MDM2 and neoplasm: Moreover, the tumor suppressor activity of Δ40p53 was partly, but significantly, attenuated in cells expressing mutant Δ40p53-R175H, although the mRNA levels of p21 and p53-induced genes, including MDM2 and FAS, did not change, providing further experimental evidence that the transcriptional activity of Δ40p53 is closely associated with the its anti-tumor effects.