Research paperIdentification of biomarkers associated with diagnosis and prognosis of colorectal cancer patients based on integrated bioinformatics analysis
Introduction
Colorectal cancer (CRC) is one of the most common cancers with high morbidity and mortality worldwide. Nearly 1.4 million new cases of CRC and 700,000 CRC-related deaths were reported each year in the world (Torre et al., 2015). Brenner et al. (2014) found that the 5-year survival rate of CRC patients was >90% when diagnosed at early stages. Due to the lack of adequate diagnostic methods, CRC is often diagnosed at an advanced stage. Despite the significant improvements in diagnosis and treatment, the 5-year survival rate for CRC patients diagnosed with metastatic is still low at approximately 12% (Siegel et al., 2015). Thus, it's urgently needed for understanding the molecular mechanisms of CRC development and identification of novel biomarkers are used for the early detection and prognosis evaluation of CRC.
Over the past decades, developing of molecular biology has increased our understanding of the pathogenesis of CRC. Previous researches have indicated that CRC is a genetic disease, which depends on alteration of numerous of oncogenes and tumor suppressor genes (Bogaert and Prenen, 2014). A growing number of genes and their coding proteins related to CRC have been explored. Previous studies revealed that they play crucial roles in a large number of physiological and pathological processes including cell proliferation, differentiation, apoptosis, and metastasis (Hisamuddin and Yang, 2006; Testa et al., 2018). However, the precise molecular mechanisms of CRC are still far from being deep understood. Recently, several studies have discovered a group of CRC related candidate genes by bioinformatics analysis. For example, Huang et al. (2018) identified hundreds of CRC associated differentially expressed genes (DEGs) based on the Gene Expression Omnibus (GEO) and The Cancer Genome Atlas (TCGA) database, and five genes of which can used as diagnostic biomarkers for CRC patients. Hou et al. (2018) found a collection of DEGs and DNA methylation aberrations in CRC. Their results indicated that the combination of DEGs, DNA methylation aberrations, and tumor stages result in more effective prognostic evaluation of patients with CRC. In addition, lncRNAs and the associated regulatory network consisting of transcription factors, microRNAs, mRNAs, and RNA-binding proteins could also be identified using bioinformatics analysis (Zhang et al., 2018). But it is still paramount to find more potential biomarkers for effective diagnosis and prognosis assessment of CRC patients.
In this study, we downloaded large-scale gene datasets regarding CRC from GEO and TCGA databases. After integrated analysis of both two databases, we identified 10 hub genes from the common DEGs by constructing protein-protein interaction (PPI) network. The results of receiver operating characteristic (ROC) curves showed that the top 10 hub genes had high diagnostic values for patients with CRC. Then, we conducted a gene signature for prognosis of CRC patients by univariate and multivariable Cox regression analyses, which performed well in predicting overall survivals of CRC patients.
Section snippets
Data collection
Series matrix files of GSE32323, GSE74602, and GSE113513 were downloaded from the GEO (http://www.ncbi.nlm.nih.gov/geo/) database. The platforms they based on were GPL570 (Affymetrix Human Genome U133 Plus 2.0 Array), GPL6104 (Illumina humanRef-8 v2.0 expression beadchip), and GPL15207 (Affymetrix Human Gene Expression Array), respectively. The datasets of GSE32323 contained 17 cancer tissues and paired adjacent non-cancerous tissues. The datasets of GSE74602 comprised 30 paired normal and
Identification of DEGs in CRC
In the present study, 1445 DEGs in GSE32323, 1484 DEGs in GSE74602, 1284 DEGs in GSE113513, and 2150 DEGs in TCGA were identified. Among the DEGs, 700, 815, 511, and 1205 genes were upregulated while 745, 669, 773, and 945 genes were downregulated in GSE32323, GSE74602, GSE113513, and TCGA, respectively (Fig. 1A). We used Volcano Plots to visualize the DEGs in different studies. Red dots represent the upregulated genes and green dots represent the downregulated genes. The consistently
Discussion
In this study, we integratedly analyzed three microarray datasets from GEO and RNA sequencing data from TCGA. A total of 207 DEGs consisting of 57 upregulated DEGs and 150 downregulated DEGs were identified between CRC tissues and normal tissues. The functional enrichment analyses demonstrated that the DEGs were enriched in some biological processes such as EMC organization, angiogenesis, cell adhesion, cell differentiation, and cell migration. The results consistent with previous knowledge
Acknowledgments
This study was supported by the Zhejiang Provincial Natural Science Foundation of China (No. LY16H160004) and Natural Science Foundation of Ningbo (No. 2018A610381). The authors thank the contributors of the TCGA (https://tcga-data.nci.nih.gov/) database and GEO (http://www.ncbi.nlm.nih.gov/geo/) database for sharing their data on open access.
Conflict of interest
The authors declare that they have no conflict of interest.
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Feng Xu and Xianpeng Li are co-corresponding authors of this work.