ABSTRACT
Objective:To determine the expression of circular RNA-SEC31A(circSEC31A) in pancreatic cancer and investigate the effects on the invasion and migration of pancreatic cancer cells and the underlying molecular mechanism.Methods:Differentially expressed circRNAs between pancreatic cancer cells (BXPC-3, PANC1, CaPan-2, SW1990) and human normal pancreatic cells (HPDE) were identified by qRT-PCR. Then, two cell lines with high circSEC31A expression were selected to conduct next experiments. According to the sequence of the back-splicing site in circSEC31A, siRNAs for downregulation of circSEC31A were designed and transfected by liposome to silence circSEC31A in pancreatic cancer cells, and grouped as followed siR-circSEC31A#1 and siR-circSEC31A#2. Meanwhile, siR-NC group transfected with non-specific siRNA served as control. Transwell assays and wound healing assays were operated to evaluate the functional role of circSEC31A on the invasion and migration of pancreatic cancer cells. RNA Pull-down assay with circSEC31A probe and oligo control probe was used to screen the miRNA combining with circSEC31A and the effects of miRNA on cell invasion and migration of pancreatic cancer cells were validated. The effect of miR-200c-3p and circSEC31A silencing on the expression of PDK1 mRNA was identified by qRT-PCR. The protein expression of PDK1, downstream Akt and p-Akt after circSEC31A silencing was verified by Western blotting assays.Results:The relative expression level of circSEC31A in HPDE (1.000±0.120) was obviously lower than that in BXPC-3 (1.920±0.130), SW1990 (2.93±0.528), PANC1 (4.557±0.692) and CaPan-2 (5.247±0.194), and all the differences were statistically significant ( P<0.001). Compared with the PANC1 siR-NC group (1301.3±94.6) and CaPan-2 siR-NC group (1835.0±70.1) per 100 high power field, transwell assays showed that the numbers of invasive pancreatic cancer cells was highly decreased in PANC1 siR-circSEC31A#1 group (727.3±92.9), siR-circSEC31A#2 group (792.0±18.1), CaPan-2 siR-circSEC31A#1 group (718.0±90.6), siR-circSEC31A#2 group (692.7±84.8). Wound healing assays showed that silencing circSEC31A decreased the wound healing rate of pancreatic cancer cells in PANC1 siR-circSEC31A#1 group (20.667±3.215)%, siR-circSEC31A#2 group (20.000±4.583)%, CaPan-2 siR-circSEC31A#1 group (28.000±8.185)%, siR-circSEC31A#2 group (29.667±5.686)%, compared with the PANC1 siR-NC group (55.000±4.359)% and CaPan-2 siR-NC group (69.000±3.606)%. RNA Pull-down assays showed that compared with PANC1 oligo probe group (1.000±0.091) and CaPan-2 oligo probe group (1.000±0.153), miR-200c-3p was significantly enriched in the PANC1 circSEC31A probe group (2.237±0.175) and CaPan-2 circSEC31A probe group (2.166±0.156). Compared with PANC1 siR-NC group (939.3±57.0) and CaPan-2 siR-NC group (786.7±51.5) per 100 high power field, the numbers of invasive pancreatic cancer cells were up-regulated in PANC1 siR-miR-200c-3p group (1206.0±99.1) and CaPan-2 siR-miR-200c-3p group (1838.0±105.7), while the low numbers of invasive pancreatic cancer cells were observed in PANC1 siR-miR-200c-3p+ siR-circSEC31A group (932.7±116.4) and CaPan-2 siR-miR-200c-3p+ siR-circSEC31A group (785.3±58.8). Compared with PANC1 siR-NC group (1.000±0.103) and CaPan-2 siR-NC group (1.000±0.107), the relative expression of PDK1 mRNA in PANC1 siR-miR-200c-3p group (1.898±0.159) and CaPan-2 siR-miR-200c-3p group (2.102±0.337) was upregulated. Furthermore, the expression of PDK1 mRNA was decreased in the siR-miR-200c-3p+ siR-circSEC31A group (0.980±0.070, 1.015±0.079). Western blot assays showed that the expression of PDK1 protein in PANC1 siR-NC group, siR-circSEC31A#1 group, siR-circSEC31A#2 group was 0.767±0.086, 0.281±0.191, 0.333±0.062 and in CaPan-2 siR-NC group, siR-circSEC31A#1 group, siR-circSEC31A#2 group was 0.712±0.038, 0.353±0.061, 0.308±0.018. The expression of p-Akt protein in PANC1 siR-NC group and siR-circSEC31A group was 0.741±0.050, 0.114±0.027, 0.139±0.041. In addition, p-Akt protein expression in CaPan-2 siR-NC group and siR-circSEC31A group was 0.823±0.052, 0.141±0.045, 0.280±0.089. PDK1 and p Akt expression in siR circSEC31A group was obviously lower than those in sir NC group. All the differences between either groups above were statistically significant ( P<0.05). Conclusions:circSEC31A is upregulated in pancreatic cancer cells, which facilitates the invasion and metastasis of pancreatic cancer cells via miR-200c-3p/PDK1/Akt signaling pathway, supporting that circSEC31A may function as a new diagnostic and therapeutic target for pancreatic cancer patients.