Conserved regulation of p53 network dosage by microRNA-125b occurs through evolving miRNA-target gene pairs

Micrornas regulate networks of genes to orchestrate cellular functions. mir-125b,the vertebrate homologue of the caenorhabditis elegans microrna lin-4,has been implicated in the regulation of neural and hematopoietic stem cell homeostasis,analogous to how lin-4 regulates stem cells in c. elegans. depending on the cell context,mir-125b has been proposed to regulate both apoptosis and proliferation. because the p53 network is a central regulator of both apoptosis and proliferation,the dual roles of mir-125b raise the question of what genes in the p53 network might be regulated by mir-125b. by using a gain- and loss-of-function screen for mir-125b targets in humans,mice,and zebrafish and by validating these targets with the luciferase assay and a novel mirna pull-down assay,we demonstrate that mir-125b directly represses 20 novel targets in the p53 network. these targets include both apoptosis regulators like bak1,igfbp3,itch,puma,prkra,tp53inp1,tp53,zac1,and also cell-cycle regulators like cyclin c,cdc25c,cdkn2c,edn1,ppp1ca,sel1l,in the p53 network. we found that,although each mirna-target pair was seldom conserved,mir-125b regulation of the p53 pathway is conserved at the network level. our results lead us to propose that mir-125b buffers and fine-tunes p53 network activity by regulating the dose of both proliferative and apoptotic regulators,with implications for tissue stem cell homeostasis and oncogenesis. © 2011 le t. n. et al.