Long Non-Coding RNA (lncRNA) Urothelial Carcinoma-Associated 1 (UCA1) Enhances Tamoxifen Resistance in Breast Cancer Cells via Inhibiting mTOR Signaling Pathway

Background: Long non-coding RNA (lncRNA) UCA1 is an oncogene in breast cancer. The purpose of this study was to investigate the role of UCA1 in tamoxifen resistance of estrogen receptor positive breast cancer cells. Material/Methods: Tamoxifen sensitive MCF-7 cells were transfected for UCA1 overexpression, while tamoxifen resistant LCC2 and LCC9 cells were transfected with UCA siRNA for UCA1 knockdown. qRT-PCR was performed to analyze UCA1 expression. CCK-8 assay, immunofluorescence staining of cleaved caspase-9, and flow cytometric analysis of Annexin V/PI staining were used to assess tamoxifen sensitivity. Western blot analysis was performed to detect p-AKT and p-mTOR expression. Results: LncRNA UCA1 was significantly upregulated in tamoxifen resistant breast cancer cells compared to tamoxifen sensitive cells. LCC2 and LCC9 cells transfected with UCA1 siRNA had significantly higher ratio of apoptosis after tamoxifen treatment. UCA1 siRNA significantly decreased the protein levels of p-AKT and p-mTOR in LCC2 and LCC9 cells. Enforced UCA1 expression substantially reduced tamoxifen induced apoptosis in MCF-7 cells, while rapamycin treatment abrogated the protective effect of UCA1. Conclusions: UCA1 upregulation was associated with tamoxifen resistance in breast cancer. Mechanistically, UCA1 confers tamoxifen resistance to breast cancer cells partly via activating the mTOR signaling pathway.