Although there are an increasing number of treatments and drugs for colon cancer, the prognosis is still not satisfactory due to various reasons(Chau and Cunningham 2006,Auclin et al. 2017,Taieb et al. 2019). In view of the high heterogeneity of colon cancer, different patients exhibit significant differences in the treatment effect, with different clinical outcomes and prognoses(Punt et al. 2017,Gallois et al. 2018). It has always been critical to find effective diagnostic and prognostic markers to improve screening and treatment in colon cancer patients. Here, the expression level and clinical significance of SPOCD1 in COAD were revealed by comprehensive bioinformatics analysis. We demonstrated that colon cancer patients with increased expression of SPOCD1 have a poor clinical outcome. In addition, our data showed that a close relationship exists between SPOCD1 and the infiltration of various immune cells, immunostimulators, immunoinhibitors, chemokines and receptors in COAD. Thus, our findings suggest that SPOCD1 may be a diagnostic and prognostic biomarker associated with immune infiltration in COAD and provide new insight into its biological function.
SPOCD1 is a gene encoding transcription factor S-II (TFIIS) family proteins(Kimura et al. 2006). Although the relevant studies on SPOCD1 are few and not in depth, some studies have confirmed that SPOCD1 can be used as an oncogenic factor related to progression and a poor outcome in multiple tumors, including ESCC, gastric cancer and glioma(Zhu et al. 2017,Liu et al. 2018a,Lin et al. 2022). However, the clinical significance of SPOCD1 and its immunomodulatory role in COAD remain unclear.
Therefore, we assessed SPOCD1 expression levels in COAD using the UALCAN database, revealing that SPOCD1 expression was elevated in colon cancer. Moreover, we further verified that colon cancer tissues expressed more SPOCD1 than adjacent tissues by immunohistochemistry, confirming the results of the database analysis. According to these results, SPOCD1 may have potential as a colon cancer diagnostic marker. In addition, we analyzed the correlation between SPOCD1 expression and OS, DSS, and PFI in colon cancer patients to determine whether it can be used as a prognostic indicator. Notably, the results showed that the higher the expression level of SPOCD1 was, the worse the OS, DSS and PFI of the patients. Taking these data together, SPOCD1 appears to be a reliable prognostic indicator for colon cancer patients.
Mounting studies have confirmed that the tumor microenvironment is populated with diverse immune cells that play a significant role throughout the tumor's lifecycle. Lin et al. conducted an analysis of the association between SPOCD1 expression and immune cell infiltration in ESCC and found positive correlations between SPOCD1 expression and the infiltration of M0 macrophages and activated mast cells and negative correlations between SPOCD1 expression and the infiltration of plasma cells and follicular helper T cells(Lin et al. 2022). However, whether there is a link between SPOCD1 expression and immune activity in colon cancer remains unclear. Thus, we comprehensively and systematically investigated the relationship between SPOCD1 expression levels and immune activity in colon cancer.
According to our study, high SPOCD1 expression is positively correlated with the infiltration of neutrophils, cancer-associated fibroblasts and macrophages. Moreover, SPOCD1 expression level is positively correlated with the expression of various immune modulators, chemokines and receptors. Additionally, our analysis results suggest that SPOCD1 expression has a positive correlation with the expression of multiple immune cell markers. For example, SPOCD1 expression is associated with the expression of cancer-related fibroblast markers such as αSMA, FAP, COL1A2, TAGLN and PDGFRB. In addition, there was a positive correlation between SPOCD1 expression and the expression of the neutrophil marker CD11b, dendritic cell markers BDCA-4 and CD11c, and the T-cell exhaustion marker PDL1. Macrophages are the key effector cells in the innate immune response and are highly heterogeneous and can form subpopulations with different functional characteristics as the environment changes(Locati et al. 2020,Hinshaw and Shevde 2019). In general, activated macrophages are mainly divided into M1 macrophages and M2 macrophages. M1 macrophages are capable of resisting pathogen invasion, while M2 macrophages are primarily in charge of inhibiting immune system function and promoting malignant progression of tumors(Mantovani et al. 2002,Zhou et al. 2014,Yang et al. 2022). Our results suggested that SPOCD1 is more correlated with M2 macrophage markers such as CD163, VSIG4 and MS4A4A than with M1 macrophage markers such as NOS2, IRF5 and ITGAL, suggesting that SPOCD1 may have the potential to regulate macrophage polarization. Moreover, high SPOCD1 expression was also observed to be linked to an increase in several chemokines and receptors. In addition, we conducted enrichment analysis of the co-expressed genes of SPOCD1 and found that the biological process of GO enrichment analysis indicated that SPOCD1 was mainly associated with the regulation of neutrophil cell activation as well as the production of cytokines in the immune response. Interestingly, by GSEA, we observed that SPOCD1 expression is positively connected with the humoral immune response, macrophage migration and activation, neutrophil migration and chemotaxis and cytokine production involved in the immune response. In conclusion, these findings suggest that SPOCD1 plays a prominent role in the immune microenvironment of colon cancer.
Neutrophils, as the most abundant leukocytes in human peripheral blood, can resist the invasion of pathogenic microorganisms and play an important role in the body's nonspecific cellular immune response(Papayannopoulos 2018). In recent years, an increasing number of studies have found that neutrophils are a double-edged sword in the process of tumorigenesis and progression. Neutrophils not only can play an anti-tumor role by secreting cytotoxic substances but also can undergo phenotypic and functional remodeling in the tumor microenvironment to promote tumorigenesis and malignant progression through various mechanisms(Jaillon et al. 2020,Giese et al. 2019,Quail et al. 2022). Depending on the composition of the tumor microenvironment, neutrophils can exhibit different functional phenotypes, which is similar to the polarization of macrophages. N1 neutrophils play a role in inhibiting tumors by secreting cytotoxic substances and stimulating the adaptive immune system, while N2 neutrophils promote tumor malignant behavior by forming neutrophil extracellular traps (NETs), producing cytokines and suppressing immune responses(Zhang et al. 2020,Cristinziano et al. 2022,Masucci et al. 2019). In this study, we found that increased expression of SPOCD1 was associated with neutrophil infiltration in colon cancer by the TISIDB and TIMER databases, and functional enrichment results suggested that SPOCD1 could be involved in neutrophil activation and migration. In addition, we further found that SPOCD1 was correlated with the neutrophil activation markers CD11b and CCR7 through the TIMER database, and we also confirmed that the increased expression of SPOCD1 was positively correlated with the expression of CD11b in colon cancer tissues by multiple immunohistochemistry experiments. It has been reported that CD11b positive neutrophils mainly play a tumor-promoting role. In addition, we also found that high expression of SPOCD1 was associated with increased expression of multiple chemokines and receptors. Therefore, we hypothesized that the tumor-promoting effect of SPOCD1 in the progression of colon cancer may be partly due to the involvement of SPOCD1 in the transformation of neutrophils into the N2 phenotype, as these activated neutrophils promote malignant tumor behavior by secreting chemokines or forming NETs.
The extracellular matrix (ECM) is a network structure composed of proteins, glycoproteins, proteoglycans and polysaccharides and is an important part of the tissue microenvironment. The ECM can act as a physical scaffold for surrounding cells and regulates their behavior. It is well known that the occurrence and progression of tumors are also affected by the ECM(Nissen et al. 2019,Le et al. 2020). According to studies, the main protein component of the ECM is collagen(Frantz et al. 2010). Under normal circumstances, the newly synthesized collagen replaces the degraded old collagen to maintain a balanced state of ECM remodeling, which is conducive to maintaining the integrity and function of body tissues. Nevertheless, in the tumor microenvironment, this balance is broken, and there is a significant amount of collagen deposition around the tumor, which can regulate the function of tumor cells and even is distinctly linked to the poor clinical outcome of patients(Bager et al. 2015,Pickup et al. 2014). Recently, it has been shown that CAFs are one of the major contributors to collagen in the ECM and can regulate ECM remodeling by increasing the collagen component in connective tissue(Le et al. 2020,Jensen et al. 2021,Pankova et al. 2016). Surprisingly, a positive connection was observed between the expression of SPOCD1 and CAF infiltration in colon cancer, and functional enrichment results suggested that SPOCD1 is mainly associated with ECM and collagen. Therefore, we hypothesized that high expression of the oncogene SPOCD1 causes the increase of CAFs infiltration in the tumor microenvironment to a certain extent and then promotes an increase in collagen deposition, leading to ECM remodeling and establishing a microenvironment conducive to the malignant progression of colon cancer.
In conclusion, in this study, we found that SPOCD1 is a promising indicator for the diagnosis and prognosis evaluation of colon cancer, is associated with the infiltration of diverse immune cells in the colon cancer microenvironment and is widely involved in the immune response process. Targeting SPOCD1 may be a potential strategy to enhance the clinical effectiveness of immunotherapy in colon cancer patients. Nevertheless, there are many shortcomings in the study. First, this study is mainly based on data from online databases, and the information will be updated and supplemented continuously, so the research results may change in the future. Second, we did not include any information concerning the treatment of patients in our study. Third, no specific experiments were conducted to explore the specific mechanism by which SPOCD1 regulates the colon cancer immune microenvironment.