Data collection. Genes were screened base on GSE45267(https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE45267), GSE101685(https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE101685), GSE121248(https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE121248), and GSE14520(https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE14520) from GEO (http://www.ncbi.nlm.nih.gov/geo) database. Probes were converted into gene symbols based on annotations of the corresponding platform. TCGA (https://portal.gdc.cancer.gov/) containing 50 normal and 371 HCC tissues was also analysed. PAMR1 expression in liver cancer was evaluated with UALCAN (http://ualcan.path.uab.edu/) and GEPIA (http://gepia.cancer-pku.cn/) databases29,30. Correlations between PAMR1-related genes from TCGA were analyzed using cBioPortal (http://www.cbioportal)31. Gene Ontology (GO) enrichment analysis of these genes was performed with DAVID (https://david.ncifcrf.gov/home.jsp)32.
Identification of differentially expressed genes. GEO2R (https://www.ncbi.nlm.nih.gov/geo/geo2r/) is a web tool for a quick identification of differentially expressed genes (DEGs) in GEO datasets. Here, it was used to identify DEGs between HCC and healthy liver samples. A log2fold change (logFC) > 1 and adjusted P < 0.05 were cut-offs for DEGs. The top 100 DEGs from each dataset (based on adjusted p-value) were selected, and overlapped by the Venn online tool (http://bioinformatics.psb.ugent.be/webtools/Venn/) for further analysis.
Cell Culture. The human normal liver cell line QSG7701 was purchased from Beyotime Biotechnology. The human HCC cell lines Hep3B, Huh7 were purchased from Procell Life Science&Technology company. Other HCC cell lines SMMC7721、HepG2 were donated by Ming Zhao's laboratory. Cell lines were cultured in DMEM with 10% fetal bovine serum at 37°C in a 5% CO2 air atmosphere. All media and supplements were purchased from Invitrogen.
Total Rna Extraction And Quantitative Real-time Pcr
Total RNA was extracted from five cell lines (SMMC7721, HepG2, Hep3B, Huh7, QSG7701) using a total RNA extraction kit (Solarbio, Beijing, China), according to the manufacturer’s instructions. RNA was reverse-transcribed into cDNA using the PrimeScript™ RT Reagent kit. Quantitative reverse transcription PCR (qRT-PCR) was performed using SYBR Green (Bio-Rad, Hercules, CA, USA).The cDNA chip was purchased from Outdo Biotech Co., Ltd (Shanghai, China), and amplificatied in the same method. Primers for PAMR1 and GAPDH were as follows:
PAMR1 forward primer: 5′-CTTCCGATGCAGGTTCAGT-3′,
PAMR1 reverse primer: 5′-GCTGGCTTCTTGGTAGGG-3′;
GAPDH forward primer: 5′-ACAGTCAGCCGCATCTTC-3′,
GAPDH reverse primer: 5′-CTCCGACCTTCACCTTCC-3′.
Immunohistochemistry(IHC). Liver cancer tissue arrays (HLivH060CS01) were purchased from Outdo Biotech Co., Ltd(Shanghai, China). After dewaxina, antigens were retrieved under high pressure followed by rinse and endogenous peroxidases block with 3% hydrogen peroxide for 10 min. Then, tissues were incubated in normal goat serum for 15 min and anti-PAMR1 rabbit polyclonal antibody (1:50, Wuhan, China) was incubated overnight at 4°C. The next day, tissue arrays were washed and incubated with secondary antibody at 37°C for 30 min. Then, DAB was incubated for 5 min, and the tissues were coverslipped for observation under a microscope. Staining intensity was scored on the following scale: 0 (none), 1 (weak), 2 (moderate), and 3 (strong). The extent (0–100%) of reactivity was scored with five levels: 0 (< 5%), 1 (5–25%), 2 (25–50%), 3 (50–75%), and 4 (> 75%). Two pathologists independently scored the staining of each slide.
Tumor immune estimation resource analysis. The Tumor Immune Estimation Resource (TIMER) (http://cistrome.org/TIMER/)33 was used to evaluate the correlation between PAMR1 expression level and the abundance of infiltrating immune cells (CD8 + T cells, CD4 + T cells, B cells, dendritic cells, macrophages, and neutrophils), as well as tumor purity in HCC.
Gene set enrichment analysis (GSEA). GSEA version 4.2.1 (http://www.gsea-msigdb.org/gsea/downloads.jsp) is a computational method based on the entire gene expression matrix34. The cases in TCGA-LIHC cohort was separated into PAMR1-low and PAMR1-high subgroups with median PAMR1 level as the cut-off point. Reference gene sets were H.all.v7. 2.symbols.gmt gene sets (Hallmarks) from MSigDB35. Each analysis required at least 100 times permutation tests. An adjusted P < 0.05 and normalized enrichment score (NES) > 2 were considered as significant enrichment.
Statistical analysis. Survival curves were calculated with the Kaplan-Meier method with log-rank tests. Data from all experiments were analyzed with unpaired t-tests or one-way ANOVA in GraphPad Prism 8 (GraphPad, San Diego, CA, USA). The receiver operating characteristic (ROC) curve analysis was performed by pROC packages in R sofware, version 3.6.3. P < 0.05 was defined as significance.