Many tumors have been found to have dysregulation of the PAX family gene [12]. The PAX family genes are evolutionarily quite conserved. They can encode a series of transcription factors and transcriptional regulators related to growth and development regulation, and exist in various organisms. It exerts its effects on cell and tissue formation and differentiation by regulating many intracellular signaling pathways. Although PAX family genes are associated with proliferation, invasion and progression of adverse outcomes in some cancers, there is no integrated analysis of PAX family genes across various tumors [20–22]. The present research systematically investigated PAX family gene expression and prognostic significance among individual malignancies, the association with clinical and immunological characterization, as well as the mechanism of tumor progression based on multi-omics data.
Our research discovered variations in the gene expression of numerous PAX family genes between para-cancerous and healthy tissues in a number of cancer types, indicating that these genes may be significant in cancer development and progression. For example, PAX8 expression of genes varied considerably between tumor tissues with high levels and noncancerous tissues (P ≤ 0.05). We speculate that this gene may promote carcinogenesis when highly expressed, but the specific mechanism remains unclear. Studies have shown that PAX8 to be a co-activator of transcription in renal cancer cells, activating genes that control regulating cell cycle and metabolic process.[23]. In addition, PAX8 can be activated in renal cell carcinoma to regulate the cell cycle and metabolic process of tumor cells. In addition, the clearance of PAX8 may reduce the invasiveness of renal cell carcinoma cells [24]. In addition, long-term Pax4 overexpression has been found to lead to hyperglycemia in pancreatic cancer by affecting β cell dedifferentiation [25]. This indicates that PAX member expression is closely related to the prognosis of some cancers In addition, we investigated the distinctions in the tumor cells and adjacent tissue in pan-cancer, as well as the impact of this gene family on the prognosis of various cancers. The analysis results show an elevated PAX1 expression is a preventive measure for KIRP [26] and THCA, as well as a risk factor for GBM; High expression of PAX8 factor for LGG [27] and susceptible to HNSC. The conclusion shows that high expression of some PAX gene members can affect the prognostic value of individuals with associated tumors, reduce OS time, and have an effect on their survival prediction. At present, our research on specific mechanisms is insufficient and has further exploration significance.
In Fig. 4A-4B, the mutation rate of PAX family genes accounted for 21.8%, and the amplification rate accounted for 15.51%, and it showed that the mutation rate of PAX1, PAX4, and PAX5 was very high, suggesting that the alteration of that gene family contributed to individual survival.. Based on this hypothesis, we analyzed the OS patients probability, and drew the survival curve between the mutant and non-mutation groups to illustrate this relationship more intuitively. The findings showed that the non-mutation group had a considerably greater OS rate than the mutant group (P ≤ 0.05). Moreover, we explored the change of overall survival probability between PAX family members and non-mutation group. The study showed that PAX gene mutation would affect the prognosis of patients and the patient’s quality of life. We investigated the association of copy number changes of PAX gene family members and the prevalence of corresponding genes. The findings revealed that the levels of mRNA expression of PAX1, PAX3, PAX5, PAX7, PAX8, and PAX9 were significantly different from the DNA copy number (P ≤ 0.05). For example, recent studies have shown that PAX8 can regulate tumor-stroma interaction, cell adhesion, proliferation, and migration, and mutations in PAX8 are thought to be associated with the development and progression of 90% of ovarian cancers [28, 29]. PAX9 gene mutation, amplification and deletion can promote the development of lung adenocarcinoma, squamous cell carcinoma, cervical cancer, ovarian cancer and breast cancer [30]. PAX8 is highly expressed in cervical cancer, and PAX8 transcripts are upregulated in cervical cancer samples, suggesting a correlation with cervical cancer development [31], and PAX8 expression is also upregulated in uterine adenocarcinoma, squamous cell carcinoma, endometrioid adenocarcinoma, and adenosquamous carcinoma [32–44]. These results suggest that PAX member gene mutations have regulatory effects on a variety of cancers. We also visualized the mutation type of each PAX gene family member and examined the link between the mutation kind and the activity of each family member.. From Figure S5, we can find that the gene expression of PAX5 gene increased after nucleotide deletion and truncation, and the difference was statistically significant (P ≤ 0.001). Previous studies have shown that PAX5 in B-acute lymphoblastic leukemia (B-ALL) can mediate the development and progression of B-ALL by not expressing or expressing truncated proteins lacking functional domains, resulting in loss of allelic function [45–48]. In addition, study found that down-regulation of PAX2 expression by antisense oligonucleotides is associated with growth inhibition of human renal cancer cells [49]. In other words, the mutation of PAX gene can affect its gene expression, thereby regulating the incidence and tumor proliferation.
The present study analyzed the PAX family expression in pan-cancer and the correlation of PAX genes with common clinical features. These clinical characteristics include the patient's disease stage and the response to initial treatment. Previous studies have shown that overexpression of PAX2 can promote tumor proliferation and growth in vivo and in vitro in a mouse ovarian cancer xenograft model, and high PAX2 expression is associated with shorter PFS in 152 patients with stage III-IV serous ovarian cancer [50–52]. In other words, the expression of PAX gene family can affect the progression-free survival of patients, reflecting that the expression of PAX gene can affect the efficacy of patients and the quality of life of patients to a certain extent.
Immune cells, tumor microenvironment and stem cell index are the focus of most scholars. By analyzing the correlation of these hot spots with PAX expression, we found that PAX5 expression correlated with previous immunophenotyping in most cancers. It has been found that PAX5 can activate the chromatin of key genes involved in B cell signal transduction, adhesion, migration and immune function during B cell development, thus affecting the immunophenotype [53]. It can be inferred that the high expression of some PAX family genes can participate in the regulation of immune process, thereby changing the interaction between tumor and immune cells and promoting the occurrence and development of tumors.
TME is composed of tumor cells and non-tumor cell components, and the non-tumor cells mainly include stromal cells and various lymphocytes. They can support the biological behavior of tumors [54], for example, tumor-associated fibroblasts can promote the epithelial-mesenchymal transition of tumor cells, thereby making tumor cells more aggressive [55]. Tumor-associated macrophages can support tumor growth, angiogenesis, invasion and metastasis by secreting a large number of cytokines and growth factors [56]. In addition, the increased content of stromal cells and the infiltration of immune cells in cancer patients will promote the proliferation, invasion and metastasis of tumors, which are positively correlated with TNM stage, T stage and M stage [57]. The matrix score of the tumor microenvironment can quantify the tumor tissue interstitial cells, and the immune score can quantify the immune cells in the tumor tissue, so as to explore the purity of the tumor. We examined the link between PAX family and pan-cancer interstitial and immunological score to investigate the interaction between tumor microenvironment and PAX genes. These members found to be significantly associated with stromal scores in pan carcinoma, as well as immune scores. This suggests that regulation of PAX gene can influence the number of tumor immune cells and stromal cells, and thus the tumor microenvironment.
The expression of PAX family genes was negatively correlated with mRNA expression based dry score (RNAss) in most tumors, and also negatively correlated with DNA methylation based dry score (DNAss) with a few positive correlations. It is speculated that the expression level of PAX gene family may affect the dryness of related tumor cells. Some scholars have shown that in glioblastoma, PAX3 knockdown can inhibit the proliferation and invasion and induce cell apoptosis, while overexpression can promote the proliferation, invasion and inhibit the apoptosis of glioma cell lines [58]. Another study found that PAX9 knockdown can inhibit some biological behaviors of ovarian cancer cells, such as proliferation, invasion and migration [59]. In summary, it can be concluded that the expression of PAX family genes is significantly correlated with the stemness of tumor cells in most cancers. There is little research on its specific mechanism, so it has further exploration significance.
Tumor immunotherapy, which uses lymphocytes to combat cancer, is being shown to be a potent anti-tumor tool and is now more common in clinical trials. However, for many patients with solid cancer, the local immunodeficient cancer environment is difficult to change, and clinical progress is minimal [60]. At present, immune checkpoint inhibitors (ICIs) targeting programmed cell death protein-1 (PD-1) and programmed cell death ligand 1 (PD-L1) have been widely used in clinical practice and are often used to treat advanced cancers [61]. As a result, research into immune checkpoints is required. We extracted over 40 typical immune checkpoint genes and studied the link between the activity of various PAX family members and such immune checkpoint genes (Figure S7). For example, in various cancers, the PAX5 gene is significantly associated with the PD-L1 immune checkpoint, indicating that the expression of the PAX gene is significantly correlated with the expression of many immune checkpoint genes (Fig. 8A), and intervention of the PAX5 gene targeting the relevant immune checkpoint may be an effective therapeutic option.
Tumor mutation burden (TMB), defined as the total number of somatic gene insertions, coding errors, deletion errors, and base substitutions detected per 1 million bases in the tumor genome, is a promising new biomarker [62]. A number of studies have shown that immunotherapy is more effective in patients with high TMB, and TMB also has a certain predictive effect in malignant tumors such as lung cancer [63] and melanoma [64]. Microsatellites are short tandem repeat sequences distributed throughout the genome. When DNA mismatch repair mechanism is damaged, mutations can occur, leading to microsatellite instability (MSI), presenting a highly mutant phenotype of genomic microsatellite [65, 66].
Immune oncology, a novel pillar of modern cancer treatment, is revolutionizing the way we approach cancer therapy. Immune checkpoint inhibitors (ICIs), such as PD-1 and PD-L1, can regulate the signaling pathways of T cell-related immune responses, enabling them to produce effective anti-tumor responses. Although ICI therapy has made a breakthrough progress, it also has side effects, and not all patients respond optimally. Therefore, it is very desirable to find biomarkers that can help identify patients who are likely to benefit from ICI treatment [67]. Currently, biomarkers used in clinical practice include PD-L1 immunohistochemistry, microsatellite instability - high (MSI-H), mismatch repair deficiency (dMMR), and tumor mutational burden (TMB). In order to explore the correlation between the expression of PAX family genes and the therapeutic effect of ICI, we analyzed the correlation among the expression of PAX family members in pancarcinoma, TMB, and MSI. According to the analysis in Fig. 8, we conclude that PAX family genes are significantly correlated with TMB and MSI in some cancers, that is to say, the expression of PAX family genes is also correlated with the therapeutic effect of ICI. We can see that the expression level of PAX5 gene in MSI was negatively correlated with most cancers, such as DLBC, TGCT, etc. (P ≤ 0.05), suggesting that MSI increases with PAX5 gene expression reduction, thus making these tumors highly responsive to immunotherapy and achieving a good ICI treatment response.
In addition, we evaluated the sensitivity of BLCA to commonly used chemotherapeutic agents based on expression of PAX family genes. Studies have shown that PAX9 is highly expressed in drug-resistant ovarian cancer cell lines and tumor tissues of drug-resistant patients, and the sensitivity of drug-resistant cells to cisplatin is also increased through further in vitro experiments by down-regulating PAX9 [68]. In non-small cell lung cancer (NSCLC), studies have shown that PAX6 can regulate the stemness and differentiation of tumor cells, affect cell resistance and proliferation, and has the potential to become an effective prognostic factor of NSCLC [69]. In addition, some scholars have pointed out that PAX6 affects the efficacy of mothiazole in glioma by affecting the mechanism of action of mothiazole in vivo, which is closely related to the drug sensitivity of mothiazole [70]. However, in our study, we observed that PAX3 expression was positively correlated with drug sensitivity of Vemurafenib, Dabrafenib, Selumetinib, and other drugs, that is, patients with higher PAX3 expression had better treatment effects receiving these drugs. While PAX8 gene expression was positively correlated with clinical chemotherapy drug resistance. Patients with elevated PAX8 expression should exercise caution when considering the use of these drugs, as higher PAX8 expression corresponds to poorer treatment outcomes. In essence, PAX family gene expression can affect the chemotherapy drug sensitivity, thus affecting the curative effect and prognosis of patients. The specific mechanisms underlying these effects warrant further exploration.
BLCA is the most common urinary system tumor, the tumor has been our research hot spot. To understand the expression of PAX gene in BLCA, we examined the expression of PAX8 gene in patient tumor tissues and adjacent tissues using qPCR and immunohistochemistry. The results showed that PAX8 gene expression was higher in tumor tissues than in adjacent tissues. This suggests that PAX8 gene is highly expressed in BLCA tumor tissues, which may be related to the occurrence and development of BLCA, and the targeted therapy of PAX8 gene may be a breakthrough point in the treatment of BLCA. In recent years, great progress has been made in the treatment of BLCA, predominantly centering on chemotherapy. Although this therapy has a survival advantage, its efficacy is unsatisfactory due to severe side effects. Therefore, targeted drug therapy for the disease has become necessary, and it can also open up promising new ways to improve the prognosis of patients [71]. At present, targeting the immune checkpoint immune drugs in metastatic bladder cancer also showed very good curative effects. Thus, our endeavor is to identify targeted molecular pathways in BLCA, thereby elevating patient prognosis and survival rates.
In this study, we initially explored the PAX family genes and suggested that their expression was correlated with the tumor microenvironment and patient prognosis of BLCA. To this end, we divided all samples into high and low expression groups based on the median PAX expression level in BLCA. Subsequently, we performed GSEA to find out which Hallmark and KEGG pathways were enriched in these high and low expression groups for each PAX gene. The data showed that the KEGG_OLFACTORY_TRANSDUCTION pathway was enriched in the high expression group of PAX1 to PAX8 genes and in the low expression group of PAX9 genes. Other pathways in different PAX gene enrichment results are not completely consistent, prompt PAX family genes may participate in the BLCA progress through different mechanisms. In addition, investigating the interplay between PAX family genes and KEGG_OLFACTORY_TRANSDUCTION pathway in BLCA enhances our understanding of targeted molecular pathway therapies for BLCA.
In the TCGA cohort, we analyzed the expression level of PAX in five immune subtypes (C1-C4 and C6). Our investigation revealed notable variations in PAX5 and PAX6 expression levels across different subtypes. In addition, we examined the relationship between PAX expression and tumor grade, tumor subtype (non-papillary or papillary), tumor stage, and tumor size range stage (T stage) in BLCA. Results showed that the different tumor stage, tumor T stage, and tumor subtypes, significantly changed the PAX5 and PAX6 expression levels within bladder tumor tissues. Some studies have shown that Pax-5 can be expressed in Neuroendocrine neoplasm (NENs), and its expression is related to G grade, stage, prognosis, and positively correlated with the malignant degree of tumor [72]. Sun Fei et al. revealed that the higher the expression of PAX8, the higher the pathological classification of glioma, and there was a significant positive correlation between the two, and stressed that PAX8 can promote the occurrence and development of glioma [73]. In the current study, gene expression levels of PAX5 and PAX6 genes significantly correlated with tumor unhealthy grade, cancer stage, and T stage, and the expression levels of PAX5 and PAX6 genes in the non-papillary type of cancer increased compared to those in the papillary type of tumor, showing that PAX5 and PAX6 gene activity relates to the invasion, appearance, and formation of BLCA and may play a role in its development.
We observed that PAX family gene expression was closely related to the infiltration of immune cells in tumors, implying that PAX levels might influence tumor immune system response. To further explore the family genome variation effect on immune infiltration, we have different CNVs BLCA PAX genes or mutations between groups common immune cells abundance variance analysis. It was concluded that PAX5 and PAX6 genes were significantly positively correlated with immune cell content, and PAX3 and PAX7 high mutations could increase CD8 + T cell content. It can be speculated that PAX5 and PAX6 gene high expression, PAX3 and PAX7 high mutation can promote tumor invasion, thereby causing a large number of immune cell infiltration in vivo. Some scholars have shown that PAX5 is expressed in breast cancer and regulates the invasion and progression of breast cancer [74]. It has also been shown that inhibition of Pax6 gene expression can greatly minimize the tendency of retinoblastoma to grow and invade [75]. In conclusion, PAX family gene expression can affect the invasive ability of BLCA tumor cells and regulate its malignant progression process. In addition, copy number variation can affect immune cell content, which may be due to its effect on gene transcription, thereby affecting immune cell infiltration, or it may be that copy number variation directly affects protein modification or expression, thereby affecting immune cell infiltration. Some investigators believe that PAX5 mutations may reduce the quantity of effector T cells that reside in the tumor's microenvironment, resulting in cancer tolerance to the immune system [76]. In summary, it is reasonable to believe that the proliferation of PAX family genes may affect the chemotaxis of immune cells via some mechanism, contribute to the control of immune invasion, and thus affect the immunotherapy effect of patients, but the specific mechanism remains unknown. The primary limitation of our research was that the data utilized came from open databases, and the particular process and method still need to be validated in vivo or in vitro. Furthermore, there is complexity because we analyzed data from multiple omics of the PAX family in pan-cancer.