2.4 Functional enrichment analysis
Gene ontology (GO) is a tool used for gene annotation that functions through the utilization of a defined, structured, and controlled vocabulary, including 3 categories, namely biological processes (BP), cellular components (CC), and molecular functions (MF) (Ashburner et al., 2000). The Kyoto Encyclopedia of Genes and Genomes (KEGG) is a database used to assign sets of DEGs to specific pathways (Kanehisa and Goto, 2000). The Database for Annotation, Visualization, and Integrated Discovery (DAVID) (https://david.ncifcrf.gov/) is an online database that offers gene enrichment analysis and functional annotation clustering from various genomic resources (Huang et al., 2009). GO and KEGG pathway analysis on significant DEGs was conducted using the DAVID database. The species selected was Homo sapiens , and the ”adjusted P value < 0.05” was considered to be of statistical significance.
2. 5 Analysis of protein‐protein interaction (PPI) networks
The Search Tool for the Retrieval of Interacting Genes/Proteins (STRING) (https://string-db.org/cgi/input.pl) is an online database, which can predict interactions of proteins by neighborhood, gene fusion, co-occurrence, co-expression experiments, databases, and text-mining (Szklarczyk et al., 2015). Significant DEGs were mapped into PPIs and a combined score of >0.4 was set as a threshold value in this study. More specifically, nodes with higher degrees of interaction were considered as hub nodes.