Cell-surface associated p43/endothelial-monocyte-activating-polypeptide-II in hepatocellular carcinoma cells induces apoptosis in T-lymphocytes.
OBJECTIVE
The novel, proinflammatory cytokine endothelial-monocyte-activating-polypeptide-II (EMAP-II) was first found in tumour cell supernatants and is closely related or identical to the p43 component of the mammalian multisynthetase complex. In its secreted form, EMAP-II has multiple cytokine-like activities in vitro, including chemotactic, procoagulant and antiangiogenic properties. We recently showed that neoplastic but not normal hepatocytes expresses the 34-kDa molecule on the cell surface in vitro and the cell-surface expression is upregulated by treatment with tumour necrosis factor (TNF)-alpha/interferon (IFN)-gamma and/or hypoxia. We hypothesized an immune-regulatory role of EMAP-II within neoplastic tissues and investigated its effects on lymphocytes.


METHODS
To study the role of EMAP-II in tumour cell-induced lymphocyte killing, Jurkat T-cells were co-cultured with a range of hepatocellular carcinoma (HCC) cell monolayers (HuH-7, HepG2 and Alexander cells), which were either untreated or treated with TNF-alpha/IFN-gamma under normoxic and hypoxic conditions over a period of 16-24 hours. Flow cytometric analysis of apoptosis in Jurkat cells was performed using the annexin-V-FITC/propidium iodide technique.


RESULTS
rEMAP-II caused a dose-dependent apoptosis in Jurkat T-cells. Co-culture of Jurkat cells with HCC cell monolayers induced significant apoptosis of the Jurkat cells. In general, under normoxic conditions, cytokine-treated HCC cell monolayer caused more apoptosis than untreated cells. This effect was enhanced by hypoxia. Critically, native EMAP-II expressed on the surface of the HCC cells also induced activation of caspase-8 and apoptosis in Jurkat cells, which was partially but significantly blocked by addition of polyclonal antibodies against EMAP-II to the incubation mixture.


CONCLUSIONS
Our data suggest that membrane-bound EMAP-II is cytotoxic to lymphocytes and, therefore, might constitute a component of a novel, immunosuppressive pathway by which HCC cells may eliminate attacking T-cells and evade the immune system. The mechanism by which it does so is currently under investigation.
Faisal
Wasek
W
Wolfson Digestive Diseases Centre, University Hospital, University of Nottingham, Nottingham, UK. mrxwf@nottingham.ac.uk
Symonds
Peter
P
Panjwani
Shiraj
S
Heng
Yee
Y
Murray
John C
JC
D000818:Animals; D017209:Apoptosis / Q000187:drug effects*; D053181:Caspase 8 / Q000378:metabolism; D015687:Cell Hypoxia; D002462:Cell Membrane / Q000378:metabolism*; D018920:Coculture Techniques; D017077:Culture Media, Conditioned; D016207:Cytokines / Q000378:metabolism / Q000494:pharmacology*; D004789:Enzyme Activation; D006801:Humans; D007150:Immunohistochemistry; D019169:Jurkat Cells; D008099:Liver / Q000378:metabolism; D008114:Liver Neoplasms, Experimental / Q000378:metabolism / Q000473:pathology*; D009363:Neoplasm Proteins / Q000378:metabolism / Q000494:pharmacology*; D016601:RNA-Binding Proteins / Q000378:metabolism / Q000494:pharmacology*; D013601:T-Lymphocytes; D014407:Tumor Cells, Cultured
D017077:Culture Media, Conditioned; D016207:Cytokines; D009363:Neoplasm Proteins; D016601:RNA-Binding Proteins; C077219:small inducible cytokine subfamily E, member 1; D053181:Caspase 8