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目的:探讨SIRT7在胰腺癌细胞上皮-间充质转化（EMT）中的作用和机制。方法:使用siRNA或质粒转染将胰腺癌细胞分为siControl组、siSIRT7组、过表达SIRT7组、siSIRT7+siCOL4A1组和siSIRT7+siSLUG组。EdU实验、细胞划痕实验和Transwell实验分别检测细胞的增殖、迁移和侵袭能力，实时荧光聚合酶链反应（qRT-PCR）和Western blot法检测EMT标志物和肿瘤干细胞标志物的表达水平。对敲低SIRT7的胰腺癌细胞进行转录组测序（RNA-seq），探究SIRT7调控的信号通路和靶基因，采用qRT-PCR验证靶基因的转录水平。定量染色质免疫共沉淀实验（q-ChIP）和染色质免疫共沉淀聚合酶链反应（ChIP-PCR）鉴定SIRT7直接调控的靶基因。免疫组织化学法检测人胰腺癌组织（2013—2016年购自武汉塞维尔生物科技有限公司）中SIRT7及靶基因的表达。癌症基因组图谱（TCGA）数据库数据分析SIRT7及其靶基因的表达相关性。KM-Plotter网站用以分析SIRT7和靶基因在胰腺癌中的生存相关性。GeneMANIA、STRING和ENCORI在线工具用以分析SIRT7相关蛋白及miRNAs等。结果:EdU实验结果显示，过表达SIRT7组PANC-1和BxPC-3细胞增殖率分别为（19.33±0.35）%和（17.00±1.89）%，均低于对照组［分别为（31.60±1.37）%和（24.33±0.78）%，均 P＜0.05］；而敲低SIRT7表达组PANC-1和BxPC-3细胞增殖率［分别为（23.94±1.00）%、（27.08±0.97）%］和［（22.00±1.86）%、（25.96±1.61）%］均高于siControl组［分别为（11.80±1.86）%和（13.42±1.39）%，均 P＜0.05］。在PANC-1细胞中，细胞划痕实验结果表明，过表达SIRT7组细胞相对迁移率为（76.67±2.74）%，低于对照组细胞［（100.00±2.13）%， P＜0.05］；而抑制SIRT7表达后细胞相对迁移率［分别为（134.22±4.08）%和（199.82±9.20）%］均高于siControl组细胞［（102.24±3.13）%，均 P＜0.05］。迁移实验中（BxPC-3细胞），过表达SIRT7组细胞迁移数为（28.33±2.62）个，低于于对照组［（45.66±1.69）个， P?0.05］；敲低SIRT7表达组细胞迁移数［分别为（65.66±2.86）个、（82.00±2.94）个］均高于siControl组细胞［（33.00±0.81）个， P＜0.01］。Transwell实验结果表明，过表达SIRT7组细胞侵袭数为（16.33±2.05）个和（34.66±1.69）个，低于对照组［分别为（54.33±4.64）个和（58.66±5.90）个，均 P＜0.05］；而敲低SIRT7表达组细胞侵袭数［分别为（63.66±2.49）个、（69.33±3.29）个和（134.33±3.09）个、（181.66±4.02）个］均高于siControl组细胞［（35.33±2.49）个和（42.00±0.81）个，均 P＜0.05］。qRT-PCR和Western blot结果显示，敲低SIRT7表达后，细胞上皮标志物表达降低，间充质标志物表达增多，肿瘤干细胞标志物增多。RNA-seq分析显示，SIRT7参与调控多种恶性肿瘤相关信号通路，其中包括胰腺癌通路和EMT通路。q-ChIP和ChIP-PCR结果显示，SIRT7可直接结合到靶基因COL4A1和SLUG等的启动子区域；EdU、Transwell和Western blot实验也证明SIRT7与靶基因COL4A1和SLUG在胰腺癌细胞中的功能呈负性相关。免疫组化结果显示，SIRT7在胰腺癌组织中表达下调，COL4A1、SLUG、SOX2在胰腺癌组织中表达上调。GeneMANIA、STRING和ENCORI在线网站分析结果显示，有众多潜在的SIRT7相互作用蛋白和相关miRNA。 结论:在胰腺癌中，SIRT7可以通过抑制COL4A1和SLUG等靶基因的转录，从而抑制胰腺癌细胞的EMT，胰腺癌中SIRT7是一个潜在的肿瘤抑制基因。

Objective:To investigate the effect and mechanism of SIRT7 in epithelial mesenchymal transformation (EMT) of pancreatic cancer cells.Methods:The pancreatic cancer cells were divided into siControl, siSIRT7, over-expression SIRT7, siSIRT7+siCOL4A1, and siSIRT7+siSLUG groups using siRNA or plasmid transfection. The proliferation, migration and invasion of pancreatic cancer cells were detected by EdU, wound healing assay and Transwell experiments, respectively. The expression of EMT and cancer stem cell (CSC) markers were detected by quantitative real-time reverse transcription polymerase chain reaction assay (qRT-PCR) and western blot. RNA sequencing (RNA-seq) in SIRT7 knockdown PANC-1 cells was performed to explore the signaling pathways and target genes regulated by SIRT7. Then the target genes directly regulated by SIRT7 were identified with quantitative chromatin immunoprecipitation experiment (q-ChIP) and chromatin immunoprecipitation polymerase chain reaction (ChIP-PCR). The expressions of SIRT7 and target genes were detected by immunohistochemical (IHC) in pancreatic cancer tissues, and the correlation between SIRT7 and target gene expression was analyzed using TCGA dataset. The correlation between expression of SIRT7 or target genes and survival was analyzed on KM-plotter website. Finally, GeneMANIA, STRING and ENCORI were used to predict SIRT7-related proteins and miRNAs.Results:EdU assay showed that the cell proliferation rates in SIRT7-overexpressed PANC-1 [(19.33±0.35)%] and BxPC-3 cells [(17.00±1.89)%] were lower than those in the control group [(31.60±1.37)% and (24.33±0.78)%, respectively, P＜0.05]. The proliferation rates of SIRT7-knockdown PANC-1 [(23.94±1.00)% and (27.08±0.97)%] and BxPC-3 cells [(22.00±1.86)% and (25.96±1.61)%] were higher than those of the siControl group [(11.80±1.86)% and (13.42±1.39)%, respectively, P＜0.05]. In PANC-1 cells, the wound healing assay showed that the relative migration rate of SIRT7-overexpression cells [(76.67±2.74)%] was lower than that of control cells [(100.00±2.13)%, P＜0.05]; the relative migration rate of cells with SIRT7 knockdown [(134.22±4.08)% and (199.82±9.20)%, respectively] was higher than that of siControl group [(102.24±3.13)%, P＜0.05]. Compared with the control group, SIRT7 overexpression decreased the number of migrated BxPC-3 cells (45.66±1.69 vs 28.33±2.62, P＜0.05); while SIRT7 knockdown increased these numbers (65.66±2.86 and 82.00±2.94 versus 33.00±0.81, P＜0.01). Transwell experiment revealed that the number of invaded cells in SIRT7 overexpression groups (16.33±2.05 and 34.66±1.69) was lower than that control groups (54.33±4.64 and 58.66±5.90, P＜0.05); with SIRT7 knockdown, the numbers of invaded PANC-1 (63.66±2.49 and 69.33±3.29) and BxPC-3 cells (134.33±3.09 and 181.66±4.02) were higher than those in control groups (35.33±2.49 and 42.00±0.81, P?0.05). Also, SIRT7 knockdown decreased the expressions of epithelial markers and increased the expressions of mesenchymal and CSC markers. RNA-seq analysis showed that SIRT7 was involved in regulating a variety of cancer-related signaling pathways, including the pancreatic cancer pathway and the EMT pathway. Furthermore, SIRT7 could directly bind to the promoter regions of target genes, such as COL4A1 and SLUG. SIRT7 was negatively correlated with the expression and function of COL4A1 and SLUG in pancreatic cancer cells. The expressions of SIRT7, COL4A1, SLUG and SOX2 were verified in pancreatic cancer tissues by IHC. Finally, SIRT7 was predicted to be associated with many proteins and miRNAs based on GeneMANIA, STRING, and ENCORI online tools. Conclusions:SIRT7 can inhibit the EMT of pancreatic cancer cells through transcriptionally inhibiting the expression of target genes, such as COL4A1 and SLUG. Thus, SIRT7 may serve as a potential tumor suppressor gene in pancreatic cancer.