Therapy-induced senescent glioblastoma cells sustain a procancer immune microenvironment by activating DDX58-mediated STAT1 signaling.

Background: Depending on the context, therapy-induced cancer cell senescence promotes or inhibits tumor progression and recurrence, but the underlying mechanism and effects on the tumor immune microenvironment are poorly understood.

Methods: Here, we developed senescent glioblastoma cell models in vitro via drug treatment. The protumor function of senescent cells was demonstrated by coinjection of chemotherapy-induced senescent cells with tumorigenic GL261 cells in C57BL/6J male mice. In addition, conditioned medium coculture experiments were used to explore the functions of senescent glioblastoma cells in vitro. Mechanistically, through a CRISPR-Cas9-based screen, we revealed that the RNA-binding protein DDX58 was induced in senescent glioblastoma cells. By combining RNA sequencing and protein mass spectrometry analysis, we observed that STAT1 signaling was activated. Immunoprecipitation experiments were subsequently performed to identify the interaction between DDX58 and STAT1.

Results: We show that glioblastoma cells can enter a senescent state after chemotherapy. In vivo, senescent glioblastoma cells have a tumor-promoting function and reduce survival in male mice. Mechanistically, we found that the RNA-binding protein DDX58 plays an important role in therapy-induced senescent glioblastoma. Inhibition of DDX58 slowed therapy-induced senescence. The activation of DDX58 depends on the accumulation of mitochondrial double-stranded RNA (mtdsRNA) in the cytoplasm via the BAX protein. Moreover, DDX58 promotes the recruitment of tumor-associated macrophages (TAMs) and their M2-like polarization by activating the STAT1-mediated transcription of colony-stimulating factor 1 (CSF1). We also revealed that DDX58 regulates STAT1 at the post-translational level by inhibiting the ubiquitin E3 ligase TRIM21-mediated STAT1 ubiquitination. Compared with temozolomide (TMZ) treatment alone, treatment with fludarabine, which blocks STAT1 signaling, combined with TMZ can more effectively reduce the recruitment of TAMs and delay tumor growth in vivo. Moreover, knockdown of STAT1 enhances the therapeutic effect of TMZ in vivo and prolongs the survival of tumor-bearing male mice.

Conclusion: A critical mechanism for the protumor immune microenvironment mediated by therapy-induced senescent glioblastoma cells, the DDX58-STAT1-CSF1 axis, may be a potential therapeutic avenue for alleviating traditional therapy-induced glioblastoma cell senescence.