p53 Tumor Suppressor Protein Stability and Transcriptional Activity Are Targeted by Kaposi's Sarcoma-Associated Herpesvirus-Encoded Viral Interferon Regulatory Factor 3

Abstract

cViruses have developed numerous strategies to counteract the host cell defense. Kaposi's sarcoma-associated herpesvirus (KSHV) is a DNA tumor virus linked to the development of Kaposi's sarcoma, Castleman's disease, and primary effusion lymphoma (PEL). The virus-encoded viral interferon regulatory factor 3 (vIRF-3) gene is a latent gene which is involved in the regulation of apoptosis, cell cycle, antiviral immunity, and tumorigenesis. vIRF-3 was shown to interact with p53 and inhibit p53-mediated apoptosis. However, the molecular mechanism underlying this phenomenon has not been established. Here, we show that vIRF-3 associates with the DNA-binding domain of p53, inhibits p53 phosphorylation on serine residues S15 and S20, and antagonizes p53 oligomerization and the DNA-binding affinity. Furthermore, vIRF-3 destabilizes p53 protein by increasing the levels of p53 polyubiquitination and targeting p53 for proteasome-mediated degradation. Consequently, vIRF-3 attenuates p53-mediated transcription of the growth-regulatory p21 gene. These effects of vIRF-3 are of biological relevance since the knockdown of vIRF-3 expression in KSHV-positive BC-3 cells, derived from PEL, leads to an increase in p53 phosphorylation, enhancement of p53 stability, and activation of p21 gene transcription. Collectively, these data suggest that KSHV evolved an efficient mechanism to downregulate p53 function and thus facilitate uncontrolled cell proliferation and tumor growth.

KSHV latent protein LANA2 inhibits sumo2 modification of p53

“…LANA2 inhibits both the transcriptional activation and apoptosis induced by p53 through the inhibition of p53 phosphorylation, by altering its oligomerization and DNA-binding affinity, and by increasing its polyubiquitylation. [3][4][5][6][7][8] Apart from p53, LANA2 also compromises the activity of other tumor suppressors such as pRb or PML. 9,10 Interestingly, the control of these 2 tumor suppressors by LANA2 involves the regulation of their SUMO conjugation.…”

Mechanism of Angiopoietin-1 Upregulation in Kaposi's Sarcoma-Associated Herpesvirus-Infected PEL Cell Lines

“…It has been reported that KSHV regulates host gene expression by expressing several viral genes, including vIRF3, vIRF7, and the gene for a viral protein kinase (ORF36) (12,33). To understand how ANGPT-1 was upregulated in KSHV-infected PEL cells and how KSHV contributed to ANGPT-1 gene expression, we constructed ANGPT-1 promoter-luciferase reporter constructs (Ϫ898 to ϩ490 of Luc, where ϩ1 is the transcription start site and ϩ490 is the A in ATG, the ANGPT-1 translation initiation codon) and measured their transcriptional activity.…”

“…These latency-related viral products may also be involved in enhancement of the expression of various cytokines and growth factors, such as angiopoietin-1 (ANGPT-1), ANGPT-2, vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), IL-8, and tumor necrosis factor alpha (6,(25)(26)(27)(28)(29). The angiogenic and inflammatory cytokines regulated by viral proteins or KSHV infection could lead to the induction of lymphangiogenesis, angiogenesis, and antiapoptosis and likely play an important role in KSHV pathogenesis (12,26,(30)(31)(32)(33).In a previous study, we compared the gene expression profiles of KSHV-infected BC1, BCBL1, and BC3 cells with those of uninfected Daudi, AKATA, Raji, Ramos, and Namalwa cells and MT4, SupT1, Jurkat, and Molt3 leukemia cells. We found that ANGPT-1, a proangiogenic and proinflammatory cytokine, was expressed at significantly higher levels only in KSHV-infected PEL cells (6).…”

“…Several viral products of KSHV have been reported to have pivotal effects that contribute to the proliferation of endothelial cells, the viral life cycle, and the secretion of cytokines associated with angiogenic and inflammatory properties; these products include LANA, vIL6, vGPCR, K15, and vIRF3 (12,(19)(20)(21)(22)(23)(24). These latency-related viral products may also be involved in enhancement of the expression of various cytokines and growth factors, such as angiopoietin-1 (ANGPT-1), ANGPT-2, vascular endothelial growth factor (VEGF), interleukin-6 (IL-6), IL-8, and tumor necrosis factor alpha (6,(25)(26)(27)(28)(29).…”

“…Though viral gene expression profiles might differ between BECs and LECs (10), KSHV is predominantly in latency with its genome binding to the host cell chromosome (10,11) and governs host gene expression profiles (12) as other viruses do (13,14). Most KSHV-infected cells are latently infected, and only a limited number of viral genes are expressed in latency: latency-associated nuclear antigen (LANA), viral cyclin (vCYC), viral FLICE inhibitory protein (vFLIP), kaposin (10,11,(15)(16)(17)(18), and viral interferon regulatory factor 3 (vIRF3) (12).…”