Xiufen Lei

Regulation of NF-κB inhibitor IκBα and viral replication by a KSHV microRNA

Kaposis sarcoma-associated herpesvirus (KSHV) is causally linked to several acquired immune deficiency syndrome-related malignancies, including Kaposis sarcoma, primary effusion lymphoma (PEL) and a subset of multicentric Castlemans disease. Control of viral lytic replication is essential for KSHV latency, evasion of the host immune system and induction of tumours. Here, we show that deletion of a 14 microRNA (miRNA) cluster from the KSHV genome significantly enhances viral lytic replication as a result of reduced NF-κB activity. The miRNA cluster regulates the NF-κB pathway by reducing expression of IκBα protein, an inhibitor of NF-κB complexes. Computational and miRNA seed mutagenesis analyses were used to identify KSHV miR-K1, which directly regulates the IκBα protein level by targeting the 3′UTR of its transcript. Expression of miR-K1 is sufficient to rescue NF-κB activity and inhibit viral lytic replication, whereas inhibition of miR-K1 in KSHV-infected PEL cells has the opposite effect. Thus, KSHV encodes an miRNA to control viral replication by activating the NF-κB pathway. These results demonstrate an important role for KSHV miRNAs in regulating viral latency and lytic replication by manipulating the host survival pathway.

Kaposi's Sarcoma-Associated Herpesvirus Latent Gene vFLIP Inhibits Viral Lytic Replication through NF-κB-Mediated Suppression of the AP-1 Pathway: a Novel Mechanism of Virus Control of Latency

ABSTRACT Kaposis sarcoma-associated herpesvirus (KSHV) latency is central to the evasion of host immune surveillances and induction of KSHV-related malignancies. The mechanism of KSHV latency remains unclear. Here, we show that the KSHV latent gene vFLIP promotes viral latency by inhibiting viral lytic replication. vFLIP suppresses the AP-1 pathway, which is essential for KSHV lytic replication, by activating the NF-κB pathway. Thus, by manipulating two convergent cellular pathways, vFLIP regulates both cell survival and KSHV lytic replication to promote viral latency. These results also indicate that the effect of the NF-κB pathway on KSHV replication is determined by the status of the AP-1 pathway and hence provide a mechanistic explanation for the contradictory role of the NF-κB pathway in KSHV replication. Since the NF-κB pathway is commonly activated during infection of gammaherpesviruses, these findings might have general implications for the control of gammaherpesviral latency.

Reactive oxygen species hydrogen peroxide mediates Kaposi's sarcoma-associated herpesvirus reactivation from latency.

Kaposis 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 Kaposis sarcoma (KS), the most common cancer in untreated AIDS patients, primary effusion lymphoma and multicentric Castlemans 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.

Mechanisms of Kaposi's Sarcoma-Associated Herpesvirus Latency and Reactivation

The life cycle of Kaposis 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 Kaposis 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.

KSHV MicroRNAs Mediate Cellular Transformation and Tumorigenesis by Redundantly Targeting Cell Growth and Survival Pathways

Kaposis sarcoma-associated herpesvirus (KSHV) is causally linked to several human cancers, including Kaposis sarcoma, primary effusion lymphoma and multicentric Castlemans disease, malignancies commonly found in HIV-infected patients. While KSHV encodes diverse functional products, its mechanism of oncogenesis remains unknown. In this study, we determined the roles KSHV microRNAs (miRs) in cellular transformation and tumorigenesis using a recently developed KSHV-induced cellular transformation system of primary rat mesenchymal precursor cells. A mutant with a cluster of 10 precursor miRs (pre-miRs) deleted failed to transform primary cells, and instead, caused cell cycle arrest and apoptosis. Remarkably, the oncogenicity of the mutant virus was fully restored by genetic complementation with the miR cluster or several individual pre-miRs, which rescued cell cycle progression and inhibited apoptosis in part by redundantly targeting IκBα and the NF-κB pathway. Genomic analysis identified common targets of KSHV miRs in diverse pathways with several cancer-related pathways preferentially targeted. These works define for the first time an essential viral determinant for KSHV-induced oncogenesis and identify NF-κB as a critical pathway targeted by the viral miRs. Our results illustrate a common theme of shared functions with hierarchical order among the KSHV miRs.

A Kaposi's Sarcoma-Associated Herpesvirus MicroRNA and Its Variants Target the Transforming Growth Factor β Pathway To Promote Cell Survival

ABSTRACT Transforming growth factor β (TGF-β) signaling regulates cell growth and survival. Dysregulation of the TGF-β pathway is common in viral infection and cancer. Latent infection by Kaposis sarcoma-associated herpesvirus (KSHV) is required for the development of several AIDS-related malignancies, including Kaposis sarcoma and primary effusion lymphoma (PEL). KSHV encodes more than two dozen microRNAs (miRs) derived from 12 pre-miRs with largely unknown functions. In this study, we show that miR variants processed from pre-miR-K10 are expressed in KSHV-infected PEL cells and endothelial cells, while cellular miR-142-3p and its variant miR-142-3p_-1_5, which share the same seed sequence with miR-K10a_ +1_5, are expressed only in PEL cells and not in uninfected and KSHV-infected TIME cells. KSHV miR-K10 variants inhibit TGF-β signaling by targeting TGF-β type II receptor (TβRII). Computational and reporter mutagenesis analyses identified three functional target sites in the TβRII 3′ untranslated region (3′UTR). Expression of miR-K10 variants is sufficient to inhibit TGF-β-induced cell apoptosis. A suppressor of the miRs sensitizes latent KSHV-infected PEL cells to TGF-β and induces apoptosis. These results indicate that miR-K10 variants manipulate the TGF-β pathway to confer cells with resistance to the growth-inhibitory effect of TGF-β. Thus, KSHV miRs might target the tumor-suppressive TGF-β pathway to promote viral latency and contribute to malignant cellular transformation.

Regulation of herpesvirus lifecycle by viral microRNAs.

Human herpes viruses have latency and lytic replication phases in their lifecycle. Proper regulation of herpes viral lifecycle is essential for the evasion of host immune surveillance and development of their related diseases. Recent advancements indicate a role of a novel class of viral non-coding RNAs, microRNAs (miRNAs), in the fine-tuning of herpes viral lifecycle. So far, herpes viral miRNAs have been shown to promote viral latency by inhibiting viral lytic replication either through direct targeting of key viral replication genes or through manipulation of host pathways that regulate viral lifecycle. The oncogenic Kaposis sarcoma-associated herpes virus (KSHV) has adapted both strategies to control viral latency. Our recent study has identified a KSHV miRNA that inhibits viral lytic replication by upregulating the NF-κB pathway.

MicroRNAs control herpesviral dormancy

Infections by herpesviruses are widespread in humans, and are the causes for several important diseases. Gammaherpesvirus Kaposis sarcoma-associated herpesvirus (KSHV) is etiologically associated with Kaposis sarcoma (KS), a highly inflammatory and angiogenic cancer commonly found in AIDS patients.1 KSHV is also associated with primary effusion lymphoma and a subset of multicentric Castleman’s disease, two rare lymphoproliferative malignancies.

Identification and function of MicroRNAs encoded by herpesviruses

MicroRNAs (miRNAs) play important roles in eukaryotes, plants and some viruses. It is increasingly clear that miRNAs-encoded by viruses can affect the viral life cycle and host physiology. Viral miRNAs could repress the innate and adaptive host immunity, modulate cellular signaling pathways, and regulate the expression of cellular and viral genes. These functions facilitate viral acute and persistent infections, and have profound effects on the host cell survival and disease progression. Here, we discuss the miRNAs encoded by herpesviruses, and their regulatory roles involved in virus-host interactions.