Colorectal cancer continues to be one of the leading malignancies and causes of cancer-related deaths worldwide. It is widely recognized that the prognosis of CRC patients is influenced by tumor infiltration in distant organs and lymph node metastasis. Telomeres have a primary function of maintaining genomic stability, which plays a critical role in cellular immortalization, a process that contributes significantly to tumorigenesis, infiltration and metastasis[39]. Hence, telomeres serve a crucial function in the progression of CRC. As far as our knowledge goes, this study is the first to evaluate the significance of telomere-related genes in the prognosis of CRC. Using public databases, we developed a prognostic model based on telomere-related genes. After verifying by external data, the results produced by the model were deemed stable and reliable. A clinical prognostic model with high predictive accuracy was constructed based on differential TMRGs and multiple clinical factors. Because just by scoring this model and some information that is commonly available in the clinic, our clinical prognostic model is more users-friendly. The low-risk group showed lower mutation rates, better response to immunotherapy response, and high-risk showed better drug sensitivity. There were no large differences in immune cell infiltration between telomere-associated molecular subtypes, but prognostic differences were still clear.
We performed GO enrichment analysis on 976 DE-TMRGs. The GO terms annotation indicated that DE-TMRGs were primarily participated in chromosome, telomeric region, and telomere maintenance. KEGG enrichment result included cell cycle, and DNA replication. It indicated that the occurrence and development of CRC are related to telomere abnormality. Several studies have suggested that cancer cells inhibit apoptosis by impairing the telomeric sheltering complex and generating short telomeres[40]. These shortened and dysfunctional telomere structures have been found to form breakage-fusion bridge cycles, which in turn can induce chromosomal instability[41], and a hallmark of oncogenesis[42]. It is known that in order to achieve a high replicative potential, cancer cells activate either the telomerase enzyme or the alternative lengthening of the telomeres (ALT) mechanism. This allows the cancer cells to obtain immortality, which is one of the key characteristics of cancer cells[43–45]. Telomeres play a crucial role in tumorigenesis, and both shortening and lengthening of telomeres may promote tumor development and progression. In addition, telomeres are closely related to the DNA biosynthesis process, replication process, and damage repair as well. Understanding the mechanisms behind telomere function and regulation is vital for developing new approaches for cancer prevention and treatment.
Through the qPCR experiment and analysis of the relevant clinical samples, we confirmed that the expressions of the three prognosis genes in CRC cell lines were lower than the normal cells and the control samples. The three genes included in the telomere-related genes risk model play distinct roles in the development of the disease. HSPA1A is one of the HSP70 family members, which is one of the more studied proteins of heat shock protein (HSP). HSP70 is found in the cytoplasm of cells, mainly helps proteins to fold correctly, and removes old or damaged cells[46, 47]. The study reported that HSPA1A was downregulated in CRC patients, and increased expression of HSPA1A1 was associated with a poor prognosis, which was consistent with our conclusion[39]. Furthermore, it was found by Hunt et al. that knocking out HSPA1A in mouse fibroblasts resulted in increased levels of spontaneous and radiation-induced chromosomal aberrations. This suggests that the HSPA1A protein may play a role in maintaining genome stability[48]. HSPA1A is associated with cancer cell proliferation, and HSPA1A promotes the proliferation of H22 hepatocellular carcinoma cells through TLR2 and TLR4 signaling. It is hypothesized that HSPA1A acts as an endogenous ligand for TLR2 and TLR4 to promote tumor growth[49].
PDE1B, also known as phosphodiesterase-1B, belongs to the family of cyclic nucleotide phosphodiesterases (PDEs). These enzymes play a crucial role in regulating the cellular levels of cAMP and cGMP by controlling their rates of degradation[50]. PDEs are classified into 11 different families (PDE1-PDE11) [51, 52]. Aberrations in PDE activity have been shown to contribute to tumorigenesis by reducing the levels of cyclic nucleotides, which are typically described as being present in malignant cells[53–55]. Interestingly, overexpression of one or more isoforms of PDE4 has been shown to promote the development of these tumors. The study reported that miR-5701 promoted apoptosis of clear cell renal cell carcinoma cells by targeting PDE1B[56]. There are few studies on PDE1B in CRC, and we found for the first time that this gene is associated with the prognosis of CRC.
TFAP2B known as transcription factor AP-2 beta Gene, belongs to TFAP2[57]. TFAP2 is a family of transcription factors that consists of five members, namely TFAP2A, TFAP2B, TFAP2C, TFAP2D, and TFAP2E14. These factors play an important role in regulating various aspects of tissue development during embryogenesis[58]. TFAP2B, as an oncogene, has been studied for several years and it has been shown that its expression can be associated with cancer prognosis[57, 59]. For example, Fu L et al. showed that TFAP2B was demonstrated to be highly expressed in human lung adenocarcinoma and it was positively correlated with the poor prognoses of lung adenocarcinomas[60]. Despite the wealth of research conducted on TFAP2B and its association with cancer prognosis, relatively little research has been conducted on its role in CRC. Further experimental and clinical studies are needed to better understand the potential implications of this transcription factor in the context of CRC.
To further confirm the differences in immune cells between the high and low risk subgroups, the infiltration abundance of 22 immune cells was calculated, and the results showed that there were significant differences in the infiltration of five immune cells, including initial B cells, M0 macrophages, and M2 macrophages, which were significantly more infiltrated in the high-risk than in the low-risk group, while the infiltration of resting CD4 memory T cells and active CD4 memory T cells were significantly less infiltrated in the high-risk group than in the low-risk group. These results suggest that immune infiltrating cells, which differ between high- and low-risk groups, play important roles in CRC. This may indicate the presence of more inflammatory responses and tumor-associated immune cells around the tumors in the high-risk group. In contrast, the levels of infiltration of resting CD4 memory T cells and active CD4 memory T cells were significantly lower in the high-risk group than in the low-risk group, which may imply that the immune system of patients in the high-risk group is less able to respond to tumors.
In order to gain a deeper understanding of the differences in the expression of immune checkpoints in patients from different risk subgroups, we examined the significance of the differences between two subgroups based on the expression of 48 immune checkpoints, thus providing important guidance and theoretical basis for individualized treatment and immunotherapy. The high expression of the majority of these checkpoints in the high-risk group may indicate some abnormalities or imbalance in the regulation of the immune system of the patients in the high-risk group, reflecting the increased immune escape mechanism of the patients in the high-risk group, i.e., the manipulation of the immune checkpoint signals by the tumor cells to evade immune attacks.
We calculated the IC50 of 367 chemotherapeutic drugs and analyzed the differences in IC50 values between the high- and low-risk groups, which showed that the high-risk group was more sensitive to 9 drugs, including pazopanib, but the low-risk group was more sensitive to 5 fluorouracil and CAY10566_416, which suggests that we should use the corresponding drugs for different conditions in order to obtain better therapeutic effects.
The prognostic clinical model, along with subtype analysis in CRC, can enable improved prediction of tumor progression, guide clinical decision-making, and facilitate personalized medicine and clinical immunotherapy. While this study has thoroughly verified the predictive ability of nomograms, further practical clinical research is still necessary to provide theoretical support.