LIHC remains one of the most malignant cancers with poor prognosis. WGCNA has been used to explore biomarkers related to pathogenesis, diagnosis and prognosis of LIHC. Immune cell infiltration related biomarkers in LIHC including CCL5, CXCR6, CD3E and LCK were identified using WGCNA(Bai et al., 2020). Another study found that 13 hub genes (GTSE1, PLK1, NCAPH, SKA3, LMNB2, SPC25, HJURP, DEPDC1B, CDCA4, UBE2C, LMNB1, PRR11, and SNRPD2) had high correlation with histologic grade in LIHC by analyzing TCGA LIHC dataset(Gu et al., 2020). While our study provides a more comprehensive and innovative idea from various sources of data.
WGCNA, a robust and reliable search tool for large-scale data analysis, was used to find effective biological mechanisms and key genes from gene expression microarrays in this study. By comprehensive bioinformatics analysis, a total of 68 significant DEGs were identified in TCGA-LIHC and GSE54236 datasets. Besides, the genes were clustered mostly in the functional set associated with complement activation, collagen trimer, receptor ligand activity, cytokine−cytokine receptor interaction. The complement system is an ancient defense mechanism preceding adaptive immunity, and complement activation is an important component of tumor-promoting inflammation(Afshar-Kharghan, 2017). Chronic infection with HBV or HCV is main risk for LIHC, and tumor-promoting effect of complement activation plays a role in the progression of inflammation to tumor. Cytokine relevant pathways and ligand-receptor relevant pathways participate in the pathogenesis of early-stage LIHC. Collagen is a major component of the extracellular matrix (ECM), collagen trimer is a biomarker of cancer metastasis (Xu et al., 2019). By PPI network construction, 10 hub genes including CFP, CLEC1B, CLEC4G, CLEC4M, FCN2, FCN3, LYVE1, MARCO, PAMR1, TIMD4 were identified. The expression of these 10 hub genes in LIHC was down-regulated compared with the normal control group. The down-regulated expression of CFP, CLEC1B, FCN3 and TIMD4 was significantly correlated with poor OS and DFS of LIHC. Through the study of TIMER, we found that the 10 hub genes were mainly expressed in LIHC cells instead of immune cells, and were absent in the immune regulation of tumor microenvironment. These findings may support CFP, CLEC1B, FCN3 and TIMD4 as new therapeutic targets of LIHC and may contribute to the assessment of prognostic biomarkers.
In our study, CFP, CLEC1B, FCN3 and TIMD4 were down-regulated in LIHC tissues compared with normal tissues, and could be strong predictors of poor outcome in LIHC. The relationship between the four genes and cancer has been confirmed by several previous studies. CFP (Complement Factor Properdin) is a protein coding gene, and can positively regulate the alternative complement pathway of the innate immune system yielding the elimination of pathogens, apoptotic and necrotic cells (Kemper, Atkinson, & Hourcade, 2010; Kemper, Mitchell, Zhang, & Hourcade, 2008). Several studies reported the tumor suppressive effect of CFP on melanoma, breast, stomach and lung cancer(Al-Rayahi, Browning, & Stover, 2017; Block et al., 2019; Cui et al., 2021). In stomach and lung cancer, the expression level of CFP was lower than in normal tissues, and low expression level of CFP was associated with poor prognosis (Cui et al., 2021). CLEC1B (C-type lectin domain family 1 member B) is a novel platelet-associated molecule secreted by activated platelets around tumors(Meng, Luo, & Liu, 2021). CLECB1 has been confirmed its inhibitory effect on platelet aggregation and tumor metastasis in colon cancer (Suzuki-Inoue et al., 2007). CLEC1B has been reported to be significantly down-regulated in liver cancer (Critelli et al., 2017). FCN3 (Ficolin 3) is a secreted lectin that activates the complement pathway (Endo, Matsushita, & Fujita, 2011). FCN3 expression was significantly down-regulated in lung cancer tissues compared with matched normal lung tissues, low expression levels of FCN3 have been described as prognostic biomarker for cancer (Jang et al., 2021). TIMD4 (T cell immunoglobulin and mucin domain containing 4) is a phosphatidylserine receptor that enhances the engulfment of apoptotic cells, and is involved in regulating T-cell proliferation and lymphotoxin signaling (Freeman, Casasnovas, Umetsu, & DeKruyff, 2010). As opposed to LIHC, TIMD4 is overexpressed in lung cancer and colorectal cancer, which is correlated with poor prognosis (Dorfman, Hornick, Shahsafaei, & Freeman, 2010; Tan, Zhang, Yao, & Shen, 2018).
We admit that this study has some limitations and deficiencies. First, this research mainly focuses on data mining and data analysis based on methodology, and the results have not been verified by experiments. Further experiments are needed to better confirm the findings of this study. Our research also has certain limitations for the classification of different subtypes of tumors. Although our comprehensive bioinformatics analysis identifies potential diagnostic genes for LIHC, it may be biased for patients with different LIHC subtypes.
By WGCNA and other analytical methods (GO, KEGG, PPI network, survival analysis and TIMER), the current study suggests that CFP, CLEC1B, FCN3 and TIMD4 may be novel potential molecular targets for prognosis prediction in LIHC for the first time.