Kaposi's Sarcoma-Associated Herpesvirus Latent Protein LANA Interacts with HIF-1α To Upregulate RTA Expression during Hypoxia: Latency Control under Low Oxygen Conditions

Abstract

Hypoxia can induce lytic replication of Kaposi's sarcoma-associated herpesvirus (KSHV) in primary effusion lymphoma (PEL) cells. However, the molecular mechanism of lytic reactivation of KSHV by hypoxia remains unclear. Here we show that the latency-associated nuclear antigen (LANA), which plays a crucial role in modulating viral and cellular gene expression, directly associated with a low oxygen responder, hypoxiainducible factor-1␣ (HIF-1␣). LANA enhanced not only the transcriptional activities of HIF-1␣ but also its mRNA level. Coimmunoprecipitation and immunofluorescence studies documented a physical interaction between LANA and HIF-1␣ in transiently transfected 293T cells as well as in PEL cell lines during hypoxia. Through sequence analysis, several putative hypoxia response elements (HRE-1 to -6) were identified in the essential lytic gene Rta promoter. Reporter assays showed that HRE-2 (؊1130 to ؊1123) and HRE-5 and HRE-6 (؉234 to ؉241 and ؉812 to ؉820, respectively, within the intron sequence) were necessary and sufficient for the LANA-mediated HIF-1␣ response. Electrophoretic mobility shift assays showed HIF-1␣-dependent binding of a LANA protein complex specifically to the HRE-2, -5, and -6 motifs within the promoter regulatory sequences. This study demonstrates that hypoxia-induced KSHV lytic replication is mediated at least in part through cooperation of HIF-1␣ with LANA bound to the HRE motifs of the Rta promoter.

Kaposi's Sarcoma–Associated Herpesvirus Viral IFN Regulatory Factor 3 Stabilizes Hypoxia-Inducible Factor-1α to Induce Vascular Endothelial Growth Factor Expression

“…The high level of VEGF expression seen in Kaposi's sarcoma lesions may correlate with the fact that KSHV encodes several viral proteins that deregulate HIF1a/VEGF pathway (10,11,41). Here, we show that vIRF3 induces VEGF production in SLK endothelial cells by stabilizing HIF-1a protein.…”

Oxidative Stress Induces Reactivation of Kaposi's Sarcoma-Associated Herpesvirus and Death of Primary Effusion Lymphoma Cells

“…Hypoxia induces KSHV reactivation (16). The transcription factors hypoxia-inducible factor 1 alpha (HIF-1␣) (6,15) and X-box binding protein 1 (XBP-1) (15,71,75) have been shown to be involved in hypoxia-induced reactivation of KSHV. ROS generated by mitochondria signal hypoxia and are required for HIF-1␣ stabilization during hypoxia (9, 10), suggesting that ROS may play a role in KSHV reactivation induced by hypoxia.…”

Hypoxia inducible factor (HIF) function in innate immunity and infection

“…HHV-8 infection of endothelial cells in vitro leads to increased stabilization of the two HIF α subunits and increased HIF-responsive gene expression [45]. The HHV-8 latency-associated nuclear antigen (LANA), which plays a critical role in modulating viral and target cell gene expression, increases HIF-1α mRNA levels, and also physically interacts with the transcription factor to enhance its promoter activities [46]. HIF-1α induction and co-activation during HHV-8 infection can then lead to activation of target genes in the genome of the virus itself, including that encoding Rta, which is involved in transition of the virus from latency to a lytic replication phase.…”

“…HIF-1α induction and co-activation during HHV-8 infection can then lead to activation of target genes in the genome of the virus itself, including that encoding Rta, which is involved in transition of the virus from latency to a lytic replication phase. Several putative HREs are identified in the essential Rta promoter, and HIF-1α-dependent binding of a LANA protein complex to such HREs can be demonstrated by electromobility shift assays [46]. In another potential example of viral-HIF crosstalk, replication of parvovirus B19, a cause of erythema infectiousum or "fifth disease", is enhanced under hypoxic conditions.…”