LncRNA PTAR promotes EMT and invasion-metastasis in serous ovarian cancer by competitively binding miR-101-3p to regulate ZEB1 expression

Abstract

Background: Ovarian cancer (OvCa) is one of the most common malignant diseases of the female reproductive system in the world. The majority of OvCa is diagnosed with metastasis in the abdominal cavity. Epithelial-to-mesenchymal transition (EMT) plays a key role in tumor cell metastasis. However, it is still unclear whether long non-coding RNA (lncRNA) is implicated in EMT and influences cell invasion and metastasis in OvCa.

Results: In this study, using bioinformatcis analysis, we constructed a lncRNA-mediated competing endogenous RNA (ceRNA) network for mesenchymal OvCa and identified lncRNA AP000695.4, which we named pro-transition associated RNA (PTAR). PTAR was significantly up-regulated in the mesenchymal subtype samples compared with the epithelial subtype samples from the TCGA OvCa data sets. In addition, our study showed that PTAR expression was positively correlated with the expression level of ZEB1 in the mesenchymal OvCa samples. Meanwhile, we found that silencing miR-101 promoted cell migration, whereas the overexpression of miR-101 suppressed EMT and cell migration in OvCa cell lines through the regulation of ZEB1. Further analysis showed that enhanced expression of PTAR promoted EMT and metastasis through the regulation of miR-101, whereas silencing PTAR led to the attenuation of TGF-β1-induced tumorigenicity in ovarian cancer cells. Mechanistically, we found that PTAR acted as a ceRNA of miR-101, as forced expression of PTAR reduced the expression and activity of miR-101. More importantly, the knockdown of PTAR reduced tumorigenicity and metastasis in vivo.

Conclusions: Taken together, the results from our study highlight a role for the PTAR-miR-101-ZEB1 axis in OvCa, which offers novel strategies for the prevention of metastasis in OvCa.

Keywords: Epithelial-mesenchymal transition; Ovarian cancer; ZEB1; lncRNA PTAR; miR-101.

Fig. 1

The identification of a ceRNA network for mesenchymal OvCa. a The ceRNA network in mesenchymal OvCa. Rounded rectangles, ellipses and hexagons denote lncRNAs, EMT genes and miRNAs, respectively. Up-regulated lncRNAs, EMT genes and miRNAs are shown in red and down-regulated lncRNAs, EMT genes and miRNAs are shown in green. b ZEB1 was significantly up-regulated in mesenchymal OvCa compared with epithelial OvCa in the TCGA data set. c Positive correlation between PTAR and ZEB1 expression in the TCGA data set. d The lncRNA PTAR was significantly up-regulated in mesenchymal OvCa compared with epithelial OvCa in the TCGA data set. e Nagative correlation between miR-101 and ZEB1 expression in the TCGA data set. f Nagetive correlation between PTAR and miR-101 expression in the TCGA data set. g miR-101 was significantly down-regulated in mesenchymal OvCa compared with epithelial OvCa in the TCGA data set

Fig. 2

Knockdown of lncRNA PTAR inhibits tumor progression in an orthotopic mouse model of OvCa. a The macroscopic observation of the size and range of metastatic lesions in nude mice. b Representative images of tumors from nude mice bearing xenograft tumors with SKOV3 cells infected with a lentivirus carrying a short hairpin RNA against PTAR (lenti-sh-PTAR) or its scramble negative control (lenti-sh-Scramble). c, d The average number of metastatic nodules and tumor xenograft weights in nude mice. n = 11–13. *P < 0.05. e An immunohistochemistry assay was applied to determine the expression of E-cadherin, fibronectin 1 (FN1), zinc finger E-box binding homeobox 1 (ZEB1) and vimentin in a cell-derived xenograft tumor model. f, g The expression of epithelial-mesenchymal transition (EMT) relevant markers, including E-cadherin, vimentin, FN1 and ZEB1 in tissues derived from xenograft tumors, as determined by qRT-PCR and western blot, respectively. n = 6. *P < 0.05

Fig. 3

PTAR promotes EMT and metastasis through the modulation of miR-101/ZEB1. The SKOV3, A2780 and OVCAR3 cells were transfected with PTAR plasmid with or without miR-101 mimic. a, b Wound healing assays showing cell migration in SKOV3 and A2780 cells. n = 4, *P < 0.05 vs. pcDNA3.1, ^#P < 0.05 vs. PTAR. c, d Migration assays in SKOV3 and A2780 cells, respectively. e The invasiveness of SKOV3 cells was determined by an invasion assay using matrigel transwell chambers. n = 4, **p < 0.01. f The protein levels of E-cadherin, vimentin, FN1 and ZEB1 in SKOV3 cells. n = 5, *P < 0.05 vs. pcDNA3.1, ^#P < 0.05 vs. PTAR. g The protein levels of E-cadherin, vimentin, FN1 and ZEB1 in A2780 cells. n = 5, *P < 0.05 vs. pcDNA3.1, ^#P < 0.05 vs. PTAR. h The protein levels of E-cadherin and ZEB1 in OVCAR3 cells. n = 3, *P < 0.05 vs. pcDNA3.1, ^#P < 0.05 vs. PTAR

Fig. 4

Silencing PTAR alleviates ovarian cancer cell tumorigenicity. The SKOV3, A2780 and OVCAR3 cells were transfected with sh-PTAR with or without miR-101 inhibition in the presence or absence of 10 ng/ml TGF-β1 for 48 h. a, b Wound healing assays were performed both in SKOV3 and A2780 cells treated as specified. n = 4, *P < 0.05 vs. Ctrl, ^#P < 0.05 vs. TGF-β1 + sh-Scram, ^&P < 0.05 vs. TGF-β1 + sh-PTAR. c, d Cell migration in SKOV3 and A2780 cells was determined using transwell chambers. n = 4, ** P < 0.01. e The invasion ability of SKOV3 cells was evaluated using matrigel transwell chambers. n = 4, ** P < 0.01. f, g The protein levels of E-cadherin, vimentin, FN1 and ZEB1 in SKOV3 and A2780 cells. n = 5, *P < 0.05 vs. Ctrl, ^#P < 0.05 vs. TGF-β1 + sh-Scram, ^&P < 0.05 vs. TGF-β1 + sh-PTAR. h The protein levels of E-cadherin and ZEB1 in OVCAR3 cells. n = 3, *P < 0.05 vs. Ctrl, ^#P < 0.05 vs. TGF-β1 + sh-Scram, ^&P < 0.05 vs. TGF-β1 + sh-PTAR

Fig. 5

PTAR negatively regulates miR-101 expression and activity in OvCa cells. a, b The expression of PTAR and miR-101 in SKOV3 and A2780 cells after treatment with 10 ng/ml TGF-β1 for 48 h. c, d Analysis with qRT-PCR was used to assess the expression of PTAR and miR-101 in SKOV3 and A2780 cells in response to PTAR overexpression. e The knockdown efficiency of the sh-PTAR plasmid was confirmed by qRT-PCR analysis. f Expression of miR-101 was detected in OvCa cells in response to PTAR suppression. g The luciferase reporter activity of chimeric vectors carrying the luciferase gene and a fragment of PTAR containing the (WT) binding site or a mutated binding site for miR-101. h, i The luciferase activity of miR-101 sensor in OvCa cells transfected as specified. n = 5. *P < 0.05

Fig. 6

Silencing miR-101 promotes OvCa cell migration by regulating ZEB1. a The western blot analysis of epithelial and mesenchymal markers in SKOV3 cells transfected with AMO-101. Wound-healing b and migration assays c were applied to determine the effect of miR-101 knockdown on OvCa cell migration. d The luciferase reporter activity of chimeric vectors carrying the luciferase gene and a fragment of the ZEB1 3′-UTR containing the wild-type or mutated miR-101 binding site. e The overexpression of miR-101 inhibited the mRNA expression of ZEB1 in SKOV3 cells. f The overexpression of miR-101 repressed the protein expression of ZEB1 in SKOV3 cells, whereas knockdown of miR-101 had the opposite effect. n = 5. *P < 0.05, **P < 0.01

Fig. 7

Overexpression of miR-101 attenuated TGF-β1-induced metastasis in OvCa cell lines. a, b Wound healing assays performed in SKOV3 and A2780 cells, respectively. Images were captured at 0, 24, and 48 h. n = 4, *P < 0.05 vs. Ctrl, ^#P < 0.05 vs. TGF-β1. c, d The migration ability of SKOV3 and A2780 cells was determined using transwell assays. n = 4, **P < 0.01. e The expression levels of epithelial and mesenchymal markers were detected by western blot in SKOV3 cells. n = 5, *P < 0.05 vs. Ctrl, ^#P < 0.05 vs. TGF-β1. f Up-regulation of lncRNA PTAR enhanced ZEB1 expression by competitively binding miR-101, which promoted OvCa cell EMT and invasion