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 Kaposi's 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-STAT6 C 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. IMPORTANCESTAT6 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. Cytokines play a critical role in many viral infections. Viruses not only manipulate host cytokine production to favor virus survival, replication, and infection but also help virus-infected cells to modulate the host immune response, which potentially results in the development of viral persistent infection, pathogenesis, or tumorigenesis (1). Kaposi's sarcoma-associated herpesvirus (KSHV), also named human herpesvirus 8 (HHV-8), is an oncogenic gammaherpesvirus that associates with several aggressive malignancies, including AIDS-related Kaposi's sarcoma (KS) (2), primary effusion lymphoma (PEL) (3), and multicentric Castleman's disease (MCD) (4). Increasing evidence has suggested that KSHV also deregulates an array of host cytokines, including interleukin-6 (IL-6), IL-8, and IL-1␣, thereby inducing cell proliferation and malignant transformation (5-8).Signal transducer and activator of transcription (STAT) proteins are a family of cytoplasmic transcription factors involved in cytokine signal transduction. STAT6 is a key member of the STAT family, whose role in the biology of cancer and immune cells has been firmly established (9, 10). STAT6 is activated by cytokine IL-4 or IL-13, via a common receptor chain, namely, IL-4R␣. Upon interleukin binding, IL-4R␣ dimerizes with IL-4R␥ or IL-13R␣1 to form type I or type II IL-4R receptor, respectively. The dimerized receptor recruits and activates phosphorylatio...

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

“…Previously, despite the absence of detectable phosphorylation of Y641 on STAT6 in KS tissue [24], we clearly observed there were more nuclear localization of total STAT6 in KS tissues than in normal skin controls (Fig 1A and 1B), which is further verified by the immunofluorescence assays against STAT6 and LANA (Fig 1C and 1D). To further confirm if infection of KSHV enhances nuclear localization of STAT6, endogenous STAT6 in iSLK cells with and without KSHV infection were monitored by immunofluorescence and cell fractionation assay.…”

“…In regards to STAT6, our previous studies have shown that KSHV blocks IL-4-induced STAT6 phosphorylation favoring latency, while stimulation with IL-4 resulted in RTA expression and reactivation of viral lytic replication [22,23]. We recently also found that KSHV retains a basal IL-13/STAT6 constitutive activation for cell survival and proliferation [24]. However, whether STAT6 plays a role in maintaining KSHV latency, independent of IL-4 or IL-13 stimulation remains unclear.…”

The regulatory role of protein phosphorylation in human gammaherpesvirus associated cancers

“…LANA reduces IL-4-mediated phosphorylation of STAT6 on Y-641 and concomitantly its DNA binding ability (Cai et al, 2010a). However, STAT6 is constitutively activated in the PEL cells due to the secretion of IL-13 and downregulation of SHP1 by KSHV (Wang et al, 2015;Wang et al, 2017). Moreover, IL-13-stimulated constitutively phosphorylation of STAT6 is tightly associated with activation of JAK1 instead of PI3K and Akt (Wang et al, 2015).…”

“…However, STAT6 is constitutively activated in the PEL cells due to the secretion of IL-13 and downregulation of SHP1 by KSHV (Wang et al, 2015;Wang et al, 2017). Moreover, IL-13-stimulated constitutively phosphorylation of STAT6 is tightly associated with activation of JAK1 instead of PI3K and Akt (Wang et al, 2015). However, both IL-4 and IL-13 also activate STAT6 and induced by LMP-1 in EBV-infected B cells (Kis et al, 2011).…”

“…Cytokine-mediated JAK/STAT signaling controls numerous important cellular processes, such as immune response, cellular growth, and differentiation. Viruses not only manipulate host cytokine production to favor virus survival, replication, and infection but also help virus-infected cells to escape the host immune response, which potentially results in the development of cancer (Wang et al, 2015). In the recent review (Wei et al, 2016), we have summarized to address how EBV and KSHV encode their own cytokines and chemokines to escape hose immune surveillance.…”