Tumor angiogenesis plays a vital role in tumorigenesis, proliferation, and metastasis. In recent years, studies have identified VEGFA and CXC chemokines as important participants in angiogenesis, particularly tumor angiogenesis 12, 22, 23. The expression levels of CXC chemokines and VEGFA have been studied in a range of tumor types; however, findings are contradictory with regard to colonic adenocarcinomas 24, 25. This study investigated expression level, gene regulatory network, prognostic value, and target prediction of the CXC chemokine-VEGFA network for COAD from the perspective of tumor angiogenesis.
In this study, we also examined whether there was correlation between pathological stage and differential expression of COAD. The expression of CXCL1/2/3/5/6/8/11/16/17 and VEGFA was upregulated in patients with COAD compared to individuals without COAD. Patients with COAD also showed downregulated CXCL12/13/14 expression. The results were same with those in a previous study in patients with COAD 25, and contradict previous findings in patients with colorectal cancer 24. This may be due to the small sample size and the many different types of colorectal cancer. We further attempted to explain the different expression levels by investigating promoter methylation and gene alteration in patients with COAD, as these are the factors that affect tumor cell proliferation, angiogenesis, and metastasis. We found that patients with COAD had different rates of genetic alteration in their genes. Moreover, the promoter methylation levels of CXCL5/6/12/14 and VEGFA were higher in patients with COAD than those in normal people. Conversely, the promoter methylation levels of CXCL1/2/3/11/13/17 were lower in patients with COAD. So, we hypothesized that genetic methylation and alteration within the CXC chemokine-VEGFA network may be the leading cause of abnormal gene expression levels in patients with COAD.
We also found a notable correlation between the CXCL9/10/11 and VEGFA expression, and the pathological stage of COAD. Furthermore, the survival time of patients with COAD was longer with low VEGFA expression levels or high CXCL8/11/14 expression levels. Therefore, the expression levels of CXCL8/11/14 and VEGFA may be potential prognostic indicators for COAD patients. CXCL8/11/14 and VEGFA promote tumor angiogenesis in different ways 26–28. Thus, they may affect the prognosis of patients with COAD through multiple biological functions.
The potential functions and interactions of the CXC chemokine-VEGFA network were explored in this study. They were found to be complex and tightly connected. Genes in the network were mainly involved in cytokine receptor binding, chemokine and cytokine activity, leukocyte chemotaxis, and migration. All were closely related to angiogenesis. For example, IL-8 (CXCL8) promotes tumor angiogenesis by binding to CXCR1 and CXCR2 receptors 29. In addition, increasing the anti-tumor activity of cytokine-induced killer cells could reduce tumor proliferation and angiogenesis 30. Taken together, these results suggest that the CXC chemokine-VEGFA network may influence the development of COAD by increasing tumor angiogenesis.
Furthermore, the functions of the CXC chemokine-VEGFA network in patients with COAD were mainly related to chemokine activity, cytokine activity, and growth factor activity with GO enrichment analysis, all functions closely related to tumor angiogenesis. More studies are needed to confirm the mechanism by which this happens. In this study, we further found through KEGG pathway analysis that the cytokine–cytokine receptor interaction signaling pathway, IL-17 signaling pathway, and NF-κB signaling pathway were highly involved in the CXC chemokine-VEGFA network in COAD patients. All of them are highly related to tumor angiogenesis 31, 32. Therefore, regulation of them may be a potential treatment strategy for patients with COAD.
Mutated or altered transcription factors represent a unique class of drug targets that mediate aberrant gene expression, and the development of these drugs may impact future cancer treatments. Thus, the targets and regulators of the CXC chemokine-VEGFA network in COAD patients were further analyzed. The transcription factor targets of the CXC chemokine-VEGFA network in patients with COAD were identify. RELA, NFKB1, ZFP36, XBP1, HDAC2, SP1, ATF4, EP300, BRCA1, ESR1, HIF1A, EGR1, STAT3, and JUN are crucial regulatory factors. Our results showed that these factors have potential functions in regulating tumor angiogenesis by targeting VEGFA. Studies have shown that RELA, NFKB1, HDAC2, SP1, ATF4, EP300, BRCA1, ESR1, HIF1A, EGR1, STAT3, and JUN regulate tumor angiogenesis, thus affecting tumor growth and prognosis 33–44. However, the role of ZFP36 and XBP1 in tumor angiogenesis has not yet been reported. miRNAs also play a crucial role in regulating gene expression. miRNAs suppress target genes expression by targeting at their 3′-untranslated regions. miRNA target discovery may ultimately help elucidate the underlying mechanisms of tumorigenesis. Thus, CXC chemokine-VEGFA network-associated miRNA targets in patients with COAD were further explored. Most of them (miR-218, miR-493, miR-221, miR-222, miR-423, miR-378, miR-381, miR-210, miR-382, and miR-199A) have been shown to regulate tumor angiogenesis 45–48. In short, our study provides potential therapeutic strategies for the treatment of COAD through the prediction of regulated factors and miRNA targets.
The correlation between CXC chemokine-VEGFA network expression and differentially expressed genes in COAD patients was explored in this study. We found that in patients with COAD, close to 20,000 genes were negatively or positively correlated with CXC chemokine-VEGFA network expression. From these, we screened for genes with the highest correlation with CXC chemokines and VEGFA. Some of the genes with the highest correlation (ZC3H12A, IL24, MMP3, IL1B, OSM, IDO1, NPR1, and TIGIT) were positively associated with tumor angiogenesis 49, 50. Regulation of these cancer-related genes may offer an alternative therapeutic strategy for the treatment of patients with COAD. Immune infiltration is highly related to the clinical prognosis of tumors. Immune cells reach the tumor site through vascular transport, and vascularization of tumors is a process mediated by angiogenesis. We found that CXC chemokine-VEGFA network expression, which regulates angiogenesis, is correlated with the infiltration of immune cell. This infiltration involved CD4 + T cells, CD8 + T cells, neutrophils, macrophages, and dendritic cells. Improving immune cell infiltration in COAD by developing drugs that act on the CXC chemokine-VEGFA network or CXC chemokines and VEGFA-related regulatory targets is a viable therapeutic oncology strategy.