Knockdown of Long Non-Coding RNA UCA1 Increases the Tamoxifen Sensitivity of Breast Cancer Cells through Inhibition of Wnt/β-Catenin Pathway

Abstract

Acquired resistance to tamoxifen remains a major obstacle in breast cancer (BC) treatment, since the underlying mechanism has not been fully elucidated. The long non-coding RNA (lncRNA) urothelial carcinoma-associated 1 (UCA1) has been recently shown to be dysregulated and plays important roles in progression of breast cancer. In the present study, we aimed to investigate the biological role and clinical significance of UCA1 in BC drug resistance. Hence, we used quantitative PCR assay to evaluate the UCA1 expression in tissues from patients with BC as well as established tamoxifen-resistant BC cell lines in vitro. We tested the viability, invasive ability and apoptosis rate in MCF-7 and T47D cells using MTT assay, transwell assay and flow cytometry assay, respectively. The influence of UCA1 on tumorigenesis was monitored by in vivo mice xenograft model. The activation of Wnt/β-catenin signaling pathway was evaluated by immunofluorescence assay, western blot assay and luciferase reporter assay, respectively. We found that the expression of UCA1 positively correlated with the pathological grade and mortality of breast cancer patients, moreover, expressions of UCA1 was increased significantly in the tamoxifen-resistant cell lines compared with the wild type parental cells. Ectopic expression of UCA1 promoted cell survival and resistance to tamoxifen treatment, whereas inhibition of UCA1 enhanced tamoxifen sensitivity of BC cells and induced more apoptotic cells. In addition, tamoxifen-resistant cells exhibited increased Wnt signaling activation as measured by the TOP/FOP Wnt luciferase reporter assay and β-catenin protein level compared with parental MCF-7 and T47D cells, respectively. In line with these data, UCA1 depletion attenuated the activity of Wnt/β-catenin pathway activation and the tumorigenicity of the tamoxifen-resistant BC cells. Taken together, our data highlights the pivotal role of UCA1-Wnt/β-catenin signaling pathway in the tamoxifen resistance in breast cancer, which could be targeted to improve the effectiveness and efficacy of tamoxifen treatment in breast cancer.

ElevatedCRB3 expression suppresses breast cancer stemness by inhibiting β‐catenin signalling to restore tamoxifen sensitivity

“…Surprisingly, treatment of the Wnt signalling pathway agonist Wnt3a in MCF7 cells led to tamoxifen resistance, while treatment of the Wnt signalling pathway inhibitor IWP‐2 restored the sensitivity of MCF7 cells to tamoxifen, suggesting that an increase in the number of breast cancer stem cells is associated with activation of the Wnt signalling pathway. In addition, inhibition of the long non‐coding RNA UCA1 in MCF7 and T47D cells resulted in reduced activity of the Wnt signalling pathway accompanied by increased tamoxifen sensitivity . Overall, these studies show that activation of the Wnt signalling pathway plays an important role in the occurrence and development of tamoxifen resistance.…”

“…In addition, inhibition of the long non-coding RNA UCA1 in MCF7 and T47D cells resulted in reduced activity of the Wnt signalling pathway accompanied by increased tamoxifen sensitivity. 29 Overall, these studies show that activation of the Wnt signalling pathway plays an important role in the occurrence and development of tamoxifen resistance. Contrary to the previous study that CRB3 knockout mice displayed high levels of cytoplasmic b-catenin in the intestine, which indicates a low activity of the Wnt signalling pathway, 30 we found that CRB3 overexpression inhibited the Wnt signalling pathway, which led to decreased expression of downstream genes (CD44 and cMyc) and cancer stem cell factors (OCT4 and NANOG), and that these genes were up-regulated when cells acquired tamoxifen resistance.…”

Crosstalk between the lncRNA UCA1 and microRNAs in cancer

“…Tamoxifen treatment up-regulated expression of UCA1 in breast cancer cells through a miR-18a-HIF1a feedback loop [110]. The overexpression of UCA1 conferred tamoxifen resistance by increasing the activity of Wntb-catenin signaling, which was accompanied by a decrease of miR-18a, an important modulator of cell cycle proteins [111,112]. Knockdown of UCA1 increased apoptosis upon tamoxifen treatment accompanied by an increase of cleaved caspase-3 and reduction in p-AKT and p-mechanistic target of rapamycin [113].…”

Critical roles of long noncoding RNAs in breast cancer

“…In addition, the knockdown of CCAT2 repressed both the levels of cytoplasmic and nuclear β‐catenin, suggesting that CCAT2 regulates the transcriptional level of β‐catenin and its expression is associated with the development of breast tumor. Furthermore, the overexpression of UCA1 elevates invasion of breast cancer cells via activating the Wnt/β‐catenin signaling pathway, which demonstrates that UCA1 has the ability to increase the activity of Wnt/β‐catenin signaling by enhancing the nuclear translocation of β‐catenin (H. Liu et al, 2016). Functionally, the UCA1 knockdown suppresses the protein levels of β‐catenin and results in decreased transcription of the downstream genes of β‐catenin, including cyclin D1 and matrix metalloproteinase‐7 (MMP‐7).…”