CHEK1 and glioblastoma: Activated downstream targets of ATM/ATR after radiation may consist of over 900 proteins [39].The In glioblastomas and atypical teratoid/rhabdoid tumors, stem cells characterized by the CD133+ phenotype demonstrated increased radiation resistance accompanied by enhanced expression of phosphorylated ATM and the checkpoint proteins Chk1, Chk2, and Rad17 compared to CD133− cells [16], [17].