Activation of the p38 Mitogen-activated Protein Kinase Pathway by Epstein-Barr Virus-encoded Latent Membrane Protein 1 Coregulates Interleukin-6 and Interleukin-8 Production

The Epstein-Barr virus-encoded latent membrane protein 1 (LMP1) is a pleiotropic protein the activities of which include effects on gene expression and cell transformation, growth, and death. LMP1 has been shown to induce nuclear factor (NF)-kappaB and c-Jun NH2-terminal kinase/AP-1 activities in target cells, and in this study we demonstrate that LMP1 also engages the p38 mitogen-activated protein kinase cascade, leading to activation of the transcription factor ATF2. Mutational analysis of the LMP1 cytoplasmic COOH terminus revealed that p38 activation occurs from both the tumor necrosis factor receptor-associated factor (TRAF)-interacting, membrane-proximal COOH-terminal activating region (CTAR)1 domain (amino acids 186-231) and the extreme tumor necrosis factor receptor-associated death domain (TRADD) binding CTAR2 region (amino acids 351-386). Because LMP1 also engages signaling on the NF-kappaB axis through CTAR1 and CTAR2, we have examined whether these two pathways are overlapping or independent. We have found that inhibition of p38 by the highly specific inhibitor SB203580 did not affect NF-kappaB binding activity. Conversely, although the metabolic inhibitor D609 blocked NF-kappaB activation, it did not impair the ability of LMP1 to signal on the p38 axis, suggesting that these two LMP1-mediated pathways are primarily independent. Divergence of signals must, however, occur downstream of TRAF2 as a dominant negative TRAF2 mutant that blocks LMP1-induced NF-kappaB activation also inhibited p38 signaling. In addition, we have found that p38 inhibition significantly impaired LMP1-mediated interleukin-6 and -8 expression. Thus, p38 may play a significant cooperative role in regulating at least some of the pleiotropic activities of LMP1.