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Non-small cell lung carcinoma (NSCLC) is a major cause of cancer mortality. High expression of the epithelial-to-mesenchymal transition transcription factor TWIST1 is strongly associated with metastatic cancers and treatment resistance. Additionally, TWIST1 can upregulate O-GlcNAcylation which (1) is required to suppress fail-safe programs such as oncogene (KRasG12D)-induced senescence (OIS) to accelerate tumorigenesis in primary NSCLC tumors, and (2) is a potential modulator of DNA repair/radiation response. We hypothesized that the transactivation function of TWIST1 and downstream target programs are critical in the promotion of tumorigenicity and radioresistance. We created a novel genetically engineered mouse model (GEMM) allowing tetracycline-inducible expression in the lung epithelium (via lung specific CCSP-reverse tetracycline transactivator (C)) of KRasG12D (R) with Twist1 wt (T) or with Twist1F191G transactivation-null mutant (F). We also created non-cancer Human Bronchial Epithelial Cell (HBEC) co-expressing HRasG12V oncogene with human TWIST1wt (HBEC- HRasG12V-TWIST1wt) or transactivation-null TWIST1F187G mutant (HBEC- HRasG12V-TWIST1F187G). CRT mice had shorter tumor-free survival and more aggressive tumors compared to CR/CRF mice indicating that the Twist1 transactivation domain is required for Twist1 -dependent tumorigenesis acceleration. Also, Twist1 wt expression promoted radioresistance in cell lines and GEMMs. Contrary to CRT, CRF showed a progressive loss of TWIST1F191G expression over time suggesting no functionality/no selective advantage. CRT lung tumors had higher proliferation (Ki67) and lower cell-cycle arrest (p16) compared to CR/CRF suggesting that the transactivation domain of Twist1 is important for OIS suppression. Supporting these data, we observed in HBEC that the co-expression of TWIST1wt could suppress HRasG12V -induced senescence while TWIST1F187G mutant could not. HBEC- HRasG12V-TWIST1wt also sustained tumorigenic/invasive programs. Interestingly, we observed that O-GlcNAcylation inhibition rescued OIS in HBEC- HRasG12V - TWIST1wt while O-GlcNAcylation stimulation in HBEC -HRasG12V - TWIST1F187G suppressed OIS. Importantly, TWIST1wt modulated MYC downstream targets, and MYC activity inhibition in HBEC- HRasG12V - TWIST1wt using the novel MYC inhibitor MYCi975 also rescued OIS induction. Altogether, these results suggest that TWIST1 may suppress OIS via MYC signaling and nominate MYCi975 as a means to activate latent OIS programs. MYC inhibiting strategies could serve as a therapeutic sensitizer for TWIST1-expressing NSCLC. This work and our future studies on TWIST1 on the control of OIS, O-GlcNAcylation, and radioresistance mechanisms may help to identify new potential NSCLC therapeutic strategies. [ABSTRACT FROM AUTHOR]