IL-1 receptor-associated kinase 1 is critical for latent membrane protein 1-induced p65/RelA serine 536 phosphorylation and NF-κB activation

Epstein-Barr virus latent infection integral membrane protein 1 (LMP1) mimics a constitutively active TNF receptor (TNFR). LMP1 has two C-terminal cytosolic domains, transformation effector sites (TES)1 and -2, that engage TNFR-associated factors (TRAFs) and the TNFR-associated death domain protein, respectively, and activate NF-kappa B. NF-kappa B activation is critical for Epstein-Barr virus-infected lymphoblast survival. TES1- and TES2-mediated NF-kappa B activations are IL-1 receptor-associated kinase 1 (IRAK1)-dependent. Because IRAK1 is upstream of TRAF6 in IL-1 activation of NF-kappa B, the potential role of IRAK1 in LMP1-mediated NF-kappa B activation through TRAF6 and inhibitor of kappa B (IKB) kinase (I kappa B) was initially investigated. Surprisingly, LMP1 expression activated TRAF6 ubiquitination, IKK beta induction of I kappa B alpha phosphorylation, and p65 nuclear translocation in both WT and IRAK1-deficient 11A 293 cells. LMP1 also induced IKK alpha-mediated p100 processing and p52 nuclear localization in WT and IRAK1-deficient 11A 293 cells. Further, LMP1 TES1 and TES2 induced p65, p50, and p52 NF-kappa B DNA binding in WT and IRAKII-cleficient 11A 293 cells. However, LMP1 induced p65/ ReIA S536 phosphorylation only in WT 293 cells or in IRAKII kinase point mutant reconstituted 11A 293 cells but not in IRAK1-deficient 11A 293 cells. IRAK1 was also required for LMP1 activation of p38, one of the kinases that can mediate p65/ReIA S536 phosphorylation and activate NF-kappa B-dependent transcription. Thus, the critical IRAK1 role in LMP1-induced NF-kappa B activation is in mediating p65/ReIA S536 phosphorylation through an effect on p38 or other p65 S536 kinases.