Generation of p53 suppressor peptide from the fragment of p53 protein.

The p53 protein, encoded by a tumor suppressor gene, mediates growth arrest or apoptosis in response to a variety of stresses. p53-dependent apoptosis, occurring in several sensitive tissues after radiation or chemotherapy, is partially responsible for the side effects of cancer treatment, making p53 a potential target for therapeutic suppression. p53 function can be suppressed by the ectopic expression of p53-derived peptides, isolated earlier using functional selection of genetic suppressor elements (GSEs) from a library of randomly fragmented p53 cDNA (Ossovskaya et al. [1996]. Proc. Natl. Acad. Sci. U.S.A. 93, 10309). The potent p53-suppressing GSE, GSE56, had been used to generate in an E. coli expression system a peptide with anti-p53 activity by fusion of the GSE-encoded sequence with penetratin, a 16-amino-acid-long peptide capable of efficient translocation through cell membranes. Fusion with penetratin does not affect the anti-p53 activity of retrovirus-transduced GSE56. The fused peptide was able to attenuate p53-mediated transactivation and apoptosis when added into culture media. Interestingly, GSE56-derived peptide with no penetratin also had accumulated in the cells and showed similar, though lower, anti-p53 activity. This study provides the rationale and methodological basis for efficient generation of biologically active peptides with therapeutic potential from GSEs isolated through functional selection.