For CRC, molecular targeted therapy and immunotherapy have played a certain therapeutic role in recent years25. For example, development of immune checkpoint inhibitors has shown clinical efficacy. However, most CRC patients do not benefit from immune checkpoint inhibitors due to adverse events 26. Therefore, further search for immune-related genes is necessary to improve the prognosis of CRC patients.
In TCGA, we obtained clinical and RNA sequencing data from 644 CRC patients, then DEGs in CRC was obtained by DESeq2 analysis, DEGs associated with CRC patient prognosis was analyzed by Survival package, and immune-related genes were downloaded from ImmPort database, and 6 genes were obtained by Venn overlap analysis of the three, and FGF19 was finally selected as the target gene by comparing the prognosis of CRC and the expression of 6 genes in cancer and adjacent non-cancerous tissues.FGF19 expression has been found to be upregulated in a variety of cancers and associated with adverse outcomes in these patients. However, FGF19 remains poorly investigated in CRC. According to the GTEx database and TCGA database, FGF19 expression levels were higher in CRC tissues compared with normal tissues, and we used GSE41328, GSE110224, and GSE41328 datasets for validation, and the results still showed that FGF19 expression was increased in CRC tissues. We also compared immunohistochemistry between normal and cancer tissues in the HPA database and found that FGF19 protein expression remained highly expressed in CRC tissues, indicating that FGF19 mRNA was consistent with FGF19 protein expression. We found that the overall survival time of CRC patients decreased with increasing FGF19 expression levels, indicating that FGF19 is not conducive to the prognosis of patients. By comparing the diagnostic efficacy of FGF19 in CRC, our analysis results confirmed that FGF19 had a good diagnostic efficacy for CRC (AUC = 0.904). We found that FGF19 expression in CRC was associated with T stage, N stage, M stage, and pathological stage. By comparing the relationship between high and low FGF19 expression and clinical parameters, we found that when FGF19 levels increased, N stage, M stage and pathological stage were more advanced. According to multivariate regression analysis, age, M stage, pathological stage, and lymphatic invasion were independent risk factors for the prognosis of CRC patients. Overall, we can conclude that FGF19 is highly expressed in CRC, and patient survival declines with increasing FGF19 levels; the effect of FGF19 on CRC prognosis may be achieved by affecting its expression in N stage, M stage, and pathological stage; in addition to the good diagnostic efficacy of FGF19, we believe that FGF19 can be used as a biomarker for CRC diagnosis and prognosis.
We have explored the impact of FGF19 on the prognosis and progression of CRC, so we wanted to explore through which pathway FGF19 impacts CRC. Through GO, KEGG, GSEA analysis of FGF19 related genes in CRC, we found that the molecular function of FGF19 was correlated with signal receptor activator activity, receptor ligand activity, and protein heterodimerization activity. Many activities in our body require signaling receptors, receptor ligands, and are essential during CRC formation. Protein dimerization often occurs in cells and plays an important role in various biological processes and cancer development27–31, and proteomic studies have also pointed to a large proportion of mammalian proteins that function only as dimers or multimers in cells. Therefore, correct dimer formation is very important for a healthy proteome as well as the body32.Through KEGG and GSEA analysis of FGF19, we found that the pathways associated with tumors were mainly neutrophil extracellular trapping network, Pi3Kakt signaling pathway, regulation of insulin-like growth factor Igf transport, and regulation of uptake by insulin-like growth factor binding protein Igfbps. NETs are fibrous mesh-like structures released into the extracellular space by neutrophils33.The main components of NETs include nuclear DNA, as well as granulin composed of matrix metalloproteinase-9, myeloperoxidase, neutrophil elastase, and cathepsin G34.NETs are highly expressed in a variety of malignant tumor tissues, and tumors have systemic effects that regulate NETs. There are two neutrophil phenotypes associated with tumors, anti-tumor N1 and tumorigenic N2 neutrophils, and both N1 and N2 neutrophils can produce NETs35.NETs are highly expressed in a variety of cancers, and promote the development of a variety of cancers 36,37.NETs has also been associated with CRC progression and metastasis38,39, and based on this, we explored the relationship between FGF19 and NETs related genes. We found a significant association between FGF19 and NETs related gene sets, so FGF19 may have an impact on CRC by affecting NETs. Pi3Kakt signaling pathway40, insulin-like growth factor, and insulin-like growth factor binding protein have all been demonstrated to be associated with cancer progression, so FGF19 may have an impact on CRC development by affecting these three pathways. In addition to this, we explored the genes involved in FGF19 in CRC and found that the top three genes most associated with FGF19 were ALB, IL1B, H3C12.
In this study, we selected four CRC gene sets to explore FGF19 variants based on the cBioPortal database. We found a low frequency of FGF19 mutations in CRC, only 1.33%, and the proportion of mutations and gene amplification was consistent. We found 18 mutation sites between amino acids 0 and 216 and found missense mutations to be the most frequent mutations. We also analyzed the relationship between specific CRC classification and mutation count and found that simple CRC adenocarcinoma corresponded to the highest mutation count, and other types of CRC adenocarcinoma corresponded to fewer mutation counts. In addition, we explored FGF19 variants in the COSMIC database and found that 62.96% of CRC samples had missense substitutions and were also the most mutated, which was consistent with the mutation type in the cBioPortal database. Among them, base substitutions were mainly C > T (46.15%). Through genetic variation analysis of FGF19 in CRC, we found that FGF19 effects on CRC were not caused by genetic mutations.
With regard to the exploration of the association of FGF19 with immune infiltrating cells, we found that FGF19 was negatively correlated with most immune cells, but interestingly we found that FGF19 was positively correlated with NK cells, which are well-known to be critical cells for inhibiting cancer progression, and there are many immunosuppressive agents based on the emergence of NK cells. In response to this interesting phenomenon, we reasoned that there would be something that inhibited the action of NK cells, and through our review of the literature, NETs could inhibit the action of NK cells. We found that FGF19 was also negatively correlated with CD8 + T cells. NETs have also been found to encapsulate and coat tumor cells, protecting them from CD8 + T cells- and NK cells-mediated cytotoxicity, thus hindering the contact between immune cells and surrounding target tumor cells and further hindering the control of tumor metastasis by immune cells41.We found that FGF19 was also negatively correlated with macrophages and dendritic cells, which were found to be two major antigen-presenting cells and key innate immune cells regulating anti-tumor immune responses. It has been shown that NETs activates macrophages and DCs by up-regulating important costimulatory molecules (CD80, CD86) early (30 min), however, macrophages and DCs undergo apoptosis after prolonged incubation with NET (56).We found FGF19 also associated with Tem cells, neutrophils,TH1 cells, TH2 cells, Treg cells, B cells, T helpe cells, T cells, and Cytotoxic cells are negatively correlated, and the relationship between NET and these cells is unclear. Because NETs is associated with these immune cells in healthy humans and autoimmune diseases42,43, so whether NETs may also have an effect on these cells during tumor development needs further validation. We explored the correlation between FGF19 and ESTIMATE scores in CRC and found that FGF19 showed a negative correlation with ESTIMATE scores, indicating that the proportion of immune cells decreased with increasing FGF19 expression levels. Overall, most immune cells decreased with increasing FGF19 levels, implying that FGF19 may contribute to CRC development and progression by suppressing immune cells. Because NETs has a significant relationship with immune cells, FGF19 may promote CRC development and progression by promoting NET expression and thus inhibiting immune cells.
We explored the relationship between FGF19 and immune checkpoints and found that FGF19 presented a negative correlation with most immune checkpoints. We subsequently analyzed eight important immune checkpoints, and we found that FGF19 was positively correlated with SIGLEC5, which has already been demonstrated to have an effect on CRC and has the potential to be an effective prognostic indicator in CRC. FGF19 is positively correlated with SIGLEC5, indicating that FGF19 and SIGLEC5 can be detected in combination and become effective prognostic indicators of CRC. In addition, we explored the relationship between FGF19 and tumor heterogeneity and found that FGF19 was negatively correlated with TMB, MSI, NEO, MMR, indicating that FGF19 was not highly sensitive to immunosuppressive agents. Next, we explored the relationship between FGF19 and MATH and found a positive correlation between FGF19 and MATH, indicating that with increasing FGF19 levels, the greater tumor heterogeneity in CRC, the less conducive to immunotherapy. Since FGF19 is not sensitive to immunosuppressive agents, we analyzed FGF19 sensitivity to drugs in the GDSA and CRTP databases and found that FGF19 is highly sensitive to BRD-K99006945, PI-103, and AT7867 in the CTRP database and JNJ − 26854165 in the GDSA database, so the scope of use of related drugs can be explored to verify the efficacy of drugs against CRC patients.
Finally, we analyzed the single cell of FGF19 and found that FGF19 mainly distributed in squamous epithelial cells, pith cells, stromal cells, T cells, NK cells and congenital lymphocytes. Myelocytes mainly include red cells, granulocytes, monocytes and macrophages. FGF19 may be distributed around granulocytes to promote the formation of NETs, and may be distributed around NK cells to inhibit NK cells. We also analyzed the distribution of FGF19 in CRC immunocytes and found that FGF19 mainly distributed around monocytes, cytotoxic T lymphocytes, promyelocytic leukemia zinc finger protein, dendritic cells and macrophages. Distribution around CD8 + T and macrophages may promote NET production and protect tumor cells. We also studied the distribution of FGF19 in T cells, NK cells and congenital lymphocytes, and found that FGF19 mainly distributed around cytotoxic T lymphocytes, CD4+T cells and promyelocytic leukemia zinc finger proteins.
In general, FGF19 is highly expressed in CRC compared with normal tissues and N stage, M stage and pathologic stage are later with the increase of FGF19 level, the prognosis of CRC is worse. FGF19 may promote the occurrence and progression of CRC by inhibiting immune cells by promoting NET expression. FGF19 is negatively correlated with most CRC immune cells, so it is feasible to study the inhibitors of FGF19 molecular targets. We believe that the study of FGF19 will benefit more CRC patients and eliminate their pain.