3.2. The expression difference and survival analysis of Hub gene in pan-cancer
We examined the expression levels of Cuproptosis-related genes in both tumor and non-tumor tissues using data from the TCGA database. As shown in Fig. 2A, with the exception of DLAT, the expression levels of the other 9 genes were significantly different (P < 0.05) between tumor and non-tumor tissues. We then further analyzed the expression levels of the hub genes, DLD and LIAS, across different cancer types using TCGA samples (Fig. 2B). To investigate the expression differences between tumor and adjacent tissues in pan-cancer and to determine which cancers show significant expression differences, we used the R package to analyze the TCGA expression matrix (Fig. 2c). We found that there were no differences in LIAS expression between tumor and adjacent tissues in ACC, COAD, KIRC, KIRP, PCPG, while the other 25 tumor types showed significant differences in expression. In the case of DLD, there were no differences in expression between tumor and adjacent tissues in CESC, COAD, ESCA, HNSC, OV, UCEC, and UCS, while significant expression differences were observed in the other 23 tumor types (see Fig. 2C). We utilized the R software package to observe the expression of DLD in six types of tumors, namely TCGA-GBMLGG (N = 619, p = 3.6e-5, HR = 1.85 (1.39, 2.47)), TCGA-LGG (N = 474, p = 9.3e-4, HR = 2.14 (1.37, 3.32)), TARGET-LAML (N = 142, p = 1.3e-5, HR = 1.46 (1.23, 1.73)), TCGA-BRCA (N = 1044, p = 0.03, HR = 1.29 (1.02, 1.64)), TCGA-LUAD (N = 490, p = 0.03, HR = 1.30 (1.03, 1.64)), and TCGA-UVM (N = 74, p = 0.03, HR = 1.82 (1.07, 3.10)). We found that medium to high expression of DLD was associated with poor prognosis and showed significant carcinogenic effects. In addition, we observed that low expression of DLD in three tumor types, TCGA-KIPAN (N = 855, p = 1.0e-9, HR = 0.67 (0.59, 0.76)), TCGA-COADREAD (N = 368, p = 1.0e-2, HR = 0.66 (0.48, 0.90)), and TCGA-KIRC (N = 515, p = 7.2e-7, HR = 0.66 (0.56, 0.78)), was also associated with poor prognosis. Furthermore, we examined the expression of the target gene LIAS and found significant carcinogenic effects in three tumor types, TARGET-LAML (N = 142, p = 0.01, HR = 1.39 (1.08, 1.80)), TCGA-THCA (N = 501, p = 0.04, HR = 3.40 (1.09, 10.64)), and TCGA-KICH (N = 64, p = 0.04, HR = 4.63 (1.00, 21.42)). However, we observed lower expression of LIAS in five additional tumors that was associated with poorer prognosis, namely TCGA-GBMLGG (N = 619, p = 3.6e-4, HR = 0.56 (0.41, 0.77)), TCGA-KIRP (N = 276, p = 0.01, HR = 0.52 (0.31, 0.88)), TCGA-KIPAN (N = 855, p = 1.4e-7, HR = 0.56 (0.45, 0.70)), TCGA-KIRC (N = 515, p = 1.8e-6, HR = 0.56 (0.44, 0.71)), and TCGA-MESO (N = 84, p = 0.02, HR = 0.63 (0.43, 0.92)) (see Fig. 2D for visualization). To validate our findings, we obtained sequencing data of acute leukemia GSE37642 with survival data from the GEO database. We then analyzed the data using the R packages "GEOquery" and "survival". As shown in Fig. 2E and Fig. 2F, we found that the expression of HUB genes LIAS and DLD was higher than normal in LAML patients (P < 0.005). Moreover, the OS was lower in patients with high DLD expression than in those with low expression (p < 0.05857), which supports our conclusion. However, the difference in the expression of the HUB gene LIAS did not lead to an overall survival difference. This could be due to issues that occurred during data cleaning, and further validation analysis is needed.
3.5. Effect of Hub gene on immune infiltration
To investigate the immune roles of Cuproptosis-related Hub genes across various cancer types, pan-cancer analyses are crucial for identifying potential candidates for immunotherapy. Our findings demonstrated that DLD had a negative correlation with most immunomodulators in KIPAN, while it was positively correlated with most immunomodulators in OV. On the other hand, LIAS had a negative correlation with most immunomodulators in NB and THCA, but was positively correlated with most immunomodulators in PRAD (Fig. 5A). Additionally, we calculated the immune infiltration scores of 10,180 tumor samples across 44 tumor types and used the corr.test function in the R package to determine the Spearman's correlation coefficient between the genes and immune infiltration scores in each tumor. We determined the immune infiltration score that was significantly correlated with gene expression across 23 different cancer types. Of these, we observed four cancer types that were significantly positively correlated with immune infiltration, including TCGA-LIHC (N = 363, R = 0.11, P = 0.03), TCGA-PAAD (N = 177, R = 0.16, P = 0.04), TCGA-LAML (N = 214, R = 0.33, P = 7.1e-7), and TARGET-ALL-R (N = 99, R = 0.43, P = 9.6e-6) (Fig. 5B). We also found 19 significant negative correlations, including TCGA-UCEC (N = 178, R=-0.22, P = 3.7e-3), TARGET-LAML (N = 142, R=-0.23, P = 7.0e-3), TCGA-BRCA (N = 1077, R=-0.08, P = 6.9e-3), TCGA-CESC (N = 291, R=-0.14, P = 0.02), TCGA-LUAD (N = 500, R=-0.11, P = 0.01), TCGA-ESCA (N = 181, R=-0.20, P = 8.4e-3), TCGA-STES (N = 569, R=-0.22, P = 5.8e-8), TCGA-SARC (N = 258, R=-0.31, P = 2.7e-7), TCGA-KIPAN (N = 878, R=-0.41, P = 3.9e-36), TCGA-STAD (N = 388, R=-0.14, P = 5.7e-3), TCGA-KIRC (N = 528, R=-0.11, P = 0.01), TCGA-LUSC (N = 491, R=-0.28, P = 3.1e-10), TARGET-WT (N = 80, R=-0.32, P = 3.6e-3), TCGA-SKCM-P (N = 101, R=-0.26, P = 8.6e-3), TCGA-BLCA (N = 405, R=-0.18, P = 3.4e-4), TCGA-THCA (N = 503, R=-0.23, P = 1.2e-7), TARGET-NB (N = 153, R=-0.36, P = 4.3e-6), TCGA-TGCT (N = 132, R=-0.35, P = 3.1e-5), and TCGA-ACC (N = 77, R=-0.23, P = 0.04). In LIAS expression analysis, we found a significant correlation between gene expression and immune infiltration in 31 cancer types. Out of these, one showed significant positive correlation, namely TCGA-LAML (N = 214, R = 0.25, P = 2.1e-4) as shown in Fig. 5B. The remaining 30 cancer types showed significant negative correlations, including TCGA-GBMLGG, TCGA-LGG, TCGA-UCEC, TCGA-BRCA, TCGA-CESC, TCGA-LUAD, TCGA-ESCA, TCGA-STES, TCGA-SARC, TCGA-KIRP, TCGA-KIPAN, TCGA-COAD, TCGA-COADREAD, TCGA-STAD, TCGA-HNSC, TCGA-LUSC, TCGA-LIHC, TCGA-SKCM-P, TCGA-SKCM, TCGA-BLCA, TCGA-SKCM-M, TCGA-THCA, TARGET-NB, TCGA-READ, TCGA-UVM, TCGA-PAAD, TCGA-TGCT, TCGA-PCPG, TCGA-ACC, TCGA- KICH. Taken together, the hub genes related to cuproptosis are strongly correlated with immune infiltration in LAML, which may be a significant contributing factor to the observed carcinogenicity of these genes.
As shown in Fig. 5C, we calculated the Pearson correlation between the expression of Hub genes and MSI in each tumor. We observed that the expression of DLD was significantly correlated with MSI in 7 tumors, of which it was significantly positively correlated in 4 tumors: UCEC (P = 0.0001), STAD (P = 0.00000043), STAD (P = 0). Additionally, it was significantly negatively correlated in 3 tumors, such as DLBC (P = 0.028) and PRAD (P = 2.7e-8). Moreover, we found that the expression of LIAS was significantly correlated with MSI in 5 tumors, with significant positive correlations observed in 4 tumors: SARC (P = 0.016), COAD (P = 0.00074), SKCM (P = 0.021), and THCA (P = 0.0031). In addition, we observed a significant negative correlation in 1 tumor, COAD (P = 0.041). As shown in Fig. 5D, we calculated the Pearson correlation between Hub gene expression and Neoantigen in each tumor. We observed a significant positive correlation between DLD expression and Neoantigen in 3 tumors, including BRCA (P = 0.0035), READ (P = 0.00025), and STAD (P = 0.003). Additionally, LIAS expression was significantly positively correlated with Neoantigen in 5 tumors, including UCEC (P = 0.043), READ (P = 0.0014), PRAD (P = 0.024), LUAD (P = 0.0045), and STAD (P = 0.00004). We also observed an inverse correlation in 1 tumor, specifically BRCA (P = 2.6*e6). As depicted in Fig. 5E, we computed the Pearson correlation between the expression of Hub genes and TMB in each tumor. Our analysis revealed that DLD expression was significantly positively correlated with TMB in 5 tumors, including LUAD (P = 0.00043), UCEC (P = 0.00025), CESE (P = 0.0082), MESO (P = 0.005), and STAD (P = 0.00001). Similarly, we observed that the expression of LIAS was significantly positively correlated with TMB in 5 tumors, such as PRAD (P = 0.00071), UCEC (P = 0.00049), COAD (P = 0.00026), STAD (P = 9.1*e11), and READ (p = 0.00063). However, we observed negative correlations in 3 tumors, including LGG (P = 0.049), BLCA (P = 0.026), and BRCA (P = 0.024). As shown in Fig. 5F, we further investigated the association of Cuproptosis-related Hub genes with immune cells in various tumors to understand their impact on immune infiltration. Our analysis revealed a significant negative correlation between DLD expression and immune cell infiltration in TGCT, SARC, LUSC, and THCA. However, for DLBC, KICH, and UCS, there is little to no effect on immune cells. We also observed a significant negative correlation between LIAS expression and immune cell infiltration in THCA, KIRP, LUSC, ACC, and LUAD. However, in ESCA, CHOL, DLBC, KICH, and UCS, an immune desert phenomenon was observed.