ATM and glioma: H2AX phosphorylation occurs effectively in the primary fibroblast cell lines lacking ATM (AT1BR and AT7BI) and in the DNA‐PK‐deficient glioma (M059J) human cell line44 This has also been observed in irradiated mouse embryonic fibroblast (MEFs) cells deficient in ATM or DNK‐PKs.44