RESUMO
Kaposi Sarcoma Herpesvirus (KSHV), a γ2-herpesvirus and class 1 carcinogen, is responsible for at least three human malignancies: Kaposi Sarcoma (KS), Primary Effusion Lymphoma (PEL) and Multicentric Castleman's Disease (MCD). Its major nuclear latency protein, LANA, is indispensable for the maintenance and replication of latent viral DNA in infected cells. Although LANA is mainly a nuclear protein, cytoplasmic isoforms of LANA exist and can act as antagonists of the cytoplasmic DNA sensor, cGAS. Here, we show that cytosolic LANA also recruits members of the MRN (Mre11-Rad50-NBS1) repair complex in the cytosol and thereby inhibits their recently reported role in the sensing of cytoplasmic DNA and activation of the NF-κB pathway. Inhibition of NF-κB activation by cytoplasmic LANA is accompanied by increased lytic replication in KSHV-infected cells, suggesting that MRN-dependent NF-κB activation contributes to KSHV latency. Cytoplasmic LANA may therefore support the activation of KSHV lytic replication in part by counteracting the activation of NF-κB in response to cytoplasmic DNA. This would complement the recently described role of cytoplasmic LANA in blocking an interferon response triggered by cGAS and thereby promoting lytic reactivation. Our findings highlight a second point at which cytoplasmic LANA interferes with the innate immune response, as well as the importance of the recently discovered role of cytoplasmic MRN complex members as innate sensors of cytoplasmic DNA for the control of KSHV replication.
Assuntos
Antígenos Virais/imunologia , Replicação do DNA , Herpesvirus Humano 8/imunologia , NF-kappa B/metabolismo , Proteínas Nucleares/imunologia , Sarcoma de Kaposi/imunologia , Transdução de Sinais , Replicação Viral , Hidrolases Anidrido Ácido , Antígenos Virais/genética , Antígenos Virais/metabolismo , Proteínas de Ciclo Celular/genética , Proteínas de Ciclo Celular/metabolismo , Citoplasma/metabolismo , Enzimas Reparadoras do DNA/genética , Enzimas Reparadoras do DNA/metabolismo , DNA Viral/genética , Proteínas de Ligação a DNA/genética , Proteínas de Ligação a DNA/metabolismo , Células HEK293 , Herpesvirus Humano 8/genética , Herpesvirus Humano 8/fisiologia , Humanos , Imunidade Inata , Proteína Homóloga a MRE11 , Modelos Biológicos , NF-kappa B/genética , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Isoformas de Proteínas , Sarcoma de Kaposi/virologia , Latência ViralRESUMO
Kaposi's sarcoma herpesvirus (KSHV) establishes lifelong latency. The viral latency-associated nuclear antigen (LANA) promotes viral persistence by tethering the viral genome to cellular chromosomes and by participating in latent DNA replication. Recently, the structure of the LANA C-terminal DNA binding domain was solved and new cytoplasmic variants of LANA were discovered. We discuss how these findings contribute to our current view of LANA structure and assembly and of its role during viral persistence.
Assuntos
Antígenos Virais/química , Antígenos Virais/metabolismo , Replicação do DNA , DNA Viral/metabolismo , Herpesvirus Humano 8/fisiologia , Proteínas Nucleares/química , Proteínas Nucleares/metabolismo , Latência Viral , Modelos Biológicos , Modelos Moleculares , Conformação ProteicaRESUMO
Many studies have proved that oncogenic viruses develop redundant mechanisms to alter the functions of the tumor suppressor p53. Here we show that Epstein-Barr virus (EBV), via the oncoprotein LMP-1, induces the expression of ΔNp73α, a strong antagonist of p53. This phenomenon is mediated by the LMP-1 dependent activation of c-Jun NH2-terminal kinase 1 (JNK-1) which in turn favours the recruitment of p73 to ΔNp73α promoter. A specific chemical inhibitor of JNK-1 or silencing JNK-1 expression strongly down-regulated ΔNp73α mRNA levels in LMP-1-containing cells. Accordingly, LMP-1 mutants deficient to activate JNK-1 did not induce ΔNp73α accumulation. The recruitment of p73 to the ΔNp73α promoter correlated with the displacement of the histone-lysine N-methyltransferase EZH2 which is part of the transcriptional repressive polycomb 2 complex. Inhibition of ΔNp73α expression in lymphoblastoid cells (LCLs) led to the stimulation of apoptosis and up-regulation of a large number of cellular genes as determined by whole transcriptome shotgun sequencing (RNA-seq). In particular, the expression of genes encoding products known to play anti-proliferative/pro-apoptotic functions, as well as genes known to be deregulated in different B cells malignancy, was altered by ΔNp73α down-regulation. Together, these findings reveal a novel EBV mechanism that appears to play an important role in the transformation of primary B cells.
Assuntos
Linfócitos B/metabolismo , Proteínas de Ligação a DNA/genética , Regulação Viral da Expressão Gênica , Herpesvirus Humano 4/genética , Proteínas Nucleares/genética , Proteínas Supressoras de Tumor/genética , Proteínas da Matriz Viral/genética , Apoptose , Linfócitos B/virologia , Transformação Celular Viral/genética , Transformação Celular Viral/fisiologia , Proteínas de Ligação a DNA/metabolismo , Regulação para Baixo , Epigênese Genética , Herpesvirus Humano 4/fisiologia , Interações Hospedeiro-Patógeno , Humanos , Proteínas Nucleares/metabolismo , Regiões Promotoras Genéticas/genética , RNA Mensageiro/genética , Análise de Sequência de RNA , Transcrição Gênica , Ativação Transcricional , Proteína Tumoral p73 , Proteína Supressora de Tumor p53/antagonistas & inibidores , Proteínas Supressoras de Tumor/metabolismo , Regulação para Cima , Proteínas da Matriz Viral/metabolismoRESUMO
Kaposi sarcoma herpesvirus (KSHV), taxonomical name human gammaherpesvirus 8, is a phylogenetically old human virus that co-evolved with human populations, but is now only common (seroprevalence greater than 10%) in sub-Saharan Africa, around the Mediterranean Sea, parts of South America and in a few ethnic communities. KSHV causes three human malignancies, Kaposi sarcoma, primary effusion lymphoma, and many cases of the plasmablastic form of multicentric Castleman's disease (MCD) as well as occasional cases of plasmablastic lymphoma arising from MCD; it has also been linked to rare cases of bone marrow failure and hepatitis. As it has colonized humans physiologically for many thousand years, cofactors are needed to allow it to unfold its pathogenic potential. In most cases, these include immune defects of genetic, iatrogenic or infectious origin, and inflammation appears to play an important role in disease development. Our much improved understanding of its life cycle and its role in pathogenesis should now allow us to develop new therapeutic strategies directed against key viral proteins or intracellular pathways that are crucial for virus replication or persistence. Likewise, its limited (for a herpesvirus) distribution and transmission should offer an opportunity for the development and use of a vaccine to prevent transmission.This article is part of the themed issue 'Human oncogenic viruses'.