TTRAP, a novel protein that associates with CD40, tumor necrosis factor (TNF) receptor-75 and TNF receptor-associated factors (TRAFs), and that inhibits nuclear factor-kappa B activation

CD40 belongs to the tumor necrosis factor (TNF) receptor family. CD40 signa ling involves the recruitment of TNF receptor-associated factors (TRAFs) to its cytoplasmic domain. We have identified a novel intracellular CD40-bind ing protein termed (T) under bar RAF and (T) under bar NF (r) under bar ece ptor-associated (p) under bar rotein (TTRAP) that also interacts with TNF-R 75 and CD30. The region of the CD40 cytoplasmic domain that is required for TTRAP association overlaps with the TRAF6 recognition motif. Association o f TTRAP with CD40 increases profoundly in response to treatment of cells wi th CD40L. Interestingly, TTRAP also associates with TRAFs, with the highest affinity for TRAF6. In transfected cells, TTRAP inhibits in a dose-depende nt manner the transcriptional activation of a nuclear factor-kappa B (NF-ka ppa B) dependent reporter mediated by CD40, TNF-R75 or Phorbol 12-myristate 13-acetate (PMA) and to a lesser extent by TRAF2, TRAF6, TNF-alpha, or int erleukin-1 beta (IL-1 beta). TTRAP does not affect stimulation of NF-KB ind uced by overexpression of the NF-kappa B-inducing kinase (NIK), the I kappa B kinase alpha (IKK alpha), or the NF-KB subunit P65/RelA suggesting it ac ts upstream of the latter proteins. Our results indicate that we have isola ted a novel regulatory factor that is involved in signal transduction by di stinct members of the TNF receptor family.