Enhancement of Epstein-Barr virus replication in producer cell lines by a combination of low temperature and corticosteroids

Effects of ambient temperature, relative humidity and absolute humidity on risk of nasopharyngeal carcinoma in China

Nasopharyngeal carcinoma (NPC) has a unique geographic distribution. It is unknown whether meteorological factors are related to the incidence of NPC. To investigate the effect of ambient temperature, relative humidity (RH), and absolute humidity (AH) on the incidence of NPC, we collected the incidence rate of NPC in 2016 and meteorological data from 2006 to 2016 from 484 cities and counties across 31 provinces in China. Generalized additive models with quasi-Poisson regression and generalized linear models with natural cubic splines were employed respectively to elucidate the nonlinear relationships and specify the partial linear relationships. Subgroup and interactive analysis were also conducted. Temperature (R2 = 0.68, p < .001), RH (R2 = 0.47, p < .001), and AH (R2 = 0.70, p < .001) exhibited nonlinear correlations with NPC incidence rate. The risk of NPC incidence increased by 20.3% (95% confidence intervals [CI]: [18.9%, 21.7%]) per 1°C increase in temperature, by 6.3% (95% CI: [5.3%, 7.2%]) per 1% increase in RH, and by 32.2% (95% CI: [30.7%, 33.7%]) per 1 g/m3 increase in AH, between their the 25th and the 99th percentiles. In addition, the combination of low temperature and low RH was also related to increased risk (relative risk: 1.60, 95% CI: [1.18, 2.17]). Males and eastern or rural populations tended to be more vulnerable. In summary, this study suggests that ambient temperature, RH, and particularly AH are associated with the risk of NPC incidence.

Robust Human and Murine Hepatocyte Culture Models of Hepatitis B Virus Infection and Replication

Hepatitis B virus (HBV) is a major cause of chronic liver diseases, including hepatitis, cirrhosis, and hepatocellular carcinoma. HBV research has been hampered by the lack of robust cell culture and small animal models of HBV infection. The discovery of sodium taurocholate cotransporting polypeptide (NTCP) as an HBV receptor has been a landmark advance in HBV research in recent years. Ectopic expression of NTCP in nonpermissive HepG2, Huh7, and AML12 cell lines confers HBV susceptibility. However, HBV replication in these human and murine hepatocyte cell lines appeared suboptimal. In the present study, we constructed stable NTCP-expressing HepG2 and AML12 cell lines and found that HBV permissiveness is correlated with NTCP expression. More significantly, we developed robust HBV cell culture models by treating the HBV-infected cells with dimethyl sulfoxide (DMSO) and hydrocortisone, which significantly promoted HBV replication and production. Mechanistic studies suggested that hydrocortisone significantly enhanced the transcription and expression of PGC1α and HNF4α, which are known to promote HBV transcription and replication. These new human and murine hepatocyte culture systems of HBV infection and replication will accelerate the determination of molecular aspects underlying HBV infection, replication, and morphogenesis in human and murine hepatocytes. We anticipate that our HBV cell culture models will also facilitate the discovery and development of antiviral drugs towards the ultimate eradication of chronic hepatitis B virus infection.IMPORTANCE HBV research has been greatly hampered by the lack of robust cell culture and small animal models of HBV infection and propagation. The discovery of NTCP as an HBV receptor has greatly impacted the field of HBV research. Although HBV infection of NTCP-expressing human and murine hepatocyte cell lines has been demonstrated, its replication in cell culture appeared inefficient. To further improve cell culture systems of HBV infection and replication, we constructed NTCP-expressing HepG2 and AML12 cell lines that are highly permissive to HBV infection. More significantly, we found that DMSO and hydrocortisone markedly enhanced HBV transcription and replication in human and murine hepatocytes when added to the cell culture medium. These new cell culture models of HBV infection and replication will facilitate HBV research and antiviral drug discovery towards the ultimate elimination of chronic hepatitis B virus infection.

Glucocorticoids activate Epstein Barr virus lytic replication through the upregulation of immediate early BZLF1 gene expression

Psychological stress-associated immune dysregulation has been shown to disrupt the steady-state expression and reactivate latent herpes viruses. One such virus is the Epstein Barr virus (EBV), which is associated with several human malignancies. EBV infects >90% of people living in North America and persists for life in latently infected cells. Although several studies have shown that glucocorticoids (GCs) can directly induce reactivation of the latent virus, the mechanism of stress hormone involvement in the control of EBV gene expression is not well understood. In this study, we tested the hypothesis that GCs can induce the latent EBV genome to lytically replicate through the induction of the EBV immediate early gene BZLF1 which encodes the lytic transactivator protein ZEBRA. We show a dose-dependent upregulation of BZLF1 mRNA expression by hydrocortisone (HC) and dexamethasone (Dex) in Daudi cells, an EBV genome positive Burkitt's lymphoma cell line, and Dex-induction of the early gene products BLLF3 (encoding for the EBV dUTPase) and BALF5 (encoding for the EBV DNA polymerase). We show that Daudi cells express glucocorticoid receptors (GR) that mediate Dex-dependent upregulation of BZLF1 mRNA levels. This effect was inhibited by both the glucocorticoid receptor antagonist RU486 and by cycloheximide. The results suggest that GCs, in addition to inducing stress-related immune dysregulation, can mediate latent EBV reactivation through the induction of the BZLF1 gene.

Stress-associated changes in the steady-state expression of latent Epstein-Barr virus: implications for chronic fatigue syndrome and cancer

Antibodies to several Epstein-Barr virus (EBV)-encoded enzymes are observed in patients with different EBV-associated diseases. The reason for these antibody patterns and the role these proteins might play in the pathophysiology of disease, separate from their role in virus replication, is unknown. In this series of studies, we found that purified EBV deoxyuridine triphosphate nucleotidohydrolase (dUTPase) can inhibit the replication of human peripheral blood mononuclear cells in vitro and upregulate the production of TNF-alpha, IL-1beta, IL-6, IL-8, and IL-10. It also enhanced the ability of natural killer cells to lyse target cells. The EBV dUTPase also significantly inhibited the replication of mitogen-stimulated lymphocytes and the synthesis of IFN-gamma by cells isolated from lymph nodes and spleens obtained from mice inoculated with the protein. It also produced sickness behaviors known to be induced by some of the cytokines that were studied in the in vitro experiments. These symptoms include an increase in body temperature, a decrease in body mass and in physical activity. The data provide a new perspective on how an early nonstructural EBV-encoded protein can cause immune dysregulation and produce clinical symptoms observed in patients with chronic fatigue syndrome (CFS) separate from its role in virus replication and may serve as a new approach to help identify one of the etiological agents for CFS. The data also provide additional insight into the pathophysiology of EBV infection, inflammation, and cancer.

Autonomic and glucocorticoid associations with the steady-state expression of latent Epstein-Barr virus

Previous studies have demonstrated the impact of psychological stress on the steady-state expression/reactivation of latent Epstein-Barr virus (EBV). Stress-induced decrements in the cellular immune response result in less control over the expression of the latent virus, resulting in increases in antibody to the virus. In Study 1, we investigated whether the steady-state expression of latent EBV in vivo differed between high and low stress reactors, as defined by sympathetic cardiac reactivity. Autonomic activity and antibody titers to Epstein-Barr virus capsid antigen (VCA) were measured in 50 elderly women latently infected with EBV. Results revealed that women who were high stress reactors were characterized by higher antibody titers to the latent virus than low stress reactors. High reactors tended to show larger stress-related increases in cortisol than low reactors, but the differences were not significant. Daily stressors can activate the autonomic nervous system and promote the release of pituitary and adrenal hormones, especially in high reactors. Glucocorticoid hormones have been shown to reactivate EBV in vitro from cells latently infected with the virus. We hypothesized that absolute levels of plasma cortisol may not be the only explanation for stress-induced reactivation of latent EBV and that the diurnal changes in the production of cortisol may be an important factor in these interactions. To examine the feasibility of this hypothesis, an in vitro study was conducted (Study 2) to determine whether changing glucocorticoid concentrations in the medium, in which EBV latently infected cells were cultured, to mimic diurnal changes in plasma cortisol concentrations would enhance the reactivation of the latent virus. Cells latently infected with EBV were exposed to either constant or varying concentrations of the synthetic glucocorticoid hormone dexamethasone (Dex), for 72 h. Results revealed a three- to eightfold enhancement of reactivation of latent EBV in cells pulsed with varying Dex concentrations when compared with cells exposed to a constant and/or a higher mean level of one Dex concentration. Together, these studies raise the possibility that differences in the kinetics of glucocorticoid concentrations may contribute to differences in the reactivation of latent EBV.

Epstein-Barr virus reactivation after superinfection of the BJAB-B1 and P3HR-1 cell lines with cytomegalovirus

BACKGROUND

Studies examining herpesvirus-herpesvirus (cytomegalovirus (CMV)-Epstein-Barr virus (EBV)) interactions are limited, and many of the studies have been clinical observations suggesting such an interaction exists. This report aims to examine the in vitro susceptibilities of BJAB-B1 and P3HR-1 cells (EBV positive Burkitt's lymphoma B-cell lines) to a CMV superinfection; and show that EBV reactivation occurs after CMV superinfects these cell lines.

RESULTS

The BJAB-B1 and P3HR-1 cells were observed to be susceptible to a CMV superinfection by detecting the major immediate early (MIE) viral transcript and protein (p52) expression. The BZLF1 transcript was observed in both cell lines superinfected with CMV, indicating EBV reactivation. BZLF1 protein was observed in the BJAB-B1 cells. Antigen detection was not performed in the P3HR-1 cells.

CONCLUSION

The results from the in vitro superinfections support the in vivo studies suggesting a CMV infection is related to an EBV reactivation and suggests that CMV may be important as a co-factor in EBV pathogenesis in the immunocompromised patient.

Determining the role of the Epstein-Barr virus Cp EBNA2-dependent enhancer during the establishment of latency by using mutant and wild-type viruses recovered from cottontop marmoset lymphoblastoid cell lines

Epstein-Barr virus (EBV) nuclear antigen (EBNA) 2 (EBNA2) is involved in upregulating the expression of both EBNAs and latency-associated membrane proteins. Transcription of the six EBNA genes, which are expressed in EBV-immortalized primary B cells, arises from one of two promoters, Cp and Wp, located near the left end of the viral genome. Wp is exclusively used to drive EBNA gene transcription during the initial stages of infection in primary B cells; induction of transcription from Cp follows. We previously have mapped an EBNA2-dependent enhancer upstream of Cp (M. Woisetschlaeger et al., Proc. Natl. Acad. Sci. USA 88:3942-3946, 1991) and, more recently, have demonstrated that deletion of this enhancer results in EBV-immortalized lymphoblastoid cell lines (LCLs) that are heavily biased toward the use of Wp to drive transcription of the EBNA genes (L. Yoo et al., J. Virol. 71:9134-9142, 1997). To assess the immortalizing capacity of this mutant EBV and to monitor the early events after infection of primary B cells, B cells isolated from cottontop marmosets were used to generate LCLs immortalized with the Cp EBNA2 enhancer deletion mutant virus. As previously reported, all EBV-infected marmoset LCLs examined could be triggered to produce significant levels of virus. Infection of human B cells with wild-type or Cp EBNA2 enhancer mutant viruses recovered from marmoset B-cell lines demonstrated that (i) the Cp EBNA2 enhancer mutant virus immortalizes primary human B cells nearly as efficiently as wild-type virus and (ii) the Cp EBNA2-dependent enhancer plays an important role in the induction of Cp activity during the early stages of infection. The latter is consistent with the phenotype of LCLs immortalized with the Cp EBNA2 enhancer mutant EBV. Finally, using an established LCL in which EBNA2 function is regulated by beta-estradiol, we showed that the loss of EBNA2 function results in an approximately 4-fold decrease in the steady-state levels of Cp-initiated transcripts and a concomitant increase in the steady-state levels of Wp-initiated transcripts. Taken together, these results provide strong evidence that EBNA2 plays an important role in regulating Cp activity. These results also demonstrate that diminished induction of Cp activity does not appear to affect the ability of EBV to immortalize primary B cells in cultures. Finally, as shown here, infection of marmoset B cells with immortalization-competent mutants of EBV provides a convenient reservoir for the production of mutant viruses.

Stress and immunity: implications for viral disease and wound healing

It is now well established that psychological stress can downregulate the cellular immune response. Communication between the central nervous system and the immune system occurs via a complex network of bidirectional signals linking the nervous, endocrine, and immune systems. Stress disrupts the homeostasis of this network, which in turn, alters immune function. In this review, we discuss the role of stress in modulating cellular immune function and the potential health implications of this downregulation.

Stress-associated immune modulation: relevance to viral infections and chronic fatigue syndrome

The frequent association of an active viral infection with the symptoms of CFS led researchers to hypothesize that chronic fatigue syndrome (CFS) is induced by a virus. Results of these studies indicated that despite clinical support for this hypothesis, there were no clear data linking viruses to CFS. In this overview, we will explore the interrelation of the immune, endocrine, and central nervous systems, and the possibility that stress and/or the reactivation/replication of a latent virus (such as Epstein Barr virus) could modulate the immune system to induce CFS. Relevant research conducted in the developing field of psychoneuroimmunology will be reviewed, with a particular focus on cytokine synthesis, natural killer (NK) cell activity, and T-lymphocyte function, as they relate to CFS.

Identification of a glucocorticoid-responsive element in Epstein-Barr virus

Immortalization of B lymphocytes by Epstein-Barr virus (EBV) is complex and poorly understood. However, some evidence suggests that glucocorticoids influence this process. We identified a glucocorticoid-responsive element in the BamHI C fragment of EBV which we call ES-1. In glucocorticoid-treated cells, ES-1 enhanced chloramphenicol acetyltransferase gene expression from the herpes simplex virus thymidine kinase promoter, as well as the EBV Bam-C promoter, from which several latent viral gene products are transcribed. By Northern blot analysis, glucocorticoid treatment enhanced transcription from the Bam-C promoter in Jijoye cells, a Burkitt's lymphoma cell line. In addition, the DNA-binding domain of the glucocorticoid receptor bound specifically to the ES-1 region. These glucocorticoid effects on the Bam-C promoter region may provide some insight into the process of EBV immortalization.

Effects of activated serum factor on the induction of Epstein-Barr virus antigens and cell differentiation

n-Butyrate and 12-0-tetradecanoylphorbol-13-acetate (TPA) have been shown to be potent inducers of Epstein-Barr virus (EBV) antigen synthesis (10, 18) and cell differentiation (1,2). Activated serum factor (SF) has also been reported to induce virus antigen synthesis and moreover it is capable of cooperative action with other inducers (5). We have demonstrated with an EBV-carrying lymphoma cell line (Raji) that activated SF can also induce the appearance of some cellular alterations, specific for early steps of the productive virus cycle in a low proportion of cells. In addition cell differentiation towards plasma cell was noted in about 8 per cent of SF-treated cells. It was confirmed that activated SF enhances the induction of virus antigens by n-butyrate or TPA as detected by the immunofluorescence technique. It was shown that it also potentiates the development of virus-induced changes in cellular morphology and the cell differentiation induced by these drugs. This effect was more pronounced in combination with TPA than with butyrate. Possible relationships between cell differentiation and virus-antigen expression are discussed.

Induction of Epstein-Barr virus early antigens by corticosteroids: inhibition by TPA and retinoic acid

Corticosteroids can induce the synthesis of EBV antigens in the Burkitt lymphoma line Daudi. As early as 12 h after application of the drug, an increase of EA-positive cells can be seen, the maximum induction being reached after 2 days. Nanogram amounts per ml of hormone are sufficient for measurable effects. Early antigen induction by corticosteroids does not require replication of viral DNA. Induction by corticosteroid differs from induction by other systems in two major respects: (1) it does not cooperate with other inducers, and (2) it is specifically inhibited by 12-O-tetradecanoyl-phorbol-13-acetate (TPA). Induction by corticosteroids, however, shares at least one retinoic acid-sensitive step with induction by chemicals such as TPA, 5-iodo-2-deoxyuridine (IdUrd), n-butyric acid (n-BA) or inducing serum factor. This study defines three qualitatively different effects of TPA in Daudi cells: an inhibitory effect on EBV induction by corticosteroids and two differential types of synergistic effects with serum factor or n-BA, respectively. In this particular cell line, TPA exhibits no inducing capacity when applied alone.

Induced hydrolytic activity of yeast phenylalanyl-tRNA synthetase by tRNAPhe-CC

"Induced hydrolysis" a new hydrolytic activity, was found by measuring AMP-production during aminoacylation of tRNAPhe-CCA by yeast phenylalanyl-tRNA synthetase in the presence of tRNAPhe-CC under conditions of low ionic strength at pH 8.5. Experiments using the elongation factor Tu . GTP provide evidence that transfer of phenylalanine to the tRNAPhe-CCA is followed by rapid hydrolysis in the presence of tRNAPhe-CC. A simple mechanism shows good agreement with the experimental data.

Cellular and Epstein-Barr virus specific DNA polymerases in virus-producing Burkitt's lymphoma cell lines

We have determined the levels of cellular DNA polymerases and Epstein-Barr virus specific DNA polymerase in three Burkitt's lymphoma cell lines producing varying amounts of EBV, one of which was induced by 12-0-tetra-decanoylphorbol-13-acetate (TPA). There was a proportional increase in the level of EBV-DNA polymerase with an increase in the percent of virus-producing cells. However, there was a reciprocal relationship between the levels of EBV-DNA polymerase and DNA polymerase alpha i.e., in cell line containing the highest level of EBV-DNA polymerase, activity of DNA polymerase alpha, but not of DNA polymerase beta, was reduced to an insignificantly low level. TPA does not have any direct effect on activities of either EBV-DNA polymerase or DNA polymerase alpha. EBV-DNA polymerases isolated from cells grown with or without TPA are indistinguishable in their properties such as elution position on phosphocellulose column, molecular weight, mono and divalent cation requirements, pH optimum, and other requirements for optimum activity. Addition of crude extracts of cells grown in presence of TPA to the purified DNA polymerase alpha did not inhibit its activity indicating that the observed loss was not due to any specific inhibitor present in TPA treated cells. Raji, a nonproducer cell line, did not contain EBV-DNA polymerase. There was no induction of EBV-DNA polymerase when Raji cells were grown in presence of TPA. The phenomenon of reduction in the levels of DNA polymerase alpha in cells induced to produce EBV may represent a mechanism by which the host DNA replication is shut off following virus infection.

Steroids inhibit tumor promoting agent induced Epstein-Barr virus early antigens in Raji cells

Four steroids and one protease inhibitor were evaluated for their effects on 12-O-tetradecanoyl phorbol 13-acetate (TPA)-induced and Epstein-Barr virus-induced early antigens (EBV-EA) in Raji cells. Continuous treatment with dexamethasone, prednisolone, hydrocortisone and cortisone inhibited TPA-induced EBV-EA to varying degrees, but the protease inhibitor N-alpha-p-tosyl L-lysine chloromethyl ketone-HCl (TLCK) had no significant effect. None of the agents tested inhibited EBV- induced EA. In addition, the effect of the steroids was reversible since the removal of these agents resulted in recovery of the percentage of EBV-EA-positive cells in TPA-treated cultures. These results were in agreement with the in vivo experiments of other investigators, who demonstrated inhibition of tumor promotion with steroids. Since TLCK failed to inhibit TPA-induced EA, it is unlikely that induction of EA by TPA is the result of production of proteases.

Epstein-Barr virus membrane antigens: characterization, distribution, and strain differences

The Epstein-Barr virus (EBV)-associated membrane antigen polypeptides (350,000, 220,000, 140,000, and 85,000 daltons) are recognized by a rabbit anti-EBV serum and are present on the plasma membranes of producer cell lines, as we demonstrated previously. In this report, we show that these polypeptides are present on intact virus particles. Subcellular fractionation revealed that these antigens are distributed throughout the cell, except for the 85,000-dalton protein, which was poorly represented in the nuclear fraction. In addition, an EBV-associated protein of 160,000 daltons, which comigrates with a major component of the viral capsid, was detected in the cytoplasmic and nuclear fractions. The immunoprecipitation patterns of 13 different EBV isolates were similar, with two exceptions. First, the 350,000- and 220,000-dalton polypeptides from marmoset cell lines had slightly larger molecular sizes than the corresponding polypeptides from human cell lines. Second, B95-8 virus and B95-8-derived human and marmoset cell lines contained little of the 220,000-dalton protein; however, 883L, the human parent line of B95-8, has a normal amount of the 220,000-dalton protein. Thus, the B95-8 strain of EBV appears to be a structurally defective variant. We have not observed any variation in protein patterns associated with different EBV disease states. The 350,000-, 220,000-, and 85,000-dalton polypeptides were shown to be glycoproteins by incorporation of [3H]mannose and [3H]glucosamine and to contain N-asparagine-linked glycosyl groups by their sensitivity to tunicamycin. To simplify future work, the following nomenclature for these EBV-associated polypeptides is suggested: 350,000 (gp350), 220,000 (gp220), 160,000 (p160), 140,000 (p140), and 85,000 (gp85).

Increased levels of (2'-5')oligo(A) polymerase activity in human lymphoblastoid cells treated with glucocorticoids

An enzymatic activity that synthesizes (2'-5')-oligo(A) from ATP is induced in animal cells treated with interferon. This activity, designated (2'-5')A polymerase, is also elevated in human lymphoblastoid Daudi and Raji cells treated with hydrocortisone. The polymerase activity increases significantly after 24 hr of treatment and declines when hydrocortisone is removed from the culture medium. The product of the enzyme prepared from hydrocortisone-treated cells is indistinguishable from (2'-5')oligo(A) synthesized with polymerase of interferon-treated cells either by an endonuclease activation assay or by chromatographic analysis. The increase in (2'-5')A polymerase is not mediated by secretion of interferon by hydrocortisone-treated cells; less than 1 unit of interferon per ml is present in the culture medium during treatment with this glucocorticoid hormone. Moreover, this increase is related to the concentration of hydrocortisone in the culture medium and is inhibited by the addition of cortexolone. This steroid interferes with the interaction between glucocorticoid hormones and their receptor. Cortexolone has no effect, however, on the induction of (2'-5')A polymerase by interferon. The synthetic glucocorticoid dexamethasone also increases the polymerase activity. Experiments with inhibitors show that such an increase requires RNA and protein synthesis.