Targeting Innate Immune Signaling in Glioma-Initiating Cells Impairs Self-Renewal and Radiation-Induced Cellular Plasticity

Purpose: Organisms constantly face environmental stressors that threaten their cellular and genomic integrity. In their response, pathogen-associated molecular patterns (PAMPs) and/or damage-associated molecular patterns (DAMPs) are detected by pattern recognition receptors (PRRs) and trigger the innate immune response. In this study we tested the hypothesis that DAMPs contribute to radiation-induced cellular plasticity in Glioblastoma (GBM). GBM is known to be organized hierarchically with a small number of glioma-initiating cells (GICs) driving treatment resistance and recurrences. Materials and Methods: Using patient-derived GBM specimens, we employed sphere forming capacity assays and in vitro extreme limiting dilution assays to examine how innate immune receptor signaling impacts the maintenance and self-renewal of GICs. By leveraging an imaging system for putative GICs we determined de novo induction of GICs from non-stem glioma cells. Results: We find that GIC maintenance after irradiation is mediated by cGAS-independent STING signaling, possibly involving signaling through TLR4 and TLR9. Induction of radiation-induced plasticity involves TLR3 signaling, with potential roles for other receptors and processes modulated by MyD88. Conclusion: These findings suggest that targeting innate immune signaling could prevent radiation-induced cellular plasticity for potential therapeutic benefit. HK-374 cells were seeded into 6-well plates as monolayer cultures at 40,000 cells/well. 4 days after seeding the cells were irradiated with 4 Gy in the presense or absence of H151. Controls were sham irradiated. RNA was harvested 48 h after irradiation.