Background Recently, emerging evidence has indicated crucial roles for long noncoding RNAs (lncRNAs) in breast cancer (BC) development and progression. Our study aimed to investigate the clinical significance of LINC01089 in patients with BC and to determine its biological functions and underlying molecular mechanisms. Materials and methods Correlations between LINC01089 expression and the clinicopathological characteristics of BC patients were assessed using chi-square tests. The Kaplan-Meier method was used to produce survival curves. The clinical risk characteristics associated with the overall survival and recurrence-free survival of patients with BC were estimated using univariate and multivariate Cox regression analyses. Several methods were used to determine the expression profile, biological functions and underlying mechanisms of LINC01089 in BC, including cell proliferation assays, colony formation assays, flow cytometry, transwell assays, wound healing assays, quantitative real-time polymerase chain reaction and Western blotting. Results LINC01089 was downregulated in BC tissues and cell lines. Low LINC01089 expression was significantly correlated with age ( P =0.026), lymph node metastasis ( P =0.003), and poor prognosis of patients with BC. According to the multivariate Cox regression analysis results, LINC01089 was an independent prognostic indicator of overall survival ( P =0.032) and recurrence-free survival ( P =0.014). Functional studies revealed significant decreases in the proliferation, migration, and invasion of tumor cells overexpressing LINC01089, and EGF could reverse above effects of LINC01089 on BC cells. Additionally, increased LINC01089 expression promoted apoptosis and cell cycle arrest at G0/G1 phase, accompanied by decreased expression of the key cell cycle regulators CDK4 and CDK6. Loss-of-function assays confirmed partial results. Mechanistically, LINC01089 blocked the Wnt/β-catenin pathway and the expression of downstream target genes by inhibiting β-catenin expression at the transcriptional level. Conclusion Based on our results, LINC01089 functions as a tumor suppressor and potentially represents a novel prognostic indicator and therapeutic target in BC.

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Background The MIR663AHG gene encode both miR663AHG and miR663a. While miR663a contributes to the defense of host cells against inflammation and inhibits colon cancer development, the biological function of lncRNA miR663AHG has not been previously reported. Methods The subcellular localization of lncRNA miR663AHG was determined by RNA-FISH. miR663AHG and miR663a were measured by qRT-PCR. The effects of miR663AHG on the growth and metastasis of colon cancer cells were investigated in vitro and in vivo. CRISPR/Cas9, RNA pulldown, and other biological assays were used to explore the underlying mechanism of miR663AHG. Results miR663AHG was mainly distributed in the nucleus of Caco2 and HCT116 cells and the cytoplasm of SW480 cells. The expression level of miR663AHG was positively correlated with the level of miR663a (r = 0.179, P = 0.015) and significantly downregulated in colon cancer tissues relative to paired normal tissues from 119 patients (P < 0.008). Colon cancers with low miR663AHG expression were associated with advanced pTNM stage (P = 0.021), lymph metastasis (P = 0.041), and shorter overall survival (hazard ratio = 2.026; P = 0.021). Experimentally, miR663AHG inhibited colon cancer cell proliferation, migration, and invasion. The growth of xenografts from RKO cells overexpressing miR663AHG was slower than that of xenografts from vector control cells in BALB/c nude mice (P = 0.007). Interestingly, either RNA-interfering or resveratrol-inducing expression changes of miR663AHG or miR663a can trigger negative feedback regulation of transcription of the MIR663AHG gene. Mechanistically, miR663AHG could bind to miR663a and its precursor pre-miR663a, and prevent the degradation of miR663a target mRNAs. Disruption of the negative feedback by knockout of the MIR663AHG promoter, exon-1, and pri-miR663A-coding sequence entirely blocked these effects of miR663AHG. Conclusion miR663AHG functions as a tumor suppressor that inhibits the development of colon cancer through its cis-binding to miR663a/pre-miR663a. The negative feedback loop between miR663AHG and miR663a expression may play dominant roles in maintaining the functions of miR663AHG in colon cancer development.

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