Activated Nrf2 Interacts with Kaposi's Sarcoma-Associated Herpesvirus Latency Protein LANA-1 and Host Protein KAP1 To Mediate Global Lytic Gene Repression

Abstract

Kaposi's sarcoma-associated herpesvirus (KSHV) is etiologically associated with Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman's disease. We have previously shown that KSHV utilizes the host transcription factor Nrf2 to aid in infection of endothelial cells and oncogenesis. Here, we investigate the role of Nrf2 in PEL and PEL-derived cell lines and show that KSHV latency induces Nrf2 protein levels and transcriptional activity through the COX-2/PGE2/EP4/PKCζ axis. Next-generation sequencing of KSHV transcripts in the PEL-derived BCBL-1 cell line revealed that knockdown of this activated Nrf2 results in global elevation of lytic genes. Nrf2 inhibition by the chemical brusatol also induces lytic gene expression. Both Nrf2 knockdown and brusatol-mediated inhibition induced KSHV lytic reactivation in BCBL-1 cells. In a series of follow-up experiments, we characterized the mechanism of Nrf2-mediated regulation of KSHV lytic repression during latency. Biochemical assays showed that Nrf2 interacted with KSHV latency-associated nuclear antigen 1 (LANA-1) and the host transcriptional repressor KAP1, which together have been shown to repress lytic gene expression. Promoter studies showed that although Nrf2 alone induces the open reading frame 50 (ORF50) promoter, its association with LANA-1 and KAP1 abrogates this effect. Interestingly, LANA-1 is crucial for efficient KAP1/Nrf2 association, while Nrf2 is essential for LANA-1 and KAP1 recruitment to the ORF50 promoter and its repression. Overall, these results suggest that activated Nrf2, LANA-1, and KAP1 assemble on the ORF50 promoter in a temporal fashion. Initially, Nrf2 binds to and activates the ORF50 promoter during early de novo infection, an effect that is exploited during latency by LANA-1-mediated recruitment of the host transcriptional repressor KAP1 on Nrf2. Cell death assays further showed that Nrf2 and KAP1 knockdown induce significant cell death in PEL cell lines. Our studies suggest that Nrf2 modulation through available oral agents is a promising therapeutic approach in the treatment of KSHV-associated malignancies.

Importance: KS and PEL are aggressive KSHV-associated malignancies with moderately effective, highly toxic chemotherapies. Other than ganciclovir and alpha interferon (IFN-α) prophylaxis, no KSHV-associated chemotherapy targets the underlying infection, a major oncogenic force. Hence, drugs that selectively target KSHV infection are necessary to eradicate the malignancy while sparing healthy cells. We recently showed that KSHV infection of endothelial cells activates the transcription factor Nrf2 to promote an environment conducive to infection and oncogenesis. Nrf2 is modulated through several well-tolerated oral agents and may be an important target in KSHV biology. Here, we investigate the role of Nrf2 in PEL and demonstrate that Nrf2 plays an important role in KSHV gene expression, lytic reactivation, and cell survival by interacting with the host transcriptional repressor KAP1 and the viral latency-associated protein LANA-1 to mediate global lytic gene repression and thus cell survival. Hence, targeting Nrf2 with available therapies is a viable approach in the treatment of KSHV malignancies.