CCT3 plays an important role in the tumorigenesis and progression of HCC. The mRNA and protein expression of CCT3 in hepatocellular carcinoma (HCC) tissues are higher than those in non-HCC tissues (33). Wong et al. founded that the expression level of CCT3 in tumors was significantly higher than that of matched adjacent non-malignant liver tissues in 10 cases of HCC with amplicon 1q21-q22 (P≦0.04) (23). The PPI of CCT3-related genes is enriched in KEGG signaling pathways, indicating that CCT3 may regulate HCC by targeting related sites and gene enrichment pathways. According to the Kyoto Encyclopedia of Genes and Genomes pathway analysis, CCT3 can influence HCC occurrence and development through the cell cycle and DNA replication pathways. Through the phosphorylation of transcription factors ( Figure 1A ) and STAT3, which enter the nucleus of liver cancer cells ( Figure 1B ), CCT3 has an impact on the development of liver cancer in HCC. CCT3 is a target affecting STAT3 activation and plays a critical role in the translocation of (p)STAT3 and STAT3 from the cytoplasm into the nucleus. HCC progression is partly affected by knockdown of CCT3, which may negatively regulate activation of the IL6/STAT3 signaling pathway and affect the progression of HCC partly by having an impact on the transport of (p)STAT3/STAT3 into the nuclei of HCC cells (42). By maintaining proper chromosome alignment and segregation (29), CCT3 can play a part in regulating microtubule structure and function (capturing the attachment site). By preventing the ubiquitination of YAP and TFCP2 brought on by poly (RC) binding protein 2 (PCBP2) in a beta-transducin repeat containing E3 ubiquitin protein ligase (trcp)-independent way, CCT3 extended their half-lives (28). YAP and TFCP2 are recognized as upstream triggers to increase the protein stability of YAP and TFCP2 in liver cancer cells. Bioinformatics prediction and luciferase reporter assays validated that circ-CCT3 could promote HCC progression through the mir-1287-5p/TEA domain transcription factor 1 (TEAD1) axis (43). Circ-CCT3 acted as a sponge for mir-1287-5p to enhance TEA domain transcription factor 1 (TEAD1) expression, which subsequently contributed to the activation of PTCH1 and LOX and consequently promotes tumorigenesis and progression. In addition, CCT3 can be associated with hepatocyte lipid metabolism in cells and in vivo via the long-stranded non-coding RNA LINC00326. Perturbation of the CCT3-LINC00326 regulatory network results in decreased intracellular lipid accumulation and increased lipid degradation, as well as diminished tumor growth in vivo (38).

Analysis of some recent cancer-driven genes identified CCT3 as a novel biomarker for liver cancer screening and diagnosis (44). In particular, for AFP-negative and small HCC patients, the CCT3 protein level showed good correlation with HCC etiology, tumor size, TNM stage, and Child-Pugh classification. The progression of malignancy is positively linked with the degree of CCT3 expression (29, 42). CCT3 overexpression is associated with poorer clinical outcomes and aggressive clinicopathological features, suggesting a poor prognosis for patients with HCC (33). In addition, CCT3 contributed to the invasion capacity of cells. This showed that CCT3 expression may be associated with metastasis in HCC. In conclusion, CCT3 is involved in the carcinogenesis and progression of HCC and serves as a potential therapeutic target and biomarker in hepatocellular carcinoma (28, 33).

CCT3 was significantly upregulated in a large proportion of human breast cancer tissues, and its overexpression was also significantly correlated with breast cancer clinical characteristics, including the clinical stage and the TNM classification. Both the mRNA and the protein levels of CCT3 are potential diagnostic biomarkers and therapeutic targets for breast cancer (45). Xu et al. found that CCT3 regulates breast cancer tumorigenesis by promoting cell proliferation and cell cycle progression. The knockdown of CCT3 inhibited proliferation, metastasis, and apoptosis of breast cancer cells, and the mechanism may be related to the regulation of the cell cycle, apoptosis, and multiple signal transduction pathways (36). They confirmed that the knockdown of CCT3 can induce apoptosis in breast cancer with the annexin method in this study. Perhaps the mechanism is related to CDC20 and p53. They are substrates of CCT. CDC20 is known to modulate key anti-apoptotic proteins Mcl-1 and Bim (46, 47), and p53 mediates cell apoptosis by activating the mitochondrial pathway and death receptor-induced apoptosis pathway (48). Secondly, down regulation of CCT3 significantly inhibited NF-κB activity and reduced the proliferation and metastatic capacity of breast cancer cells (30, 36). Qu et al. further explored the mechanism of action of CCT3 in breast cancer was performed through gain-and loss-of-function studies and found that CCT3 can directly bind mir-223 through the ceRNA network between mir-223 and β-catenin, thus affecting the activation of the Wnt/β-catenin signaling pathway, attenuating the regulation of mir-223 in the Wnt/β-catenin pathway and promoting breast cancer cell proliferation and tumorigenicity (45). In this study, they found that CCT3 can promote β-catenin nuclear translocation, and there is a high possibility that CCT3 may recruit β-catenin into the nucleus through direct binding. Wnt/β-catenin signaling was activated when CCT3 was knocked down. The target genes downstream, such as cyclin D1 and c-myc, were then transcribed with the help of β-catenin. These Wnt/β-catenin target genes promote breast cancer cell G1/S transition and other oncogene transcriptions, maintaining the malignant proliferative ability ( Table 2 ). In breast and prostate cancers, miRNA-mediated CCT3 inhibition can disrupt intracellular ROS homeostasis, leading to elevated ROS levels, altering intracellular free amino acid water and distribution for energy metabolism and promoting apoptotic mechanisms through oxidative stress and energy deprivation (39).

Investigations according to the GEPIA (Gene Expression Profiling Interactive Analysis) web portal demonstrated that CCT3 expression levels were significantly upregulated in both lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) tissues. Furthermore, it was concluded from the Cancer Genome Atlas (TCGA) and Genotype-Tissue Expression (GTEx) databases that a high expression level of CCT3 was associated with the poor prognosis of LUAD patients, albeit not in LUSC patients. Therefore, Xu et al. speculated that CCT3 may be closely involved in the tumorigenesis and progression of non-small cell lung cancer (NSCLC), and it might have a more prominent role in LUAD (40). Shi et al. found through further studies revealed that silencing of CCT3 resulted in the inhibition of Yes-associated protein 1 (YAP1) in NSCLC cells, decreasing the expression of YAP1 target genes and producing antitumor effects in NSCLC. In NSCLC cells, activation of the YAP1 by forced expression of constitutively active YAP1 mutants reversed the antitumor effects induced by CCT3 inhibition. This study unveils a possible role for the CCT3/YAP1 axis in NSCLC and suggests CCT3 as a candidate anticancer target (49). The increased expression of CCT3 in lung adenocarcinoma may lead to uncontrolled cell proliferation by promoting the expression of cyclin B1/CDK1 and thus accelerating cell cycle progression (40). Under cisplatin treatment, cell cycle protein B1 and CDK1 protein levels in lung adenocarcinoma cells were significantly reduced after CCT3 knockdown. The downregulation of CCT3 significantly inhibited the proliferation, invasion, and migration of lung adenocarcinoma cells, resulting in increased apoptosis and enhanced expression of the apoptosis marker cleaved caspase-3 (34) and leading to significant G2/M cell cycle arrest and apoptosis in lung adenocarcinoma cells, significantly reducing the tumorigenicity of cisplatin-treated lung adenocarcinoma cells. In addition, CCT3 downregulation could sensitize lung adenocarcinoma cells to cisplatin by inhibiting the Janus kinase 2/signal transducer and activator of the transcription 3 (JAK2/STAT3) pathway. It is suggested that CCT3 may be a new molecular target to overcome cisplatin resistance in LUAD patients (40) ( Table 2 ).

Dou et al. examined the effect of CCT3 on the proliferation and migration of cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC) in vitro through various experiments, including proliferation, Transwell, and flow cytometric assays. The results showed that CCT3 expression was significantly upregulated in CESC. In vitro, silencing CCT3 inhibited the proliferation, migration, and invasion of CESC cells. Downregulation of the CCT3 gene promoted apoptosis and cell cycle arrest in CESC cells and inhibited the expression of fibronectin 1 (FN1) protein. Furthermore, rescue assays demonstrated that CCT3 could promote the proliferation and migration process of CESC through FN1 (50). Saioa Mendaza et al. experimentally found that mir-877-3p promotes Squamous Cell Carcinoma of the Cervix (SCCC) cell migration and invasion by regulating cytoskeletal protein folding, mainly through the CCT complex, and that anti-mir-877-3p increased the expression of CCT3 in SCCC, leading to abnormal folding of actin and microtubulin, thereby impairing cell migration and invasion ability. Overall, CCT3 may be considered a new and promising biomarker that is closely related to the progression, prognosis, and survival of CESC and may become a therapeutic target for CESC (26).

Qian et al. study analyzed 2220 multiple myeloma patients (2380 samples) using 10 independent GEO datasets with different bioinformatics analysis methods and found that CCT3 was significantly overexpressed in multiple myeloma patients and that CCT3 overexpression was a poor predictor of survival, and its functional intensity was positively correlated with disease progression. CCT3 may play a supporting role in myeloid diagnosis. KEGG pathway analysis indicated that the CCT3 targeted genes were involved in the JAK-STAT3 signaling pathway, the Hippo signaling pathway, the WNT signaling pathway, and two pathways centralizing in leukemia-related terms (namely acute myeloid leukemia and chronic myeloid leukemia) (41, 51, 52). GSEA of gene sets differentially regulated in the CCT3 high and CCT3 low groups revealed that leukocyte migration, regulation of leukocyte migration, IL6/JAK/STAT3 signaling, and regulation of STAT cascade gene sets were significantly upregulated in the CCT3 high group. These results suggest that high CCT3 expression is associated with leukemia and the JAK-STAT3 signaling pathway, and that CCT3 expression may promote multiple myeloma progression by regulating MYC mainly through the JAK-STAT3 signaling pathway. These findings suggest that high CCT3 expression may serve as an indicator for the diagnosis and prognosis of multiple myeloma patients and a potential target for the future treatment of multiple myeloma (53).

Susannah Hallal et al. used TCGA data to interrogate gene expression levels and DNA copy numbers in silico for all eight subunits. Glioblastoma tissue had significantly higher levels of CCT2, CCT3, CCT5, CCT6A, and CCT7 gene expression relative to healthy brain tissue (52, 54). Human papillary thyroid cancer (PTC) tissues had significantly greater levels of CCT3 expression than did healthy paraneoplastic tissues (21). CCT3 is essential for the survival and growth of PTC cells, and the lentivirus-mediated knockdown of the CCT3 gene significantly reduced the proliferation and cell cycle progression of K1 cells and induced apoptosis in K1 cells. In addition, enhanced G2/M cycle blockade could also lead to increased apoptosis after CCT3 knockdown. The current findings suggest that CCT3 is a significant oncogene in PTC, and it was found that an increase in CCT3 expression was associated with the tumor area of PTC. In conclusion, CCT3 may be a promising potential candidate gene for molecular diagnosis and treatment of PTC and may serve as a predictive prognostic indicator for PTC patients and a molecular target for PTC treatment (21).

Protein is the actual functional molecule in cells and is responsible for almost all the biochemical activities of cells and is the basis of biological functions. CCT3 regulates the pathogenesis and metastasis of melanoma at the protein level. Roobol et al. reported that CCT3 is an important partner of the folded cytoskeletal component, and elevated CCT3 expression might impair the proper folding and assembly of complex proteins (35). CCT3 may regulate IGF-1 signaling, actin cytoskeletal signaling, and PTEN signaling pathways, which are known to function in epithelial tumorigenesis and cancer cell growth and play an important role in survival. CCT3 might play a role in regulating microtubule structure and function (capturing centromeres), which would affect the sensitivity of cells to these microtubule targets. In addition, cytoskeletal proteins (27), including actin and tubulin (31, 37), many cell cycle regulators (7), and tumor suppressors (37), are also substrates of CCT.

Numerous studies have shown that many proteins play a key role in the occurrence and metastasis of malignant melanoma (MM). Baruthio et al. detected a total of more than 100 proteins in the detergent-resistant membrane of melanoma cell lines, and melanoma cells are particularly resistant to detergents. Membrane protein structure is related to the degree of malignancy, suggesting that some membrane proteins might play a role in the progression of melanoma (55). Sinha et al. used two-dimensional electrophoresis and proteomics methods to analyze the protein expression profiles of drug-resistant melanoma cells and found that voltage-dependent anion channel proteins were overexpressed. Molecular chaperones were also overexpressed in resistant melanoma cells, including heat shock proteins (32). BRaf proto-oncogene, serine/threonine kinase (BRAF) is the most frequently mutated serine-threonine protein kinase involved in the pathogenesis of melanoma and is mutated in most melanoma and melanocyte lesions. However, BRAF mutations mainly occur in the progression of melanoma and rarely occur in the advanced stages, suggesting that this pathway plays a role in the initiation and progression of melanoma (56). The dephosphorylated protein cuts the filaments near the serosa to cause actin to polymerize to create new spikes to promote melanoma cell invasion.

In other settings, increased levels of plasma membrane intrinsic protein 2 (PIP2) can be achieved by binding and replacing actin filament capping proteins, such as gelsolin, at the ends of actin filaments (high levels of gelsolin reduce melanoma cell metastasis), thereby promoting actin polymerization. The mechanism of actin polymerization is dependent on the availability of intracellular actin monomers, which are associated with melanoma metastasis (24) ( Figure 2 ). The structure of actin is V-shaped, and the two arms are composed of two large and one small domain, and the gap between them is visible with nucleotide (ATP) adhesion. CCT binds to ATP and has weak ATPase activity. After actin enters the CCT side cavity, it binds tightly to the apical domain of CCT through the arm of the large domain. The driving force for cell body movement comes from the interaction of actin and myoglobin, which is mainly regulated by phosphorylation of non-muscle cell types. Many phosphorylation pathways that affect regulatory myosin subunits are up-regulated in metastatic melanoma cells. Rhoc increases actin-myosin contractility by binding to ROCK1 and ROCK2, and high expression of Rhoc is associated with melanoma metastasis. Inhibition of rhoc reduces the invasiveness of melanoma cells (57). Experiments have shown that the microtubule network acts on the adhesion point to separate it, which is beneficial to the protein transfer induced by dynein. Homomorphic tubulin is homomorphic. It enters the inner cavity of the CCT side loop to form a CCT-tubulin complex. When tubulin binds to the CCT side loop, it stops the information exchange of the loops, preventing the other loop from binding to other substrates. Some proteins are currently used for the diagnosis of MM. However, the diagnosis of melanoma by using a single protein index remains insufficient.

At present, there are many researches on CCT3 in liver cancer, breast cancer, lung cancer, and so on. There has also been some research into other tumors.

Tumor-repopulating cells (TRCs) are cancer stem cell (CSC)-like cells with highly tumorigenic and self-renewing abilities. Huang et al. identified CCT3 as a potential new stem cell-associated gene by integrating a network of membrane proteins, the WNT pathway, and cancer-related genes. Not only is it a key molecule in the selection of tumor-repopulating cells (TRCs), but it is also important for mechanotransduction and influences the selection process of TRCs. The number of TRC colonies was dramatically decreased by silencing CCT3, and TRC growth and selection were also slowed. Additional research revealed that CCT3 increased stemness and cell proliferation in vitro, while its inhibition prevented the development of tumors brought on by TRCs (64).