Kaposi's Sarcoma-Associated Herpesvirus Latency-Associated Nuclear Antigen Induction by Hypoxia and Hypoxia-Inducible Factors

Abstract

Hypoxia and hypoxia-inducible factors (HIFs) play an important role in the Kaposi's sarcoma-associated herpesvirus (KSHV) life cycle. In particular, hypoxia can activate lytic replication of KSHV and specific lytic genes, including the replication and transcription activator (RTA), while KSHV infection in turn can increase the levels and activity of HIFs. In the present study, we show that hypoxia increases the levels of mRNAs encoding KSHV latency-associated nuclear antigen (LANA) in primary effusion lymphoma (PEL) cell lines and also increases the levels of LANA protein. Luciferase reporter assays in Hep3B cells revealed a moderate activation of the LANA promoter region by hypoxia as well as by cotransfection with degradation-resistant HIF-1␣ or HIF-2␣ expression plasmids. Computer analysis of a 1.2-kb sequence upstream of the LANA translational start site identified six potential hypoxia-responsive elements (HRE). Sequential deletion studies revealed that much of this activity was mediated by one of these HREs (HRE 4R) oriented in the 3= to 5= direction and located between the constitutive (LTc) and RTA-inducible (LTi) mRNA start sites. Site-directed mutation of this HRE substantially reduced the response to both HIF-1␣ and HIF-2␣ in a luciferase reporter assay. Electrophoretic mobility shift assays (EMSA) and chromatin immunoprecipitation (ChIP) assays demonstrated binding of both HIF-1␣ and HIF-2␣ to this region. Also, HIF-1␣ was found to associate with RTA, and HIFs enhanced the activation of LTi by RTA. These results provide evidence that hypoxia and HIFs upregulate both latent and lytic KSHV replication and play a central role in the life cycle of this virus.

Kaposi's Sarcoma-Associated Herpesvirus (KSHV) Latency-Associated Nuclear Antigen Regulates the KSHV Epigenome by Association with the Histone Demethylase KDM3A

“…As HIF-1␣ functionally and physically associates with KDM3A (34,62), it is possible that LANA, HIF-1␣, and KDM3A can form a ternary complex under hypoxic conditions. In accord with this, the KDM3A recruitment sites that we identified significantly overlap HIF-1␣ binding sites (63).…”

Inhibition of KAP1 Enhances Hypoxia-Induced Kaposi's Sarcoma-Associated Herpesvirus Reactivation through RBP-Jκ

“…tent with a recent report showing that hypoxia enhanced LANA expression (43). In addition, the role of KAP1 in response to extracellular stress like hypoxia or TPA-NaB treatment is not unique.…”

“…However, it is not fully understood how hypoxia induces reactivation from KSHV latency. To address this question, we and other groups have found that hypoxia not only induces the key latent antigen LANA encoded by KSHV but also cooperates with HIF-1␣ bound to HREs within the RTA promoter (10,43) to directly induce lytic gene expression (i.e., ORF34-37) for lytic replication (44). Interestingly, we and other groups have found that HIF-1␣ is stabilized and accumulated in both PEL and KS cells in normoxia (29,36).…”

Fumagillin, a potent angiogenesis inhibitor, induces Kaposi sarcoma-associated herpesvirus replication in primary effusion lymphoma cells

“…Several inducers of RTA expression have been reported in PEL cell lines. Hypoxia induces RTA expression through the hypoxia-inducible factor-1α pathway in vitro [10]. RTA is also induced by the unfolded protein response, endoplasmic reticulum stress 11], unspliced X-box-binding protein 1 [12], Toll-like receptor 7 and 8 activation, and Ras signaling (Raf/MEK/ERK/Ets-1 pathways) [13].…”