| Objective:Colon cancer is on the list of top lethal gastrointestinal tumors,and the most common subtype of it is colon adenocarcinoma(COAD).Recently,imbalances of the immune system have been verified to be of significance in the development of cancer.And in clinical practice,the efficacy of immunotherapy has gradually been confirmed.In this study,we are intended to establish an immune-related risk model that can predict the prognosis of colon cancer patients,and identify potential therapeutic targets for colon cancer,so that to provide new ideas for the diagnosis and treatment of colon cancer.Methods:1.Clinical data and gene expression data of COAD patients were downloaded and extracted from the Cancer Genome Atlas(TCGA)database.2.All differentially expressed genes were identified by Wilcoxon test.Then,the differentially expressed matrixes of immune-related genes were extracted.3.Differentially expressed immune-related genes,which were associated with patients’prognosis,were identified by Kaplan-Meier analysis and univariate Cox regression analysis.4.The function of immune-regulated genes which were prognosis-associated was explored by the Gene Ontology(GO)and Kyoto Encyclopedia of Genes and Genomes(KEGG)functional enrichment analysis.5.The prognostic risk model was constructed through multivariate Cox regression analysis.The AIC(Akaike information criterion)method was utilized to select the best model,taking the model with the lowest AIC value as the target model.6.Kaplan-Meier analysis and receiver operating characteristic curve(ROC curve)were used to verify the accuracy and reliability of the model.7.The univariate and multivariate Cox regression analysis were utilized to assess whether risk score could act as an independent prognostic factor.8.The correlation analysis was used to study the relationship between the expression level of the signature gene and clinicopathological characteristics.9.The associations between the risk score and immune cells in the immune microenvironment was studied through correlation analysis.10.The expression of STC1 was inhibited by transfecting the lentivirus,and the interference efficiency was tested by Real-time PCR technology.11.The effect of STC1 expression level on colon cancer cell proliferation was detected by MTT assay.12.The effect of STC1 expression level on colon cancer cell migration ability was validated through wound healing assay.13.GTEx(Genotype-Tissue Expression)database was used to analyze the distribution of STC1 in normal human tissues and organs.Results:1.A total of 484 differentially expressed immune-related genes(311 down-regulated and 173 up-regulated)were identified(fold change>2,false discovery rate<0.05).2.22 differentially expressed immune-related genes were found to be related to prognosis of CO AD patients(Kaplan-Meier survival analysis met P<0.05;univariate Cox regression analysis met HR>1or<1,P<0.05).3.Functional enrichment analyses indicated that the products of 22 immune-regulated genes were mainly enriched in the extracellular region,could bind to receptors on the cell surface,and participated in inflammatory reactions.The most significant pathway that they may participate in was cytokine-cytokine receptor interactions(P<0.05).4.The prognostic risk model containing 9 immune-related genes was screened out(has the smallest AIC value).Risk scores were calculated.5.The prognosis of patients in the high-risk group is significantly worse than that in the low-risk group(P<0.05).The ROC curve shows the accuracy and reliability of the model(Area under the curve>0.7).6.Multivariate Cox regression analysis showed that the risk score could be used as an independent prognostic factor(HR>1,P<0.05).7.The expression levels of 5 signature genes in the prognostic risk model were related to the depth of tumor invasion,lymph node metastasis,distant metastasis,tumor stage and other factors,relatively.8.The risk score was positively correlated with neutrophils,CD4+ T lymphocytes,CD8+T lymphocytes,macrophages,and dendritic cells infiltrated in the immune microenvironment(correlation coefficient>0 and P<0.05)9.The proliferation and migration ability of colon cancer cells can be inhibited when the expression level of STC1 was decreased.10.STC1 is widely distributed in normal human tissues,and its expression is tissue-specific(relatively low in intestinal tissues,and significantly high in thyroid,pituitary,and other tissues).Conclusion:The immune-related prognostic risk model established in this study could be used to identify high-risk colon adenocarcinoma patients and guide clinical treatment.Nine signature genes in the model(FABP4,CHP2,IGHV3-64,GCG,GUCA2A,CD1B,CXCL3,STC1,and OXTR)might be involved in the evolution of colon adenocarcinoma.In addition,preliminary studies in this paper indicated that down-regulating the expression of STC1 could inhibit the proliferation and migration ability of colon cancer cells,and STC1 could be used as a therapeutic target for colon adenocarcinoma.However,STC1 is widely distributed in human tissues and organs,and its expression is tissue-specific.It is necessary to further explore immune-related adverse reactions that may occur if it is used as a therapeutic target. |
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