Caixia Zhu

A Unique SUMO-2-Interacting Motif within LANA Is Essential for KSHV Latency

Kaposis sarcoma-associated herpesvirus (KSHV) stabilizes hypoxia-inducible factor α (HIF-1α) during latent infection, and HIF-1α reactivates lytic replication under hypoxic stress. However, the mechanism utilized by KSHV to block lytic reactivation with the accumulation of HIF-1α in latency remains unclear. Here, we report that LANA encoded by KSHV contains a unique SUMO-interacting motif (LANASIM) which is specific for interaction with SUMO-2 and facilitates LANA SUMOylation at lysine 1140. Proteomic and co-immunoprecipitation analysis further reveal that the SUMO-2 modified transcription repressor KAP1 is a critical factor recruited by LANASIM. Deletion of LANASIM led to functional loss of both LANA-mediated viral episome maintenance and lytic gene silencing. Moreover, hypoxia reduced KAP1 SUMOylation and resulted in dissociation of both KAP1 and Sin3A repressors from LANASIM-associated complex. Therefore, the LANASIM motif plays an essential role in KSHV latency and is a potential drug target against KSHV-associated cancers.

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

ABSTRACT Hypoxia-inducible factor 1α (HIF-1α) has been frequently implicated in many cancers as well as viral pathogenesis. Kaposis sarcoma-associated herpesvirus (KSHV) is linked to several human malignancies. It can stabilize HIF-1α during latent infection and undergoes lytic replication in response to hypoxic stress. However, the mechanism by which KSHV controls its latent and lytic life cycle through the deregulation of HIF-1α is not fully understood. Our previous studies showed that the hypoxia-sensitive chromatin remodeler KAP1 was targeted by the KSHV-encoded latency-associated nuclear antigen (LANA) to repress expression of the major lytic replication and transcriptional activator (RTA). Here we further report that an RNA interference-based knockdown of KAP1 in KSHV-infected primary effusion lymphoma (PEL) cells disrupted viral episome stability and abrogated sub-G1/G1 arrest of the cell cycle while increasing the efficiency of KSHV lytic reactivation by hypoxia or using the chemical 12-O-tetradecanoylphorbol-13-acetate (TPA) or sodium butyrate (NaB). Moreover, KSHV genome-wide screening revealed that four hypoxia-responsive clusters have a high concurrence of both RBP-Jκ and HIF-1α binding sites (RBS+HRE) within the same gene promoter and are tightly associated with KAP1. Inhibition of KAP1 greatly enhanced the association of RBP-Jκ with the HIF-1α complex for driving RTA expression not only in normoxia but also in hypoxia. These results suggest that both KAP1 and the concurrence of RBS+HRE within the RTA promoter are essential for KSHV latency and hypoxia-induced lytic reactivation. IMPORTANCE Kaposis sarcoma-associated herpesvirus (KSHV), a DNA tumor virus, is an etiological agent linked to several human malignancies, including Kaposis sarcoma (KS) and primary effusion lymphoma (PEL). HIF-1α, a key hypoxia-inducible factor, is frequently elevated in KSHV latently infected tumor cells and contributes to KSHV lytic replication in hypoxia. The molecular mechanisms of how KSHV controls the latent and lytic life cycle through deregulating HIF-1α remain unclear. In this study, we found that inhibition of hypoxia-sensitive chromatin remodeler KAP1 in KSHV-infected PEL cells leads to a loss of viral genome and increases its sensitivity to hypoxic stress, leading to KSHV lytic reactivation. Importantly, we also found that four hypoxia-responsive clusters within the KSHV genome contain a high concurrence of RBP-Jκ (a key cellular regulator involved in Notch signaling) and HIF-1α binding sites. These sites are also tightly associated with KAP1. This discovery implies that KAP1, RBP-Jκ, and HIF-1α play an essential role in KSHV pathogenesis through subtle cross talk which is dependent on the oxygen levels in the infected cells.

Constitutive Activation of Interleukin-13/STAT6 Contributes to Kaposi's Sarcoma-Associated Herpesvirus-Related Primary Effusion Lymphoma Cell Proliferation and Survival

ABSTRACT Activation of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT) signaling pathway has been associated with numerous human malignancies, including primary effusion lymphomas (PELs). PEL, a cancerous proliferation of B cells, is caused by Kaposis sarcoma-associated herpesvirus (KSHV). Previously we identified constitutive phosphorylation of STAT6 on tyrosine 641 (p-STAT6C) in PEL cell lines BC3 and BCBL1; however, the molecular mechanism leading to this activation remains unclear. Here we demonstrate that STAT6 activation tightly correlates with interleukin-13 (IL-13) secretion, JAK1/2 tyrosine phosphorylation, and reduced expression of SHP1 due to KSHV infection. Moreover, p-STAT6C and reduction of SHP1 were also observed in KS patient tissue. Notably, blockade of IL-13 by antibody neutralization dramatically inhibits PEL cell proliferation and survival. Taken together, these results suggest that IL-13/STAT6 signaling is modulated by KSHV to promote host cell proliferation and viral pathogenesis. IMPORTANCE STAT6 is a member of signal transducer and activator of transcription (STAT) family, whose activation is linked to KSHV-associated cancers. The mechanism through which STAT6 is modulated by KSHV remains unclear. In this study, we demonstrated that constitutive activation of STAT6 in KSHV-associated PEL cells results from interleukin-13 (IL-13) secretion and reduced expression of SHP1. Importantly, we also found that depletion of IL-13 reduces PEL cell growth and survival. This discovery provides new insight that IL-13/STAT6 plays an essential role in KSHV pathogenesis.

Cell Cycle Regulatory Functions of the KSHV Oncoprotein LANA

Manipulation of cell cycle is a commonly employed strategy of viruses for achieving a favorable cellular environment during infection. Kaposi’s sarcoma-associated herpesvirus (KSHV), the primary etiological agent of several human malignancies including Kaposi’s sarcoma, and primary effusion lymphoma, encodes several oncoproteins that deregulate normal physiology of cell cycle machinery to persist with endothelial cells and B cells and subsequently establish a latent infection. During latency, only a small subset of viral proteins is expressed. Latency-associated nuclear antigen (LANA) is one of the latent antigens shown to be essential for transformation of endothelial cells in vitro. It has been well demonstrated that LANA is critical for the maintenance of latency, episome DNA replication, segregation and gene transcription. In this review, we summarize recent studies and address how LANA functions as an oncoprotein to steer host cell cycle-related events including proliferation and apoptosis by interacting with various cellular and viral factors, and highlight the potential therapeutic strategy of disrupting LANA-dependent signaling as targets in KSHV-associated cancers.

Nuclear Localization and Cleavage of STAT6 Is Induced by Kaposi's Sarcoma-Associated Herpesvirus for Viral Latency.

Emerging evidence implies that STAT6 plays an important role in both the adaptive and innate immune responses to virus infection. Kaposi’s sarcoma-associated herpesvirus (KSHV) is an oncogenic γ-herpesvirus agent associated with several human malignancies, including Kaposi’s sarcoma (KS) and primary effusion lymphomas (PELs). Previously, we demonstrated that KSHV blocks IL-4-induced STAT6 phosphorylation and retains a basal IL-13/STAT6 constitutive activation for cell survival and proliferation. However, the mechanism by which KSHV regulates STAT6 remains largely unknown. Here, we found that KSHV-encoded LANA interacts with STAT6 and promotes nuclear localization of STAT6 independent of the tyrosine 641-phosphorylation state. Moreover, nuclear localization of STAT6 is also dramatically increased in KS tissue. The latent antigen LANA induces serine protease-mediated cleavage of STAT6 in the nucleus, where the cleaved STAT6 lacking transactivation domain functions as a dominant-negative regulator to repress transcription of Replication and Transcription Activator (RTA) and in turn shut off viral lytic replication. Blockade of STAT6 by small interference RNA dramatically enhances expression of RTA, and in turn reduces KSHV-infected endothelial cell growth and colony formation. Taken together, these results suggest that nuclear localization and cleavage of STAT6 is important for modulating the viral latency and pathogenesis of KSHV.

Hostile takeover: Manipulation of HIF-1 signaling in pathogen-associated cancers (Review)

Hypoxia-inducible factor (HIF)-1 is a central regulator in the adaptation process of cell response to hypoxia (low oxygen). Emerging evidence has demonstrated that HIF-1 plays an important role in the development and progression of many types of human diseases, including pathogen-associated cancers. In the present review, we summarize the recent understandings of how human pathogenic agents including viruses, bacteria and parasites deregulate cellular HIF-1 signaling pathway in their associated cancer cells, and highlight the common molecular mechanisms of HIF-1 signaling activated by these pathogenic infection, which could act as potential diagnostic markers and new therapeutic strategies against human infectious cancers.

Prevalence and correlates of Mycoplasma genitalium infection among prostatitis patients in Shanghai, China.

Background: Mycoplasma genitalium (M. genitalium) has been shown to be involved in chronic non-gonococcal urethritis (NGU). However, the prevalence and determinants of this emerging sexually transmissible infection among prostatitis patients remain obscure. Methods: Two hundred and thirty-five patients diagnosed with prostatitis and 152 health controls from sexually transmitted diseases (STD) clinics in Shanghai, China, were selected. M. genitalium was detected in the initial voided urine (VB1), midstream of urine (VB2), expressed prostatic secretion (EPS) and the opening urine after massage (VB3) by quantitative polymerase chain reaction (Q-PCR) targeting the Mycoplasma genitalium adhesion protein (MgPa). An infection of the prostate was considered positive if a uropathogen was found only in the EPS sample or VB3, or if it was at least four-fold greater in EPS or VB3 than in VB1 or VB2. The prostatitis patients with M. genitalium infection were treated with azithromycin. Results: The prevalence of M. genitalium infection was significantly higher among the prostatitis group than the control group (10 vs 3%, P = 0.005). Among the prostatitis group, M. genitalium infection was significantly associated with those patients who received treatment for genitourinary infection previously than those patients who did not (17 vs 6%; adjusted OR, 4.011; 95% CI, 1.562-10.300). The symptoms were totally or partially improved in 83% per cent (19/23) of prostatitis patients with M. genitalium, positive in EPS and M. genitalium turned negative after azithromycin treatment. Conclusions: M. genitalium was prevalent in the patients with prostatitis, particularly in those who received ineffective antibiotic treatment for the bacterium, and was identified as having a significant association of prostatitis.

High prevalence and correlates of human herpesvirus-6A in nevocytic nevus and seborrheic diseases: Implication from a pilot study of skin patient tissues in Shanghai: DING et al.

Skin disorders vary greatly in symptom and severity, and the causes of these disorders are largely unknown. Human herpesvirus (HHV) has been shown to cause many diseases. However, the prevalence and correlation of each HHV infection with different skin disorders remains obscure. To reveal the potential link of a certain type of skin disease with herpesvirus infection, a total of 272 patient tissues with inflammatory or neoplastic skin diseases including 7 subtypes in Shanghai, China, were investigated. We found that the overall prevalence of HHV‐6A in inflammatory or neoplastic skin tissues is the most common (40.3%), followed by Epstein‐Barr virus (17.6%), Kaposi’s sarcoma‐associated herpesvirus (KSHV; 9.2%), HHV‐6B (4.4%), human cytomegalovirus (1.1%), and varicella‐zoster virus (0.7%); albeit the co‐infection of HHV‐6A, Epstein‐Barr virus, and KSHV presents to a less extent and none of HSV‐1, HSV‐2, or HHV‐7 were detected. Moreover, HHV‐6A infection is highly associated with nevocytic nevus and seborrheic dermatitis/keratosis diseases, which mainly occur in the head and the neck or the lower limb. Despite no significant difference among the HHV infections in different age groups of skin patient tissues, the distribution of KSHV infection was exclusively and significantly higher (~3.7‐fold) in male skin patients.

Interplay Between Microenvironmental Abnormalities and Infectious Agents in Tumorigenesis

Emerging evidence has shown that the cell of microenvironmental abnormalities is a key factor that controls many cellular physiological processes including cellular communication, homing, proliferation, and survival. Given its central regulatory role, it is therefore not surprising that it is widely exploited by infectious agents for inducing pathogenesis. In the past decade, a number of oncogenic pathogens including viruses, bacteria, and parasites are demonstrated to take advantage of the tumor microenvironmental factors including hypoxia, oxidative stress, and cytokines, to create an extracellular environment more favorable for pathogen survival and propagation and escape from the host immune surveillance. Here we summarize and highlight the current understanding of the interplay between common tumor microenvironmental factors and oncogenic pathogens in promoting tumorigenesis.

Bacterial Infection and Associated Cancers

Bacterial infections were traditionally not considered as major causes of cancer. However, increasing evidence in the past decades has suggested that several cancers are highly associated with bacterial infection. The bacterial infections have evolved some unique strategies including lateral gene transfer, biofilm and microbiome to induce genome instability and chronic inflammation, as well as escape of immune surveillance for carcinogenesis. Here we summarize and highlight the recent progress on understanding of how bacterial infection plays a role in tumor formation and malignancy.