TRAF6 binding to MAPK kinase kinase 1 (MEKK1) is mediated by the adapter protein evolutionarily conserved signaling intermediate in Toll pathway or in short ECSIT (Kopp E et al 1999). Induced MEKK1 can activate both IKK alpha and IKK beta thus leading to induction of NF-kappa-B activation. MEKK1 was also shown to induce ERK1/2 and JNK activation [Yujiri T et al 1998].
Although TRAF6 interacts with several upstream mediators (IRAK1, IRAK2, TRIF), there is no data showing MEKK1 participating in the interaction with the TRAF6 activators. Therefore this reaction is simplified to include only TRAF6 and MEKK1.