Abstract
Human herpesvirus 8 (HHV-8) infection is associated with Kaposi's sarcoma, primary effusion lymphoma (PEL), and multicentric Castleman's disease. HHV-8-encoded viral interleukin-6 (vIL-6) is believed to contribute to pathogenesis via proproliferative, antiapoptotic, and proangiogenic activities. In PEL cells, vIL-6 is produced in functional amounts during viral latency and promotes the growth of these cells, mediating its activity from the endoplasmic reticulum (ER), where it is predominantly localized. This vIL-6 activity is dependent, in part, on its interaction with a splice variant of vitamin K epoxide reductase complex subunit 1 (VKORC1), termed VKORC1 variant 2 (VKORC1v2). Here we report that the IL-6 signal transducer, gp130, which can support vIL-6 signaling from the ER, is also required for optimal PEL cell growth and viability. Levels of activated extracellular regulated kinases (ERKs) 1 and 2 and signal transducer and activator of transcription 1 (STAT1) and STAT3, phosphorylated following gp130 stimulation, were reduced in gp130-depleted BCBL-1 and BC-1 cells. Diminished STAT activation was also detected in JSC-1 and BC-3 cells. Effects of gp130 depletion on growth could be mimicked by short hairpin RNA targeting of ERKs 1 and 2 or by depletion of STAT3. Finally, inhibition of vIL-6-gp130 association specifically within the ER compartment suppressed cell proliferation and viability, mirroring the effects of gp130 depletion. Combined, these data demonstrate that gp130, in addition to VKORC1v2, is essential for normal PEL cell growth and survival and that ER-localized vIL-6-gp130 interactions are critical for these activities. Targeting of intracellular vIL-6-gp130 interactions could potentially provide a means of PEL therapy.