The estrogen receptor-α-induced microRNA signature regulates itself and its transcriptional response

Abstract

Following estrogenic activation, the estrogen receptor-␣ (ER␣) directly regulates the transcription of target genes via DNA binding. MicroRNAs (miRNAs) modulated by ER␣ have the potential to fine tune these regulatory systems and also provide an alternate mechanism that could impact on estrogen-dependent developmental and pathological systems. Through a microarray approach, we identify the subset of microRNAs (miRNAs) modulated by ER␣, which include upregulation of miRNAs derived from the processing of the paralogous primary transcripts (pri-) mir-17-92 and mir-106a-363. Characterization of the mir-17-92 locus confirms that the ER␣ target protein c-MYC binds its promoter in an estrogen-dependent manner. We observe that levels of pri-mir-17-92 increase earlier than the mature miRNAs derived from it, implicating precursor cleavage modulation after transcription. Pri-mir-17-92 is immediately cleaved by DROSHA to pre-miR-18a, indicating that its regulation occurs during the formation of the mature molecule from the precursor. The clinical implications of this novel regulatory system were confirmed by demonstrating that pre-miR-18a was significantly upregulated in ER␣-positive compared to ER␣-negative breast cancers. Mechanistically, miRNAs derived from these paralogous pri-miRNAs (miR-18a, miR-19b, and miR-20b) target and downregulate ER␣, while a subset of pri-miRNA-derived miRNAs inhibit protein translation of the ER␣ transcriptional p160 coactivator, AIB1. Therefore, different subsets of miRNAs identified act as part of a negative autoregulatory feedback loop. We propose that ER␣, c-MYC, and miRNA transcriptional programs invoke a sophisticated network of interactions able to provide the wide range of coordinated cellular responses to estrogen.AIB1 ͉ autoregulatory feedback loop ͉ primary transcript ͉ processing U pon 17-␤-estradiol (E2) binding, estrogen receptors (ERs) mediate transcription by interacting directly to specific estrogen response elements (EREs) located in the promoter/ enhancer region of its target genes or indirectly by tethering to nuclear proteins, such as AP1 and SP1 transcription factors (2-4). The cellular response to estrogen is highly regulated at multiple levels including transcription, RNA stability, and posttranslational modifications (5-8). Following treatment with E2, ER␣ transcription and mRNA stability is substantially reduced within 1 h of stimulation (7). Furthermore, E2-ER␣ interactions accelerate receptor degradation through the ubiquitinproteasome pathway, an effect associated with its major coactivator AIB1 (8).MicroRNAs (miRNAs) are a class of noncoding short RNAs, 21-24 nucleotides (nt) in length, that play a role in gene regulation. They downregulate expression of their target genes by base pairing to the 3Ј-UTR of target messenger RNAs (mRNAs) (9). During their biogenesis most miRNAs are transcribed as part of a longer transcript named pri-miRNA (10). These molecules are processed inside the nucleus by DROSHA, producing a pre-miRNA that is a 70-nt ''imperfect'' stem loop ...

Expression of miR-18a and miR-210 in Normal Breast Tissue as Candidate Biomarkers of Breast Cancer Risk

“…1) and validation set (Fig. 2) but did not reach statistical significance, which is similar to the report from Castellano and colleagues (34). In the benign breast tissues, there was no significant difference between the CUB of ER-positive cases and the CUB of ER-negative cases but both were significantly higher than the reduction mammoplasty controls, suggesting that miR-18a acts as a breast cancer risk marker without ER subtype specificity.…”

“…Transfection of miR-18a into breast cancer cell lines (MCF7 and BT-474) suppressed ER expression (33). However, in another study, expression levels of miR-18a showed no significant differences between ER-positive and ER-negative tumors (34). Instead, pre-miR-18a levels were significantly higher in ER-positive tumors than in those that were ER-negative.…”

MiR‐17~92 ablation impairs liver regeneration in an estrogen‐dependent manner

“…For miR‐17~92, various research groups have found that these miRNAs are regulated by oestrogen stimuli in vivo and in vitro 25, 33, 34, 35. The molecule basis of the phenomenon has been described above for the co‐regulation effects of activated ESα (oestrogen‐binding ESα) and transcription factor c‐myc 25, 36, 37. Based on our results, we added new evidence that the expression of miR‐17~92 was modulated by oestrogen and then showed sex disparity in the liver.…”

Direct regulation of microRNA biogenesis and expression by estrogen receptor beta in hormone-responsive breast cancer

“…Several evidences indicate that ERa is among the transcription factors regulating miRNA biogenesis in hormone-responsive BC cells (Bhat-Nakshatri et al, 2009;Castellano et al, 2009;Maillot et al, 2009;Yamagata et al, 2009;Cicatiello et al, 2010;Ferraro et al, 2010Ferraro et al, , 2011. More recently, global mapping of ERb binding to ERa-positive, hormone-responsive BC cells chromatin in vivo showed ERb interaction with several miRNA genes, suggesting the possible involvement of this receptor in hormonal control of small noncoding RNA biogenesis in this cell type (Grober et al, 2011).…”