A small synthetic peptide, which inhibits the p53-hdm2 interaction, stimulates the p53 pathway in tumour cell lines

The hdm2 protein negatively regulates p53 tumour suppressor activity. Upon binding to p53, hdm2 stimulates p53 degradation and inhibits its transcript ional activity. Moreover, the hdm2 protein is overexpressed in various tumo urs inactivating p53. We report here that an octamer synthetic peptide deri ved from p53 inhibits the p53-hdm2 interaction in vitro. In cellular assays , this untagged peptide penetrates tumour cells and induces the accumulatio n of p53. The accumulation of p53 leads to its activation. Two gene product s transcriptionally regulated by p53, p21(Waf1/Cip1) and hdm2, are induced in the presence of the peptide. When used with tumour cells that overexpres s hdm2, the peptide induces the death of these tumour cells by apoptosis. T he mode of action of this peptide differs from that of DNA-damaging agents (e.g. cisplatin) in that it does not induce p53 phosphorylation on serine 1 5. This work validates with a low molecular mass molecule our current knowl edge on the regulation of the p53 pathway by the hdm2 protein. It also show s that inhibitors of the p53-hdm2 interaction are very attractive candidate s for the activation of the p53 pathway in tumours expressing wild-type p53 . (C) 2000 Academic Press.