2.1 Materials and patients:
CDK1 and RRM2 Antibodies purchased from SAB company, China; Immunohistochemical kit and DBA color developing solution purchased from BOSTER Biological Technology co.ltd, China. 71 cases of primary HCC and matched para-cancer tissues were collected between 2013 and 2015 from the Affiliated Hospital of North Sichuan Medical College. The study was approved by the Ethics Committee of Affiliated Hospital of North Sichuan Medical College.
2.2 Microarray data information:
We selected gene expression profiles GSE101685、GSE112791、GSE62232、GSE45267 from GPL570 platform ([HG-U133_Plus_2] Affymetrix Human Genome U133 Plus 2.0 Array) from NCBI-GEO, is a free public gene database(http://www.ncbi.nlm.nih.gov/geo); Organism: Homo sapiens; Experiment type: Expression profiling by array. The microarray contains 336 HCC cases and 72 cases of para-cancerous tissue, and was published in 2019 or 2014, including Asian and European-American (Table1).
2.3 Data processing and screening of DEGs:GEO2R(http://www.ncbi.nlm.nih.gov/geo/geo2r) is an important online tool in NCBI-GEO for comparing two or more datasets to identify DEGs. We compared cancer tissue and para-cancerous tissue DEGs in gene profile datasets GSE101685, GSE112791, GSE62232 and GSE45267 respectively by GEO2R. Defined those with logFC (fold change)>2 and adj. P-value < 0.05 as Up- regulated DEGs and those with logFC (fold change)<-2 and adj. P-value < 0.05 as Down-regulated DEGs. Then Venn online software was used to screen the co-expressed DEGs in the four profiles.
2.4 Gene ontology and KEGG pathway enrichment analysis:
The Database for Annotation, Visualization and Integrated Discovery (DAVID,http://david.ncifcrf.gov) (version 6.8)(8) is an integrated biological knowledgebase and analytic tool aimed at systematically extracting biological meaning from large gene/protein lists. Gene ontology(9) is a comprehensive resource of computable knowledge regarding the functions of genes and gene products. KEGG(10) is a reference knowledge base for biological interpretation of genome sequences and other high-throughput data. In this study, we selected and analyzed the biological processes (BP), molecular function (MF), cell component (CC) and KEGG pathway enrichment of DEGs in David website. P-Value<0.05 was considered statistically significant.
2.5 PPI network and module analysis:
STRING(http://string-db.org) (version 11.0)(11) online database aims to collect, score and integrate all publicly available sources of protein-protein interaction information, and to complement these with computational predictions. Cytoscape(12) is network biology analysis and visualization tools. MCODE is an APP of Cytoscape for finding densely connected regions from PPI networks. In this study, PPI network of DEGs was drawn by STRING and Cytoscape, the most significant hub module in the PPI networks was identified by MCODE.
2.6 Survival analysis and RNA sequencing expression of Hub genes:
UALCAN(13) is an interactive web-portal and user-friendly tool to perform in-depth analyses of TCGA gene expression data. GEPIA (Gene Expression Profiling Interactive Analysis)(http://gepia.cancer-pku.cn)(14) web server is a valuable resource for gene expression analysis based on tumor and normal samples from the TCGA and the GTEx databases. We used UALCAN to obtain the survival analysis results of hub genes. And the RNA sequencing expressions of Hub genes in cancer tissues and paracarcinoma tissue were analyzed with GEPIA. P-Value<0.05 was considered statistically significant.
2.7 Re-analysis core genes via KEGG pathway enrichment:
Hub genes associated with poor prognosis and high expressions in cancer tissues were selected and named as core genes, which were identified by KEGG pathway enrichment analysis with DAVID.
2.8 Immunohistochemical analysis
Immunohistochemical(IHC) staining was used to detect the expression and localization of CDK1 and RRM2 in 71 HCC tissues and matched para-cancer tissues. Then, to follow up the 5-year overall survival rate, and analysis of the correlation between age, gender, tumor size, AFP, AST, ALT, etc. and key genes.
Paraffin section was deparaffined in xylene for 30 min three times at 37℃, hydrated in a series of 100, 95, 90, 85and 80% ethanol solutions, oxidize in 3% hydrogen peroxide solution for 30 min and washed in phosphate-buffered saline (PBS) for 2 min six times. The antigen was recovered in boiling sodium citrate buffer (10mmol/L, pH=6.0) for 5 min. Then the sections were cooled down to room temperature, BSA blocks unwanted antigenic sites for 30 min at 37℃, incubated with anti-CDK1 and anti-RRM2 monoclonal antibody (dilution 1:100) overnight at 4˚C. After washing with PBS, the slides were incubated with SABC for 30 min at 37˚C, DAB staining solution was used to dye the slides for 5 min and hematoxylin for counterstaining the nuclei for 1 min. The sections were then dehydrated in ethanol, coverslips were placed on the slides. Evaluation of immunohistochemical staining: staining included the intensity of staining (scored as: 0, no staining; 1, weak staining; 2, moderate staining; and 3, strong staining) and the percentage of positive tumor cells (scored as: 0, <5%; 1, 5-25%; 2, 26-50%; 3, 51-75%; and 4, 76-100%). Staining intensity and frequency were transformed into a Composite Expression Score (CES) (The formula: CES = Intensity×Frequency). The range of CES was from 0 to 12, according to the score definition that: 0-6, low expression; 7-12 high expression. These scores were independently determined by three senior pathologists. Images of sections were captured using an Olympus (100X-200X) microscope (Olympus, Tokyo, Japan).
2.9 Statistical analysis:
Data and figures were processed via GraphPad Prism7.0 software and IBM SPSS25. Comparisons of CDK1, RRM2 gene expression were performed with independent samples t-test, or using one-way of ANOVA and Bonferroni's multiple comparison tests. Correlation between the CDK1, RRM2 expression and clinicopathological features was detected with chi-square test. Kaplan-Meier and Cox regression model analyze are used to analysis the associated overall survival and clinicopathological factors. p-value< 0.05 was considered statistically significant.