Background/Aims: High levels of cancer stem cells (CSCs) in patients with triple-negative breast cancer (TNBC) correlate with risk of poor clinical outcome and possibly contribute to chemoresistance and metastasis in patients with highly malignant TNBC. Aberrant microRNA expression is associated with the dysfunction of self-renewal and proliferation in cancer stem cells, while there is little information about the TNBC-specific microRNAs in regulating CSC ability. Methods: Solexa deep sequencing was performed to detect the expression levels of TNBC or non-TNBC stem cells (CSCs) microRNAs. Mammosphere formation assay, qRT-PCR and the xenograft model in nude mice were performed. Bioinformatic analysis and microarray were used to select the target gene, and luciferase reporter assays were used to confirm the binding sites. Results: Solexa sequencing data exhibited differential expression of 193 microRNAs between TNBC and non-TNBC stem cells. The gene ontology analysis and pathways analyses showed that genes were involved in the maintenance of stemness. MiR-4319 could suppress the self-renewal and formation of tumorspheres in TNBC CSCs through E2F2, and also inhibited tumor initiation and metastasis in vivo. Moreover, increased E2F2 could reverse the effect of miR-4319 on the self-renewal in TNBC CSCs. Conclusions: MiR-4319 suppresses the malignancy of TNBC by regulating self-renewal and tumorigenesis of stem cells and might be a remarkable prognostic factor or therapeutic target for patients with TNBC.

Key WordsHer-2-positive breast cancer • Trastuzumab resistance • MiR-129-5p • RpS6 Abstract Background/Aims: Trastuzumab is an important treatment used for patients with Her-2-positive breast cancer, but an increasing incidence of trastuzumab resistance has been observed clinically during the past decade. Aberrant microRNA (miR) expression levels are correlated with prognosis and response to trastuzumab in breast cancer. MiR-129-5p is downregulated in trastuzumab-resistant human breast cancer cells (JIMT-1), but its potential function and underlying mechanism remain unclear. Methods: Quantitative RT-PCR (qRT-PCR) was used to determine the expression levels of miR-129-5p and its potential target genes. The effects of miR-129-5p on cell responses to trastuzumab were analyzed by CCK-8 and flow cytometry assays in Her-2-positive breast cancer cells (SKBR-3 and JIMT-1). Bio-informatics analyses were performed to predict target genes of miR-129-5p, and luciferase assays were carried out to confirm the binding of miR-129-5p and rpS6. Results: MiR-129-5p, which was downregulated and predicted to target rpS6 in trastuzumab-resistant breast cancer cells, enhanced the sensitivity of breast cancer cells to trastuzumab by reducing the expression of rpS6. Moreover, the overexpression of rpS6 reversed the sensitivity of cells to trastuzumab induced by miR-129-5p. Conclusions: MiR-129-5p sensitized Her-2-positive breast cancer to trastuzumab by downregulating rpS6. These findings provide novel insights into the common role of rpS6 and its related molecular mechanisms in mediating trastuzumab-resistance in Her-2-positive breast cancers.

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Circular RNAs (circRNAs) are becoming new therapeutic drug targets. However, their profiles under astilbin treatment have not been reported yet. In this study, we analysed the global reprogramming of circRNA transcriptome and a regulatory network of circRNAs with their targeted genes under astilbin treatment in pulmonary fibrosis. A total of 145 circRNAs were differentially expressed in the astilbin‐treated group compared with the bleomycin‐treated group using RNA sequencing. In the bleomycin‐ and astilbin‐treated groups, 29 coexpressed circRNAs were found. The maximum number of circRNAs was distributed on chromosome two, and their length varieties were mainly within 1000 bp. Four differentially expressed circRNAs (circRNA‐662, 949, 394 and 986) were tested to validate the RNA sequencing data, and their targeted microRNAs and genes were analysed by qRT‐PCR, Western blot, Pearson correlation coefficient, a dual‐luciferase reporter system and anti‐AGO2 RNA immunoprecipitation. The results showed that circRNA‐662 and 949 can act as “miR‐29b sponges” targeting Gli2 and STAT3 to exert their functions. Our work suggests that the transcriptome complexity at the circRNA level under astilbin treatment. These circRNAs may be potential molecular targets for drug action.