Although the diagnosis, prognosis prediction, and treatment strategies of HCC have made great progress, hepatocellular carcinoma remained to be the major cause of cancer death worldwide[23–25]. At the same time, the PI3K/AKT/mTOR signaling pathway acted as a key cellular signaling pathway associated with the appearance of several human cancers. The inhibitors of the PI3K/AKT/mTOR signaling pathway were thoroughly studied and evaluated in clinical trials in human cancers. It had been suggested that PI3K/AKT signaling pathway associated genes can serve as the potential biomarkers for the development of numerous human cancer. However, few studies mentioned the prognostic value of PAGs in HCC. Some research indicated constructing the early predictive model for prognosis in human cancer is necessary, and the different therapeutic strategy should be formulated according to different prognosis of patients[30, 31]. Currently, an opinion had been recommended that clinicopathological characteristics can be employed to predict prognosis of patients, but some studies highlighted that clinicopathological characteristics can’t provide adequate evidence for accurate prognostic evaluation[32, 33]. Thus, we constructed a novel prognostic signature based on the PI3K/AKT signaling pathway associated genes in HCC. Recent studies have shown that the immune escape and tolerance can be mediated through various signaling pathways in tumor microenvironment. Hence, the association between constructed prognostic signature and immune infiltration was also determined.
In this study, we developed a 4-gene prognostic signature based on TCGA database. The prognostic value and accuracy of constructed prognostic signature were further validated in GSE14520 dataset and ICGC database. First of all, the mRNA sequencing data and corresponding clinical information were downloaded from the TCGA database, and 105 PAGs were obtained from GSEA online website. Subsequently, 9 upregulated PAGs were screened out from 374 HCC tissue samples and 50 normal tissue samples. The GO and KEGG enrichment analysis were further employed to investigate the biological processes correlated with the upregulated PAGs. The PPI network was utilized to exhibit the connection between encoded proteins, and the hub genes (HRAS, MAPK8, PTEN, NGF, GRB2, RAC1, EGFR, MAPK1, AKT1 and GSK3B) were screened out in the PPI network. The univariate and multivariate Cox regression analyses were employed to identify the differently expressed genes associated with the prognosis of patients. We developed the prognostic signature based on the 4 PAGs. The independent prognostic value of 4-gene-signature was identified by univariate and multivariate regression analyses. The KM curve showed the low-risk cohort had the higher survival probability in comparison to the high-risk cohort. The area under the ROC curve indicated the 4-gene-signature had a larger prognostic value compared with other clinicopathologic characteristics. The consistent results were obtained in the GSE14520 dataset and ICGC database. Ultimately the nomogram was created to accurately predict the 1-year, 3-year, and 5-year overall survival rates in HCC. The risk score was correlated with the infiltration of monocytes and macrophages M0 in HCC, and the expression levels of common immune checkpoints (PDCD1, CTLA4, TIM3 and TIGIT) was associated with the risk score.
It was proved that immunosuppressive microenvironment enhanced the evasion and immune tolerance in HCC. HCC is a type of malignant tumor accompanied by chronic liver inflammation and liver cirrhosis, some HCC cases expressed gene markers indicating the existence of immune response, which provided a novel insight into immunotherapy in HCC. Our results showed the immune infiltration of monocyte and macrophages M0 were higher in high-risk group, which had poorer survival in HCC. Tumor associated macrophages (TAMs) are essential elements in HCC microenvironment and lead to the poor survival in HCC patients. TAMs obtained the immunosuppressive function to regulate the tumor microenvironment as they grow from monocytes to macrophages. Current studies even reported that macrophages were the most common immune cells in tumor tissues and it induced the invasion, proliferation and metastasis in tumor cells, it also mediated the immune tolerance in tumor microenvironment[38–40]. We further calculated the correlation between the risk score and several common immune checkpoints including PDCD1(PD-1), PDL1, PDL2, CTLA4, TIM3, LAG3, TIGIT and CD96. And the results showed the expression levels of PDCD1, CTLA4, TIM3 and TIGIT were associated with risk score. Some research indicated that anti-PD-1 and anti-CTLA4 antibodies tended to be the effective clinical therapeutic targets in HCC, and PD-1 inhibitor (nivolumab ) can stimulate the specific immune response with controllable side effects in tumor. However, the response to immune checkpoints in HCC was different among various organs. Our results hinted that our risk score can revealed the expression of immune checkpoints and explained why the efficacy of anti-immune checkpoints was low in some HCC patients. The four-gene-signature has potential to predict the immunotherapeutic efficacy of PD-1, CTLA4, TIM3 and TIGIT, and directs immunotherapeutic strategy in HCC.
Previous research had pointed out the crucial role of PRKAA2 in human cancers. PRKAA2 functioned as a member of heterotrimeric AMP-activated protein kinase (AMPK) complex, and was reported to be involved in the p53 and mTOR signaling pathways in carcinogenesis of human cancers. In our study, PRKAA2 was identified as the PAG and determined its prognostic value. Current studies indicated that MiR-4999-5p can promote the cell growth and glycolysis by targeting PRKAA2 in colorectal cancer, and PRKAA2 was also dysregulated in cervical cancer cells and had potential to be the prognostic biomarker in cervical cancer. Some research had likewise suggested that metformin suppressed the proliferation of HCC cells by targeting miR-378/CDK1 axis. The inhibition of CDK1/PDK1/β-Catenin pathway can improve the therapeutic effect of sorafenib and suppress the proliferation of HCC cells. SNHG16 activated the let-7b-5p/CDC25B/CDK1 axis to influence the G2/M transition resulting in the accelerating progression of EMT and cell metastasis. Circular RNA (circ-ADD3) suppressed the metastasis of HCC cells through the ubiquitination mediated by CDK1. We therefore can summarize that CDK1 was an important regulatory factor in the carcinogenesis of HCC. PITX2 also plays a carcinogenic role in several human cancers. The overexpression of PITX2 can induce the letrozole-resistance in breast cancer cells, and it also participated in the progression of ovarian cancer by promoting the proliferation and invasion of ovarian cancer cells. The methylation of PITX2 also served as a prognostic biomarker in colorectal cancer, and it was reported to mediate proliferation and invasion of colorectal cancer cells in vitro experiment. In human gliomas, SFN was reported to be the potential prognostic biomarker, and it provided great prognostic value in the progression of esophageal squamous cell carcinoma. The overexpression of SFN was correlated with the poor prognosis in ovarian cancer and pancreatic ductal adenocarcinoma[57, 58].