P53-independent downregulation of p73 in human cancer cells treated with Adriamycin

P73, a new p53 homologue, has been recently identified as a candidate tumor suppressor gene. Pul pose: We studied the alterations in p73 in a panel of human cancer cell lines treated with the chemotherapeutic agent, Adriamyci n (ADR), in comparison with the changes in p53. Metlzocis: P73 and p53 mRNA and protein were determined using semiquantitative reverse transcription-p olymerase chain reaction (RT-PCR) and Western blotting, respectively. ADR c ytotoxicity was examined by a trypan blue dye exclusion assay. Results: The cell lines bearing wild-type p53 were more susceptible to ADR than the cel l lines bearing mutant p53. ADR treatment resulted in a significant accumul ation of p53 protein and mRNA expression in the wild-type p53 cell lines an d caused little (slight increase) or no influence on p53 expression in the cell lines with p53 mutation and deletion. However, in striking contrast to the alterations in p53, a decline in p73 at both the protein and mRNA leve ls was observed in all the cell lines examined following ADR treatment. Fur ther studies indicated that this p53-independent downregulation of p73 was induced by ADR in a dose- and time-dependent manner. Moreover, the p73 prot ein decline was abrogated by the presence of proteasome inhibitors. Conclus ions: Our findings revealed that although p73 shares a similar structural a nd functional composition with p53, there is a significant difference in th e mechanisms that govern the responses of p53 and p73 to ADR-induced DNA da mage.