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The cancer-risk-associated rs6983267 single nucleotide polymorphism (SNP) and the accompanying long noncoding RNA CCAT2 in the highly amplified 8q24.21 region have been implicated in cancer predisposition, although causality has not been established. Here, using allele-specific CCAT2 transgenic mice, we demonstrate that CCAT2 overexpression leads to spontaneous myeloid malignancies. We further identified that CCAT2 is overexpressed in bone marrow and peripheral blood of myelodysplastic/myeloproliferative neoplasms (MDS/MPN) patients. CCAT2 induces global deregulation of gene expression by down-regulating EZH2 in vitro and in vivo in an allele-specific manner. We also identified a novel non-APOBEC, non-ADAR, RNA editing at the SNP locus in MDS/MPN patients and CCAT2-transgenic mice. The RNA transcribed from the SNP locus in malignant hematopoietic cells have different allelic composition from the corresponding genomic DNA, a phenomenon rarely observed in normal cells. Our findings provide fundamental insights into the functional role of rs6983267 SNP and CCAT2 in myeloid malignancies.

BACKGROUND & AIMS: Chromosomal instability (CIN) is a carcinogenesis event that promotes metastasis and resistance to therapy by unclear mechanisms. Expression of the colon cancer-associated transcript 2 gene (CCAT2), which encodes a long noncoding RNA (lncRNA), associates with CIN, but little is known about how CCAT2 lncRNA regulates this cancer enabling characteristic.METHODS: We performed cytogenetic analysis of colorectal cancer (CRC) cell lines (HCT116, KM12C/SM, and HT29) overexpressing CCAT2 and colon organoids from C57BL/6N mice with the CCAT2 transgene and without (controls). CRC cells were also analyzed by immunofluorescence microscopy, gamma-H2AX, and senescence assays. CCAT2 transgene and control mice were given azoxymethane and dextran sulfate sodium to induce colon tumors. We performed gene expression array and mass spectrometry to detect downstream targets of CCAT2 lncRNA. We characterized interactions between CCAT2 with downstream proteins using MS2 pull-down, RNA immunoprecipitation, and selective 2'-hydroxyl acylation analyzed by primer extension analyses. Downstream proteins were overexpressed in CRC cells and analyzed for CIN. Gene expression levels were measured in CRC and non-tumor tissues from 5 cohorts, comprising more than 900 patients.RESULTS: High expression of CCAT2 induced CIN in CRC cell lines and increased resistance to 5-fluorouracil and oxaliplatin. Mice that expressed the CCAT2 transgene developed chromosome abnormalities, and colon organoids derived from crypt cells of these mice had a higher percentage of chromosome abnormalities compared with organoids from control mice. The transgenic mice given azoxymethane and dextran sulfate sodium developed more and larger colon polyps than control mice given these agents. Microarray analysis and mass spectrometry indicated that expression of CCAT2 increased expression of genes involved in ribosome biogenesis and protein synthesis. CCAT2 lncRNA interacted directly with and stabilized BOP1 ribosomal biogenesis factor (BOP1). CCAT2 also increased expression of MYC, which activated expression of BOP1. Overexpression of BOP1 in CRC cell lines resulted in chromosomal missegregation errors, and increased colony formation, and invasiveness, whereas BOP1 knockdown reduced viability. BOP1 promoted CIN by increasing the active form of aurora kinase B, which regulates chromosomal segregation. BOP1 was overexpressed in polyp tissues from CCAT2 transgenic mice compared with healthy tissue. CCAT2 lncRNA and BOP1 mRNA or protein were all increased in microsatellite stable tumors (characterized by CIN), but not in tumors with microsatellite instability compared with nontumor tissues. Increased levels of CCAT2 lncRNA and BOP1 mRNA correlated with each other and with shorter survival times of patients.CONCLUSIONS: We found that overexpression of CCAT2 in colon cells promotes CIN and carcinogenesis by stabilizing and inducing expression of BOP1 an activator of aurora kinase B. Strategies to target this pathway might be developed for treatment of patients with microsatellite stable colorectal tumors.

The pervasive role of microRNAs (miRNAs) in cancer pathobiology drives the introduction of new drug development approaches such as miRNA inhibition. In order to advance miRNA-therapeutics, meticulous screening strategies addressing specific tumor targets are needed. Small molecule inhibitors represent an attractive goal for these strategies. In this study, we devised a strategy to screen for small molecule inhibitors that specifically inhibit, directly or indirectly, miR-10b (SMIRs) which is overexpressed in metastatic tumors. We found that the multi-tyrosine kinase inhibitor linifanib could significantly inhibit miR-10b and reverse its oncogenic function in breast cancer and liver cancer both in vitro and in vivo. In addition, we showed that the efficacy of linifanib to inhibit tyrosine kinases was reduced by high miR-10b levels. When the level of miR-10b is high, it can “hijack” the linifanib and reduce its kinase inhibitory effects in cancer resulting in reduced anti-tumor efficacy. In conclusion, our study describes an effective strategy to screen for small molecule inhibitors of miRNAs. We further propose that miR-10b expression levels, due to the newly described “hijacking” effect, may be used as a biomarker to select patients for linifanib treatment.

Altered energy metabolism is a cancer hallmark as malignant cells tailor their metabolic pathways to meet their energy requirements. Glucose and glutamine are the major nutrients that fuel cellular metabolism, and the pathways utilizing these nutrients are often altered in cancer. Here, we show that the long ncRNA CCAT2, located at the 8q24 amplicon on cancer risk-associated rs6983267 SNP, regulates cancer metabolism in vitro and in vivo in an allele-specific manner by binding the Cleavage Factor I (CFIm) complex with distinct affinities for the two subunits (CFIm25 and CFIm68). The CCAT2 interaction with the CFIm complex fine-tunes the alternative splicing of Glutaminase (GLS) by selecting the poly(A) site in intron 14 of the precursor mRNA. These findings uncover a complex, allele-specific regulatory mechanism of cancer metabolism orchestrated by the two alleles of a long ncRNA., G.A.C. is The Alan M. Gewirtz Leukemia & Lymphoma Society Scholar. Work in G.A.C.’s laboratory is supported in part by the NIH/NCI grants 1UH2TR00943-01 and 1 R01 CA182905-01, the UT MD Anderson Cancer Center SPORE in Melanoma grant from NCI (P50 CA093459), Aim at Melanoma Foundation and the Miriam and Jim Mulva research funds, the Brain SPORE (2P50CA127001), the Center for Radiation Oncology Research Project, the Center for Cancer Epigenetics Pilot project, a 2014 Knowledge GAP MDACC grant, a CLL Moonshot pilot project, the UT MD Anderson Cancer Center Duncan Family Institute for Cancer Prevention and Risk Assessment, a SINF grant in colon cancer, the Laura and John Arnold Foundation, the RGK Foundation, and the Estate of C.G. Johnson, Jr. I.B.-N. was financed by a grant entitled Non-Invasive Intelligent Systems for Colorectal Cancer Diagnosis and Prognosis Based on circulating miRNAs Integrated in the Clinical Workflow – INTELCOR. S.M.G.D., A.L.B.A., and D.A. are supported by the São Paulo Research Foundation FAPESP under grants 2014/15968-3, 2014/20673-2, and 2014/17820-3, respectively. W.L. was partly supported by grants from The University of Texas MD Anderson Cancer Center Sheikh Ahmed Bin Zayed Al Nahyan Center for Pancreatic Cancer Research. J.A.B. was supported by the Cancer Center Support Grant (P30 CA016672), and the HP imaging program of the Small Animal Facility (SAIF) was supported by the Cancer Prevention and Research Institutes of Texas grant RP-101243P5. H.L. was supported by NIH/NCI grant R01CA175486, a grant (RP140462) from the Cancer Prevention and Research Institute of Texas, and the R. Lee Clark Fellow Award from The Jeanne F. Shelby Scholarship Fund. I.B.-N. was financed by a Fulbright fellowship and by a grant entitled Non-Invasive Intelligent Systems for Colorectal Cancer Diagnosis and Prognosis Based on circulating miRNAs Integrated in the Clinical Workflow – INTELCOR.

MicroRNAs (miRNAs) are evolutionarily conserved, small, regulatory RNAs that negatively regulate gene expression. Extensive research in the last decade has implicated miRNAs as master regulators of cellular processes with essential role in cancer initiation, progression, and metastasis, making them promising therapeutic tools for cancer management. In this article, we will briefly review the structure, biogenesis, functions, and mechanism of action of these miRNAs, followed by a detailed analysis of the therapeutic potential of these miRNAs. We will focus on the strategies presently used for miRNA therapy; discuss their use and drawbacks; and the challenges and future directions for the development of miRNA-based therapy for human cancers.

Development of improved RNA interference–based strategies is of utmost clinical importance. Although siRNA-mediated silencing of EphA2, an ovarian cancer oncogene, results in reduction of tumor growth, we present evidence that additional inhibition of EphA2 by a microRNA (miRNA) further “boosts” its antitumor effects. We identified miR-520d-3p as a tumor suppressor upstream of EphA2, whose expression correlated with favorable outcomes in two independent patient cohorts comprising 647 patients. Restoration of miR-520d-3p prominently decreased EphA2 protein levels, and suppressed tumor growth and migration/invasion both in vitro and in vivo. Dual inhibition of EphA2 in vivo using 1,2-dioleoyl-sn-glycero-3-phosphatidylcholine (DOPC) nanoliposomes loaded with miR-520d-3p and EphA2 siRNA showed synergistic antitumor efficiency and greater therapeutic efficacy than either monotherapy alone. This synergy is at least in part due to miR-520d-3p targeting EphB2, another Eph receptor. Our data emphasize the feasibility of combined miRNA–siRNA therapy, and will have broad implications for innovative gene silencing therapies for cancer and other diseases. Significance: This study addresses a new concept of RNA inhibition therapy by combining miRNA and siRNA in nanoliposomal particles to target oncogenic pathways altered in ovarian cancer. Combined targeting of the Eph pathway using EphA2-targeting siRNA and the tumor suppressor miR-520d-3p exhibits remarkable therapeutic synergy and enhanced tumor suppression in vitro and in vivo compared with either monotherapy alone. Cancer Discov; 3(11); 1302–15. ©2013 AACR. See related commentary by Kasinski and Slack, p. 1220 This article is highlighted in the In This Issue feature, p. 1207

Background Non-coding RNAs have been drawing increasing attention in recent years as functional data suggest that they play important roles in key cellular processes. N-BLR is a primate-specific long non-coding RNA that modulates the epithelial-to-mesenchymal transition, facilitates cell migration, and increases colorectal cancer invasion. Results We performed multivariate analyses of data from two independent cohorts of colorectal cancer patients and show that the abundance of N-BLR is associated with tumor stage, invasion potential, and overall patient survival. Through in vitro and in vivo experiments we found that N-BLR facilitates migration primarily via crosstalk with E-cadherin and ZEB1. We showed that this crosstalk is mediated by a pyknon, a short ~20 nucleotide-long DNA motif contained in the N-BLR transcript and is targeted by members of the miR-200 family. In light of these findings, we used a microarray to investigate the expression patterns of other pyknon-containing genomic loci. We found multiple such loci that are differentially transcribed between healthy and diseased tissues in colorectal cancer and chronic lymphocytic leukemia. Moreover, we identified several new loci whose expression correlates with the colorectal cancer patients’ overall survival. Conclusions The primate-specific N-BLR is a novel molecular contributor to the complex mechanisms that underlie metastasis in colorectal cancer and a potential novel biomarker for this disease. The presence of a functional pyknon within N-BLR and the related finding that many more pyknon-containing genomic loci in the human genome exhibit tissue-specific and disease-specific expression suggests the possibility of an alternative class of biomarkers and therapeutic targets that are primate-specific. Electronic supplementary material The online version of this article (doi:10.1186/s13059-017-1224-0) contains supplementary material, which is available to authorized users.

MicroRNAs (miRNAs) are evolutionarily conserved class of small, regulatory RNAs that negatively regulate gene expression, and control multiple cellular processes involved in cancer initiation, progression, and metastasis. Extensive research in the past decade has identified vital role of miRNAs in hematopoiesis and leukemogenesis, with miRNAs functioning as oncogenes or tumor suppressors. Several miRNAs are extensively dysregulated in acute myeloid leukemia (AML), and their expression patterns are useful diagnostic and prognostic markers in AML. Furthermore, miRNA expression patterns have been associated with specific cytogenetic and molecular aberrations in AML subsets. Based on these observations, miRNAs have emerged as promising therapeutic tools for AML. In this chapter, we focus on the roles of miRNAs in AML tumorigenesis, their widespread deregulation, the rationale and strategies for their use as AML therapeutic targets, and the advantages and current challenges to their use in the clinic.

Non-coding RNAs have been commanding increasingly greater attention in recent years as the few that have been functionalized to date play important roles in key cellular processes. Here we show that N-BLR, a ~900 bp non-coding RNA, modulates the epithelial-to-mesenchymal transition, increases colorectal cancer invasion, and functions as a migration enabler by affecting the expression of ZEB1 and E-cadherin. In patients with colorectal cancer, N-BLR expression associates with tumor stage and invasion potential. As N-BLR contains several instances of a category of DNA motifs known as pyknons, we also designed a custom-made array to investigate the possibility that other pyknon loci may be transcribed. For several of the loci probed by the array we found that the corresponding pyknons are differentially expressed between cancer and normal tissue samples. Taken together the data suggest that a systematic study of other pyknon-containing non-coding RNAs like N-BLR may be warranted in the context of colorectal cancer.

5-Fluorouracil (5-FU) is a classic chemotherapeutic drug that has been widely used for breast cancer treatment. Although aberrant expression of protein-coding genes was observed after 5-FU treatment, the regulatory mechanism remains poorly understood. MicroRNAs (miRNAs) are a newly identified class of small regulatory RNAs which play an important role in gene regulation at the post-transcriptional levels. Recent evidence suggests an important role of miRNAs in initiation, progression, and metastasis of human cancers. In this study, using a combined advanced microarray and quantitative real-time PCR (qRT-PCR) technology, we show that 5-FU significantly alters the global expression profile of miRNAs in vitro. After 48 h of treatment with a low dose (0.01 µM), 42 miRNAs were differentially expressed in MCF-7 breast cancer cell line. Of these, 23 miRNAs were up-regulated with up to 4.59-fold changes, while 19 were down-regulated with up to 1.89-fold changes. A majority of these miRNAs are associated with cancer development, progression, and metastasis. Target prediction and GO analysis suggest that these differentially expressed miRNAs potentially target many oncogenes, tumor suppressor genes and genes related to programmed cell death, activation of immune response, and cellular catabolic processes.

Long non-coding RNAs (lncRNAs) form the largest part of the mammalian non-coding transcriptome and control gene expression at various levels including chromatin modification, transcriptional and post-transcriptional processing. LncRNAs are implicated in initiation and progression of several cancers.Cancer-associated genomic regions are regions showing high frequency of cancer related abnormalities, such as loss of heterozygosity or amplifications. One such widely studied CAGR is the 8q24.21 genomic region. One SNP of particular importance present at this locus is rs6983267, with the G allele of the SNP conferring increased risk of colorectal, prostate, breast and bladder cancers. CCAT2 is a lncRNA that spans this highly conserved region. CCAT2 has been shown to play an important role in inducing chromosomal instability and supporting cell proliferation and cell cycle arrest. Despite advances in diagnosis of MDS patients, the underlying mechanisms that lead to spontaneous induction of MDS remains poorly understood. Here we attempted to elucidate the role of CCAT2 and its specific alleles (G/T) in regulation of cellular processes that drive spontaneous tumorigenesis using a genetically engineered mouse model. We generated transgenic mice for each CCAT2 allele using random integration approach in C57Bl6/N background, expressing CCAT2 in all tissues of mice. In this study, we identified that CCAT2 plays an important role in regulation of normal hematopoiesis. Constitutive in vivo overexpression of each CCAT2 transcript in the mice resulted in spontaneous induction of widespread pancytopenias. CCAT2(G/T) BM biopsies displayed severe myeloid or erythroid hyperplasia, and dysplastic megakaryocytic proliferation, along with enhanced proliferation and excessive apoptosis. Interestingly, we identified two distinct phenotypes in CCAT2(G/T) mice with equal prevalence of MDS or mixed MDS/MPN. This suggests that CCAT2 overexpression might affect regulation of hematopoietic stem cells, disturbing their self-renewal or maturation capacity, and subsequently resulting in BM failure. Percentage of HSPCs was significantly reduced in BM of MDS mice, with increased presence of immature erythroid blasts and granulocyte-macrophage progenitors suggesting a block in differentiation. HSPCs of CCAT2(G/T) mice also showed increased frequency of cytogenetic aberrations, including breaks and chromosomal fusions. However, these mice don't develop sAML, suggesting CCAT2 is critical in initiation of MDS. We further identified significantly higher CCAT2 expression in the MDS patients as compared to healthy volunteers. Patients with sAML had significantly lower expression of CCAT2 as compared to patients with only MDS. To determine the mechanism by which CCAT2 induces genomic instability and myelodysplasia, we screened for several genes that have been previously reported to induce myelodysplasia as potential targets of CCAT2. Interestingly, EZH2 was downregulated in the BMCs of CCAT2(G/T) mice compared to WT littermates. EZH2 downregulation was observed in both MDS only and MDS/MPD mice. In CCAT2(G/T) mice, EZH2 and H3K27Me3 reduction was observed in hematopoietic stem and progenitor cells (HSPCs) as well as lineage positive bulk cells,suggesting that CCAT2 might induce alteration in EZH2 levels in the HSC compartment. Interestingly, we identified miR-26a and miR-26b, that were already reported to target EZH2, were significantly overexpressed only in BM of CCAT2-G mice. These data suggests that CCAT2-G regulates EZH2 expression primarily through regulation of target miRNAs. On the other hand, we identified EZH2 to interact preferentially to CCAT2-T compared to WT or CCAT2-G transcript. These data confirmed that EZH2 preferentially binds to the CCAT2 in an allele-specific manner. In conclusion, deciphering the role of CCAT2 in spontaneously induced myelodysplasia and cytopenias will help us further characterize the poorly understood MDS/MPN phenotype. CCAT2 mice can serve as a robust model for studying initiation of de novo MDS/MPN that does not progress to secondary AML, and as a pre-clinical model for evaluation of new therapies for MDS. It has high translational potential as CCAT2 can be developed into a diagnostic and prognostic marker, as well as a novel intervention target for MDS therapy. Disclosures No relevant conflicts of interest to declare.

Background. Posttranscriptional regulation is a critical control point for the expression of genes that promote or retard tumor growth. The mRNA-binding protein hnRNP A1 is required for the processing of miR-18a, an inhibitor of k-ras expression. In this study we hypothesized that downmodulation of hnRNP A1 by miR-25 and miR-15a controls the expression of miR-18a and k-ras by modulating nuclear and cytoplasmic miRNA processing at the posttranscriptional level. Methods. In this study, we determined the expression of hnRNP A1 at mRNA and protein levels in three parental ovarian cancer cells lines (Skov3ip1, HeyA8, and A2780) and their chemotherapy-resistant derivatives (Skov3-TR, HeyA8 MDR, and A2780 cp20). We also predicted in silico which miRNAS can target hnRNP A1 and confirmed the miRNA expression by real-time PCR. Moreover, we inhibited miR-25 and mir-15a to determine their tumorigenic potential in vitro. We also correlated the expression of miR-25 and miR-15a and/or miR-18a and k-ras expression in the TCGA data. Results. Downregulation of hnRNP A1 at the RNA and protein levels was observed in the taxane-resistant cell lines but not in the cisplatin-resistant cell line. Furthermore, we predicted in silico that miR-25and miR-15a can target hnRNP A1 and confirmed the overexpression of these microRNAs in SKOV3-TR (5- and 3-fold, respectively) and HeyA8 MDR (3-fold) by real-time PCR. We also analyzed overall survival, trying to find a correlation between k-ras and miR-15a (high 23.77, low 33.97 months), k-ras and miR-25 (high 16.95, low 35.21 months), and the combination of k-ras, miR-25, and miR18a (k-ras high, miR25 high, mir18a low, 20.73 months; k-ras low, miR25 low, mir18a high, 31.49 months). Comparison of these data with a validation set yielded similar results. Conclusion. These results underscore the importance of a previously uncharacterized circuit of posttranscriptional regulation between miR-25 or -15a and RNA-binding protein hnRNP A1 that regulates miR-18a and k-ras expression. This circuit represents a unique opportunity for novel therapeutics approaches. Citation Format: Cristian Rodriguez-Aguayo, Paloma Monroig, Maria I. Almeida, Cristina Ivan, Vianey Gonzalez-Villasana, Maitri Y. Shah, Anil K. Sood, George Calin, Gabriel Lopez-Berestein. Downregulation of hnRNP A1 by miRNAs as a new mechanism of survival in ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 539. doi:10.1158/1538-7445.AM2014-539

EphA2 has emerged as an important target for ovarian cancer therapy in recent years. In the present study, we identified miR-520d-3p as an independent favorable prognostic marker for epithelial ovarian cancer patients. We demonstrate that dual targeting of EphA2 in vitro using EphA2-siRNA and miR-520d-3p exhibits synergistic downregulation of EphA2 and inhibits cell proliferation, migration and invasion. In vivo treatment using DOPC (1,2-dioleoyl-sn-glycero-3-phosphatidylcholine) nano-liposomes conjugated with miR-520d-3p and EphA2-siRNA showed synergistic therapeutic efficacy and superior inhibition of tumor proliferation and angiogenesis than either monotherapy alone. We also identified that EphA2(low)/EphB2(low)/miR-520d-3p(high) gene signature predicts favorable clinical prognosis for ovarian cancer patients. This study addresses a new concept of RNA inhibition therapy by combining miRNA and siRNA to target oncogenic pathways altered in ovarian cancer. Citation Format: Maitri Shah, Gabriel Berestein Lopez, Anil Sood, George Calin. Therapeutic synergy between novel tumor suppressor miR-520d-3p and EphA2-targeting siRNA in ovarian cancer. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1455. doi:10.1158/1538-7445.AM2014-1455

Selective ER modulators (SERMs) have shown significant efficacy for the prevention of ER-positive breast cancer, however, SERMs are not effective for patients whose tumors do not express ER. Therefore, novel agents are needed for prevention and intervention of high risk ER-breast cancers. The c-Src plays a pivotal role in the progression of EGFR- and HER2-dependent ER negative breast cancer. Thus, targeting Src using agents with minimal toxicity or in combination with other novel agents may prevent/intervene progression of early stage ER- breast cancer. In this study we used Saracatinib (AztraZeneca), a Src inhibitor well-tolerated in phase II clinical trials. We examined the effect of Src inhibition using Saracatinib alone or with other agents for cancer prevention using human mammary epithelial pre-malignant cell lines (MECs) and MMTV-neu mouse model. The MCF10A MECs stably overexpressing ErbB2 (10A.ErbB2 cells) form irregular (grape-like) acini in 3D culture condition. Saracatinib treatment prevents the progression of abnormal 3D acini growth as well reverses the abnormal 3D acini growth of 10A.ErbB2 cells to normal phenotype. Our reverse phase protein array data showed that Saracatinib induces the expression of cell cycle inhibitors and apoptosis related molecules, e.g. P27kip1, RAR beta, and PDCD4. Our 3D acini confocal microscopy experiment showed that it induces luminal apoptosis and suppresses cell proliferation in 10A.ErbB2 cells as detected by activated caspase-3 and ki-67 staining respectively. Next, we used MMTV-neu mouse model which develop ER negative lesions at early stage, to examine correlation between Src activation and ER negative mammary cancer progression. MMTV-neu mice mammary lesions exhibited super-activated Src which were negatively associated with estrogen receptor (ER) expression. Our preliminary data showed that Saracatinib-containing regimen inhibited MMTV-neu mice mammary lesions. Our study demonstrated that targeting Src by Saracatinib may be effective for the chemoprevention of early stage ER negative breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1857. doi:10.1158/1538-7445.AM2011-1857

MicroRNAs (miRNAs) are crucial in the initiation and progression of tumors. A recent study has reported that the miRNAs miR-221 and miR-222 are involved in the promotion of an aggressive basal-like phenotype in breast cancer, functioning downstream of the RAS pathway and triggering epithelial-to-mesenchymal transition. These new insights into the roles of miR-221/222 in breast cancer metastasis, drug resistance and RAS pathways could potentially have applications in medical practice.