MicroRNA-18a inhibits hypoxia-inducible factor 1α activity and lung metastasis in basal breast cancers

Abstract

IntroductionIn breast cancer, distinct expression profiles of microRNAs (miRNAs) have been associated with molecular subgroups and clinicopathological characteristics, implicating a diagnostic and prognostic role of miRNAs. However, the biological functions of deregulated miRNAs in tumor progression are not yet completely defined. In this study, we investigated the function of miR-18a in regulating breast cancer metastasis through the hypoxia-inducible factor 1α (HIF1A)–dependent hypoxic response.MethodsAn orthotopic metastatic breast cancer xenograft model (MDA-MB-231 cells) was used to identify miRNAs associated with spontaneous lung metastasis. The function of miR-18a in regulating HIF1A expression, as well as cellular responses to hypoxia and metastasis, were then studied in vitro and in vivo by assessing ectopic miR-18a expression or miR-18a inhibition. miRNA–mRNA interactions (AGO2 immunoprecipitation and 3′ untranslated region Luciferase reporter assays), gene expression (quantitative PCR and microarray), cell migration and invasion, and cell growth were assessed under normoxic or hypoxic conditions, complemented by orthotopic xenograft of tumor cells to the mammary fat pad to investigate the effect of modulating miR-18a expression on primary tumor growth and lung metastasis. Last, clinically relevant correlations between miR-18a, HIF1A, hypoxia-responsive gene expression and distant metastasis–free survival (DMFS) were assessed using published expression array breast tumors data sets.ResultsmiRNAs encoded by the MIR17HG gene were downregulated in lung metastases compared to primary tumors. Ectopic expression of miR-18a, a MIR17HG family member, in a metastatic variant of MDA-MB-231 cells reduced primary tumor growth and lung metastasis, whereas miR-18a inhibition in the parental cells promoted tumor growth and lung metastasis. We identified HIF1A as a direct target of miR-18a. Modulating miR-18a expression significantly affected hypoxic gene expression, cell invasiveness and sensitivity to anoikis and hypoxia in vitro in a HIF1A-dependent manner. Analysis of previously published data revealed that higher expression of HIF1A and a panel of hypoxic genes is associated with shorter DMFS interval in patients with basal-like breast tumors, and that, within this subtype, miR-18a expression is inversely correlated with hypoxic gene expression. Together, these data support a role of miR-18a in repressing distant metastasis through a HIF1A-dependent pathway.ConclusionsThe results of this study reveal a novel role for miR-18a in targeting HIF1A and repressing metastasis of basal-like breast tumors.Electronic supplementary materialThe online version of this article (doi:10.1186/bcr3693) contains supplementary material, which is available to authorized users.

MiR-18a increased the permeability of BTB via RUNX1 mediated down-regulation of ZO-1, occludin and claudin-5

“…MiR-18a functions as a tumor suppressor to suppress cell proliferation by targeting Dicer in bladder cancer T24 cells [30]. Ectopic expression of miR-18a in a metastatic variant of MDA-MB231 cells reduced primary tumor growth and lung metastasis in basal breast cancers through a HIF1A-dependent pathway [31]. And ectopic expression of miR-18a significantly diminished cell proliferation in SGC-7901 cells, causing a marked reduction in tumor angiogenesis assessed by CD31-stained microvessel count [14].…”

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

“…miR-18a may directly target ER (28,29) and suppress hypoxia-inducible factor 1a activity (30) and ATM expression (31,32). The expression of miR-18a was at higher levels in ER-negative tumors than in ERpositive tumors (20,27).…”

MiR-492 contributes to cell proliferation and cell cycle of human breast cancer cells by suppressing SOX7 expression

“…Increasing evidences indicated that some miRNAs act as either tumor suppressors or promoters in the development of various cancers and play crucial roles in causing messenger RNA (mRNA) degradation or translational inhibition by interacting with the 3′-untranslated region (3′-UTR) of the target mRNA [2][3][4]. Treatment by targeting microRNAs (miRNAs) has attracted extensive research attention in various cancers, including breast cancer [5][6][7][8]. However, the molecular underpinnings of cell proliferation and cell cycle in breast cancer remain incompletely understood.…”