Downregulated lncRNA ADAMTS9-AS2 in breast cancer enhances tamoxifen resistance by activating microRNA-130a-5p.

OBJECTIVE: The aim of this study was to elucidate the regulatory effect of long non-coding RNA (lncRNA) ADAMTS9-AS2 on Tamoxifen (TAM) resistance in breast cancer (BC), and to explore its underlying mechanism. PATIENTS AND METHODS: TAM-resistant BC cell lines were first verified. Subsequently, cell proliferation and apoptosis were detected using cell counting kit-8 (CCK-8), 5-ethynyl-2'-deoxyuridine (EdU) assay and flow cytometry, respectively. Protein levels of ABCB1, ABCC1, and ABCG2 in TAM-treated MCF-7 and MCF-7R cells were determined by Western blot. ADAMTS9-AS2 expression in BC tissues, para-cancerous tissues, as well as MCF-7 and MCF-7R cells, was accessed by quantitative Real Time-Polymerase Chain Reaction (qRT-PCR). The correlation between ADAMTS9-AS2 expression with pathological grade and tumor size of BC was explored. Chromatin fractionation was conducted to elucidate the subcellular distribution of ADAMTS9-AS2. The binding condition between ADAMTS9-AS2 and microRNA-130a-5p, as well as microRNA-130a-5p and PTEN, was verified by the dual-luciferase reporter gene assay. Furthermore, regulatory effects of ADAMTS9-AS2, microRNA-130a-5p, and PTEN on the proliferation and apoptosis of MCF-7R cells were determined. RESULTS: MCF-7R cells were identified with TAM resistance. ADAMTS9-AS2 was lowly expressed in BC tissues and MCF-7R cells. Particularly, ADAMTS9-AS2 expression in BC tissues with grade III-IV or tumor size ≥2 cm was significantly lower than that of controls. Dual-luciferase reporter gene assay confirmed the binding condition between ADAMTS9-AS2 and microRNA-130a-5p, showing a negative correlation indicated by Pearson correlation analysis. PTEN was positively correlated with ADAMTS9-AS2. Overexpression of ADAMTS9-AS2 reversed the increased viability and decreased apoptosis induced by microRNA-130a-5p mimics transfection. In addition, PTEN knockdown reversed the decreased viability and accelerated apoptosis caused by ADAMTS9-AS2 overexpression. CONCLUSIONS: We found that ADAMTS9-AS2 is lowly expressed in BC tissues and drug-resistant BC cells. Low expression of ADAMTS9-AS2 inhibits PTEN expression and enhances tamoxifen resistance through targeting microRNA-130a-5p.