Fibroblast activation protein promotes progression of hepatocellular carcinoma via regulating the immunity.

Fibroblast activation protein (FAP) has been indicated to express in cancer-associated fibroblasts (CAFs) in most cancers. This work was dedicated to exploring FAP's effects on hepatocellular carcinoma (HCC). The data were extracted from The Cancer Genome Atlas, Gene Expression Omnibus, ImmPort, and Reactome databases. The correlation between FAP and HCC patients' prognosis was explored via survival analysis. The qRT-PCR and western blot analysis were used to analyze the FAP mRNA and protein expression levels, respectively. The cell proliferation and apoptosis were determined using the cell counting kit-8 assay kit and Annexin V-FITC/PI apoptosis kit, respectively. The HCC patients with FAP overexpression displayed a worse prognosis. The FAP expression was positively associated with the infiltration levels of tumor purity, B cell, CD8 + T cell, CD4 + T cell, macrophage, neutrophil, and dendritic cell. The optimal nine immune related genes were screened between two groups (FAP high vs. low). Moreover, we identified 24 energy metabolism related genes (FAP high vs. low) and these 24 genes were highly expressed in the high FAP expression group. The FAP expression had a significant positive correlation with the expression of PD-1, CTLA4, PDL-1, and PDL-2. The FAP overexpression promoted proliferation and migration while inhibiting the apoptosis of HCC cells. The FAP overexpression promoted the progression of HCC by regulating the immunity to affect the prognosis of HCC patients, thereby serving as a poor prognostic marker for HCC patients.