Relationship between IκBα constitutive expression, TNFα synthesis, and apoptosis in EBV-infected lymphoblastoid cells

Abstract

In order to understand the role of NF-κB in EBV transformation we have established stably transfected IκBα into lymphoblastoid cells. Two clones were obtained in which the loss of NF-κB binding activity correlated with the constitutive expression of the transgenic IκBα. Protein latency expression was determined by immunocytochemistry. Expression of surface markers, intracytoplasmic content of cytokines cell cycle analysis after BrdU incorporation and DNA staining with propidium iodide were studied by flow cytometry. Percentage of apoptotic cells was determined by in-situ labelling of DNA strand breaks. No significative changes in EBV latency nor in cell surface marker expression was found. In contrast, intracytoplasmic TNFα levels were strongly reduced in transfected clones. Furthermore, 30% of IκBα transfected cells were apoptotic after 8 h of TNFα treatment. This correlated with a strong reduction of BrdU incorporation after 24 h of TNFα treatment. No effect was seen with non transfected cells or with cells transfected with a control plasmid. Our results suggest that the TNFα gene could be one of the targets of NF-κB in EBV infected cells and that NF-κB protects EBV-infected cells from apoptosis induced by TNFα, which may favour the proliferative effect of this cytokine.