Cancer is a genetic disease, as occurrence, development, and metastasis are controlled by some genetic and epigenetic alterations in the genome (15). Pan-cancer analysis of multi-omics data, combined with bioinformatics methods, can provide a special platform to identify the common molecular characteristics and the molecular mechanisms of various cancer types (16). In this study, we analyzed the molecular alterations of CDK family genes in multiple aspects, such as the genome, transcriptome, and epigenome. Firstly, gene expression levels of CDK family members were extracted from TCGA Pan-cancer. Across various cancers, we observed that CDK1, CDK5, CDK4, CDK2, CDK16, CDK7, CDK6, CDK12, CDK8, CDK17, and CDK13 were up-regulated in a wide range of cancers, whereas, CDK14, CDK15, and CDK20 were down-regulated in some cancer types, and CDK9, CDK11A, and CDK11B remained unchanged. Moreover, aberrant methylation of many genes has been associated with transcriptional inactivation of genes in various cancers (17). To determine the correlation between methylation and expression, we screened tumors with different levels of methylation and analyzed the correlation between methylation and target gene expression in different types of cancers. We found that the methylation levels of CDK4, CDK6, and CDK18 genes were significantly associated with gene expression in some cancer types. Previous evidence demonstrated that CDK4 and CDK6 could be frequently considered together as promoters of G1 progression (18). As a new regulator of genome stability, CDK18 could prevent DNA damage accumulation and genome instability (19).
Due to the deregulation of cell cycle across a broad range of cancers, cancer cells can frequently show aberrant proliferation, genomic instability consisting of increased DNA mutations and chromosomal aberrations, as well as chromosomal instability (1). In the present study, we identified the genetic mutations in the frequently mutated genes of the CDK family in different cancers. The most mutation frequency was CDK12, followed by CDK13. In line with the above, CDK12 mutations have also been reported in some cancer types, such as lung cancer (20) lymphoma (21), and advanced carcinoma of unknown primary (22). Notably, it is well known that CDK12 and CDK13 have similar biological processes, with both regulating RNA splicing and alternative splicing, maintaining self-renewal in embryonic stem cells (23). Collectively, these findings indicated that multilevel data integration exhibited CDK members with epigenetic phenotypes and distinct mutations.
To understand the functional relevance of CDK family genes, we further assessed their involved signaling pathways. We showed that activation of CDK6, CDK4, CDK2, and CDK1 could activate apoptosis and cell cycle, and inhibit RAS/MAPK. CDK17, CDK15, and CDK14 activation could activate EMT and suppress cell cycle. Besides, activation of CDK16 could activate the cell cycle, and CDK7 could inhibit RAS/MAPK, RTK, and TSC/mTOR pathways. Since cell cycle abnormalities are common in different types of cancer, it has always been considered a potential therapeutic target (24). Thus, it is of great significance to elucidate the functional roles of these CDK genes as biomarkers for therapeutic intervention. In addition, due to their role in cell cycle control, CDKs are viewed as targets of genetic manipulations in various cancers, leading to accelerate the development of small molecule drugs against CDKs as an anticancer approach (25). Therefore, we screened the CDK family genes with small molecule drugs to find potential candidate drugs that could reverse abnormally expressed CDK genes in various cancer tissues. Our analysis revealed that BX-912, PIK-93, XMD13-2, and KIN001-236 were negatively associated with CDK13 expression. Z-LLNle-CHO was negatively correlated with CDK6. PLX4720 was negatively associated with CDK2. Besides, NPK76-Ⅱ-72-1 was negatively related to CDK11A. PIK-93 was negatively associated with CDK14. Trametinib was positively associated with CDK19 and CDK1. TGX221 was positively correlated with CDK8. Navitoclax was positively associated with CDK7. Furthermore, Methotrexate presents the most significant positive correlation with CDK16 expression and has a significant negative correlation with CDK9 and CDK11B. Previous studies have demonstrated that P276-00, as an inhibitor of CDK1, CDK4, and CDK9, could make pancreatic cancer cells sensitive to gemcitabine-induced apoptosis, and inhibit tumor growth and angiogenesis (26). Flavopiridol could also act as a pan-CDK-inhibitor of CDK1, 2, 4, 6, 7 and 9 (27), and the application of this drug in the treatment of chronic lymphocytic leukemia has achieved satisfactory results (28). Likely, these drugs of our research results could act as chemotherapeutic agents and be widely used to improve the effects of cancer therapeutics.