Beclin-1 heterozygosity reverts the induction of macroautophagy and reduced levels of the oxidative sensor DJ-1 in ATM-null cells but delays tumorigenesis in ATM-null mice. (A) Allelic loss of Beclin-1 reverses the increases in autophagic signaling and the reduced levels of DJ-1 manifest in ATM^−/− thymocytes. Proteins from freshly isolated thymocytes were analyzed by SDS-PAGE immunoblotting for detection of the autophagic markers p62 and LC3 and the oxidative stress sensor DJ-1. Band intensities of the cytoplasmic (-I) and autophagosome-associated (-II) forms of LC3 were determined using the ImageJ processing program, and the ratio of the LC3-I/LC3-II forms was calculated for each sample. (B) Allelic loss of Beclin-1 reverses the increased autophagic response and the reductions in DJ-1 protein levels observed in early passage ATM^−/− MEFs. P2 MEFs were treated with either DMSO or 50μM chloroquine (CQ; Sigma-Aldrich) for 4 hours, and total proteins were analyzed for the autophagic markers p62 and LC3, or for DJ-1. Transient treatment with CQ did not significantly alter p62 expression but affected LC3-I/II conversion in MEFs. (C-D) Allelic loss of Beclin-1 delays death of ATM^−/− mice (C), while accelerating onset of B-cell lymphoma in Eμ-Myc–transgenic mice (D). Kaplan-Meier survival plots of mice with desired genotypes are shown. P values were obtained by the log-rank (Mantel-Cox) test. The nonsurviving ATM^−/− and ATM^−/−Beclin-1^+/− all died of T-cell lymphomas.