lncRNA UASR1 sponges miR-107 in colorectal cancer to upregulate oncogenic CDK8 and promote cell proliferation

Abstract

lncRNA UASR1 (UASR1) has been characterized as an oncogenic lncRNA in breast cancer. UASR1 was predicted to interact with miR-107, which serves tumor suppressive roles mainly by targeting CDK8. The present study was performed to investigate the interactions among UASR1, miR-107 and CDK8 in colorectal cancer (CRC). A total of 62 patients with CRC, including 40 males and 22 females (age range, 38-67 years; mean age, 57.2±7.6 years) were enrolled at the Second Hospital of Shandong University between July 2012 and July 2014. The expression of UASR1 in tissues and cells were detected by reverse transcription-quantitative polymerase chain reaction. The interaction between UASR1 and miR-107 was investigated by performing dual luciferase activity assay, and the effects of overexpression of UASR1, miR-107 and CDK8 on the proliferation of CR4 cells were analyzed by performing cell proliferation analysis. It was observed that UASR1 is upregulated in CRC and its high expression levels predicted poor survival in patients with CRC. RNA-RNA interaction prediction demonstrated that UASR1 may interact with miR-107. In CRC cells, overexpression of UASR1 and miR-107 did not affect each other. However, the expression of CDK8, a target of miR-107, was upregulated following overexpression of UASR1. Notably, overexpression of UASR1 decreased the inhibitory effects of miR-107 on cell proliferation and the expression of CDK8. Therefore, UASR1 may sponge miR-107 to upregulate oncogenic CDK8, thereby promoting CRC cell proliferation.

Keywords: CDK8; UASR1; colorectal cancer; miR-107; proliferation.

Figure 1.

UASR1 and CDK8 were upregulated in CRC and high expression levels of UASR1 in CRC predicted poor survival. The expression of (A) UASR1 and (B) CDK8 in paired CRC and non-tumor tissues from 62 patients with CRC were determined by reverse transcription-quantitative polymerase chain reaction. ***P<0.001. The 62 patients with CRC were divided into high and low UASR1 expression groups (n=31) with the median level of UASR1 in CRC tissues as the cut-off value. Survival curves were plotted for the two groups based on follow-up data. Survival curves were compared using the log-rank test. (C) It is worth noting that miR-107 expression was not significantly correlated with patient survival (P=0.488; HR=1.123; 95% CI: 0.598–2.117), while the expression of CDK8 was correlated with patient survival (P=0.0167; HR=2.376; 95% CI: 1.237–4.417). CRC, colorectal cancer; HR, hazards ratio; CI, confidence interval.

Figure 2.

UASR1 and miR-107 interacted with each other but did not regulate the expression of each other. (A) The interaction between UASR1 and miR-107 was predicted using IntaRNA2.0. The interaction between UASR1 and miR-107 was investigated by performing a dual luciferase activity assay, which was performed by co-transfecting CR4 cells with UASR1 luciferase vector + miR-107 mimic (miR-107 group) or UASR1 luciferase vector + NC miRNA (NC group). (B) Luciferase activity was measured at 48 h post-transfection. To further investigate the interaction between UASR1 and miR-107, CR4 cells were transfected with the UASR1 expression vector or miR-107-mimic. (C) Overexpression of UASR1 and miR-107 was confirmed by performing RT-qPCR. (D) The effects of overexpression of UASR1 and miR-107 on the expression of each other were also analyzed by RT-qPCR. *P<0.05. RT-qPCR, reverse transcription-quantitative polymerase chain reaction; NC, negative control.

Figure 3.

The expression of CDK8 was upregulated in CR4 cells with UASR1-overexpression. To test the possibility of UASR1 as an internal sponge of miR-107, the effects of overexpression of UASR1 and miR-107 on the expression of CDK8, a miR-107 target, were analyzed by (A) reverse transcription-quantitative polymerase chain reaction and (B) western blot analysis. All polymerase chain reaction reactions were repeated 3 times and mean values were presented and compared. *P<0.05. NC, negative control.

Figure 4.

UASR1 promoted CR4 cell proliferation through the miR-107/CDK8 axis. (A) The effects of overexpression of UASR1, miR-107 and CDK8 on the proliferation of CR4 cells were analyzed by performing cell proliferation. (B) Reverse transcription-quantitative polymerase chain reaction was performed to confirm the overexpression of CDK8 in cells with the CDK8 expression vector and UASR1-overexpression and miR-107 in cells co-transfected with UASR1 expression vector and miR-107 mimic. *P<0.05. NC negative control.