5 years ago

Human Herpesvirus 8 Interleukin-6 Interacts with Calnexin Cycle Components and Promotes Protein Folding.

Chen D, Nicholas J, Xiang Q
Viral interleukin-6 (vIL-6) encoded by human herpesvirus 8 (HHV-8) is believed to contribute via mitogenic, survival, and angiogenic activities to HHV-8-associated Kaposi's sarcoma, primary effusion lymphoma (PEL), and multicentric Castleman's disease through autocrine or paracrine mechanisms during latency or productive replication. There is direct evidence that vIL-6 promotes latently infected PEL cell viability and proliferation and also viral productive replication in PEL and endothelial cells. These activities are mediated largely through endoplasmic reticulum (ER)-localized vIL-6, which can induce signal transduction via the gp130 signaling receptor, activating mitogen-activated protein kinase (MAPK) and signal transducer and activator of transcription (STAT) signaling, and interactions of vIL-6 with the ER membrane protein vitamin K epoxide reductase complex subunit 1 variant 2 (VKORC1v2). The latter functional axis involves suppression of pro-apoptotic lysosomal protein cathepsin D by promotion of the ER-associated degradation of ER-transiting, pre-proteolytically processed pro-cathepsin D. Other interactions of VKORC1v2 and activities of vIL-6 via the receptor have not been reported. Here, we show that both vIL-6 and VKORC1v2 interact with calnexin cycle proteins UDP-glucose:glycoprotein glucosyltransferase 1 (UGGT1), catalyzing monoglucosylation of N-glycans, and oppositely-acting glucosidase II (GlucII) and that vIL-6 can promote protein folding. This activity was found to require VKORC1v2 and UGGT1, to involve vIL-6 associations with VKORC1v2, UGGT1 and GlucII, and to operate in the context of productively infected cells. These findings document new VKORC1v2-associated interactions and activities of vIL-6, revealing novel mechanisms of vIL-6 function within the ER compartment.IMPORTANCE HHV-8 vIL-6 pro-survival (latent) and pro-replication functions are mediated from the ER compartment through both gp130 receptor-mediated signal transduction and interaction of vIL-6 with the ER membrane protein VKORC1v2. This report identifies interactions of vIL-6 and VKORC1v2 with calnexin cycle enzymes GlucII and UGGT1, which are involved in glycan processing and nascent protein folding. The presented data show that vIL-6 and VKORC1v2 can co-complex with GlucII and UGGT1, that vIL-6 promotes protein folding, and that VKORC1v2, UGGT1, and vIL-6 interactions with GlucII and UGGT1 are important for the pro-folding activity of vIL-6, which can be detected in the context of infected cells. This newly identified ER activity of vIL-6 involving VKORC1v2 may promote viral latency (in PEL cells) and productive replication by limiting the damaging effects of unfolded protein response signaling in addition to enhancing viral protein folding. This is the first report of such a function for a cytokine.

Publisher URL: https://www.ncbi.nlm.nih.gov/pubmed/28878084

DOI: PubMed:28878084

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