Genome wide screen of estrogen receptor α regulated microRNAs reveals a negative autoregulatory feedback loop

Estrogen receptor alpha (ERα) is a nuclear receptor linked to progression of the majority of human breast cancers. Following activation ERα regulates the transcription of target genes via DNA binding. Through a genome wide approach we have identified a subset of microRNAs (miRNAs or miRs) modulated by ERα. Among them, miRNAs encoded from 2 paralogous clusters, miR-17-92 and miR-106a-363, were up-regulated. In addition, increased expression of miR-424, miR-542-3p and miR-450, located within the same genomic region and down-regulation of miR-181 family members were observed during the estrogenic response. We observed that ERα alone is sufficient for sustained transcription of miR-17-92 and we show that levels of this cluster increase earlier than miRNAs encoded by it, implicating post-transcriptional regulation. Since miR-17-92 a pri-miRNA, is immediately cleaved by DROSHA to pre-miR-18a, this regulation occurs during the formation of the mature molecule from the precursor. Moreover, pre-miR-18a was significantly up-regulated in ERα-positive breast cancers compared to ERα-negative breast cancers. We also demonstrate that the miRNAs belonging to these paralogous clusters target and down-regulate ERα, while a subset of cluster-derived miRNAs inhibit protein translation of its major oncogenic transcriptional p160 co-activator by targeting AIB1 revealing a negative autoregulatory feedback loop. This pathway adds to the highly regulated cellular response to estrogen that fine tunes ERα transcriptional activity and cell proliferation. 4 time points (0hr,3hr,6hr,12hr) and 4 treatments (TO,JP,TO+TET,JP13+TET) x 3 biological replicates of each condition = 24 arrays