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

SummaryThe 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 antiapoptotic 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 unphosphorylatable p50 mutant blocks inhibition of NF-κB-regulated antiapoptotic 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.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (187 K)Download as PowerPoint slideHighlights► p50 is phosphorylated by Chk1 in response to SN1-methylation/O6-MeG:T mismatches ► Phosphorylation of p50 blocks NF-κB DNA binding and transcriptional activity ► Phospho-p50 mediates inhibition of NF-κB-regulated antiapoptotic gene expression ► p50 pathway is necessary for efficient O6-methylguanine-induced cytotoxicity