CD95 Signaling Inhibits B Cell Receptor-Mediated Gammaherpesvirus Replication in Apoptosis-Resistant B Lymphoma Cells

Abstract

While CD95 is an apoptosis-inducing receptor and has emerged as a potential anticancer therapy target, mounting evidence shows that CD95 is also emerging as a tumor promoter by activating nonapoptotic signaling pathways. Gammaherpesviral infection is closely associated with lymphoproliferative diseases, including B cell lymphomas. The nonapoptotic function of CD95 in gammaherpesvirus-associated lymphomas is largely unknown. Here, we show that stimulation of CD95 agonist antibody drives the majority of sensitive gammaherpesvirus-transformed B cells to undergo caspase-dependent apoptosis and promotes the survival and proliferation of a subpopulation of apoptosis-resistant B cells. Surprisingly, CD95-mediated nonapoptotic signaling induced beta interferon (IFN-␤) expression and correlatively inhibited B cell receptor (BCR)-mediated gammaherpesviral replication in the apoptosis-resistant lymphoma cells without influencing BCR signaling. Further analysis showed that IFN-␤ alone or synergizing with CD95 blocked the activation of lytic switch proteins and the gene expression of gammaherpesviruses. Our findings indicate that, independent of its apoptotic activity, CD95 signaling activity plays an important role in blocking viral replication in apoptosis-resistant, gammaherpesvirus-associated B lymphoma cells, suggesting a novel mechanism that indicates how host CD95 prototype death receptor controls the life cycle of gammaherpesviruses independent of its apoptotic activity. IMPORTANCEGammaherpesviruses are closely associated with lymphoid malignancies and other cancers. Viral replication and persistence strategies leading to cancer involve the activation of antiapoptotic and proliferation programs, as well as evasion of the host immune response. Here, we provide evidence that the stimulation of CD95 agonist antibody, mimicking one of the major mechanisms of cytotoxic T cell killing, inhibits B cell receptor-mediated gammaherpesviral replication in CD95 apoptosis-resistant lymphoma cells. CD95-induced type I interferon (IFN-␤) contributes to the inhibition of gammaherpesviral replication. This finding sheds new light on the CD95 nonapoptotic function and provides a novel mechanism for gammaherpesviruses that helps them to escape host immune surveillance. C D95 (also called APO-1 or FAS) is a death receptor belonging to the tumor necrosis factor receptor family that is characterized by the presence of a death domain within its cytoplasmic region (1, 2). Stimulation of CD95 cognate ligand (CD95L) or specific agonistic antibodies results in the assembly of the deathinducing signaling complex (DISC), composed of CD95, the adaptor molecule FADD (FAS associated with a death domain), procaspase 8, procaspase 10, and the caspase 8/10 regulator c-FLIP (3-7). Activated caspase 8 subsequently cleaves the effector caspases 3 and 7, initiating the apoptotic program. Apoptosis mediated by CD95-CD95L interaction is crucial for the immune system to maintain homeostasis and eliminate virus-infected and cancer cells (6,(8)(9)(10)....

Inhibition of Herpes Simplex Virus-1 Replication by Natural Compound Honokiol

“…Acyclovir (114798-25MGCN) was from Merck Millipore. MHV68 lytic antigen was previously described (Tan et al 2016).…”

“…Genomic DNA was isolated from HSV-1-GFP infected Vero cells. Real-time quantitative PCR (qPCR) was performed to measure HSV-1 viral DNA as previously described (Tan et al 2016). Total RNA isolation, cDNA synthesis and quantitative RT-PCR (qRT-PCR) to measure HSV-1 viral gene expression were performed as previously described (Tan et al 2016).…”

“…Real-time quantitative PCR (qPCR) was performed to measure HSV-1 viral DNA as previously described (Tan et al 2016). Total RNA isolation, cDNA synthesis and quantitative RT-PCR (qRT-PCR) to measure HSV-1 viral gene expression were performed as previously described (Tan et al 2016). The primers for HSV-1 ICP8, ICP27, VP16, and 18S rRNA were described elsewhere (Sato et al 2016).…”

Regulation of gammaherpesvirus lytic replication by endoplasmic reticulum stress–induced transcription factors ATF4 and CHOP

“…The program T20 was used for SL-1, M12, and other selected cells, whereas the program D17 was used for CHOP knockout C-4 cells in the CHOP overexpression rescue experiments. The MHV68 RTA promoter luciferase assay was performed as described previously (54).…”

Virus Infection and Death Receptor-Mediated Apoptosis

“…In addition to the role in the cytotoxic activity of innate immune NK cells and pDC cells, death receptor-mediated apoptosis plays an important role in the cytotoxic T cell killing during viral infection. It is well demonstrated that some virus-specific cytotoxic T lymphocytes (CTLs) use the FasL/Fas-dependent lytic mechanism to kill virus-infected or bystander cells, such as lymphocytic choriomeningitis virus (LCMV)-infected cell lysis by LCMV-specific CD4+ CTL [ 167 ], MHC class I-restricted killing of neurons by LCMV-specific CD8+ T lymphocytes [ 168 ], Ag-bearing cell killing and non-Ag-bearing bystander cell killing by HCV-specific CTLs [ 169 , 170 ], and growth inhibition of EBV- or MHV68-infected B cells by virus-specific CTLs [ 171 , 172 , 173 ]. In addition, Fas- and TRAIL-mediated apoptosis regulate clearance of influenza A virus (IAV) by IAV-specific CD8+ T cells [ 174 , 175 ].…”