In the past few years, a large number of studies have been conducted on the initiation, diagnosis and treatment of HCC (Ayuso et al. 2018; Yang et al. 2020). At present, traditional clinicopathological features are still used as a tool to predict the prognosis of HCC (Fujiwara et al. 2018). Imaging examination is indispensable for the diagnosis of liver cancer, but the sensitivity of imaging examination will be greatly reduced due to the small lesions and insignificant symptoms of early liver cancer (Lin et al. 2016). In recent decades, among all biomarkers for the diagnosis of HCC, AFP is the most widely used and relatively reliable. Abnormal plasma AFP level is closely related to the HCC malignancy (Waldmann et al. 1974). But due to its lack of sensitivity and specificity, its results are not satisfactory in the diagnosis of early liver cancer (Wang et al. 2020). Therefore, it is urgent to find new reliable prognostic indicators to evaluate the prognosis of HCC patients.
In recent years, with the rapid development of high-throughput sequencing technology, GI-LncRNAs have been gradually identified as potential prognostic indicators (Aguilera et al. 2013; Munschauer et al. 2018). It is reported that genomic instability is one of the ubiquitous characteristics of cancer (Negrini et al. 2010; Bartkova et al. 2005; Gorgoulis et al. 2005). It also has great potential as one of the prognostic factors of HCC patients (Rao et al. 2017). In addition, aberrant expression of LncRNAs may affect cell proliferation, tumor progression or metastasis, suggesting that LncRNA may also become a new prognostic factor for HCC by affecting GI (Sanchez et al. 2018). A considerable number of researches have found that some LncRNAs are associated with gene instability, thus affecting the prognosis of cancer, such as MANCR (Tracy et al. 2018), CCAT2 (Chen et al. 2020) and NORAD (Munschauer et al. 2018). Nevertheless, it is still difficult to identify GI-LncRNAs, its significance in predicting the clinical outcome of HCC is unclear, and their potential as a new prognostic marker remains to be explored. Thus, we constructed a computational framework for identifying genome instability-related LncRNAs by combining LncRNA expression with tumor mutant phenotype.
In this study, we first obtained 88 GI-LncRNAs by comprehensive analysis of the LncRNA profile and somatic mutation downloaded from TCGA database. PCGs closely associated with LncRNAs were identified and analyzed for functional enrichment. Through KEGG and GO pathway analysis, we found that its biological process and biological pathway mainly involved small molecule catabolic process and fatty acid metabolic process, pyrimidine metabolism, purine metabolism, and folate biosynthesis. Pyrimidine metabolism, purine metabolism and folate biosynthesis are involved in DNA synthesis. Dysfunction related to DNA damage will lead to cell cycle imbalance and genomic instability (Wenzel et al. 2018). In addition, Fanconi anemia pathway is composed of a complex DNA damage signal and repair network, which is very important to prevent genomic instability (Palovcak et al. 2017).
In addition, we obtained five GI-related LncRNAs (MIR210HG, AC016735.1, AC116351.1, AC010643.1 and LUCAT1), and further explored the GI-related LncRNAs plays the role in predicting the clinical outcome of HCC patients. Based on this, GILncSig was established. Subsequently, GILncSig was used to divide the patients into two groups with high and low risk. In the training set, patients in the low-risk group survived longer than those in the high-risk group, and the independent TCGA set, testing set further validated this result. The ROC curves of GILncSig in the three groups mentioned above were respectively 0.773, 0.679 and 0.736, which means that GILncSig has excellent prognostic ability. In all HCC cohorts, we found that the number of somatic mutations was higher in the high-risk group than in the low-risk group. In addition, the expression of UBQLN4 and H2AX was significantly higher in high-risk patients than that in the low-risk patients either. UBQLN4 is an identified driver of gene instability in a variety of cancers, and its overexpression in HCC tissues leads to poor prognosis (Jachimowicz et al. 2019; Yu et al. 2020). A recent study indicated that HCC patients with high expression of MIR210HG had a worser prognosis than those with low expression (Wang et al. 2019). LUCAT1 has also been found to be directly associated with the development and progression of cancers, including HCC, and its inhibition of ANXA2 phosphorylation in hepatocellular carcinoma promotes tumorigenesis (Xing et al. 2021; Lou et al. 2019). AC010643.1 and AC116351.1 have been used as key components of the recently published LncRNA signatures for predicting HCC prognosis, suggesting that they have great potential as new prognostic markers (Wu et al. 2021; Xu et al. 2021; Zeng et al. 2021). But little is known about AC016735.1. In general, these 5 LncRNAs play a crucial role in the pathogenesis of cancer and show their prognostic value potential. TP53 is a common mutation site of cancer, and its mutation type is significantly associated with lower survival rate of HCC patients (Gao et al. 2019; Yang et al. 2021). According to GILncSig, the mutation rate of TP53 in high-risk patients was significantly higher than that in low-risk patients. In addition, there was a significant difference in survival between high-risk and low-risk patients with TP53 mutations. Therefore, it is of great significance for personalized prognostic evaluation of HCC patients.
Many previous studies have used similar methods to find prognosis related LncRNA and establish LncRNA signatures to predict the prognosis of HCC, such as the study of Huang et al. and Wu et al (Wu et al. 2021; Huang et al. 2021). Moreover, since all data used in this study were collected from TCGA database, similar results could be obtained when searching for GI-LncRNAs and exploring their functional pathways. The difference is that all HCC patients were divided into the training set and the testing set according to the principle of random grouping. As a result, the calculated prognosis related LncRNAs were different, and the established formula of GILncSig was also different. In addition, the AUC of the GILncSig in this study was relatively high. Subsequently, GILncSig showed good performance in both the independent testing set and TCGA set either. Although this study quantified the GI index of HCC patients and established GILncSig to assess patient outcomes, there are still some limitations that need to be further investigated. Firstly, GILncSig is based on a single TCGA database, which requires an independent, large and comprehensive comprehensive database for further verification. Due to the limited availability of LncRNAs of HCC samples in GEO database, we did not use GEO database for further study. In addition, GILncSig is determined using the computational framework based on mutation hypothesis. In the future, in vivo or in vitro experiments are needed to verify its mechanism in the development of liver cancer.
In general, we established a computational framework for identifying genome instability-related LncRNAs by combining LncRNA expression with tumor mutant phenotype. It can be used as an independent biomarker to predict the clinical outcome of HCC patients. This is helpful for prognosis assessment and further clinical decision making in HCC patients.