title: The Viral Bcl-2 Homologs of Kaposi's Sarcoma-Associated Herpesvirus and Rhesus Rhadinovirus Share an Essential Role for Viral Replication.
abstract: KS-Bcl-2 is a Kaposi's sarcoma-associated herpesvirus (KSHV)-encoded viral Bcl-2 (vBcl-2) homolog which has apoptosis- and autophagy-inhibiting activity when expressed in transfected cells. However, little is known about its function during viral infection. As KS-Bcl-2 is expressed during the lytic replication cycle, we used constitutively lytic and inducibly lytic KSHV mutants to investigate the role of KS-Bcl-2 during the lytic cycle. We show that KSHV cannot complete the lytic replication cycle and produce infectious progeny in the absence of KS-Bcl-2, indicating that the protein is essential for KSHV replication. Replacement of the KS-Bcl-2 coding sequence, ORF16, by sequences encoding a potent cellular apoptosis and autophagy inhibitor, Bcl-XL, or the cytomegalovirus mitochondrial inhibitor of apoptosis, vMIA, did not rescue KSHV replication, suggesting that KS-Bcl-2 has a function that goes beyond apoptosis and autophagy inhibition. Strikingly, the vBcl-2 proteins of the related γ2-herpesviruses murine herpesvirus 68 and herpesvirus saimiri did not rescue the replication of a KS-Bcl-2 deletion mutant, but rhesus rhadinovirus (RRV) vBcl-2 did. Deletion of ORF16 from the RRV genome abrogated viral replication, but its replacement by KSHV ORF16 rescued RRV replication, indicating that the essential vBcl-2 function is conserved between these two primate rhadinoviruses. We further show that the KSHV and RRV Bcl-2 homologs localize to the mitochondria and nuclei of infected cells. Deletion of 17 amino acids from the N terminus of KS-Bcl-2 abrogates nuclear localization and KSHV replication, suggesting that KS-Bcl-2 might execute its essential function in the nuclei of infected cells.IMPORTANCESeveral viruses express proteins homologous to cellular Bcl-2. Viral Bcl-2 proteins have functions similar to those of cellular Bcl-2: they can inhibit apoptosis, a form of programmed cell death, and autophagy, a self-degradative process for the disposal of dysfunctional or unwanted components. This study shows that the vBcl-2 proteins of KSHV and RRV differ from other vBcl-2 proteins in that they are essential for viral replication. The essential function is separate from the apoptosis- and autophagy-inhibiting activity but correlates with an unusual localization within the cell nucleus, suggesting that these proteins exert a novel function in the nucleus.
authors.affiliation: Heinrich Pette Institute, Leibniz Institute for Experimental Virology, Hamburg, Germany.
authors.forename: Antonio
authors.initials: A
authors.lastname: Gallo
authors.affiliation: Heinrich Pette Institute, Leibniz Institute for Experimental Virology, Hamburg, Germany.
authors.forename: Melanie
authors.initials: M
authors.lastname: Lampe
authors.affiliation: Heinrich Pette Institute, Leibniz Institute for Experimental Virology, Hamburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Günther
authors.affiliation: Heinrich Pette Institute, Leibniz Institute for Experimental Virology, Hamburg, Germany wolfram.brune@hpi.uni-hamburg.de.
authors.forename: Wolfram
authors.identifier: http://orcid.org/0000-0002-6078-5255
authors.initials: W
authors.lastname: Brune
mesh_terms: D002460:Cell Line; D002467:Cell Nucleus / Q000737:chemistry; D017353:Gene Deletion; D005816:Genetic Complementation Test; D019288:Herpesvirus 8, Human / Q000235:genetics / Q000502:physiology*; D006801:Humans; D008928:Mitochondria / Q000737:chemistry; D018144:Rhadinovirus / Q000235:genetics / Q000502:physiology*; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism*; D014779:Virus Replication
chemical_list: D014764:Viral Proteins
keywords: KS-Bcl-2; Kaposi's sarcoma-associated herpesvirus; apoptosis; autophagy; rhesus rhadinovirus; vBcl-2; viral replication