| Background:Gastric cancer(GC)is one human malignant tumor with a high incidence in the world.With the advancement of science and the continuous improvement of medical technology,the treatment of gastric cancer is gradually developing.New views such as minimally invasive surgery,neoadjuvant chemotherapy or immunotherapy are emerging one after another,but the prognosis of patients with gastric cancer is still unsatisfactory.Therefore,it's important to seek out new targets that affect the progress and prognosis of gastric cancer constantly,and explore the guiding significance in clinical treatment.The difficulty in the treatment of cancer is uncontrollable cell proliferation,invasion and metastasis,which involves various molecules and complex network regulation.Epithelial Mesenchymal Transition(EMT)is one of the important regulatory mechanisms.The loss of polarity of epithelial cells weakens the function of tight connection and adhesion between cells.It empowers the tumor cells strong infiltration and migration ability,which result in invasion and distant metastasis of tumors.The Transforming growth factor ?(TGF-?)signaling pathway is considered as a classic signaling pathway that regulates EMT transformation.As a multifunctional and multi-directional cytokine,TGF-? can combine with receptors on the cell surface to regulate cell proliferation and apoptosis,epithelial mesenchymal transformation,angiogenesis,immunosuppression and other biological functions closely related to cancers.In general,TGF-? in vivo cannot react with the receptors directly,and only a small amount of dissociative TGF-? can bind to receptors.The role of TGF-? in cancers is complex and diverse,including pro-cancer and anti-cancer effects.TGF-? reveals different regulatory effects on tumors.In the early stage of tumors,TGF-? inhibits the growth of tumors by triggering the cell stagnation and apoptosis,while in the advanced stage,the inhibition effects on proliferation of tumors will reduce or even disappear.Tumor cells secrete a large number of TGF-? at this time and it becomes a tumor growth promotion factor.Fibrillin-1(FBN1)gene is the coding gene of fibrillin.At first,the main function of fibrillin was thought to serve for the formation of elastic fibers.Later,biochemical studies and genetic evidence in humans and mice revealed the key role of FBN1 in genetic diseases such as Marfan syndrome.In addition,a new and very important function of fibrillin has been discovered and proposed:targeting and isolating the members of TGF-? superfamily,which reflected the biological role of fibrin in cancer research.Studies indicated that FBN1 has biological functions related to signal transduction,attachment or migration in multiple cancers.However,the role of FBN1 in gastric cancer is still vague.In this study,data mining combined with basic experiment validation were performed to explore new prognostic targets of gastric cancer.Six target genes,FBN1,FN1,HGF,MMP9,THBS1 and VCAN,were identified by the analysis of TCGA,CCLE and GDSC databases.The expression,mutation,copy number variation(CNA),tumor mutation burden(TMB),tumor purity and other aspects were investigated in detailed in order to expound the important role of the target genes in the progression and prognosis of gastric cancer.Through qRT-PCR,transcriptome sequencing and GEO database validation,FBN1 was selected as the target gene for subsequent basic studies.The role and potential mechanism of FBN1 in cancer proliferation,apoptosis,invasion and metastasis were investigated by various experiment methods.Objectives:1.To screen potential targets that affect the prognosis of gastric cancer by the combination of multi-databases and explore their potential function.2.To verify the expression of selected genes got by bioinformatics analysis,and explore the expression and function of FBN1 on gastric cancer cells both in vitro and in vivo3.To explore the potential mechanism of FBN1 affecting the phenotype of gastric cancer cells.Methods:1.Target genes were selected by the analysis of the differential genes and the protein interaction network through the combination of multi databases.Then the potential relationship between the target genes and tumor purity,tumor microenvironment score,clinical phenotype and other important indicators affecting the prognosis of gastric cancer was elaborated.2.The expression of the target gene was verified in vitro and FBN1 was screened as the subsequent target gene.Phenotypic changes incuding proliferation,apoptosis,invasion and migration of gastric cancer cells after the knockdown of FBN1 expression were detected in vitro and in vivo by CCK8,clonogenesis,Edu staining,flow cytometry,nicks assay,Transwell,Western blot and other experiments.3.Gastric cancer cells were subjected for transcriptome sequencing analysis to search for potential regulatory pathways after FBN1 expression was silenced,and then we verify the expression of key proteins in the pathways and the changes in cell biological behavior.Result:1.6 target genes(FBN1,FN1,HGF,MMP9,THBS1,VCAN)were selected.Except for MMP9,the high expression of other target genes in gastric cancer indicated a poor prognosis and a higher grade degree.It reflected that patients with stage I showed significantly low expression of FBN1,THBS1 or VCAN.2.Patients of non-silent mutation group showed higher TMB and TME scores,and patients with copy number variant of target genes showed higher tumor purity,lower immune score and lower stromal score.3.Mutations or copy number variations of target genes can affect one or more classic carcinogenic signaling pathways.4.FBN1 and VCAN showed the same expression trend by the three validation methods,and both of them showed high expression in gastric cancer.Moreover,FBN1 was selected as the target gene for subsequent studies due to the greater differential expression detected by qRTPCR and transcriptome sequencing.5.It showed that the expression of FBN1 was higher compared with that in adjacent tissues,and patients with high FBN1 expression had relatively poor clinical staging and prognosis.Biological behavior experiments showed that the apoptotic progress of GC cells was promoted,while the ability of proliferation,invasion and migration of gastric cancer cells decreased significantly after knocking down the expression of FBN1.6.Enrichment analysis of the differential genes got after knocking down FBN1 shows that they were mainly involved in the adhesion and junction between cells,and enrichment in the pathways related to protein synthesis and regulation.7.Western blot showed that the expression of EMT-related protein E-cadherin increased,while the expression of N-cadherin and Vimentin protein decreased after knocking down the expression of FBN1.The protein expression of TGF-?1 and P-smad3 also decreased after knocking down the expression of FBN 1.Rescue experiments show that the addition of TGF?1 cytokine can partially rescue the weakening of gastric cancer cell proliferation and invasion caused by FBN1 knockdown.8.The expression of integrin av?6 and TGF-?1 protein decreased after silencing FBN1 expression.However,the expression of TGF-?1 decreased but the expression of FBN1 protein had no significant change after silencing av?6.Conclusions:1.FBN1,FN1,HGF,MMP9,THBS1,VCAN may play an important role in the prognosis of gastric cancer by affecting tumor purity,TMB,TME scores and multiple carcinogenic pathways.2.FBN1 is highly expressed in gastric cancer tissues,and patients with high expression of FBN1 reflected more advanced clinical stage and poorer prognosis.Down-regulation of FBN 1 can inhibit the proliferation,invasion,migration and other biological functions of gastric cancer cells both in vivo and in vitro.3.FBN1 could regulates the proliferation,invasion,migration and other biological functions of gastric cancer cells through the TGF-?/Smad3 signaling pathway by affecting the expression of integrin av?6. 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