Kaposi's Sarcoma-associated Herpesvirus-encoded Viral Interleukin-6 Is Secreted and Modified Differently Than Human Interleukin-6

Abstract

Viral interleukin-6 (vIL-6) is a homolog of cellular IL-6 that is encoded by the Kaposi's sarcoma-associated herpesvirus (KSHV) genome. vIL-6 binds to the IL-6 signal transducer gp130 without the cooperation of the IL-6 high affinity receptor to induce STAT3 DNA binding and cell proliferation. Although vIL-6 is believed to be important in the pathogenesis of KSHV-induced diseases, its secretion and post-translational modifications have not previously been characterized. Pulse-chase analysis revealed that the half-time of vIL-6 secretion is ϳ8-fold longer than that of human IL-6. Yet, the vIL-6 signal sequence targets human IL-6 secretion to nearly wildtype levels. Surprisingly, vIL-6 was not secreted from a cell line that does not express gp130 but expression of human gp130 in these cells enabled the secretion of vIL-6. Consistent with this observation, complete maturation of gp130 N-glycans is inhibited by vIL-6 coexpression, suggesting that the binding of the receptor to vIL-6 occurs intracellularly in early or pre-Golgi compartments. Furthermore, a vIL-6 mutant containing an endoplasmic reticulum retention signal is not secreted but does still induce receptor activation and signaling. Secreted vIL-6 is completely glycosylated at both possible N-glycosylaton sites and contains a large proportion of immature high-mannose glycans that is not typical of cytokines. These findings suggest that vIL-6 may induce gp130 signaling by an exclusively autocrine mechanism that relies on intracellular binding to its receptor. During KSHV infection, vIL-6 may only induce signaling in KSHV-infected cells to benefit the viral life cycle and promote oncogenic transformation.Kaposi's sarcoma-associated herpesvirus (KSHV) 1 is the causative agent of Kaposi's sarcoma and is associated with two lymphoproliferative disorders: multicentric Castleman's disease (MCD) and AIDS-related primary effusion lymphoma (PEL). DNA sequences and latency-associated nuclear antigen

Abrogation of Viral Interleukin-6 (vIL-6)-Induced Signaling by Intracellular Retention and Neutralization of vIL-6 with an Anti-vIL-6 Single-Chain Antibody Selected by Phage Display

“…Using this cell model system, secretion of vIL-6 was completely eliminated. Recently, a model of an intracellular signaling mechanism of vIL-6 was reported (43), and this model is further supported by our data. It was shown that only a small proportion of synthesized vIL-6 is secreted and that intracellular signal activation via a vIL-6-gp130 interaction in the ER is predominant.…”

“…It was speculated that only a small proportion of synthesized vIL-6 is secreted and that intracellular signal activation via a vIL-6-gp130 interaction in the ER is predominant (43). To evaluate this model and to demonstrate the relevance of our scFv-vIL-6-ER retention strategy, we generated a vIL-6 cDNA C-terminally fused to the ER retention signal KDEL.…”

“…It was reported previously that secretion of vIL-6 is not necessarily needed for signal induction. Moreover, vIL-6 seems to have the ability to induce signals by an autocrine mechanism that relies on intracellular binding to its receptor gp130 within the endoplasmic reticulum (ER) (43). Therefore, we decided to use MAV as an intrabody (antibodies for intracellular applications) to influence the intracellular localization of vIL-6.…”

Human Herpesvirus 8 Viral Interleukin-6 Signaling through gp130 Promotes Virus Replication in Primary Effusion Lymphoma and Endothelial Cells

“…Human IL-6 forms hexameric signaling complexes comprised of two gp80 receptor subunits, two gp130 signal transducers, and two hIL-6 molecules (gp80 2 -gp130 2 -IL-6 2 ) (10). Viral IL-6 can also form signaling hexamers at the cell surface, but its unique signaling from the endoplasmic reticulum (ER) occurs via tetrameric complexes (gp130 2 -vIL-6 2 ) exclusively (8,12,15,16). Viral IL-6 can be expressed during latent stages, in addition to lytic stages, of the viral life cycle (8,17).…”

KSHV Paracrine Effects on Tumorigenesis

“…The common hypothesis is based on the fact that KSHV encodes many viral lytic genes whose products are secreted factors homologous to cellular chemokines, cytokines, and growth factors, such as the viral interleukin (IL)-6 and the three viral chemokines (vCCL-1, -2, and -3, or alternatively named viral macrophage inflammatory protein, vMIP-I, -II, and III) (Nicholas, 2003). The vIL-6 is produced and released by infected cells during lytic infection and activates cell proliferation (Meads & Medveczky, 2004) and local angiogenesis (Aoki et al, 1999), while the viral MIPs are agonists for cellular chemokine receptors and exhibit angiogenic properties (Boshoff et al, 1997;Endres et al, 1999;C. Liu et al, 2001;Stine et al, 2000).…”