Although most TCs have a better prognosis after surgery and adjuvant treatment with radioactive iodine 131, some TCs can progress to advanced refractory cancer, which is prone to metastasis and recurrence. Drugs currently used for advanced TC include sorafenib and levatinib[4], which are multi-target inhibitors that lack specificity and have particularly strong adverse effects. The translation of immunosuppressive agents, such as PD-1 and CTLA-4, from laboratory to clinical patient applications over the past decade [34] has been highly efficacious in the treatment of many patients with malignant tumors and has improved patient survival. Treatment of some advanced TCs with immunosuppressants alone or in combination with multi-target inhibitors can increase patient survival and improve the quality of life [35], but their efficacy is limited. Therefore, new biomarkers and drug targets are urgently required for early detection and individualized treatment to prolong survival.
Tumors are multigene, multipathway, multilevel, multifactorial joint actions in which the genes of certain tissue cells of the organism have lost the normal regulation of their own growth, resulting in abnormal cell proliferation. This ultimately leads to the formation of new organisms, that is, the formation of proteins encoded by the genes controlling tumorigenesis, resulting in the occurrence of tumors. Protein misfolding and assembly are the molecular basis of many diseases, including tumors[36]. Molecular chaperone proteins play important roles in protein folding and homeostasis. CCT, an important member of the type II molecular chaperone family, mainly consists of eight different subunits that are essential for maintaining the homeostasis of cytoskeletal proteins (including microtubule proteins and actin) and protein folding, and can be involved in the folding of proteins related to tumorigenesis [14]. It is well known that rapid proliferation of tumor cells requires large amounts of protein synthesis, and CCT may play an important role in tumorigenesis by regulating cancer cell growth, apoptosis, and genomic instability [9]. The clinical significance of the altered expression of various CCT subunits has been reported in many malignant tumors, and only a few studies have demonstrated the expression of the CCT complex in TC and the underlying mechanisms. It has been reported that CCT3 is significantly overexpressed in TC tissues compared to normal tissues adjacent to the cancer, and silencing of CCT3 inhibits tumor cell viability, proliferation, and induces apoptosis [37].
In this study, we first analyzed the expression differences of each CCT subunit in TC using TCGA database. Among them, CCT3, CCT7, and CCT8 were highly expressed in TC samples compared to normal tissues next to cancer, while TCP1, CCT2, CCT5, and CCT6B were expressed at low levels. This was verified using the GSE33630 and GSE27155 datasets in the GEO database, and there were differences in the analyzed results, which might be due to the number of samples and other factors. However, TCGA and GEO database analyses revealed that each subunit of CCT was abnormally expressed in TC compared with normal tissue samples next to cancer. In addition, our stage and pathological stage (T, N, M) correlation analysis using TCGA database showed that the expression of each subunit of CCT generally increased with tumor progression, which was consistent with the results of previous studies on CCT and hepatocellular carcinoma [38]. However, among them, only CCT6B was statistically correlated with N stage, whereas the others were not significantly correlated with N, T and M stages. In the prognostic analysis, high expression of TCP1, CCT2, CCT4, CCT5, CCT6A, CCT6B, and CCT8 and low expression of CCT3 and CCT7 were associated with low patient survival, of which only CCT6B was statistically significant, contrary to the results of a previous study in hepatocellular carcinoma[38]. This further suggests their potential role in cancer migration and metastasis and that CCT6B is the most valuable to study. Analysis of the possible pathway mechanisms involved in the CCT complex in TC showed that ALLOGRAFT_REJECTION, COMPLEMENT, and INTERFERON_GAMMA_RESPONSE, which are common to all CCT subunits, are involved in immune-related pathways.
The normal microenvironment (immune cells, fibroblasts, blood and lymphatic vessels, and interstitial extracellular matrix (ECM)) maintains tissue homeostasis and prevents tumorigenesis. Inflammatory mediators, reactive oxygen species, cytokines, and chemokines in the altered microenvironment promote tumor growth. Cells in the TME can be either tumor suppressors or tumor supports, which play a critical role in tumor progression and in modulating the efficacy of cancer therapy[39]. Immune escape in immunotherapy is a popular research topic for many scholars. The ESTIMATEScore represents the purity of the tumor, and in one study, it was found that a low purity of the tumor indicates an advanced stage and poor prognosis of the tumor [40]. In a previous study, CCT subunits were found to be associated with TME[23], and in the results of pathway enrichment analysis, each subunit of CCT was mostly enriched in immune-related pathways. Therefore, in this study, we first analyzed the expression of each subunit of CCT by correlating it with the immune infiltration of the stromalscore, immuneScore, and ESTIMATEScore. The results showed that CCT expression level was negatively correlated with the StromalScore, ImmuneScore, and ESTIMATEScore, and its immune index decreased with an increase in CCT expression. Immune cells are the most abundant non-cancerous cells in the TME and play important roles in regulating immune defense and tissue homeostasis. Tumor infiltration is usually regulated by T cells but also contains B cells, NK cells, DCs, macrophages, and neutrophils, which play an important role in the TME[41]. CD4 + T cells act as antitumor agents by regulating innate immunity, adaptive immunity, and immune detection[42]. In one study, T cell CD8 + subpopulation characteristics were identified by immunoassay as a prognostic marker for the recurrence of thyroid carcinoma [43]. Therefore, in the present study, the correlation of each subunit of CCT with immune cell infiltration was further analyzed using TIMER2.0 database, and the results showed a positive correlation with CD8 + T cell, B cells, and macrophages and a negative correlation with CD4 + T cells. CCT subunits are positively correlated with neutrophils and myeloid dendritic cells. CCT subunits were positively correlated with neutrophils and myeloid dendritic cells and negatively correlated only with CCT6B. CCT may contribute to the progression by affecting immune cells in the microenvironment, which needs to be confirmed in further experiments.
Immune checkpoints play an important role in maintaining self-tolerance and regulating physiological immune responses, and immune checkpoint dysregulation is an important mechanism for tumor immune escape [43]. Multi-target inhibitors such as sorafenib and levatinib, are generally used for the treatment of advanced TCs. Owing to the wide clinical application of immunosuppressants, such as PD-1 and CTLA-4, in recent years, they have been gradually applied to TC. Immunosuppressants alone or in combination with multi-target inhibitors are used for the treatment of advanced TCs with mutations, such as BRAF, and the emergence of drug resistance [44]. PD-L1 was more highly expressed in ATC than in the other TCs[45 46]. PD-1 immunosuppressants have better therapeutic efficacy in patients with PD-1/PD-L1-positive advanced ATCs and BRAF-mutated wild-type TCs, and improve patient survival. The results of this study showed that the expression level of each CCT subunit had a significant effect on the sensitivity and immune checkpoints of some drugs commonly used for TC. These findings suggest that CCT may be a potential therapeutic target.
The current study demonstrated that the expression levels of various CCT subunits differed significantly in TC, among which the expression of CCT6B was significantly associated with prognosis and may influence the progression through immune-related pathways. In addition, each subunit of CCT is closely related to immune regulation. Although we analyzed multiple databases, this study had some limitations. Although the results of bioinformatics analyses showed that the expression of CCT subunits was different in TC and correlated with clinical prognosis, and that there was a significant correlation with TME, we still need to further validate our results by in vitro or in vivo biological experiments. Moreover, whether CCT subunits affect tumor progression and clinical prognosis through the immune pathway remains unclear, and further studies are needed to verify our findings.