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

S Wang,C-K Lee,J Huang,H Lyu,B Liu,J Wang,J Tan

doi:10.1038/cddis.2013.79

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.

Highlights

The erbB receptor tyrosine kinase (RTK) family, including the epidermal growth factor receptor (EGFR), erbB2 (HER2/neu), erbB3, and erbB4, is arguably the most important receptor family in the context of development and tumorigenesis.[1,2] ErbB2 amplification and/or overexpression occur in B25
We reported that the class I Histone deacetylases (HDACs) inhibitor entinostat induced apoptosis in erbB2-overexpressing breast cancer cells via downregulation of erbB2 and erbB3
In studying whether entinostat may target the erbB receptors, we have shown that entinostat selectively induces apoptosis in erbB2-overexpressing breast cancer cells via downregulation of erbB2/erbB3, but not EGFR expression,[24] and it enhances trastuzumab efficacy and exhibits the potential to overcome trastuzumab resistance.[25]

Summary

Introduction

The erbB receptor tyrosine kinase (RTK) family, including the epidermal growth factor receptor (EGFR), erbB2 (HER2/neu), erbB3, and erbB4, is arguably the most important receptor family in the context of development and tumorigenesis.[1,2] ErbB2 amplification and/or overexpression occur in B25–. Numerous studies have established the critical role of erbB3 as a co-receptor of erbB2, and the expression of erbB3 is a rate-limiting factor for erbB2-induced breast cancer cell survival and proliferation.[8,9] novel strategies/agents targeting both erbB2 and erbB3 receptors should be more effective to treat the breast cancer patients whose tumors overexpress erbB2. MicroRNAs (miRNAs) are endogenous, small noncoding RNAs that regulate gene expression by targeting mRNAs for degradation or translational repression via sequence-specific recognition.[26,27] Recent studies demonstrate that miRNAs can function as oncogenes or tumor suppressors to regulate tumor cell proliferation and apoptosis, and have highly diverse roles in the development of human cancers,[28,29,30] including breast cancer.[31] the underlying mechanisms of miRNA deregulation in human cancer remain unclear. We test the hypothesis that entinostat downregulates erbB2/erbB3 receptors via induction of specific miRNAs that target erbB2 and/or erbB3 in erbB2-overexpressing breast cancer cells

Methods

Results

Conclusion