Kaposi’s sarcoma-associated herpesvirus (KSHV) is causally linked to several acquired immune deficiency syndrome related malignancies including Kaposi’s sarcoma (KS), primary effusion lymphoma (PEL), and a subset of multicentric Castleman’s disease1. Control of viral lytic replication is essential for KSHV latency, evasion of host immune system, and induction of tumors1. Here, we show that deletion of a cluster of 14 microRNAs (miRs) from KSHV genome significantly enhances viral lytic replication as a result of reduced NF-κB activity. The miR cluster regulates NF-κB pathway by reducing the expression of IκBα protein, an inhibitor of the NF-κB complexes. Computational and miR seed mutagenesis analyses identify KSHV miR-K1 that directly mediates IκBα ?protein level by targeting the 3’UTR of its transcript. Expression of miR-K1 is sufficient to rescue the NF-κB activity and inhibit viral lytic replication while inhibition of miR-K1 in KSHV-infected PEL cells has the opposite effects. Thus, KSHV encodes a miR to control viral replication by activating NF-κB pathway. These results illustrate an important role for KSHV miRs in regulating viral latency and lytic replication by manipulating a host survival pathway.

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The life cycle of Kaposi’s sarcoma-associated herpesvirus (KSHV) consists of latent and lytic replication phases. During latent infection, only a limited number of KSHV genes are expressed. However, this phase of replication is essential for persistent infection, evasion of host immune response, and induction of KSHV-related malignancies. KSHV reactivation from latency produces a wide range of viral products and infectious virions. The resulting de novo infection and viral lytic products modulate diverse cellular pathways and stromal microenvironment, which promote the development of Kaposi’s sarcoma (KS). The mechanisms controlling KSHV latency and reactivation are complex, involving both viral and host factors, and are modulated by diverse environmental factors. Here, we review the cellular and molecular basis of KSHV latency and reactivation with a focus on the most recent advancements in the field.

Kaposi's sarcoma-associated herpesvirus (KSHV) establishes a latent infection in the host following an acute infection. Reactivation from latency contributes to the development of KSHV-induced malignancies, which include Kaposi's sarcoma (KS), the most common cancer in untreated AIDS patients, primary effusion lymphoma and multicentric Castleman's disease. However, the physiological cues that trigger KSHV reactivation remain unclear. Here, we show that the reactive oxygen species (ROS) hydrogen peroxide (H2O2) induces KSHV reactivation from latency through both autocrine and paracrine signaling. Furthermore, KSHV spontaneous lytic replication, and KSHV reactivation from latency induced by oxidative stress, hypoxia, and proinflammatory and proangiogenic cytokines are mediated by H2O2. Mechanistically, H2O2 induction of KSHV reactivation depends on the activation of mitogen-activated protein kinase ERK1/2, JNK, and p38 pathways. Significantly, H2O2 scavengers N-acetyl-L-cysteine (NAC), catalase and glutathione inhibit KSHV lytic replication in culture. In a mouse model of KSHV-induced lymphoma, NAC effectively inhibits KSHV lytic replication and significantly prolongs the lifespan of the mice. These results directly relate KSHV reactivation to oxidative stress and inflammation, which are physiological hallmarks of KS patients. The discovery of this novel mechanism of KSHV reactivation indicates that antioxidants and anti-inflammation drugs could be promising preventive and therapeutic agents for effectively targeting KSHV replication and KSHV-related malignancies.