KIF23 gene, located on chromosome ch15q23, was discovered in the 1992 (27). KIF23 is involved in cell proliferation and differentiation (28), and abnormally expressed in glioma (29), liver cancer (30), breast cancer (31) and non-small cell lung cancer (32, 33).
In this study, the expression level of KIF23 was high in GC tissues compared to that in adjacent normal tissues by several public databases. Recent studies suggested that KIF23 was highly expressed in GC (14, 17), and related to its poor prognosis (17). Herein, we found that the profile of KIF23 expression in GC tissue was consistent across different databases. Consistently, in our study, we also validated that the expression of KIF23 was highly expressed in GC tissues compared to adjacent tissues, whereby KIF23 expression was an independent predictor of diagnostic in GC. On the contrary, we found that overexpressed KIF23 was related to longer OS and PFS. This may be due to different stages, grade of invasiveness and lymph node metastasis of GC were included in the study. We found that the expression of KIF23 was increased in GC tissues compared with that in normal tissues in TCGA cohort and GEO cohort and suggested that KIF23 might be used as a potential diagnostic biomarker in GC.
Kaplan-Meier plotter database incorporates the mRNA expression data of more than 50000 genes and more than 10000 cancer samples, half of which are from GC patients. Our Kaplan-Meier plotter database analysis showed that the high expression of KIF23 was related to the good prognosis of GC patients, suggesting that KIF23 may inhibit the growth of GC, and can be used to mark its prognosis. In addition, HER-2 is linked to GC prognosis (34). Our subgroup analysis showed that KIF23 expression level had a significant effect on OS in HER-2 negative patients, but not in HER-2 positive patients, indicating that KIF23 may be related to HER-2 status, and both may jointly decide the prognosis of patients. In this study, high KIF23 expression was correlated with a longer prognosis of GC patients in early stages (stage 1 + 2), and longer OS and PFS of GC patients with high KIF23 expression (Table 2). These data strongly suggest that KIF23 is a potential prognostic biomarker of GC, especially for patients in early stages. Next, high KIF23 expression was also related to lymph node metastasis in GC patients, indicating that KIF23 may be a valuable prognostic indicator of GC metastasis. Furthermore, KIF23 expression was correlated with gender, stage (TNM), Lauren classification, differentiation and treatment. In TNM system, N0 indicates no regional lymph node metastasis, and N1–N3 indicate regional lymph node metastasis (35). In addition, high KIF23 expression demonstrated the highest HR value in predicting OS in GC patients in N1 stage, and PFS in GC patients in all the four N stages. Especially, high KIF23 expression was correlated with longer OS and PFS of GC in stage N (1 + 2 + 3) with a higher HR (Table 2). These results suggest that KIF23 mRNA expression level is highly indicative for good prognosis in GC patients with lymph node metastasis.
Although KIF23 is a transformation factor, we still do not know the mechanism through which it regulates GC. In general, we found several mutational expressional alterations of KIF23 in GC, mainly missense substitutions. However, the mutation frequency was relatively low (only 1.8%), and we failed to find a relation between these mutations and prognosis. More researches are needed to illustrate the clinical significance of these mutations. First, we analyzed the protein-coding genes related to KIF23 and its co-expression genes in GC tissues. The top 10 protein-coding genes positively correlated with KIF23 were BUB1B, BUB1, PRC1, ARHGAP11A, C15orf23, TPX2, CCNB2, FANCI, NUSAP1 and ZWILCH. On the other hand, the top 10 negatively correlated genes included LTC4S, MARCH2, GYPC, FXYD1, CLEC3B, CBX7, JAM2, PBXIP1,GFRA1 and MFAP4. Furthermore, STRING and Gene MANIA databases illustrated the protein interaction between KIF23 and other partners. The proteins related to KIF23 perform following biological functions: cell cycle, mitosis, DNA damage response, cell proliferation, and aging.
Thereafter, GO and KEGG pathway analysis revealed that an up-regulated expression of KIF23 was primarily related to cell cycle, and DNA replication, oocyte meiosis. Previous studies have also reported that KIF23 is associated with cell proliferation (13), and it also regulates cell cycle in many types of cancers (14). A large amount of evidence shows that Wnt/β-catenin signaling plays an important role in the proliferation, migration, invasion and angiogenesis of cancer cells (36, 37). Specifically, Wnt/β-catenin signaling can promote cancer development by regulating the tumor-immune cycle in tumor microenvironment, including T cell infiltration, dendritic cells, T cells and tumor cells (38, 39). The Wnt signaling pathway has been demonstrated to be one of the most frequently pathways in GC and controls several fundamental cell functions, including proliferation, differentiation, migration, and stemness (40). KIF23 promotes GC cell proliferation by activating the Wnt/β-catenin signaling pathway. Cell cycle proteins in malignant cells have attracted considerable interest as potential targets for cancer therapy. Further studies could help verify which processes and pathways KIF23 functions through in GC in vivo. Our results help to advance the understanding of the biological functions of KIF23 which make its overexpression so detrimental in GC.
We further found that KIF23 expression changed with the expression of marker genes of immune cells, thus highlighting the possible role of KIF23 in immunological regulation in GC. As the tumor develops, immune cells migrate from the blood into tumor tissue, a process closely related to clinical outcomes. TIICs are an independent predictor of sentinel lymph node status and cancer survival (41). TIICs exert an anticancer effect relying on immune cancer escape mechanism. Nevertheless, it remains challenging to confirm the interaction between immune cells and tumor cells using genomics analysis.
This study also found that the expression of KIF23 was correlated with the degree of immune infiltration in multiple cancer types, particularly in GC. We found that KIF23 expression was moderately and positively correlated with the degree of macrophage infiltration, and weakly and positively correlated with that of B cell, CD8+, CD4+, DC and neutrophil in GC (Fig. 7A). In addition, the correlation between KIF23 and immunological marker genes strongly suggests that in GC, KIF23 can control immune cell infiltration within the tumor micro-environment (TME). We observed a weak correlation between KIF23 and neutrophage markers, including NOS2 and CCR7 (Table 3). This suggests that KIF23 plays a role in regulating TAM polarization. Shu et al reviewed that target TAMs can achieve cancer immunotherapy (42), inhibiting the growth of tumors. TAMs have been widely deemed as a favorable condition for tumor development, including tumor cell growth, EMT, and immune suppression in TME.
We further found KIF23 level was correlated with markers of exhausted Treg cells and T cells in GC (CTLA4 and GZMB) (Table 3). This suggests that KIF23 can enhance Treg response to suppress T cell-mediated immunity. Furthermore, we found that KIF23 expression was correlated with that of multiple T cell markers (Th1, Th2, Tfh and Th17) in GC. This may correspond to the ability of KIF23 to regulate T cell responses in GC. Together, these results highlight the ability of KIF23 to regulate immune cell recruitment and activation in GC. In HCC,Pu et al. has investigated that KIF23 expression was correlated to immune cell infiltration, including B cells, CD8 + T cells, CD4 + T cells, monocytes, macrophages, neutrophils, and dendritic cells (43).
We further analyzed the correlation between KIF23 and monocytes and TAMs markers in the GEPIA database. Correlation results were similar to those in TIMER (Table 4). These findings suggest that KIF23 may regulate macrophage polarization in GC and ESCA. KIF23 expression increased with the infiltration of DCs in GC and ESCA. DC markers, such as HLA-DPB1、BDCA-1(CD1C) and BDCA-4(NRP1), also showed significant correlations with KIF23 expression. These results further reveal a strong relationship between KIF23 and DCs infiltration. In addition, KIF23 expression displayed a positive correlation with TGFB1 expression in Treg cells in GC. DCs can promote tumor metastasis by increasing the levels of Treg cells and reducing CD8 + T cell cytotoxicity (44). Further studies should be organized to prove whether KIF23 can mediate DC activity and tumor metastasis.
Several limitations may challenge the results of this study. First, this study is based on data retrieved from published articles and public repositories. Hence, the quality of some original data may be not unsatisfied. Second, the quantity of samples in the databases is in consistent change. Third, the statistical methods used in database analysis may influence the interpretation of the study results. However, we obtained similar results from multiple databases, which upholds our conclusion. Furthermore, we have not conducted in vitro and animal experiments to confirm our findings.
These results are helpful to understand the biological role played by KIF23 in the development of GC. In future clinical practice, the expression of KIF23 in gastric adenocarcinoma tissue may be used to predict the diagnosis and the efficacy of immunotherapy of patients.