Figure S1, Related to Figure 1. A, miRNA microarray data of the top 50 most variant miRNAs across 17 breast cancer cell lines representing either basal/TNBC (top left blue bar) or luminal (top right red bar) breast cancer subgroups. Amongst these miRNAs, miR-34a (red asterisk) was found to be uniquely downregulated in basal lines. B-C, qPCR validation of array data in TNBC and Luminal-A cancer cell lines as compared to normal mammary epithelial lines (CRCs were cultured using the ROCK inhibitor and condition medium from the 3T3 feeder system as previously described(20)). D, Schematic of WebGestalt 2 analysis of Affymetrix microarray data across 19 cell lines. ¬¬miR-34a is one of several miRNAs with target enrichment in the TNBC overexpressed gene set. E, Results of hypergeometric analysis of miR-34a targets using a more stringent context score cutoff of -0.27. F, SRB growth assays on additional TNBC and normal cell lines.
ARTICLE ABSTRACTTriple-negative breast cancer (TNBC) is an aggressive subtype with no clinically proven biologically targeted treatment options. The molecular heterogeneity of TNBC and lack of high frequency driver mutations other than TP53 have hindered the development of new and effective therapies that significantly improve patient outcomes. miRNAs, global regulators of survival and proliferation pathways important in tumor development and maintenance, are becoming promising therapeutic agents. We performed miRNA-profiling studies in different TNBC subtypes to identify miRNAs that significantly contribute to disease progression. We found that miR-34a was lost in TNBC, specifically within mesenchymal and mesenchymal stem cell–like subtypes, whereas expression of miR-34a targets was significantly enriched. Furthermore, restoration of miR-34a in cell lines representing these subtypes inhibited proliferation and invasion, activated senescence, and promoted sensitivity to dasatinib by targeting the proto-oncogene c-SRC. Notably, SRC depletion in TNBC cell lines phenocopied the effects of miR-34a reintroduction, whereas SRC overexpression rescued the antitumorigenic properties mediated by miR-34a. miR-34a levels also increased when cells were treated with c-SRC inhibitors, suggesting a negative feedback exists between miR-34a and c-SRC. Moreover, miR-34a administration significantly delayed tumor growth of subcutaneously and orthotopically implanted tumors in nude mice, and was accompanied by c-SRC downregulation. Finally, we found that miR-34a and SRC levels were inversely correlated in human tumor specimens. Together, our results demonstrate that miR-34a exerts potent antitumorigenic effects in vitro and in vivo and suggests that miR-34a replacement therapy, which is currently being tested in human clinical trials, represents a promising therapeutic strategy for TNBC. Cancer Res; 76(4); 927–39. ©2015 AACR.