Profiles of miRNAs matched to biology in aromatase inhibitor resistant breast cancer.

Reiner Hoppe,V Craig Jordan,Stefan Winter,Heather Cunliffe,Florian Büttner,Ping Fan,Amit K Tyagi,Hiltrud Brauch

doi:10.18632/oncotarget.12103

Abstract

Aromatase inhibitor (AI) resistance during breast cancer treatment is mimicked by MCF-7:5C (5C) and MCF-7:2A (2A) cell lines that grow spontaneously. Survival signaling is reconfigured but cells are vulnerable to estradiol (E2)-inducible apoptosis. These model systems have alterations of stress related pathways including the accumulation of endoplasmic reticulum, oxidative, and inflammatory stress that occur prior to E2-induced apoptosis. We investigated miRNA expression profiles of 5C and 2A to characterize their AI resistance phenotypes. Affymetrix GeneChip miRNA2.0 arrays identified 184 miRNAs differentially expressed in 2A and 5C compared to E2-free wild-type MCF-7:WS8. In 5C, 34 miRNAs of the DLK1-DIO3 locus and miR-31 were overexpressed, whereas miR-222 was low. TCGA data revealed poor and favorable overall survival for low miR-31 and miR-222 levels, respectively (HR=3.0, 95% CI:1.9-4.8; HR=0.3, 95% CI:0.1-0.6). Targets of deregulated miRNAs were identified using CLIP-confirmed TargetScan predictions. KEGG enrichment analyses for 5C- and 2A-specific target gene sets revealed pathways associated with cell proliferation including insulin, mTOR, and ErbB signaling as well as immune response and metabolism. Key genes overrepresented in 5C- and 2A-specific pathway interaction networks including EGFR, IGF1R and PIK3R1 had lower protein levels in 5C compared to 2A and were found to be differentially modulated by respective miRNA sets. Distinct up-regulated miRNAs from the DLK1-DIO3 locus may cause these attenuative effects as they are predicted to interact with corresponding 3′ untranslated regions. These new miRNA profiles become an important regulatory database to explore E2-induced apoptotic mechanisms of clinical relevance for the treatment of resistant breast cancer.

Highlights

Long-term estrogen deprivation is the standard of care in patients with estrogen receptor (ER)-positive breast cancer
We identified more than two hundred up- and down regulated miRNAs relevant to the E2-independent growth phenotype inherent to Phase I/II endocrine resistance (Figure 2)
Thirtyfour 5C-specific miRNAs are located at Chr. 14q32.31 (Supplementary Table 2 and 3), a chromosomal region that hosts the largest microRNA cluster in the genome known as the DLK1-DIO3 domain-containing cluster of 54 miRNAs

Summary

Introduction

Long-term estrogen deprivation is the standard of care in patients with estrogen receptor (ER)-positive breast cancer. Two proven treatment options exist: tamoxifen, a selective ER modulator which blocks 17ß-estradiol (E2) binding to ER to stop tumor growth, and aromatase inhibitors (AI), which block the aromatase enzyme that prevents the conversion of androgens to estrogens. Despite their well-established effectiveness [1, 2], patients frequently display de novo or acquired resistance which leads to disease progression and death. Laboratory models of long-term E2-deprived breast cancer cells provide a valuable surrogate approach to study clinical AI resistance. Endocrine resistance evolves over time and manifests in phase I and phase II of which the latter refers to the cellular reprogramming towards E2-inducible apoptosis, for which clinical evidence exists

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Conclusion