Altered expression of microRNAs (miRNA), an abundant class of small nonprotein-coding RNAs that mostly function as negative regulators of protein-coding gene expression, is common in cancer. Here, we analyze the regulation of miRNA expression in response to estrogen, a steroid hormone that is involved in the development and progression of breast carcinomas and that is acting via the estrogen receptors (ER) transcription factors. We set out to thoroughly describe miR-NA expression, by using miRNA microarrays and real-time reverse transcription-PCR (RT-PCR) experiments, in various breast tumor cell lines in which estrogen signaling has been induced by 17β-estradiol (E 2 ). We show that the expression of a broad set of miRNAs decreases following E 2 treatment in an ER-dependent manner. We further show that enforced expression of several of the repressed miRNAs reduces E 2 -dependent cell growth, thus linking expression of specific miRNAs with estrogen-dependent cellular response. In addition, a transcriptome analysis revealed that the E 2 -repressed miR-26a and miR-181a regulate many genes associated with cell growth and proliferation, including the progesterone receptor gene, a key actor in estrogen signaling. Strikingly, miRNA expression is also regulated in breast cancers of women who had received antiestrogen neoadjuvant therapy. Overall, our data indicate that the extensive alterations in miRNA regulation upon estrogen signaling pathway play a key role in estrogen-dependent functions and highlight the utility of considering miRNA expression in the understanding of antiestrogen resistance of breast cancer. [Cancer Res 2009;69(21):8332-40]

Of critical importance in the stress response is the post-transcriptional control of the expression of important genes involved in the control of cell survival and apoptosis. Here we report that miR-19, an oncogenic component of the miR-17-92/Oncomir-1 microRNA polycistron, regulates the expression of Ras homolog B (RhoB) in keratinocytes upon exposure to ultraviolet (UV) radiation. Strikingly, we could not find any evidence for deregulated expression of miR-19 during UV treatment. However, we show that miR-19-mediated regulation of antiapoptotic RhoB expression requires the binding of human antigen R (HuR), an AU-rich element binding protein, to the 3 0 -untranslated region of the rhoB mRNA. We propose that the loss of the interdependent binding between HuR and miR-19 to the rhoB mRNA upon UV exposure relieves this mRNA from miR-19-dependent inhibition of translation and contributes to the apoptotic response.

Endocrine resistance is a major clinical issue. AP-1 is a transcription factor downstream of different growth factor receptors (GFR) and stress-related signaling cascades implicated in endocrine resistance. We have previously shown that acquired endocrine resistance is associated with increased AP-1 activity. Moreover, AP-1 modulates the estrogen receptor (ER) transcriptional program, especially upon high GFR signaling. We therefore hypothesized that interfering with AP-1 could circumvent endocrine resistance. Methods and results: AP-1 was genetically inhibited by siRNA or by stable expression of an inducible dominant-negative (DN) c-Jun in MCF7 cells. In vitro, siRNA c-Jun significantly inhibited the growth of acquired tamoxifen resistant (TamR) MCF7 derivatives (>95% inhibition, p = .001) but not of parental cells ( p = .06). Xenografts of two inducible DN c-Jun clones were established in nude mice. Mice were randomized to continued estrogen (E2) supplementation or to either estrogen deprivation (ED) or Tam, all in the presence or absence of DN c-Jun. AP-1 blockade significantly reduced time to tumor response ( p = .014 and p = .006 for the two clones) and time to tumor disappearance ( p = .001 and p = .0034) in the Tam group, with similar results in the ED group. In addition, AP-1 blockade significantly delayed TamR by increasing time to tumor doubling ( p = .002). Furthermore, induction of DN c-Jun resulted in dramatic tumor shrinkage after long-term Tam treatment, suggesting reversal of endocrine resistance with AP-1 blockade. Interestingly, no significant effect was observed on E2-stimulated tumor growth. Immunohystochemistry showed that AP-1 blockade reduced proliferation and induced apoptosis. A gene signature of our TamR MCF7 xenografts significantly overlapped ( p < 2E-16) with a putative gene list associated with EGF-induced ER-DNA binding sites that mostly contain the AP-1 motif. Pathway analysis of these genes identified the AP-1 member c-Fos as the most represented transcription factor. Conclusions: We show that AP-1 blockade increases tumor sensitivity and circumvents resistance to endocrine therapy. We suggest that AP-1 is critical in a switch in the ER transcriptional program and may be a new hallmark of endocrine resistance. Disclosure: All authors have declared no conflicts of interest. Background: Triple negative breast cancer (TNBC), defined by estrogen, progesterone and HER2 negativity, is a heterogeneous disease with limited targeted therapy. Molecular and immunohistochemical stratification have already identified several TNBC subgroups, characterised by different biological processes with possible implication for therapy. A clear picture of the various TNBC entities and their relationship(s), however, is still missing. Aim: To shed light on this problem we have analysed a collection of 111 needle-macrodissected, clinically-annotated TNBCs using an approach based on the integration of DNA copy-number aberrations, transcriptional data and publically available gene signatures. Methods: Allel...

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Supplementary Figures 1-7, Tables 1-9 from Widespread Estrogen-Dependent Repression of microRNAs Involved in Breast Tumor Cell Growth

<div>Abstract<p>Altered expression of microRNAs (miRNA), an abundant class of small nonprotein-coding RNAs that mostly function as negative regulators of protein-coding gene expression, is common in cancer. Here, we analyze the regulation of miRNA expression in response to estrogen, a steroid hormone that is involved in the development and progression of breast carcinomas and that is acting via the estrogen receptors (ER) transcription factors. We set out to thoroughly describe miRNA expression, by using miRNA microarrays and real-time reverse transcription-PCR (RT-PCR) experiments, in various breast tumor cell lines in which estrogen signaling has been induced by 17β-estradiol (E₂). We show that the expression of a broad set of miRNAs decreases following E₂ treatment in an ER-dependent manner. We further show that enforced expression of several of the repressed miRNAs reduces E₂-dependent cell growth, thus linking expression of specific miRNAs with estrogen-dependent cellular response. In addition, a transcriptome analysis revealed that the E₂-repressed miR-26a and miR-181a regulate many genes associated with cell growth and proliferation, including the progesterone receptor gene, a key actor in estrogen signaling. Strikingly, miRNA expression is also regulated in breast cancers of women who had received antiestrogen neoadjuvant therapy. Overall, our data indicate that the extensive alterations in miRNA regulation upon estrogen signaling pathway play a key role in estrogen-dependent functions and highlight the utility of considering miRNA expression in the understanding of antiestrogen resistance of breast cancer. [Cancer Res 2009;69(21):8332–40]</p></div>

Supplementary Table 4 from Widespread Estrogen-Dependent Repression of microRNAs Involved in Breast Tumor Cell Growth

Supplementary Table 2 from Widespread Estrogen-Dependent Repression of microRNAs Involved in Breast Tumor Cell Growth