c-MYC-retrovirus driven lymphomas lacking Puma, Noxa, and Bim. (A) Western blot analysis of PUMA, BIM, p19^Arf, p53, and β-actin or heat shock protein 70 (loading controls) of cell lines derived from rv c-MYC–driven lymphomas lacking p53 (A), or lacking both PUMA and BIM (B), or lacking NOXA, PUMA and BIM (C), confirmed allele-specific genotyping data (data not shown). BIM protein was variably expressed in cell lines lacking p53. Immortalized mouse embryo fibroblasts (MEFs) were included as positive controls for p19^Arf overexpression. MN97 = Eμ-Myc/Noxa^−/− lymphoma was included as a positive control for PUMA expression, and MP24 = Eμ-Myc/Puma^−/− lymphoma was included as a negative control for PUMA expression. (D) Genomic PCR for the Cdkn2a locus of rv c-MYC–driven cell lines of the different genotypes: exons 1α, 1β, 2. For 2 of the 5 rv c-MYC–driven Puma^−/−Bim^−/− cell lines tested, deletion of both exons 1α and 2 was observed, consistent with the loss of p16^Ink4a and p19^Arf.