86. To determine which amino acid variations or mutations accounted for the differences in transcriptional activation, they were individually tested in the WT Towne IEP86 background. K455E, M242I, and the eighth serine had little effect on transcriptional activation or sumoylation when inserted into the Towne background. T541A significantly increased transcriptional activation on all promoters tested and showed increased sumoylation; T541A is the primary reason that WT AD169 IEP86 has increased activity over WT Towne IEP86. The increased sumoylation seen with T541A was quantitatively reduced to WT Towne levels when the K455E alteration was present, suggesting that K455 may be a sumoylation site or that E455 may cause alterations in the IEP86 structure which affect overall sumoylation. A463T was very deleterious to transcriptional activation and caused reduced sumoylation. The A436T mutation in the original cDNA is partially compensated by the presence of the T541A variation. Phosphopeptide mapping suggests that a threonine at 463 or 541 does not introduce a phosphorylation site. However, the A463T mutation does affect phosphorylation at a distant site, suggesting that it alters the conformation of the protein. Promoter-specific effects were noted with some of the amino acid variations, particularly T541A. Structural modeling is presented which suggests how A463T and T541A alter the functional structure of WT Towne IEP86. A hydrophobic core containing A463 is predicted to be responsible for the functional integrity of the carboxy-terminal region of IEP86 between amino acids 344 and 579.

The human cytomegalovirus UL82 gene product (pp71) accelerates progression through the G1 phase of the cell cycle

As viruses are reliant upon their host cell to serve as proper environments for their replication, many have evolved mechanisms to alter intracellular conditions to suit their own needs. For example, human cytomegalovirus induces quiescent cells to enter the cell cycle and then arrests them in late G(1), before they enter the S phase, a cell cycle compartment that is presumably favorable for viral replication. Here we show that the protein product of the human cytomegalovirus UL82 gene, pp71, can accelerate the movement of cells through the G(1) phase of the cell cycle. This activity would help infected cells reach the late G(1) arrest point sooner and thus may stimulate the infectious cycle. pp71 also induces DNA synthesis in quiescent cells, but a pp71 mutant protein that is unable to induce quiescent cells to enter the cell cycle still retains the ability to accelerate the G(1) phase. Thus, the mechanism through which pp71 accelerates G(1) cell cycle progression appears to be distinct from the one that it employs to induce quiescent cells to exit G(0) and subsequently enter the S phase.

Human cytomegalovirus pp71 stimulates cell cycle progression by inducing the proteasome-dependent degradation of the retinoblastoma family of tumor suppressors

The oncoproteins of the DNA tumor viruses, adenovirus E1A, simian virus 40 T antigen, and papillomavirus E7, each interact with the retinoblastoma family of tumor suppressors, leading to cell cycle stimulation, apoptosis induction, and cellular transformation. These proteins utilize a conserved LXCXE motif, which is also found in cellular proteins, to target the retinoblastoma family. Here, we describe a herpesvirus protein that shares a subset of the properties of the DNA tumor virus oncoproteins but maintains important differences as well. The human cytomegalovirus pp71 protein employs an LXCXD motif to attack the retinoblastoma family members and induce DNA synthesis in quiescent cells. pp71 binds to and induces the degradation of the hypophosphorylated forms of the retinoblastoma protein and its family members p107 and p130 in a proteasome-dependent manner. However, pp71 does not induce apoptosis and fails to transform cells. Thus, the similarities and differences in comparison to E1A, T antigen, and E7 make pp71 an interesting new tool with which to further dissect the role of the retinoblastoma/E2F pathway in cellular growth control and carcinogenesis.

Human cytomegalovirus immediate-early protein 2 (IE2)-mediated activation of cyclin E is cell-cycle-independent and forces S-phase entry in IE2-arrested cells

In human cytomegalovirus (HCMV) infection, the isolated expression of the viral immediate-early protein 2 (IE2) 86 kDa regulatory protein coincides with an up-regulation of cyclin E gene expression, both in fibroblasts and U373 cells. Since IE2 also interferes with cell-cycle progression, it is unclear whether IE2 is a genuine activator of cyclin E or whether IE2-arrested cells contain elevated levels of cyclin E primarily as a consequence of them being arrested at the beginning of S phase. It is important to distinguish between these possibilities in order to define and analyse at a mechanistic level the proliferative and anti-proliferative capacities of IE2. Here we have shown that IE2 can activate cyclin E independent of the cell-cycle state and can therefore function as a genuine activator of cyclin E gene expression. A mutant of IE2 that failed to activate cyclin E also failed to promote G1/S transition. Instead, cells became arrested in G1. S-phase entry could be rescued in these cells by co-expression of cyclin E, but these cells still arrested in early S phase, as is the case with wild-type IE2. Our data demonstrate that IE2 can promote two independent cell-cycle functions at the same time: (i) the induction of G1/S transition via up-regulation of cyclin E, and (ii) a block in cell-cycle progression in early S phase. In G1, the proliferative activity of IE2 appears to be dominant over the anti-proliferative force, whereas after G1/S transition, this situation is reversed.

Disruption of mitochondrial networks by the human cytomegalovirus UL37 gene product viral mitochondrion-localized inhibitor of apoptosis

By 24 h after infection with human cytomegalovirus, the reticular mitochondrial network characteristic of uninfected fibroblasts was disrupted as mitochondria became punctate and dispersed. These alterations were associated with expression of the immediate-early (alpha) antiapoptotic UL37x1 gene product viral mitochondrion-localized inhibitor of apoptosis (vMIA). Similar alterations in mitochondrial morphology were induced directly by vMIA in transfected cells. A 68-amino-acid antiapoptotic derivative of vMIA containing the mitochondrial localization and antiapoptotic domains also induced disruption, whereas a mutant lacking the antiapoptotic domain failed to cause disruption. These data suggest that the fission and/or fusion process that normally controls mitochondrial networks is altered by vMIA. Mitochondrial fission has been implicated in the induction of apoptosis and vMIA-mediated inhibition of apoptosis may occur subsequent to this event.

Strategies for the identification and analysis of viral immune-evasive genes--cytomegalovirus as an example

Co-evolution of herpesviruses with their hosts has resulted in multiple interactions between viral genes and cellular functions. Some interactions control genomic maintenance and replication in specific tissues, other affect the immune control at various stages. Few immunomodulatory functions of genes can be predicted by sequence homology. The majority of genes with immunomodulatory properties only become apparent in functional assays. This chapter reviews procedures which have been used for successful identification of immunomodulatory genes in the past and deals with recent methods which may be applicable for the identification of additional immunomodulatory functions unknown so far.

Herpesviral proteins regulating apoptosis

The induction of apoptosis of virus-infected cells is an important defense mechanism of the host. Apoptosis of an infected cell can be induced cell autonomously as a consequence of viral replication or can be mediated by CTLs attacking the infected cells. Herpesviruses have developed different strategies to interfere with cell-autonomous apoptosis and to block CTL-induced apoptosis mediated by death receptors such as Fas and TRAIL. Herpesviruses, which establish a lifelong persistence in the infected host, can be found principally in two different conditions, episomal persistence with a limited number of genes expressed and lytic replication with expression of almost all genes. To meet the need of the virus to enhance survival of the infected cell, herpesviruses have evolved different strategies that function during both episomal persistence and lytic replication. Herpesviruses, which encode 70 to more than 200 genes have incorporated cell homologous antiapoptotic genes, they code for multifunctional genes that can also regulate apoptosis, and, finally, they modulate the expression of cellular apoptosis-regulating genes to favor survival of the infected cells. Viral interference with host cell apoptosis enhances viral replication, facilitates virus spread and persistence, and may promote the development of virus-induced cancer.

Specific localisation of human cytomegalovirus nucleic acids and proteins in human colorectal cancer

BACKGROUND

Colorectal cancer is the second most frequent cause of death from cancer in the USA, and most tumours arise sporadically with no clear cause or genetic predisposition. Human cytomegalovirus is a beta-herpesvirus that is endemic in the human population and can cause life-threatening disease in immunosuppressed adults. In vitro, human cytomegalovirus can transform cells and dysregulate many cellular pathways relevant to colon adenocarcinoma pathogenesis, especially those affecting the cell cycle, mutagenesis, apoptosis, angiogenesis, and cyclo-oxygenase-2 (COX-2) expression. We aimed to assess whether gene products of human cytomegalovirus could be detected in colorectal cancers.

METHODS

We obtained formalin-fixed, paraffin-embedded pathological specimens of colorectal polyps, adenocarcinomas, and adjacent normal mucosa from 29 patients. To detect human cytomegalovirus proteins and nucleic acids, we used immunohistochemistry with two different monoclonal antibodies, in-situ hybridisation, and PCR with DNA sequencing.

FINDINGS

Human cytomegalovirus proteins IE1-72 and pp65 were detected in a tumour cell-specific pattern in 14 (82%) of 17 and seven (78%) of nine colorectal polyps, respectively, and 12 (80%) of 15 and 11 (92%) of 12 adenocarcinomas, respectively, but not in adjacent non-neoplastic colon biopsy samples from the same patients (none of seven and none of two, respectively). Human cytomegalovirus infection of colon-cancer cells (Caco-2) in vitro resulted in specific induction of Bcl-2 and cyclo-oxygenase-2 proteins, both of which are thought to contribute to progression of colon cancer.

INTERPRETATION

Human cytomegalovirus nucleic acids and proteins can be found that specifically localise to neoplastic cells in human colorectal polyps and adenocarcinomas, and virus infection can induce important oncogenic pathways in colon-cancer cells.

Human cytomegalovirus-caused damage to placental trophoblasts mediated by immediate-early gene-induced tumor necrosis factor-alpha

Infection of the fetal epithelium (trophoblast) lining the villous placenta by human cytomegalovirus (HCMV) accompanies placental inflammations and fetal intrauterine growth restriction. However, the consequences of infection on the villous trophoblast have not been explored. We show that HCMV infection of primary immature (cytotrophoblast-like) or mature (syncytiotrophoblast-like) cultures results in loss of half of the cells within 24 hours of virus challenge. Two-color immunofluorescence of HCMV immediate early (IE) gene expression and apoptosis (terminal dUTP nick-end labeling) revealed apoptosis only in uninfected cells. Antibody to tumor necrosis factor (TNF)-alpha completely inhibited infection-induced trophoblast apoptosis and cell loss, as did co-incubation with epidermal growth factor, known to inhibit trophoblast apoptosis. Transfection with HCMV immediate early- (IE)1-72 and IE2-86, but not IE2-55, expression plasmids induced paracrine trophoblast apoptosis inhibitable by epidermal growth factor or antibody to TNF-alpha. These results show that HCMV infection of villous trophoblasts leads to rapid loss of neighboring cells mediated by viral IE protein-induced TNF-alpha secretion. We propose that HCMV infection damages the placental trophoblast barrier by accelerating trophoblast turnover and decreasing its capacity for renewal.