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

Background: The abnormal expression of genes in serum may be associated with early diagnosis of patients with malignant tumors. This study aimed to screen potential genes that may be associated with gastric cancer using bioinformatics methods. Methods: RNA-seq data of gastric cancers were downloaded from The Cancer Genome Atlas and Gene Expression Omnibus databases, and 1903 secretory genes were downloaded from the Human Protein Atlas 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 matrix. 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, IHC results showed that the COL4A1 protein level in gastric cancer was also higher than that in the matched paracancerous tissues. Conclusions: In this study, we found six upregulated secretory genes, including OLFM4 , CEMIP , APOC1 , CST1 , COL4A1 , and CD55 , so we speculate that these six genes may be significant DEGs for the diagnosis of gastric cancer. And COL4A1 may also play an important role in the diagnosis and prognosis of gastric cancer.