Identifying Diagnostic and Prognostic Differentially Expressed Genes of Gastric Cancer Based on Bioinformatics Analyses of RNA-seq Data.

Background: The abnormal expression of genes in serum may be associated with early diagnosis of patients with malignant tumors. This study was designed to screen for significantly differentially expressed genes (DEGs) that may be associated with gastric cancer using bioinformatic methods. Methods: RNA-seq data from gastric cancers were downloaded from the TCGA and GEO databases, and 1903 secretory genes were downloaded from the HPA database. The diagnostic secretory RNAs of gastric cancer were screened using least absolute shrinkage and selection operator regression analysis. Univariate Cox regression analysis was used to evaluate the prognostic significance of the results. Biological functions were performed using gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Then, 640 cases of gastric cancer and paracancerous tissues were collected, and immunohistochemistry (IHC) was used to detect the expression of COL4A1 . Results: In total, 25 upregulated differentially expressed genes (DEGs) were identified, which were secreted mainly in the blood and cell matrices. Six secretory genes ( OLFM4 , CEMIP , APOC1 , CST1 , COL4A1 , and CD55 ) with diagnostic significance were identified, and the enrichment scores of these six genes were significantly associated with tumor stage. In addition, we found that increased COL4A1 expression might be associated with a poor prognosis in patients with gastric cancer. Based on GO and KEGG analyses, we found COL4A1 -related DEGs were mainly enriched in connective tissue development, collagen fibrous tissue-related processes, extracellular structure, extracellular matrix (ECM) tissue, and related to the ECM receptor-related pathway, focal adhesion, and PI3K-Akt signaling pathway. Moreover, the results of immunohistochemical analyses showed that the COL4A1 protein level in gastric cancers was also higher than in the matched paracancerous tissues. Conclusions: In this study, we found six upregulated secretory genes, including OLFM4 , CEMIP , APOC1 , CST1 , COL4A1 , and CD55 which we hypothesized to be significant DEGs for the diagnosis of gastric cancer. Our data also suggest that COL4A1 may play an important role in the diagnosis and prognosis of gastric cancer.