A model depicting distinct and common steps between NF-κB signaling induced by TNFα and DNA damaging agents. TNFα stimulation of TNFR1 engages receptor adaptor proteins (TRADD and RIP1) and results in the recruitment of ubiquitin conjugating enzymes (Ubc13/Uev1A and UbcH5) and E3 ligases (cIAP1/2, TRAF2/5 and HOIL/HOIP) to promote K63-linked, mixed and linear polyubiquitination of multiple target proteins. These polyubiquitin chains form the scaffold on which TAK1/TAB2/3 and IKK/NEMO complexes are formed and TAK1-dependent activation of IKKβ is induced. DNA damaging agents, such as etoposide, cause ATM activation via induction of DSB and SUMOylation of NEMO through a mechanism dependent on PARP1, PIASy and Ubc9. PIASy dependent SUMOylation of NEMO may also be induced by additional stress conditions. ATM then phosphorylates NEMO, which results in cIAP1-dependent monoubiquitination of NEMO. ATM and NEMO are exported to the cytoplasm where K63-linked polyubiquitination of ELKS and TRAF6 via ATM-dependent mechanism, as well as monoubiquitination of NEMO on lysine 285 via cIAP1, are induced. The polyubiquitin scaffolds then activate IKK via TAK1, similar to the mechanism induced by TNFα. Active IKK then phosphorylates IκBα, which then causes K48-linked polyubiquitination and degradation of IκBα by the proteasome to liberate active NF-κB (p50/p65) dimer. Polyubiquitin is represented in repeated yellow units, phosphate is shown in orange oval with “P” and SUMOylation is shown in purple circle with “S”. LUBAC, linear ubiquitin assembling complex.