Determinants of secretion and intracellular localization of human herpesvirus 8 interleukin-6.
Human herpesvirus 8 (HHV-8) interleukin-6 (vIL-6) is distinct from human and other cellular IL-6 proteins in that it does not require the nonsignaling alpha-receptor subunit for the formation of gp130-based signal transducing complexes and also is largely retained intracellularly rather than being secreted. We and others have reported that vIL-6 is retained and is active in the endoplasmic reticulum (ER) compartment, and data from our laboratory have demonstrated that intracellular vIL-6 is functional in the autocrine promotion of proliferation and survival of HHV-8 latently infected primary effusion lymphoma cells. It has also been reported that vIL-6 secretion in gp130-deficient cells can be enhanced by introduced gp130, thereby implicating the signal transducer in vIL-6 trafficking to the cell surface. We examine here the requirements for intracellular retention and localization of vIL-6. Using vIL-6-hIL-6 chimeric and point-mutated vIL-6 proteins, we identified regions and residues of vIL-6 influencing vIL-6 secretion. However, there was no correlation between vIL-6 secretion and gp130 interaction. We found that vIL-6, but not hIL-6, could associate stably with ER-resident chaperone protein calnexin. Glycosylation-dependent interaction of vIL-6 with calnexin correlated with proper protein folding, but there was no direct relationship between vIL-6-calnexin interaction and intracellular retention. While calnexin depletion had little influence on absolute amounts of secreted vIL-6, it led to markedly reduced levels of intracellular cytokine. This was reversed by gp130 transduction, which had no detectable effect on vIL-6 secretion, but redistributed vIL-6 into ER-distinct locations in calnexin-depleted cells, specifically. Our data reveal that calnexin plays a role in ER localization of vIL-6 and that gp130 promotes ER exit, but not secretion, of the viral cytokine.
Chen
Daming
D
Sidney Kimmel Comprehensive Cancer Center, Department of Oncology, Johns Hopkins University School of Medicine, 1650 Orleans St., Rm. 309, Baltimore, MD 21287, USA.
Choi
Young Bong
YB
Sandford
Gordon
G
Nicholas
John
J
D000595:Amino Acid Sequence; D037281:Calnexin / Q000378:metabolism; D002460:Cell Line; D050822:Cytokine Receptor gp130 / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000821:virology*; D006031:Glycosylation; D019288:Herpesvirus 8, Human / Q000235:genetics / Q000502:physiology*; D006801:Humans; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D017354:Point Mutation; D017510:Protein Folding
C494199:IL6ST protein, human; D015850:Interleukin-6; D050822:Cytokine Receptor gp130; D037281:Calnexin