LUBAC regulates NF-κB activation upon genotoxic stress by promoting linear ubiquitination of NEMO

The transcription factor nuclear factor kappa B (NF-kappa B) regulates various cellular processes such as inflammation and apoptosis. The NF-kappa B essential modulator (NEMO/IKK gamma) is indispensable for NF-kappa B activation by diverse stimuli including genotoxic stress. Here, we show that NEMO linear ubiquitination on K285/309 is critical for genotoxic NF-kappa B activation. The E3 ligase linear ubiquitin chain assembly complex (LUBAC) facilitates NEMO linear ubiquitination upon genotoxic stress. Inhibiting LUBAC function interrupts the genotoxic NF-kappa B signalling cascade by attenuating the activation of IKK and TAK1 in response to DNA damage. We further show that the linear ubiquitination of NEMO is a cytoplasmic event, potentially downstream of NEMO nuclear exportation. Moreover, ELKS ubiquitination appears to facilitate linear ubiquitination of NEMO through stabilizing NEMO: LUBAC association upon DNA damage. Deubiquitinating enzyme CYLD inhibits NEMO linear ubiquitination, possibly by disassembling both K63-linked and linear polyubiquitin. We also found that abrogating linear ubiquitination of NEMO significantly increased genotoxin-induced apoptosis, resulting in enhanced sensitivity to chemodrug in cancer cells. Therefore, LUBAC-dependent NEMO linear ubiquitination is critical for genotoxic NF-kappa B activation and protects cells from DNA damage-induced apoptosis. The EMBO Journal (2011) 30, 3741-3753. doi: 10.1038/emboj.2011.264; Published online 2 August 2011