A Cytoplasmic ATM-TRAF6-cIAP1 Module Links Nuclear DNA Damage Signaling to Ubiquitin-Mediated NF-κB Activation

As part of the genotoxic stress response, cells activate the transcription factor NF-kappa B. The DNA strand break sensor poly(ADP-ribose)-polymerase-1 (PARP-1) and the kinase ataxia telangiectasia mutated (ATM) act as proximal signal mediators. PARP-1 assembles a nucleoplasmic signalosome, which triggers PIASy-mediated IKK gamma SUMOylation. ATM-dependent IKK gamma phosphorylation and subsequent ubiquitination were implicated to activate the cytoplasmic I kappa B kinase (IKK) complex by unknown mechanisms. We show that activated ATM translocates in a calcium-dependent manner to cytosol and membrane fractions. Through a TRAF-binding motif, ATM activates TRAF6, resulting in Ubc13-mediated K63-linked polyubiquitin synthesis and cIAP1 recruitment. The ATM-TRAF6-cIAP1 module stimulates TAB2-dependent TAK1 phosphorylation. Both nuclear PARP-1- and cytoplasmic ATM-driven signaling branches converge at the IKK complex to catalyze monoubiquitination of IKK gamma at K285. Our data indicate that exported SUMOylated IKK gamma acts as a substrate. IKK gamma monoubiquitination is a prerequisite for genotoxic IKK and NF-kappa B activation, but also promotes cytokine signaling.