MicroRNA (miRNA) expression is shown dysregulated in tumors. It has been reported that miR-451 alters gene expression and regulates tumorigenesis in various cancer tissues. However, its underlying biological significance in bladder cancer remains to be clarified. In the present study, we investigated the function and molecular mechanism of miR-451 involved in bladder cancer cell migration and invasion. Our results showed that miR-451 was downregulated in clinical bladder carcinoma tissues compared with adjacent bladder tissues. Overexpression of miR-451 significantly retarded the proliferation, migration and invasion of bladder cancer T24 and 5637 cells in vitro. Moreover, the attenuated cell migration and invasion by miR-451 was correlated with increased apoptosis. However, our dual-luciferase reporter assay validated that c-Myc, an oncogene in many tumors, was a direct target gene of miR-451 in bladder cancer. The expression of c-Myc was repressed by miR-451 in bladder cancer cells, and knockdown of c-Myc mimicked the effects of miR-451 overexpression. This discovery suggested that miR-451 is a tumor suppressor modulating bladder cancer cell migration and invasion by directly targeting c-Myc. In addition, apoptosis promoted by miR-451 may participates in this biological behavior. Therefore, target miR-451 may be a novel therapeutic intervention for bladder cancer.

Aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that interacts with multiple signaling pathways during prostate development. In the present study, LNCaP cells were knocked down of AhR by siRNA, or treated with the AhR agonist 3-methylcholanthrene (3MC). The effects of AhR on LNCaP cells and the associated mechanisms were studied both under normal condition and under hydrogen peroxide (HO)induced oxidative stress. MTT, transwell chamber assays and flow cytometry were employed to investigate cell proliferation, invasion, and apoptosis, respectively, whereas the DNA damage response (DDR) signaling (phosphorylation of ataxia-telangiectasia mutated [ATM], check-point kinase 2 [Chk2], histone H2AX, p53, and cleaved poly-ADP-ribose polymerase [PARP]) was detected by western blotting. Exposure of LNCaP cells to HO inhibited their viability and migration, and induced apoptosis, at a greater extent compared with the culture under normal conditions. In addition, the oxidative stress increased p-ATM, p-Chk2, p-p53, and p-H2AX expression levels significantly. Knockdown of AhR attenuated the aforementioned effects caused by HO-induced oxidative stress. Activation of AhR by 3MC treatment, further aggravated these changes of LNCaP cells on oxidative stress. The findings indicated that AhR suppresses the viability and migration of LNCaP cells notably under oxidative stress, and this process is associated with positive regulation of the responses to oxidative DNA damage.

Background: Bladder cancer (BC) is a common cause of cancer-relevant deaths globally. This study is designed to delve into expressions, biological functions and molecular mechanisms of circ_0000515 in BC. Methods: Quantitative real-time polymerase chain reaction was accomplished to examine circ_0000515, miR-542-3p and integrin-linked kinase (ILK) mRNA expressions in BC tissues and cell lines. In RT-4 and RT-112 cells with circ_0000515 depletion and UMUC3 and BIU-87 cells with this circ RNA overexpression, a cell counting kit-8 assay was adopted to monitor the viability. Besides, transwell assay was conducted to detect cell migration and aggressiveness, and luciferase reporter gene assay was applied to probe the interplay among circ_0000515, miR-542-3p and ILK mRNA. Additionally, Besides, the regulatory function of circ_0000515 on miR-542-3p expression was under the assay of quantitative real-time polymerase chain reaction, and western blot was fulfilled to determine the regulative function of circ_0000515/miR-542-3p axis on ILK protein expressions. A xenograft animal was modeled to examine lung metastasis in vivo . Results: Circ_0000515 and ILK expressions were significantly elevated in BC tissues and cell lines, while that of miR-542-3p was dramatically suppressed. Knocking down circ_0000515 could significantly repress the growth, migration and aggressiveness of BC cells while overexpression of circ_0000515 showed opposite effects. Moreover, circ_0000515 knockdown inhibited pulmonary metastasis in vivo . Circ_0000515 was validated to adsorb miR-542-3p, and ILK was testified as the downriver target of miR-542-3p. Circ_0000515 could ascend ILK expression through repressing that of miR-542-3p. Conclusions: Circ_0000515, as a tumor promoter, strengthens the viability, migration and aggressiveness of BC cells via modulating miR-542-3p/ILK axis.