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

Lingbing Tan, Chaocan Zhang, Julien Dematos, Linlin Kuang, Jae U. Jung and Xiaozhen Liang

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-β) 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-β 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.

IMPORTANCE
Gammaherpesviruses 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-β) 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.

http://jvi.asm.org/content/90/21/9782.full