p50 (NF-κB1) Is an Effector Protein in the Cytotoxic Response to DNA Methylation Damage

Abstract

SUMMARY The functional significance of the signaling pathway induced by O6-methylguanine (O6-MeG) lesions is poorly understood. Here, we identify the p50 subunit of NF-κB as a central target in the response to O6-MeG and demonstrate that p50 is required for SN1-methylator-induced cytotoxicity. In response to SN1-methylation, p50 facilitates the inhibition of NF-κB-regulated anti-apoptotic gene expression. Inhibition of NF-κB activity is noted to be an S-phase specific phenomenon that requires the formation of O6-MeG:T mismatches. Chk1 associates with p50 following SN1-methylation and phosphorylation of p50 by Chk1 results in the inhibition of NF-κB DNA binding. Expression of an un-phosphorylateable p50 mutant blocks inhibition of NF-κB-regulated anti-apoptotic gene expression and attenuates SN1-methylator-induced cytotoxicity. While O6-MeG:T-induced, p50-dependent signaling is not sufficient to induce cell death, this pathway sensitizes cells to the cytotoxic effects of DNA breaks.

Mismatch repair-dependent metabolism of O 6 -methylguanine-containing DNA in Xenopus laevis egg extracts

“…S2A). It is possible that this transient activation reflected an interaction of MMR with the checkpoint machinery as observed previously both in vitro [17,18] and in vivo [19,29].…”

Decoy Receptor DcR1 Is Induced in a p50/Bcl3–Dependent Manner and Attenuates the Efficacy of Temozolomide

“…While all NF-κB subunits contain a conserved N-terminal rel homology domain (RHD), only p65, relB and crel have a C-terminal transactivation domain (TAD). p50 is a ubiquitously expressed NF-κB subunit that is targeted by the temozolomide-induced DNA damage response (8). Despite the lack of a TAD, p50 can induce NF-κB-dependent gene expression by associating with other rel subunits or co-regulator proteins.…”

The importance of the p50 NF-κB subunit

“…DNA replication stress results in the activation of the checkpoint kinases ATR and Chk1. Building on previous work from the Yamini group demonstrating that Chk1 can phosphorylate p50 at serine 329, 3 here it is shown that this modification is required for NF-kB dependent cell death following DNA replication stress. 1 This effect, which is associated with down regulation of anti-apoptotic genes such as Bcl-xL, is lost in NF-kB1 null cells reconstituted with S329 mutant forms of p50.…”