IL-1 receptor-associated kinase 1 is critical for latent membrane protein 1-induced p65/RelA serine 536 phosphorylation and NF-[kappa]B 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 (I[kappa]B) kinase (IKK) 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 I1A 293 cells. LMP1 also induced IKK[alpha]-mediated p100 processing and p52 nuclear localization in WT and IRAK1-deficient I1A 293 cells. Further, LMP1 TES1 and TES2 induced p65, p50, and p52 NF-[kappa]B DNA binding in WT and IRAK1-deficient I1A 293 cells. However, LMP1 induced p65/ RelA S536 phosphorylation only in WT 293 cells or in IRAK1 kinase point mutant reconstituted I1A 293 cells but not in IRAK1-deficient I1A 293 cells. IRAK1 was also required for LMP1 activation of p38, one of the kinases that can mediate p65/RelA 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.