The chemotherapeutic drug doxorubicin and the anti-proliferative long-acting somatostatin analogue octreotide, both used in cancer treatment, have been shown to increase the expression of the p53 tumour suppressor protein. In the present study, we demonstrate by Western-blot analysis that, in addition to the p53 protein, these molecules were able to induce the expression of a shorter protein with an apparent molecular mass of 40kDa (p40), recognized by antibodies raised against the N-terminus of p53. This induction was present in tumoral and non-tumoral cells and did not depend on the status of the endogenous p53 protein. The p40 protein was significantly induced after 3h of cell treatment with doxorubicin or octreotide, remained stable until 24h and was located in the nuclear extract. Using reverse primers corresponding to each exon of the p53 gene, only one transcript was amplified by reverse transcriptase—PCR. This suggested that p40 was issued from a post-translational modification and not from an alternative splicing. This protein was not recognized by the PAb421 antibody, suggesting that it was issued from a cleavage of the p53 C-terminal region (p40ΔC). Furthermore, this cleavage was not dependent on caspase activity. In conclusion, these results support the hypothesis that this post-translational modification plays a significant role in the regulation of multiple p53 signalling pathways. These results also suggest that octreotide, a molecule with different signalling pathways, was able as doxorubicin to generate a p53 breakdown product.
Abbreviations used: FCS, fetal calf serum; IHH, immortalized human hepatocytes; RT, reverse transcriptase.
Present address: CNRS UMR 1598, Institut Gustave Roussy, 39 rue Camille Desmoulins, 94805 Villejuif, France.
Present address: 3001, 12ème Avenue Nord, Département de Médecine, Gastroentérologie, Fleurimont, Québec, Canada J1H5N4.