The suppression of the apoptosisenhancing effect of c-myc by mutant p53 thus allows expression of these other functions of c-myc (95). bcl-2 also suppresses the apoptosis-enhancing effect of deregulated c-myc (103, 104). Therefore it was suggested (96) that c-myc and mutant p53 may cooperate in tumor development as occurs with c-myc and bcl-2 (105, 106). This was confirmed in experiments showing that coexpression of mutant p53 in myeloid leukemic cells expressing deregulated c-myc increased leukemogenicity in vivo compared to cells only expressing deregulated c-myc (Fig. 4) (107).