ALBERT

Description: Abortive viral infections are usually studied in populations of susceptible but nonpermissive cells. Single-cell studies of viral infections have demonstrated that even in susceptible and permissive cell populations, abortive infections can be detected in subpopulations of the infected cells. We have previously identified abortive infections in HeLa cells infected with herpes simplex virus 1 (HSV-1) at high multiplicity of infection (MOI). Here, we tested 4 additional human-derived nonneuronal cell lines (cancerous or immortalized) and found significant subpopulations that remain abortive. To characterize these abortive cells, we recovered cell populations that survived infection with HSV-1 at high MOI. The surviving cells retained proliferative potential and the ability to be reinfected. These recovered cell populations maintained the viral genomes in a quiescent state for at least 5 wk postinfection. Our results indicate that these viral genomes are maintained inside the nucleus, bound to cellular histones and occasionally reactivated to produce new progeny viruses. We conclude that abortive HSV-1 infection is a common feature during infection of nonneuronal cells and results in a latency-like state in the infected cells. Our findings question the longstanding paradigm that alphaherpesviruses can establish spontaneous latency only in neuronal cells and emphasize the stochastic nature of lytic versus latency decision of HSV-1 in nonneuronal cells.

Description: Abstract 1736 EBV and KSHV are associated with a variety of lymphoid malignancies. Bortezomib, a proteasome inhibitor, is among the most potent activators of EBV and KSHV lytic infection and is active at nanomolar concentrations. Studying EBV Burkitt's cell lines, KSHV primary effusion lymphoma cell lines and EBV myeloma cell lines, we found that lytic gene expression is a class effect shared by other proteasome inhibitors, such as MG-132 and epoxomicin. Proteasome inhibition results in IKB stabilization and inhibition of NFKB activity and this effect has been implicated in many of the effects of bortezomib. We studied the promoters of EBV and KSHV immediate early viral protein reporters (EBV Zta and KSHV Rta) and found that IKB super-repressor did not activate promoter reporters suggesting that other pathways must be important in activation. Therefore, we sought to better understand the drug's impact on viral gene expression in virus-associated tumor cells. ER stress has been implicated in bortezomib's antitumor effects. Thapsigargin and tunicamycin are classic activators of ER stress that do not act through proteasomal inhibition. These agents were found to be potent activators of the EBV and KSHV lytic cycle. Previous studies have identified C/EBP family members (C/EBP alpha and beta) as activators of EBV and KSHV immediate early gene expression. In other studies, C/EBP family members (C/EBP beta, CHOP10) have been implicated in regulating the ER stress response. We found that bortezomib, thapsigargin and tunicamycin increased levels of the activating C/EBP beta LAP isoform as assessed by immunoblot and by real-time RT-PCR. Treatment also led to increase in ATF4, XBP1(s), CHOP10, and ATF6 cleavage, all consistent with induction of the ER stress response. Additionally, we showed that treatment with bortezomib increased C/EBP beta binding to previously characterized binding sites in the Zta promoter and expression of C/EBP beta LAP isoform was sufficient to activate EBV immediate early lytic promoters. Finally, we demonstrated that in tumor cell lines with C/EBP beta silenced by doxycycline regulated siRNA, induction of EBV lytic induction by bortezomib and thapsigargin was blocked. These results demonstrate that both human lymphoma associated herpesviruses (EBV and KSHV) are activated into lytic cycle by bortezomib and that these effects are mediated through ER stress pathways and specifically involve C/EBP beta. Disclosures: No relevant conflicts of interest to declare.

Description: Epstein-Barr virus (EBV) is associated with a variety of lymphoid malignancies. Bortezomib activates EBV lytic gene expression. Bortezomib, a proteasome inhibitor, leads to increased levels of CCAAT/enhancer-binding proteinβ (C/EBPβ) in a variety of tumor cell lines. C/EBPβ activates the promoter of the EBV lytic switch gene ZTA. Bortezomib treatment leads to increased binding of C/EBP to previously recognized binding sites in the ZTA promoter. Knockdown of C/EBPβ inhibits bortezomib activation of EBV lytic gene expression. Bortezomib also induces the unfolded protein response (UPR), as evidenced by increases in ATF4, CHOP10, and XBP1s and cleavage of ATF6. Thapsigargin, an inducer of the UPR that does not interfere with proteasome function, also induces EBV lytic gene expression. The effects of thapsigargin on EBV lytic gene expression are also inhibited by C/EBPβ knock-down. Therefore, C/EBPβ mediates the activation of EBV lytic gene expression associated with bortezomib and another UPR inducer.

Description: Background Epstein-Barr virus (EBV) is harbored as latent virus within the tumor cells of a subset of classical Hodgkin lymphoma (HL) and HIV-associated Burkitt lymphoma (BL). In HL, we and others have previously shown that elevated EBV DNA copies in plasma accurately distinguish EBV(+) tumors from EBV(-) tumors. However, EBV DNA may be present in plasma due to apoptosis of latently infected EBV(+) tumor cells (or latent EBV(+) benign lymphocytes), as a result of replicative lytic infection (particularly in immunocompromised hosts), or both. Thus, detecting elevated EBV DNA copies in plasma by does not always signify the presence of an EBV(+) tumor. However, a distinction is that the EBV DNA derived from latently infected cells is replicated by cellular DNA polymerase and is usually CpG methylated, whereas EBV DNA in lytic infection is replicated by the viral DNA polymerase and is never CpG methylated. Methods To improve upon plasma EBV DNA as a tumor-specific marker in EBV(+) lymphomas, we assessed the CpG methylation of EBV DNA in a subset of plasma specimens from immunocompetent patients with HL (enrolled in the Eastern Cooperative Oncology Group E2496 trial) and a subset from patients with HIV-associated BL (enrolled in the AIDS Malignancy Consortium 048 trial). The EBV tumor status was determined by in situ hybridization (ISH) on tissue for EBV RNAs (EBER). For the CpG methylation assay, methyl binding domain paramagnetic beads were used to first fractionate CpG methylated DNA from CpG unmethylated DNA in plasma. EBV DNA in each fraction were quantified by real time polymerase chain reaction (qPCR) to determine the percentage of methylated EBV DNA. Specimens with 〉 100 EBV DNA copies/mL plasma were analyzed. Results Among patients with EBER(+) HL and elevated EBV DNA in plasma prior to therapy (n=8), EBV DNA was largely CpG methylated (median 95%, range 54%-99%). By contrast, in the rare cases where patients with EBER(-) HL tumors had high EBV DNA copy number in plasma prior to therapy (4 of 92, 4%), only small percentages of EBV DNA were methylated in 3 patients (5%, 9%, and 12%). In the fourth patient, the plasma EBV DNA was 99% CpG methylated. We suspect that patient 4 had an EBV-associated HL with either a technical failure of EBER-ISH or an instance of a tumor that harbors viral DNA but does not express EBERs. In patients with HIV-associated BL, plasma EBV DNA copies were elevated in 100% of patients with EBER(+) BL (n=4), but also in 4 of 9 (56%) patients with EBER(-) BL. This propensity to detect EBV DNA in the plasma of patients with HIV but without EBV(+) BL likely reflects replicative lytic infection in immunocompromised hosts, making plasma EBV DNA less reliable as a marker of EBV(+) lymphoma in this setting. Thus, we applied the methylation assay to specimens from patients with HIV and BL. Patients with HIV and EBER(+) BL tumors (n=4), EBV DNA was 28%, 46%, 47%, and 60% methylated, whereas a patient with HIV and EBER(-) BL had lower methylation at 8%. To better elucidate the meaning of plasma EBV DNA elevations during lymphoma treatment, we applied the methylation assay to specimens from patients with EBV(+) HL and elevated EBV DNA in plasma at month 6 of therapy (n=4). Dense CpG methylation (96%) of plasma EBV DNA was detected in 1 patient who went on to relapse at Month 15, while the plasma EBV DNA was largely unmethylated in 3 patients who remain in remission each with over 5 years of follow-up. Conclusion In settings where EBV DNA is detected in plasma, the CpG methylation assay helps differentiate patients with EBV(+) HL or BL from those with EBV(-) tumors. In patients with HIV where lytic EBV replication can contribute greatly to elevations of EBV DNA in plasma, the fractionated quantification of plasma EBV DNA by the methylation assay aids in distinguishing EBV DNA that is tumor-derived from that which is the result of lytic replication. With growing interest in plasma EBV DNA as a serial marker of disease activity in EBV(+) lymphomas, the methylation assay is promising in its ability to differentiate patients with elevated EBV DNA in plasma but ongoing remission from those in whom plasma EBV DNA is tumor-derived and an early harbinger of relapse. Disclosures: No relevant conflicts of interest to declare.