Kaposi's Sarcoma-Associated Herpesvirus (Human Herpesvirus 8) Contains Hypoxia Response Elements: Relevance to Lytic Induction by Hypoxia

Abstract

Kaposi's sarcoma (KS)-associated herpesvirus (KSHV), also known as human herpesvirus 8, is an etiologic agent of KS, primary effusion lymphoma (PEL), and multicentric Castleman's disease. We recently demonstrated that hypoxia can induce lytic replication of KSHV in PEL cell lines. Hypoxia induces the accumulation of hypoxia-inducible factors (HIF), and we hypothesized that the KSHV genome may respond to hypoxia through functional hypoxia response elements (HREs). Here, we demonstrate the presence of at least two promoters within the KSHV genome that are activated by hypoxia or hypoxia mimics. One is in the promoter region of the gene for Rta, the main lytic switch gene, and the other is within the promoter region of ORF34, a lytic gene of unknown function. The ORF34 promoter contains three putative consensus HREs oriented in the direction of the gene. Dissection and site-directed mutagenesis studies confirmed that one of the HREs of the ORF34 promoter is functional. Under conditions of hypoxia, the ORF34 promoter was strongly upregulated by HIF-1␣ and HIF-2␣. By contrast, the promoter of the gene for Rta appeared to be preferentially upregulated by HIF-2␣. Reverse transcription-PCR analysis revealed that specific messages for ORF34 and ORF50 are upregulated in BCBL-1 cells exposed to hypoxia. An HIF-1 binding and competition assay demonstrated that the HRE sequence from the ORF34 promoter can compete for HIF-1␣ binding to an erythropoietin HRE oligonucleotide while a mutant sequence cannot. Thus, we demonstrated that a viral gene can be activated by hypoxia through activation of a functional viral HRE. To our knowledge, this is the first example of a functional HRE in a viral promoter.

The Effects of Heat Shock Protein 90 Inhibitors on Apoptosis and Viral Replication in Primary Effusion Lymphoma Cells

“…These findings suggest a novel application of Hsp90 inhibitors in the treatment of KSHV infection. Not only NF-κB signaling but also several cell signaling pathways, such as hypoxia inducible factor (HIF), mitogen-activated protein kinase (MAPK), and Akt signaling, 21,22) regulate the initiation of KSHV lytic replication, and these pathways regulator molecules, such as HIF-1a, Raf-1, and Akt have been identified as clients of HSP90. 20) Inhibition of these signaling pathways by HSP90 inhibitors may contribute to the suppression of KSHV replication.…”

A novel role of hydrogen peroxide in Kaposi sarcoma-associated herpesvirus reactivation

“…6,7 We observed a dose-dependent induction of KSHV lytic gene expression and virion production from latently infected human primary effusion lymphoma ( Previously, 12-O-tetradecanoyl phorbol-13-acetate (TPA), hypoxia and inflammatory cytokines have been shown to induce KSHV lytic replication. [9][10][11] We found that these stimuli also increased intracellular H 2 O 2 and that antioxidants such as catalase, reduced glutathione and N-acetyle-cysteine (NAC) attenuated viral reactivation induced by these factors. The antioxidants also abolished spontaneous KSHV lytic replication under normal culture conditions.…”

“…induced hypoxiainducible factor-1α (HIF-1α), which is known to upregulate expression of several key KSHV lytic genes through direct binding to the viral promoters. 10,11 In summary, due to oxidative stress and chronic inflammation, the higher level of H 2 O 2 in KS patients likely plays a pivotal role in KS tumorigenesis through induction of KSHV reactivation, cell proliferation, angiogenesis and inflammation. This new finding not only defines a novel role of H 2 O 2 in KSHV pathogenesis but also highlights the great potentials of using antioxidants and anti-inflammatory drugs for the prevention and treatment of KS.…”

Interaction des virus avec la voie cellulaire de réponse à l’hypoxie

“…L'activation des kinases cellulaires conduit également à la stabilisation et à la migration nucléaire du facteur HIF-1α (➜), ce qui exacerbe encore la synthèse de VEGF au niveau des lésions du sarcome de Kaposi, caractérisées par la prolifération de cellules fusiformes et une angiogenèse importante. [16]. En condition d'hypoxie, la fixation de HIF-1 en amont des gènes viraux stimule l'expression des protéines lytiques et structurales du HHV8 ainsi que sa réplication in vitro dans des cellules de lymphome B des séreuses infectées chroniquement ( Figure 2C et Tableau I) [17].…”

“…La protéine HIF-1α ainsi stabilisée va s'associer avec ses partenaires nucléaires et activer la synthèse de VEGF qui va induire la prolifération des cellules tumorales et des cellules endothéliales. Le facteur HIF se fixe également au niveau de sites HBS présents dans les promoteurs viraux et augmente la production de particules virales [16,17]. circulation où l'hématocrite, et donc la concentration en oxygène, est très faible.…”