A microRNA component of the p53 tumour suppressor network

Abstract

The tumour suppressor p53 is the most commonly mutated gene in human cancers, and probably nearly all tumours have a lesion somewhere in this pathway. The p53 network is activated in response to numerous insults to restrain inappropriate cell proliferation either via growth arrest or cell death. MicroRNAs (miRNAs) are increasingly recognized for playing important parts in cancer, but little is know about how miRNA expression is regulated. Now a miRNA component of the p53 tumour suppressor network has been identified: p53 directly activates the transcription of the miR-34 family of miRNAs, which themselves suppress cell proliferation. Though dozens of p53 targets are known in mammals, miR-34 is unusual in that it is also present in Drosophila and the nematode worm C. elegans. This suggests that the link between p53 and miR-34 may have arisen early in the evolution of the p53 network. The tumour suppressor p53 directly activates the transcription of family of microRNAs, miR-34 family, which themselves suppress cell proliferation. The study also identifies miR-34 target genes that have roles in cell cycle progression. A global decrease in microRNA (miRNA) levels is often observed in human cancers1,2, indicating that small RNAs may have an intrinsic function in tumour suppression. To identify miRNA components of tumour suppressor pathways, we compared miRNA expression profiles of wild-type and p53-deficient cells. Here we describe a family of miRNAs, miR-34a–c, whose expression reflected p53 status. Genes encoding miRNAs in the miR-34 family are direct transcriptional targets of p53, whose induction by DNA damage and oncogenic stress depends on p53 both in vitro and in vivo. Ectopic expression of miR-34 induces cell cycle arrest in both primary and tumour-derived cell lines, which is consistent with the observed ability of miR-34 to downregulate a programme of genes promoting cell cycle progression. The p53 network suppresses tumour formation through the coordinated activation of multiple transcriptional targets, and miR-34 may act in concert with other effectors to inhibit inappropriate cell proliferation.