The important role of metabolism in tumors is gradually being recognized. Increasing evidence has proven that abnormal metabolic features exist in tumors[43, 44]. Dysfunctional metabolic activities can promote tumor cell proliferation, recurrence and metastasis, affecting the immunosuppressive properties and malignant phenotype of tumors[45–48]. With the rapid development of bioinformatics technology, more and more studies have illustrated the metabolism-related risk profile of the tumor, including STAD[49–51]. However, there is still a lack of study on amino acid metabolism-related genes in STAD. Thus, in this study, we analyzed the characteristic of amino acid metabolism-related genes in STAD.
We firstly extracted prognosis-related amino acid metabolism genes by analyzing transcriptomic gene expression data and clinical parameters of STAD patients in TCGA and successfully constructed an amino acid metabolism genes-related prognostic model, consisting of 3 genes (SERPINE1, NRP1, MATN3). SERPINE1, a member of the serine protease inhibitor family, has been reported to promote tumor progression and metastasis[52–54]. Recent studies have reported that SERPINE1 is a reliable prognostic marker for gastric cancer, breast cancer, ovarian cancer, colorectal cancer, bladder cancer and many other cancers[55–61]. Our study identified SERPINE1 as a prognostic marker in STAD and found the potential role of SERPINE1 in regulating the immune cells infiltration, which is consistent with previous studies[62, 63]. NRP-1, a transmembrane protein, acts as a multifunctional coreceptor involved in cancer initiation, growth and metastasis[64]. NRP-1 is a potential target in cancer therapy and negatively correlates with the prognosis of esophageal squamous cell carcinoma, hepatocellular carcinoma and colorectal cancer[65–67]. In gastric cancer, NRP-1 promotes the gastric cancer cells proliferation and migration of and is associated with the clinicopathological staging[42]. In our study, we further confirmed its role in predicting the prognosis and immunotherapy efficacy of STAD patients. MATN3, a protein-encoding gene, has been mainly focused on its role in cartilage and skeletal development in past studies[68]. Recently, MATN3 was reported to be highly expressed in STAD patients[69]. However, the role of MATN3 in the prognosis of STAD patients was still unclear. In our study, we found that MATN3 might influence the prognosis of STAD patients by involving in the metabolism acid metabolism and immune infiltration in the tumor microenvironment. In addition, we further confirmed the importance of MATN3 in promoting the proliferation and migration ability in gastric cancer through in vitro studies.
Immunometabolism provides an understanding of the relationship between immune response and metabolism[70]. Amino acids, as the main raw materials for protein synthesis, regulate the immune function through energy metabolism, redox balance, epigenetic modification and protein post-translational modification[71]. Tumor cells require a continuous supply of amino acids, which leads to a metabolic competition between tumor cells and immune cells[22]. Metabolic remodeling of immune cells in the tumor microenvironment plays a potential role in the progression and metastasis of the tumor[24, 72]. We explored the role of amino acid metabolism-related model in immune infiltration in STAD. In this study, we found immune-related pathways, such as cytokine-cytokine receptor interaction, TLR signaling pathway, chemokine signaling pathway and nod like receptor signaling pathway were significantly enriched in the high-risk group. Further analysis demonstrated that the high-risk scores were associated with higher immune cell infiltration and TGF-β dominant immune subtype, demonstrating that amino acid metabolism-related genes might influence STAD patient prognosis through regulating immune-related pathways and TGF-β dominant immune subtype cell infiltration. In gastric cancer, CXC chemokines and their receptors regulate cell transport into and out of tumor microenvironment, influence tumorigenesis indirectly by regulating tumor growth, survival, transformation, invasion, and metastasis, as well as indirectly by modulating tumor-leukocyte interactions and angiogenesis[73]. TLRs are key innate immunopathogenic sensors mediating chronic inflammation and carcinogenic responses. TLR9 promotes gastric cancer initiation and the gastric inflammation and hyperplasia induced by Helicobacter pylori[74]. Nod like receptor family are patterns recognition receptors related with innate immunity. NLRX1, a member of the nod like receptor family, is reported to be associated with increased risk of Helicobacter pylori infection, which is common risk factor for developing gastric cancer[75]. TGF-β, a key factor of immune homeostasis and tolerance, inhibits the expansion and function of the immune system[76]. TGF-β signaling has dual roles in the development and progression of gastrointestinal tumor as both a suppressor and promoter[77]. Furthermore, we revealed that the high-risk group had a higher immune escape potential, indicating a poorer immunotherapy effect, which provided a potential reference for applying immunotherapy in STAD patients.
KEGG functional enrichment analysis revealed the possible mechanisms of amino acid metabolism genes in STAD. We found that the tumor-associated pathways, such as the JAK-STAT signaling pathway, TGF-β signaling pathway and MAPK signaling pathway were enriched in the high-risk group, suggesting that amino acid metabolism genes may affect STAD prognosis through these pathways. The relationship between MAPK signaling pathway and amino acid metabolism has been reported. A previous study showed that L-Glutamine deficiency disturbed amino acid metabolism and attenuated mTOR and MAPK/ERK signaling pathways, thereby affecting protein synthesis and cell proliferation[78]. The JAK-STAT signaling pathway is related with varieties of physiological processes such as cell proliferation, immune response, and stem cell self-renewal[79–81]. Aberrant activation of the JAK/STAT pathway has also been reported to be related to gastric cancer progression[82]. Inhibition of STAT3 significantly reduces the expression of the anti-apoptotic protein survivin, which promotes gastric cancer cell death[83]. TGF-β signaling pathway can affect cancer progression by regulating the immune response, tumor microenvironment, epithelial-mesenchymal transition, and cancer cell stemness[84–86]. A previous study showed that TGF-β expression was elevated in the tumor tissue of gastric cancer patients and was associated with a poorer prognosis[87].
To further increase the clinical translational value of our study, we performed the FDA-approved drug sensitivity analysis. By analyzing data from the CellMiner database, we found that our model genes were associated with the patient’s sensitivity to many FDA-approved drugs. The expression of SERPINE1 was positively correlated with the therapeutic sensitivity to lenvatinib. It has been reported that the combination of lenvatinib with pembrolizumab has promising antitumor activity in patients with advanced gastric cancer[88]. In addition, our study found that MATN3 expression was positively correlated with the therapeutic sensitivity to dacomitinib. In a previous clinical trial, dacomitinib showed good efficacy in HER2-positive gastric cancer patients[89]. Therefore, our study may provide a potential reference for drug selection in STAD patients.