Exacerbation of genomic instability and radiosensitization upon RUNX3 or HMOX1 depletion in the presence of TGFβ. Exacerbation of genomic instability and radiosensitization upon RUNX3 or HMOX1 depletion in the presence of TGFβ. A, Lung adenocarcinomas were stratified on the basis of TGFβ signature and RUNX3 expression levels utilizing median expression values. Copy number alterations are shown in the scatter plot with bar (mean ± SEM). B, Lung adenocarcinomas were stratified on the basis of TGFβ signature and RUNX3 expression levels utilizing median expression values. Mutations per megabase of the genome are shown in the scatter plot with bar (mean ± SEM). C, Kaplan–Meier survival curve of the indicated cohorts is shown. n = 181, P = 0.0955, HR = 1.845. Statistical analysis was done with the Mann–Whitney U test. D, A549 cells were subjected to control or RUNX3-KD and exposed to vehicle control or TGFβ for 48 hours. Cells were exposed to increasing doses of X-irradiation in clonogenic assay. E, For experiment described in D, percent survival was plotted relative to radiation-untreated controls. F, A549 cells were subjected to control or HMOX1-KD and exposed to TGFβ or vehicle control. Forty-eight hours following TGFβ addition, cells were exposed to increasing doses of X-irradiation. G, For experiment described in F, percent survival was plotted relative to radiation-untreated controls. H, RUNX3 provides defense against TGFβ-dependent promotion of cancer progression. Top, TGFβ signaling induces ROS production, which participates in redox signaling and promotes TGFβ-mediated EMT. However, RUNX3 mitigates the accumulation of excessive ROS via the transcriptional upregulation of the HMOX1 and thus curtails tumor progression. Under these conditions, where RUNX3 levels are intact, TGFβ-mediated EMT is associated with low levels of DNA damage and genomic instability. Bottom, in the absence of RUNX3, low HMOX1 levels perpetrate high levels of ROS, which promotes cancer progression by the induction of DNA damage and senescence. Cellular senescence, in turn, fuels the production of inflammatory cytokines that further amplify the pro-oncogenic state. The reinstatement of HMOX1 expression in RUNX3-depleted cells restored cellular ROS, rescued DNA damage and premature senescence in the presence of TGFβ. Thus, HMOX1 downregulation seems to be one of the major mechanisms by which genomic instability is brought about by the TGFβ exposure of RUNX3-deficient cells. Vaidehi Krishnan et al. Cancer Res 2018;78:88-102 ©2018 by American Association for Cancer Research