Sequential Modification of NEMO/IKKγ by SUMO-1 and Ubiquitin Mediates NF-κB Activation by Genotoxic Stress

Abstract

The transcription factor NF-kappaB is critical for setting the cellular sensitivities to apoptotic stimuli, including DNA damaging anticancer agents. Central to NF-kappaB signaling pathways is NEMO/IKKgamma, the regulatory subunit of the cytoplasmic IkappaB kinase (IKK) complex. While NF-kappaB activation by genotoxic stress provides an attractive paradigm for nuclear-to-cytoplasmic signaling pathways, the mechanism by which nuclear DNA damage modulates NEMO to activate cytoplasmic IKK remains unknown. Here, we show that genotoxic stress causes nuclear localization of IKK-unbound NEMO via site-specific SUMO-1 attachment. Surprisingly, this sumoylation step is ATM-independent, but nuclear localization allows subsequent ATM-dependent ubiquitylation of NEMO to ultimately activate IKK in the cytoplasm. Thus, genotoxic stress induces two independent signaling pathways, SUMO-1 modification and ATM activation, which work in concert to sequentially cause nuclear targeting and ubiquitylation of free NEMO to permit the NF-kappaB survival pathway. These SUMO and ubiquitin modification pathways may serve as anticancer drug targets.

Global genome splicing analysis reveals an increased number of alternatively spliced genes with aging

“…Furthermore, explorative network analysis identified AS genes involved in RNA post‐transcriptional modifications in direct relation with histone H3 and RNA polymerase II and the NF‐κB complex as a major upstream and central node. Interestingly, the IKK/NF‐κB signaling pathway has been proposed to be one of the key mediators of aging (Huang et al ., 2003; Wu et al ., 2006). …”

Ubiquitylated Tax targets and binds the IKK signalosome at the centrosome

“…Protein ubiquitylation has been previously reported as a critical step for NF-kB activation either through proteolytic or non-proteolytic mechanisms. ATM-dependent ubiquitylation of IKK-g mediates NF-kB activation by genotoxic stress (Huang et al, 2003) and the deubiquitylation enzyme CYLD negatively regulates NF-kB signaling (Kovalenko et al, 2003). K63-poly-ubiquitylation of TRAF6 mediates IKK activation by interleukin-1 (Deng et al, 2000).…”

p53-induced protein with a death domain (PIDD) isoforms differentially activate nuclear factor-kappaB and caspase-2 in response to genotoxic stress

“…Moreover, treatment of human embryonic kidney (HEK) 293T cells that stably express PIDD isoforms with etoposide resulted in increased NF-kB, as assessed by a luciferase assay (Figure 4c). In the course of a response to DNA damage, NEMO is sequentially sumoylated, phosphorylated and ubiquitinated to activate NF-kB (Huang et al, 2003;Hay, 2004). PIDD isoform 1 is essential for NEMO sumoylation and its overexpression increases SUMO-NEMO levels (Janssens et al, 2005).…”

“…Activation of NF-kB in response to DSB depends on two parallel signaling cascades, namely those orchestrated by the PI3 kinase like ataxia-telangectasia mutated (ATM), which is activated by DSB or higher order chromatin changes (Bakkenist and Kastan, 2003) and those regulated by PIDD, which is activated by an as yet unknown signal (Janssens et al, 2005). In response to DSB, NEMO (also known as IKKg) is sumoylated on K277 and K309 by PIASg in a PIDD-dependent fashion, and SUMO-NEMO accumulates in the nucleus (Huang et al, 2003;Janssens et al, 2005;Mabb et al, 2006). Activated ATM phosphorylates SUMO-NEMO to allow its desumoylation and subsequent monoubiquitination on the same lysine residues (Huang et al, 2003).…”

“…In response to DSB, NEMO (also known as IKKg) is sumoylated on K277 and K309 by PIASg in a PIDD-dependent fashion, and SUMO-NEMO accumulates in the nucleus (Huang et al, 2003;Janssens et al, 2005;Mabb et al, 2006). Activated ATM phosphorylates SUMO-NEMO to allow its desumoylation and subsequent monoubiquitination on the same lysine residues (Huang et al, 2003). NEMO then shuttles back to the cytoplasm where it can associate with IKKa and IKKb to form an active IKK complex that will lead to NF-kB activation and cell survival.…”