Signaling mechanism of protein kinase PKR in the regulation of cytokine expression by Epstein-Barr virus latent membrane protein 1

Abstract

The oncogenic Epstein-Barr virus latent membrane protein 1 (LMP1) has been known to have cellular transformation properties and it induces cytokine expression including TNF. We previously showed that TNF and interferon interact to induce cellular effects via the activation of an dsRNA-activated protein kinase PKR, a signal transducer that regulates MAPK activities and cytokine induction. We investigated whether PKR plays a critical role in LMP1-regulated cytokine expression. BJAB (EBV-negative B-lymphoma) cells were transfected with pcDNA3 encoding LMP1-sense cDNA. Here, we showed that LMP-1 expression induces the synthesis of IL-6, IL-10 and GM-CSF in the cells. Suppression of PKR by 2-aminopurine (2AP, a PKR-specific inhibitor) resulted in abrogation of the cytokine expression in these cells. There were concomitant decreases in phosphorylation levels of p38 kinase in these 2AP-treated, LMP1-expressing BJAB cells. The results suggest that PKR is upstream of p38K in the LMP1-induced signaling pathways. Additionally, we showed that transcription factor NF-kB was activated in the LMP1-expressing BJAB cells as compared to the control LMP1-negative BJAB cells. The NF-kB activation also was dependent on PKR activity. In summary PKR may play a critical role in mediating the effects of LMP1 on the immune system, via the induction of p38K and NF-kB. (Supported by grants to ASL from HK Research Grants Council).