Functional cooperation of miR-125a, miR-125b, and miR-205 in entinostat-induced downregulation of erbB2/erbB3 and apoptosis in breast cancer cells

Abstract

We reported that the class I HDAC inhibitor entinostat induced apoptosis in erbB2-overexpressing breast cancer cells via downregulation of erbB2 and erbB3. Here, we study the molecular mechanism by which entinostat dual-targets erbB2/erbB3. Treatment with entinostat had no effect on erbB2/erbB3 mRNA, suggesting a transcription-independent mechanism. Entinostat decreased endogenous but not exogenous erbB2/erbB3, indicating it did not alter their protein stability. We hypothesized that entinostat might inhibit erbB2/erbB3 protein translation via specific miRNAs. Indeed, entinostat significantly upregulated miR-125a, miR-125b, and miR-205, that have been reported to target erbB2 and/or erbB3. Specific inhibitors were then used to determine whether these miRNAs had a causal role in entinostat-induced downregulation of erbB2/erbB3 and apoptosis. Transfection with a single inhibitor dramatically abrogated entinostat induction of miR-125a, miR-125b, or miR-205; however, none of the inhibitors blocked entinostat action on erbB2/erbB3. In contrast, co-transfection with two inhibitors not only reduced their corresponding miRNAs, but also significantly abrogated entinostat-mediated reduction of erbB2/erbB3. Moreover, simultaneous inhibition of two, but not one miRNA significantly attenuated entinostat-induced apoptosis. Interestingly, although the other HDAC inhibitors, such as SAHA and panobinostat, exhibited activity as potent as entinostat to induce growth inhibition and apoptosis in erbB2-overexpressing breast cancer cells, they had no significant effects on the three miRNAs. Instead, both SAHA- and panobinostat-decreased erbB2/erbB3 expression correlated with the reduction of their mRNA levels. Collectively, we demonstrate that entinostat specifically induces expression of miR-125a, miR-125b, and miR-205, which act in concert to downregulate erbB2/erbB3 in breast cancer cells. Our data suggest that epigenetic regulation via miRNA-dependent or -independent mechanisms may represent a novel approach to treat breast cancer patients with erbB2-overexpressing tumors.

Histone deacetylase inhibition reveals a tumor-suppressive function of MYC-regulated miRNA in breast and lung carcinoma

“…10,11,13,14 Altered expression and/or recruitment of HDACs have been shown to contribute to dysregulation of specific miRNA (e.g., miR-29, miR-200b, miR-31, miR-125a, miR-125b and miR-205) in human breast and lung cancers. [5][6][7][8] Our data show that treatment with Depsi (class I HDAC inhibitor), SAHA (pan-HDAC inhibitor) or 966 (HDAC3-selective inhibitor) resulted in elevated levels of mature miRNA of the miR-15 and let-7 families. This increase in miRNA expression was selective as not all miRNA assessed were induced by HDACi.…”

“…One such mechanism that has been linked to HDAC regulation includes microRNA (miRNA). [5][6][7][8] miRNA comprise a class of noncoding RNA that post-transcriptionally regulate the expression of target mRNA, typically resulting in decreased translation. 9 The potential for miRNA-guided regulation of gene expression is significant, as it is predicted that the majority of all mRNAs are under miRNA control and that a single miRNA can target many mRNA.…”

Recent trends in microRNA research into breast cancer with particular focus on the associations between microRNAs and intrinsic subtypes

“…Wang et al and Lyu et al also demonstrated that the overexpression of HER2 promotes HER3 expression via a mechanism involving miR-125a, miR-125b and miR-205 in vivo. 90,91 Bischoff et al found that miR-148b, miR-149, miR-326, and miR-520a-3p directly reduced HER3 mRNA and protein levels. 85 Yan et al 92 provided insights into the role of the miR-143/145 cluster as a tumor suppressor in breast cancer; that is, they suggested that it inhibits HER3 translation in vivo.…”

Emerging anti-cancer antibodies and combination therapies targeting HER3/ERBB3

“…3). [60][61][62][63] As we describe below, 2 major lines of evidence motivated the current intensified interest in intercepting HER3 in human tumors: First, oncogenic mutant forms have recently been identified in approximately 10% of solid tumors and second, several studies indicated that HER3 plays pivotal roles in several compensatory processes that underlay emergence of resistance to certain cancer drugs. 64,65 …”

“…Entinostat downregulates HER3 and HER2 via induction of specific microRNAs (miR-125a, miR125b, and miR205) in HER2-overexpressing breast cancer cells. 63 Likewise, several antisense oligonucleotides or microRNAs seems able to downregulate HER3, such as a locked nucleic acid (LNA)-based HER3 antisense oligonucleotide called EZN-3920, 95 which improves the anti-tumor activity of TKIs, and miR-450b-3p, which inhibits proliferation of breast cancer cells. 60 Targeting mRNAs with LNA EZN-3920 provided promising preclinical strategy but further development remains a challenge.…”