Circ0007707/miR-429/PDGFD Pathway Regulates Progression Of Gastric Cancer By Modulating Immune-gene Signature

Objective:The relationship between competing endogenous RNA（ce RNA）networks and gastric adenocarcinoma has been extensive discussed in these years,but the connection between ce RNA networks and the tumor immune microenvironment is unclear.This study aimed to explore how ce RNA networks influence the development and prognosis of gastric cancer by regulating the immune microenvironment.Methods:The differential expression profiles of circular RNAs（circ RNAs）,micro RNAs（mi RNAs）and m RNAs were acquired from the Gene Expression Omnibus（GEO）.The micro RNA（mi RNA）binding sites of the circ RNAs and mi RNA target genes were determined by Circular RNA Interactome web tool and Target Scan.Prognostic genes of gastric cancer were gained from The Cancer Genome Atlas（TCGA）and ce RNA networks were established by Cytoscape.QRT-PCR and western blot assay were utilized to detect how the ce RNA network regulates the expression of the hub gene.In addition,the TISIDB and TIMER database were utilized to evaluate the connection between hub gene and immunotherapy,the immune genes that co-expressed with hub gene were obtained from TISIDB.Furthermore,through Univariate Cox regression analysis and multivariate Cox regression analysis,the immune-gene signature was constructed.Moreover,the nomogram was constructed according to the immune-gene signature.Results:（1）49 circ RNAs differentially expressed in gastric cancer were identified from the GSE89143 dataset,192 differentially expressed mi RNAs were identified in the GSE63121 dataset,and 114 m RNAs differentially expressed in gastric cancer were obtained in the GSE118916 dataset.And through the cancer-specific circ RNA database,the target mi RNAs of 47 differentially expressed circ RNAs were predicted.A total of1541 mi RNAs were found.By comparing with the differentially expressed mi RNAs in gastric cancer,39 differentially expressed targeted mi RNAs in gastric cancer can be obtained.We identified 17,600 m RNAs associated with 39 target mi RNAs through the Target Scan database,and finally identified 104 m RNAs that could bind to mi RNAs and were highly correlated with gastric cancer.（2）2483 immune genes were collected through IMMPORT（www.immport.org）.349 immune genes from The Cancer Genome AtlasStomach Adenocarcinoma（TCGA-STAD）have been shown to differ in gastric cancer tissues.Finally,by comparing with 104 mi RNA target genes,the roles of 10 mi RNA target immune genes in gastric cancer were determined.And through Cytoscape,a ce RNA network of 8 circ RNAs,6 mi RNAs,and 8 immune genes was constructed.In addition,among the eight immune genes,PDGFD was the only gene involved in the prognosis of gastric cancer.（3）When Circ-0007707 was overexpressed,the expression level of mir429 was significantly decreased and the expression of PDGFD was significantly increased in AGS cell lines.It is suggested that circ-0007707 can be adsorbed to mir429 to control the expression of PDGFD in gastric cancer.（4）Through Western Blot and Kaplan-Meier survival analysis,it was determined that the expression level of PDGFD in cancer tissues was higher,and the patients with higher PDGFD expression had a poorer prognosis.（5）597 PDGFD-related genes were stabilized through the Cancer Cell Line Encyclopedia database.GO enrichment analysis and KEGG pathway analysis showed that PDGFD was highly correlated with the metabolic pathways and gene functions associated with tumor development.（6）Analysis by ss GSEA.We found a significant correlation between B cell receptor signaling and PDGFD.In addition,through the TIMER database,we further confirmed that PDGFD can regulate immune infiltration in gastric cancer.Various immune cells（naive B cells,plasma cells,T cells CD4 memory,T cells follicular helper cells,monocytes,macrophages M0 and M1,dendritic cells,mast cells,neutrophils）are associated with PDGFD show corresponding trends.（7）In TISIDB,the expression of PDGFD was higher in TGF-B subtype,suggesting that PDGFD may act as an immunomodulator of TGF-B subtype.And multiple immune molecules have been found to be associated with PDGFD,which acts as a type III receptor tyrosine kinase.It provides a new direction for exploring the effect of PDGFD on gastric cancer immunotherapy.（8）Through Cox regression analysis,a gene chip composed of gastric cancer prognosis genes CXCR4 and TAP1 was obtained.（9）Based on the median of risk scores,CXCR4 and TAP1 showed opposite expression trends in high-risk and low-risk groups.The two risk groups differed significantly in tumor size and presence of distant metastases.Survival analysis showed that as risk increased,so did patient mortality.（10）The ROC curve showed that the gene chip has obvious value in predicting the prognosis of gastric cancer patients.（11）A nomogram was constructed to predict 1-,3-,and 5-year overall survival in gastric cancer patients.The C-index of this nomogram was 0.776（se= 0.028）,which supports the certain feasibility of our nomogram for predicting the survival status of GC patients.In addition,the results of Cox regression analysis further revealed the importance of gene signatures as relatively independent prognostic factors for gastric cancer.Conclusions:The circ0007707/mi R-429/PDGFD pathway may involve in the progress of gastric cancer through intervening the tumor microenvironment,and the PDGFDrelated gene signature could be used a meaningful prognostic factor for gastric cancer and may instruct the immunotherapy programs.