EGFR-Mediated Chromatin Condensation Protects KRAS-Mutant Cancer Cells against Ionizing Radiation

Authors:
  • MWMeng Wang
    Meng Wang
  • AKAshley M. Kern
    Ashley M. Kern
  • MHMarieke Hülskötter
    Marieke Hülskötter
  • PGPatricia Greninger
    Patricia Greninger
  • ASAnurag Singh
    Anurag Singh
  • YPYunfeng Pan
    Yunfeng Pan
  • DCDipanjan Chowdhury
    Dipanjan Chowdhury
  • CBCyril H. Benes
    Cyril H. Benes
  • JEJason A. Efstathiou
    Jason A. Efstathiou
  • JSJeff Settleman
    Jeff Settleman

Abstract
Therapeutics that target the epidermal growth factor receptor (EGFR) can enhance the cytotoxic effects of ionizing radiation (IR). However, predictive genomic biomarkers of this radiosensitization have remained elusive. By screening 40 non–small cell lung cancer cell (NSCLC) lines, we established a surprising positive correlation between the presence of a KRAS mutation and radiosensitization by the EGFR inhibitors erlotinib and cetuximab. EGFR signaling in KRAS-mutant NSCLC cells promotes chromatin condensation in vitro and in vivo, thereby restricting the number of DNA double-strand breaks (DSB) produced by a given dose of IR. Chromatin condensation in interphase cells is characterized by an unexpected mitosis-like colocalization of serine 10 phosphorylation and lysine 9 trimethylation on histone H3. Aurora B promotes this process in a manner that is codependent upon EGFR and protein kinase C α (PKCα). PKCα, in addition to MEK/ERK signaling, is required for the suppression of DSB-inducible premature senescence by EGFR. Blockade of autophagy results in a mutant KRAS-dependent senescence-to-apoptosis switch in cancer cells treated with IR and erlotinib. In conclusion, we identify EGFR as a molecular target to overcome a novel mechanism of radioresistance in KRAS-mutant tumor cells, which stands in contrast to the unresponsiveness of KRAS-mutant cancers to EGFR-directed agents in monotherapy. Our findings may reposition EGFR-targeted agents for combination with DSB-inducing therapies in KRAS-mutant NSCLC. Cancer Res; 74(10); 2825–34. ©2014 AACR.