The high morbidity and mortality of CRC have become a major risk to people's physical and mental health. Although the current therapeutic system for CRC is well established, the spread of tumor cells and the recurrence of primary foci are still the leading causes of treatment failure. Previous research has revealed that tumor is a class of cell cycle diseases whose occurrence and development are closely related to the deregulation of the normal cell cycle17. Therefore, the in-depth study of therapy targeting cell cycle-related genes could have a broad prospect.
CCNB1 is a representative member of the cyclin protein B family, which is a mitosis-related regulatory protein mostly produced during the G2/M phase8, 9. Cell cycle dysregulation is one of the hallmarks of cancer. Overexpression of CCNB1 can lead to uncontrolled growth of cancer cells throughout the cell cycle9. Numerous studies have demonstrated that CCNB1 presents high expression in various tumor tissues, including in CRC18–20. However, the diagnostic and prognostic value of CCNB1 in CRC has not yet been thoroughly investigated. Therefore, in the present study, we explored the clinical and prognostic value of CCNB1 in CRC by bioinformatics approaches, aiming to provide new molecular markers for CRC treatment.
We first observed the distribution of CCNB1 expression in normal human tissues and vertebrates, finding that CCNB1 was widely expressed in various normal tissues while having conserved expression in vertebrates. Importantly, CCNB1 expression was significantly upregulated in several tumor tissues, showing low tissue and tumor specificity. Subsequent analysis of the data in the TCGA database revealed that CCNB1 expression was significantly higher in CRC tumor tissues than in normal tissues, and the results of paired difference analysis of cancer and paracancerous tissues from patients with CRC supported this conclusion. Clinicopathological characterization further showed a significant correlation between CCNB1 expression, CRC pathological grade, and TNM stage. Moreover, we found that CCNB1 expression had a decreasing trend with increasing CRC pathological stage, suggesting that lower CCNB1 expression may indicate poor prognosis in CRC patients. Moreover, CCNB1 expression decreased with the progress of the CRC clinical stage.
Next, we divided CRC cases into high and low-expression groups according to CCNB1 mRNA levels. Analysis of the prognostic relationship between CCNB1 and CRC patients revealed that PFS was significantly prolonged in the high CCNB1 expression group compared with the low CCNB1 group, which was consistent with the results of the prior clinical characteristics analysis. Univariate and multifactorial independent prognostic analysis suggested that CCNB1 was not an independent prognostic factor for patients with CRC. In addition, ROC curves demonstrated that CCNB1 was useful in predicting the survival probability at 3 and 5 years.
We then analyzed the regulatory genes and differentially expressed genes associated with CCNB1 to further explore the mechanism of CCNB1 in CRC. Our results showed that CCNB1 expression was negatively correlated with genes such as BCAS3 and ZBTB4 and positively correlated with the expression of PTTG1 and H2AZ1. Genes like PTTG1 and CDC25C primarily promote tumor development by affecting cell transformation, aneuploidy cell division, apoptosis, and mitosis21, 22, 24. The results suggest that the mechanism of CCNB1 promoting tumor development may be associated with the above biological processes. Meanwhile, differential gene analysis revealed that PIWIL1, PLA2G2A, LRP1B, KCNJ9, and other genes were significantly different between high and low CCNB1 expression groups, indicating that these genes may be potential regulatory genes of CCNB1. Based on CCNB1 interacting proteins and co-expressed genes, we performed GO, KEGG, and GSEA enrichment analysis to explore the molecular mechanism and function of CCNB1 in CRC pathogenesis, finding that CCNB1 was involved in various biological processes and related signaling pathways in cancer development. Further analysis by the STRING database revealed that the process of CCNB1 promoting tumorigenesis development was associated with driving the cell cycle and promoting cell division, which was consistent with our previous results of differential gene analysis.
The TME is becoming an increasingly important and challenging field of current tumor research. Herein, we analyzed the immune correlation between CCNB1 and CRC TME. Immune and stromal cells are two important non-tumor components of the TME, where the immune and stromal scores are two vital predictors of tumor purity. The ability to predict the composition of stromal and immune cells is extremely valuable for tumor diagnosis and prognosis evaluation. ESTIMATE algorithm results showed that the stromal score and composite score of the CCNB1 high expression group were considerably lower than the low expression group, indicating that the CCNB1 high expression group had higher tumor purity. Immune cell differential analysis showed that the percentage of CD4 (+) T cells, resting NK cells, and active mast cells were all considerably greater in the CCNB1 high expression group than in the low expression group. Also, in terms of Tregs, the high-expression group was significantly lower than the low-expression group. We also evaluated the relationship between CCNB1 expression and the infiltration of various immune cells, finding that CCNB1 expression was positively correlated with CD4 (+) T cells, M1 and M2 Macrophages, while it was negatively related with regulatory T cells (Tregs), and M0 Macrophages.
The tumor mutation burden (TMB) was used as an updated independent predictor for the outcome of immuno-checkpoint inhibitor (ICI) across multiple tumor types. Although this method can predict the efficacy of PD-L1, its positive rate in CRC patients is low15. TMB assay could be a more comprehensive biomarker for assessing the efficacy of immunotherapy in patients with CRC. Our results showed that CCNB1 was positively correlated with TMB, which suggests that CCNB1 could be an important predictor of tumor immunotherapy. Immune checkpoint correlation analysis revealed significant negative regulatory relationships between CCNB1 and TNFSF4, TNFRSF8, and NRP1. Tumor drug sensitivity screening is a precondition for clinical medication. If medications are prescribed based on clinical experience, individual distinctions are frequently overlooked, resulting in poor overall efficacy. Therefore, conducting tumor drug sensitivity screening before or during clinical use and selecting sensitive drugs for individualized treatment based on the results are of utmost importance. The therapeutic efficacy of the medicine can be enhanced, and the harmful side effects can be minimized, thus helping to avoid the blindness of empirical medication. Drug sensitivity analysis revealed significant differences in the efficacy of chemotherapeutic medicines such as 5-Fluorouracil, bexarotene, bleomycin, camptothecin, and cisplatin between the high and low CCNB1 expression groups. These drugs are potential targeting agents against CCNB1.
In conclusion, our investigation demonstrated that CCNB1 expression is considerably elevated in CRC tissues and is linked with the clinicopathological and TNM stage of CRC patients. Furthermore, it regulates many genes and is involved in regulating multiple genes. In addition, CCNB1 is involved in the development of CRC through related pathways. Expression of CCNB1 may also affect the level of immune cell infiltration and the regulation of immune checkpoints. To sum up, CCNB1 may be used as a diagnostic and sensitive prognostic marker for CRC, which participates in the infiltration of immune cells in TME and may serve as a new direction for clinical diagnosis and treatment of CRC.