ATM and glioblastoma: Importantly, four cell lines in figures 1 and 2 show diminished levels of p21 expression: 80S4 cells, that represents abrogation of p21 in a wildtype TP53 background; 19S186 cells represent abrogation of p21 in a mutant TP53 background; the cell line mutant in ATM and the radioresistant glioblastoma line.