Raphin-1 mediates the survival and sensitivity to radiation of pediatric-type diffuse high-grade glioma via phosphorylated eukaryotic initiation factor 2α-dependent and -independent processes.

The primary treatment for fatal pediatric-type diffuse high-grade glioma (PED-DHGG) which harbor the H3K27M or H3G34R/V mutation is radiation, but it provides only short-term relief. Inhibitors of phosphorylated eIF2α (PeIF2α) phosphatase-namely raphin-1 and salubrinal-decrease survival of PED-DHGG cell lines and sensitize them to radiation. However, although both drugs increase PeIF2α, they have different effects on common targets and different targets altogether. Here, we aimed to identify PeIF2α-phosphatase-dependent and PeIF2α-phosphatase-independent molecular targets. Raphin-1 but not salubrinal, decreased the level of BiP and CReP and increased that of DR5, in an ISRIB-independent manner. Raphin-1 induced similar changes in MEF(S51A) cells and in irradiated PED-DHGG, suggesting a PeIF2α-independent contribution to raphin-1's radiosensitizing effect. Importantly, while the expression of [S51D] eIF2α decreased the survival of PED-DHGG and both raphin-1 and salubrinal decreased the survival of MEF(WT) cells, only raphin-1 decreased the survival of mutant MEF(S51A) cells. Our results suggest that the sensitivity of PED-DHGG to raphin-1 is mediated by both PeIF2α-dependent and PeIF2α-independent processes. Elucidating these processes could reveal targets for the development of drugs to overcome radiotherapy resistance of PED-DHGG.