Stomach cancer (SC) is 5th most prevalent malignancy and 3rd most common cause of cancer mortality globally [33], due to its bad incidence, prognosis, cellular and molecular heterogeneity [34]. Systemic chemotherapy, radiation, surgery, immunotherapy, and targeted therapy have all been shown to be effective in STAD treatment [35]. Identified biomarkers, such as programmed cell death ligand 1 (PD-L1), and microsatellite instability (MSI) that can be used to determine which patients will respond favorably to immunotherapy or targeted therapy [35]. However, these are not sufficient to all patients. Significant novel biomarkers remain to be developed to provide the opportunity for personalized therapy. ECM is a ubiquitous tissue component that is constantly being remodeled [36]. Dysregulation of ECM composition, structure, stiffness, and abundance are linked to neoplastic progression, like SC [37, 38]. A recent study has reported that ECM-related hubs genes have adverse effects on STAD prognosis [39]. However, the potential molecular mechanism and the predictive value of ECM in this malignancy remain unknown.
In our study, 12 ECMOGs were identified to predicted the prognosis and immune microenvironment in STAD. The prognosis-related genes in STAD were determined, and we found that ECM organization was the significant biological process with 41 genes enriched in. Among the 41 genes, 12 (ADAMTS1, ADAMTS12, AGT, ANTXR1, COL5A2, COL10A1, FAP, LOX, LUM, OLFML2B, POSTN, and NFKB2) were found to be differentially expressed in STAD, and three (NFKB2, LOX, ADAMTS1) were identified as independent prognostic signature after undergoing LASSO and multivariate cox regression analysis, indicating that the 12 ECMOGs may be involved in STAD development, and expression levels of three-gene independent prognostic signature might contribute to the prediction of the outcome. The protein encoded by NFKB2 is a subunit of transcription factor complex nuclear factor-kappa-B (NF-kB). NF-kB family components play a critical role as stressors and act as transcription factors in regulating essential regulatory genes expression, such as those involved in immunology, inflammation, cell death, and cell proliferation [40]. In the mouse model, Nfkb2 gene is needed for cancer initiation and progression in Kras-mutation driven models by regulating proliferation pathways [41]. In glioblastoma, diabetic neovascularization, osteogenic differentiation, bone matrix formation, ligament remodeling, polycystic ovarian syndrome, fetal membrane rupture, and tumor progression and metastasis, LOX plays a catalytic activity-related, primary role in assembly of ECM [42]. ADAMTS1 promotes the adhesion to ECM proteins, and increased abundance of the metalloprotease ADAMTS1 strongly correlated with metastasis in many kinds of human cancer [43–47]. In addition, other prognosis-related ECMOGs were studied to play important roles in ECM regulation and the further cancer progression. In SC, for instance, the tumor-promoting gene ADAMST12 is responsible of TME status and metabolic conversion of tumor energy [48]. ANTXR1 is predicted to serve as a valuable prognostic biomarker in stomach cancer, as well as a potential immunotherapeutic target and useful biomarker of sensitivity to chemotherapy [49]. COL5A2 is increased in several cancers, and the enhanced this gene is associated with cancer stages, recurrence, microsatellite instability [50]. High expression of COL5A2 revealed poor survival and aided cell migration in SC [51]. COL10A1 is studied to be a predictor for the poor prognosis in stomach cancer, and silencing this gene inhibited cell proliferation, migration, and invasion [52, 53]. LUM and OLFML2B are also predicted to be an oncogene in the progression of stomach cancer [54, 55]. Our founding here was not only consistent with these previous studies, but also illustrated that these 12 ECMOGs might be an independent prognostic signature to predict the OS in STAD.
According to the expressional levels of the 12 ECMOGs, the 348 STAD samples were divided into two diverse clusters by the unsupervised clustering analysis, and 11 ECMOGs were highly enriched in the subgroup of cluster 1, which was thus called as high ECMOGs subgroup. Moreover, patients in cluster 1 were featured by the poor outcome and the higher risk score, indicating that the population with high levels of the ECMOGs represented the high-risk subgroup in STAD. Increased ECM remodeling enzymes, recruited CAFs, immune cells, and other stromal cells, secreted several growth factors, and stimulated collagen deposition are all known to participate to ECM remodeling at tumor site, which in turn leads to elevated ECM stiffness, abnormal cell-cell adhesion, up-regulation of integrin signaling, and subsequent activation of downstream cascades, and hence stimulate tumor development and progression [38]. Here, we found that the 12 ECMOGs could act as a gene signature to expect prognosis in STAD, overexpression of these ECMOGs may promote the progression of STAD.
A total of 514 genes were identified as DEGs between two ECMOGs-related clusters, and among these, 506 genes were highly expressed in cluster 1. The subsequent GO enrichment analysis revealed that these ECMOGs-related DEGs were associated with biological processes of extracellular structure organization, extracellular matrix organization, ossification, cell-substrate adhesion, and connective tissue development, as well as KEGG pathways of PI3K-Akt signaling pathway, focal adhesion, protein digestion and absorption, and ECM-receptor interaction. These showed that two ECMOGs-related populations may have distinct biological characteristics that may thus possess discrepant outcome. Obviously, the main different pathways enrich in the two cluster were PI3K-Akt signaling pathway, and focal adhesion. Phosphoinositide 3-kinases (PI3Ks) are a broad family of lipid enzymes that can phosphorylate 3'-OH group of phosphatidylinositols (PtdIns) in plasma membrane. PI3K pathway is one of the most commonly activated signal transduction pathways in human cancer [56]. PI3K/AKT signaling is essential for chemoresistance and contributes to epithelial mesenchymal transition (EMT) in drug-resistant and metastatic human cancer cells [57]. Additionally, the hub genes identified by the PPI network, such as COL1A2, MMP2, COL6A1, COL1A1, COL3A1, COL5A1, THBS1, were ECM organization-related genes. These all demonstrated that elevated the ECMOGs expression caused the dysregulated ECM, and activated PI3K/AKT signaling and focal adhesion, that further promoted cancer progression in STAD.
The tumor immune microenvironment is environment in which anticancer immunological response of the host occurs. [58]. Important contributions to tumor immune microenvironment are tumor-infiltrating immune cells, such as neutrophils, macrophages, dendritic cells, and various types of T cells. [59]. Previous studies have demonstrated that tumor-infiltrating lymphocytes proportion were linked to patients survival with SC [60]. In SC, for instance, infiltrating macrophages have been implicated as facilitators of metastasis formation by acting as alternative regulators of tumor cell proliferation, angiogenesis, as well as tissue remodelling [61]. In this study, we found that the immune score was higher in the ECMOGs-related cluster 1, and different pattern of tumor-infiltrating lymphocytes was also existed between the two subgroups. What stands out is that, macrophages (M1 and M2) were infiltrated higher in the population of cluster 1 than in those of cluster 2. What’s more, nine of the twelve ECMOGs we detected were positively associated with infiltrated abundance of M2 macrophages, and five ECMOGs were correlated with M1 macrophages infiltration. These all indicated that high expression of detected ECMOGs could stimulate M1 and M2 macrophages infiltration during STAD progression. Tumor-associated macrophages (TAMs) principal population of tumor-invading immune cells, which typically support tumor immune evasion, angiogenesis, tumor development, and metastasis. Macrophages are always polarized into different subtypes (M1 macrophages and M2 macrophages) by the specific factors according to changes in their environment [62]. In contrast to M1 macrophages, which are largely anti-tumor and immune-promoting, M2 macrophages have a similar profile to TAMs, that stimulate tumor development and metastasis [62]. Our results showed that both infiltrated M1 and M2 macrophages were higher in ECMOGs-enriched cluster 1, and this seems contradictory. That might be attributed to the basic function of the macrophages. Tissue damage induced by the pro-inflammation of M1 macrophages may promote that M2 macrophages polarization to repair the damage tissue, and thus tumor-associated M1 and M2 macrophages may be in a state of dynamic equilibrium. However, our results showed a more prominent correlation between the ECMOGs and M2 macrophages infiltration in STAD, which further demonstrated that highly expressed ECMOGs have the potential to promote tumor development by enhancing M2 macrophages invasion.
Moreover, the potential immunotherapy effect of STAD patients in the two ECMOGs-related clusters were assessed. We found that cluster 1patients had a greater TIDE score, as well as higher levels of four immune checkpoint genes (CD274, HAVCR2, PDCD1LG2, and TIGIT). It is clear that certain immune checkpoint pathways play a crucial role in immunological resistance, notably versus T cells which are tumor specific antigens [63]. The most studied and identified inhibitory checkpoint mechanisms are cytotoxic T lymphocyte-associated molecule-4 (CTLA-4), (PD-1), and (PD-L1 (CD274)) [64]. PD-1 signaling inversely modulates T cell-mediated immune responses and facilitates tumor evasion of an antigen-specific T cell immunologic response. It contributes to tumorigenesis and progression through tumor survival boosting [65]. HAVCR2 (T cell immunoglobulin and mucin domain 3 (TIM3)) additionally serves as a tumor-infiltrating lymphocyte-expressed inhibitory checkpoint protein. TIM3 and Gal9 interaction inhibit innate and adaptive immune cell anti-tumor immunity [66]. TIGIT is an inhibitory receptor primarily expressed on NK, CD8 + T, CD4 + T, and T regulatory (Treg) cells. Interaction of CD155 and TIGIT always inhibits the function of T and NK cells. In addition, TIGIT blockade was supported to be used combining with other immune checkpoint inhibitors to treat advanced solid malignant tumors [67]. ICB, which blocks inhibitory pathways of T cells activation, has shown tremendous success in treating cancer [68]. Our result that the TIDE score was higher in cluster 1 further indicated that these patients may had a poor ICB response and the potential immunotherapeutic resistance. These all demonstrated that the detected ECMOGs may be correlated with a higher immune checkpoint and the poor anti-tumor immune response.
The patients in the subgroup of ECMOGs high expression were identified as high-risk population, who had worse prognosis. To predict possible chemotherapeutics suitable for the population of cluster 1, we used (moa) module of CMap dataset to determine small-molecule chemotherapeutics targeting 50 hub genes that were highly expressed among cluster 1. Cluster 1 was shown to have 37 possible chemotherapeutic perturbagens. Among these, dasatinib, sorafenib, sunitinib, and dovitinib were predicted as the prominent ones targeting PDGFRB, that had the largest moa modules, such as PDGFR receptor inhibitor, and VEGFR inhibitor. Dasatinib, a short-acting oral multiple tyrosine kinase inhibitor, approved to treat chronic myeloid leukemia. [69]. Besides, Dasatinib is a promising safe medication for treating refractory metastatic solid cancers [70]. Oral kinase inhibitor sorafenib suppresses tumor cell growth and angiogenesis as well as promotes cancer apoptosis [71]. From 2005 to 2013, sorafenib was the first targeted therapy authorized for renal cell carcinoma, hepatocellular carcinoma, and thyroid cancer patients [72]. Sunitinib is an orally bioavailable, multi-target tyrosine kinase inhibitor that has been shown to be effective against imatinib-resistant gastrointestinal stromal tumors (GISTs), renal carcinomas, and pancreatic neuroendocrine tumors. [73]. Dovitinib is a kind of FGFR3 tyrosine kinase inhibitors [74], and it has been employed extensively in clinical practice and FDA-approved for cancer treatment. [75]. In addition, three metalloproteinase inhibitors targeting MMP2 and MMP14 were also forecasted to be possible therapeutic schedule for those cluster 1 patients, such as ilomastat, PD-166793, and UK-356618. For example, ilomastat is one kind of derivatives of batimastat that are in clinical or experimental usage for anti-cancer therapy through inhibiting neutrophil inflammatory responses [76]. These inhibitors were all anticipated to be beneficial for STAD patients in cluster 1 of high risk, however, more experiment in vitro and in vivo should be conducted for the subsequent analysis.
In this paper, we provided the systematic analysis of prognostic genes in STAD using public database data and by bioinformatics. According to the GO enrichment and PPI results, ECM organization was identified to be the significant biological process with 41 genes enriched in. Therewith, we systematically evaluated immune microenvironment and prognosis in STAD patients with different ECMOGs expression subgroups. This is the first study to illustrate the association between ECM organization dysregulation and immune microenvironment changes, and to provide a novel biological target for the targeted therapy of STAD. However, there are still some deficiencies in this current paper. First of all, although some correlation prediction analysis can be performed by using bioinformatics techniques, simple analysis is not enough to explain the molecular mechanism of ECMOGs affecting poor prognosis of STAD. Therefore, large numbers of experimental assays both in vitro and in vivo should be carried out to subsequent study the molecular mechanism of these ECMOGs in promoting the development of STAD. Second, the clinical samples with STAD should be collected for the high-throughput sequencing to further validate the correlation of the ECMOGs and immune microenvironment. Besides, the protein expressional levels of these detected ECMOGs in the clinical STAD samples also should be detected. Finally, the predicted chemotherapeutics in this study should be evaluated by the experimental assays.
To sum up, this paper demonstrated that dysregulation of ECM organization was associated to worse STAD prognosis, and 12 ECMOGs were identified to be implicated in STAD development and progression, which could predict the immune microenvironment and thus the potential immunotherapy effect in STAD.