KEY POINTS
- Using HeLa cervical cancer cells, U2OS DNA-break reporter systems, human tumor samples and xenograft models, investigators studied how Ku70–Ku80 assembly is regulated after ionizing radiation and whether that process contributes to radioresistance.
- Radiation induced deacetylation of Ku70 at K265 and K331. Mimicking persistent acetylation at these residues weakened Ku70–Ku80 interaction, whereas the deacetylation-mimetic state strengthened heterodimer formation, identifying these sites as functional regulators of NHEJ assembly.
- SIRT1 was identified as the relevant Ku70 deacetylase. TIMELESS acted as a scaffold bringing SIRT1 and Ku70 together after irradiation; TIMELESS knockout disrupted this interaction, prevented radiation-induced Ku70 deacetylation and reduced Ku70–Ku80 assembly.
- Functional assays showed that TIMELESS depletion reduced 53BP1 foci and NHEJ reporter activity, while re-expression restored repair. Combining TIMELESS loss with radiation also reduced clonogenic survival substantially more than TIMELESS inhibition alone.
- Human cervical-cancer tissue microarrays included 63 tumors and 48 adjacent normal samples. TIMELESS expression correlated with the radioresistance marker BCL2 and with increased SIRT1–Ku70 colocalization; an additional analysis examined this interaction in 21 radiotherapy-treated cervical cancer samples.
- In xenograft experiments with 5 mice per group, TIMELESS inhibition alone had limited antitumor activity, whereas combining TIMELESS suppression with local 3-Gy irradiation markedly increased tumor radiosensitivity. The paper reports the effect graphically rather than providing a simple clinically transferable effect size.
- TCGA and additional tumor samples suggested elevated TIMELESS expression across several cancer types, but no clinically available TIMELESS-directed drug was tested. The pan-cancer implications therefore remain mechanistic rather than therapeutic.
CLINICAL TAKEAWAY
The study identifies a plausible new mechanism of radioresistance: TIMELESS helps tumor cells assemble the Ku complex required for efficient NHEJ after radiation. Disrupting this pathway could become a radiosensitization strategy, but the evidence is currently limited to molecular, cellular and mouse models and does not yet support clinical intervention.