CReP-mediated control of eIF2α phosphorylation is a critical node in MYC-driven medulloblastoma

Medulloblastoma (MB) is the most common malignant pediatric brain tumor. The MYC‑amplified group 3 (G3) MB represents a high‑risk disease lacking effective therapies. A genetic screen identified the endoplasmic reticulum chaperone HSPA5 (BiP/GRP78) as a critical dependency in G3 MB. Its silencing induces apoptosis and suppresses tumor growth, with strong activation of the unfolded protein response (UPR). The UPR includes three branches, including the PERK–eIF2α axis, which transiently reduces global protein synthesis while enabling selective translation of stress‑responsive factors such as ATF4. We show that G3 MB requires sustained eIF2α activity for survival. Its inhibition triggers cell death through ATF4‑dependent and ‑independent transcriptional programs and translational reprogramming that deplete essential proteins and promote accumulation of detrimental factors. The eIF2α phosphatase PPP1R15B (CReP) maintains basal eIF2α activity and prevents apoptosis. These findings identify the eIF2α axis and its regulators as a crucial node and a targetable vulnerability in G3 MB. Group 3 (G3) medulloblastoma is an aggressive paediatric brain tumour with limited treatment options. Here, the authors show that CReP phosphatase maintains eIF2α activity, thereby protecting G3 MB cells from apoptosis, and that these cells are sensitive to eIF2α inactivation.