Celastrol Sensitizes Bladder Cancer to Gemcitabine by Regulating LINC00839-Mediated Homologous Recombination DNA Repair.

Gemcitabine resistance remains a major obstacle in the treatment of advanced bladder cancer. Celastrol, a bioactive triterpenoid derived from traditional Chinese medicinal plants, has been reported to enhance chemosensitivity in multiple malignancies. However, the molecular mechanisms by which celastrol modulates gemcitabine response in bladder cancer remain largely unclear. Human bladder cancer cell lines (T24 and J82) and a gemcitabine-resistant T24 model (T24GEM) were used to investigate the chemosensitizing effects of celastrol. Cell proliferation, colony formation, and drug sensitivity were evaluated in vitro, while a xenograft mouse model was used for in vivo validation. DNA damage and repair were assessed by γH2AX immunofluorescence and homologous recombination (HR) reporter assays. Celastrol significantly enhanced the sensitivity of bladder cancer cells to gemcitabine and suppressed tumor growth. Mechanistically, celastrol downregulated the oncogenic long non-coding RNA LINC00839, leading to inhibition of ATR/CHK1 signaling and impairment of HR-mediated DNA repair. Although the miR-142/SOX5 axis was responsive to celastrol, it was not the primary mediator of chemosensitization. In contrast, activation of the LINC00839-dependent ATR/CHK1 pathway was required for efficient HR-mediated DNA repair and gemcitabine resistance. Pharmacological inhibition of CHK1 phenocopied the effects of celastrol and acted synergistically with gemcitabine. In conclusion, LINC00839-ATR/CHK1-HR repair axis is a key driver of gemcitabine resistance in bladder cancer. Celastrol sensitizes bladder cancer cells to gemcitabine by targeting this pathway, highlighting LINC00839 and ATR/CHK1 as promising therapeutic targets for overcoming chemoresistance.