3.1 Screening of TMGs
A total of 1437 differentially expressed genes (DEGs) were identified from the GSE15605 dataset, which includes 16 normal skin samples and 58 CMM samples. These DEGs were selected based on the criteria of |logFC| > 1 and adjusted p-value < 0.05 (Figure 2A). By intersecting this set of DEGs with the 3182 TMGs obtained from Genecards, we narrowed down to 346 DEGs for further investigation (Figure 2B). Next, we performed univariate Cox analysis on these 346 DEGs, and showed the correlation between TMGs in CMM(Figure 2C). Among them, 97 DEGs were found to have a significant impact on the OS of CMM patients. These 97 DEGs were used to construct TM patterns (Figure 2D). Additionally, we explored the correlations between these 97 DEGs, as illustrated in Figure 3D.
3.2 Construction of telomere maintenance patterns
Based on the expression of TMGs, patients were categorized into two distinct TM modification patterns using the "ConsensusClusterPlus"28 package, These patterns are referred to as TM cluster A and TM cluster B (Figure 3A). The CMM samples exhibited clear separation into two clusters based on various techniques: principal component analysis (PCA), t-distributed stochastic neighbor embedding (tSNE) and Uniform Manifold Approximation and Projection (UAMP) (Figure 3B-3D). The differentially expressed TMGs between TM cluster A and TM cluster B are visualized in Figure 3E. Notably, TM cluster A demonstrated significantly better OS compared to TM cluster B (Figure 3F). The survival analysis revealed that TM cluster A showed a significantly better OS compared to TM cluster B (Figure 3F). Further analysis of both TM clusters and the clinical features of patients was conducted using a heatmap, revealing significant differences in transcriptional profiles between the distinct TM clusters (Figure 3G). Additionally, the investigation of innate immune cell (IC) infiltration in the tumor microenvironment (TME) highlighted substantial differences in infiltration levels. Specifically, Activated B Cells, Activated CD4 T cells, Activated CD8 T cells, Activated dendritic cells, Eosinophils, and CD56dim natural killer cells exhibited varying levels of infiltration among the two TM clusters (Figure 4A). Most ICs showed decreased infiltration in TM cluster A, suggesting that lower IC infiltrations may correlate with better OS in CMM. To explore the biological behavior of the two TM clusters, we conducted Gene Set Enrichment Analysis (GSEA) and Gene Set Variation Analysis (GSVA). As depicted in Figures 4B and 4C, both TM clusters displayed differences in the enrichment of biological pathways.
3.3 Identification of risk score
The LASSO algorithm was employed to analyze TM modification patterns based on OS-related TMGs (Figure 5A and 5B). Six hub-genes were considered by LASSO: TAP2, SOCS3, SLC20A1, PROM1, KPNA2, and CENPO (Figure 5C). Subsequently, multivariate Cox analysis was utilized to assess the coefficients of these hub-genes. Survival analyses were conducted on the training, testing, and entire patient cohorts, revealing a higher OS rate among patients in the low-risk group (refer to Figure 5D-F). To further evaluate the performance of risk scores, receiver operating characteristic (RCMM) curves and area under the curve (AUC) values were utilized. The results demonstrated strong predictive capabilities for survival at 1, 3, and 5 years across all three patient groups (see Figure 5G-I).
3.4 Immune landscape between risk groups
To investigate the relationship between hub-genes and IC infiltration, we employed the CIBERSORT algorithm to quantify the proportion of ICs. Additionally, we conducted an in-depth analysis of the correlation between ICs and hub-genes (Figure 6A-D). Figure 6A illustrated the composition of ICs in each CMM sample, revealing significant differences in IC infiltration across risk groups. Notably, positive correlations were observed between the risk score and T cells CD8 as well as T cells CD4 memory activated (Figure 6E-6F). Conversely, negative correlations were found with Mast cells resting and Macrophages M0, suggesting a potential immunological mechanism underlying the risk score (Figure 6G-6H).
3.5 Validation of hub-genes by single-cell sequencing
The single-cell sequencing dataset GSE12313929 was meticulously employed to validate the expression profiles of the hub genes. Subsequently, this dataset underwent a comprehensive assessment using TISCH, a robust tool proficient in batch effect correction, clustering, and precise cell-type annotation (Figure 7A-7C).
The detailed evaluation of the relative abundance of hub genes across diverse cell types is visually presented in Figure 7D-7O. Notably, KPNA2, SLC20A1, SCMMS3, and TAP2 exhibited remarkable expression in various cell types, which may provide compelling evidence suggesting that the hub-genes probably influence the composition and dynamics of the TME.
3.6 Establishment of prognostic signature
The TM clusters and their correlation with risk scores have undergone thorough investigation. Patients in TM cluster A predominantly exhibited low risk scores (Figure 8A). This alignment with the results from survival analysis (Figure 3F, 5D-5F) underscored the reliability of risk scores in predicting the OS of CMM. A comprehensive multivariate analysis was conducted to assess the impact of risk score and clinical features, including age, gender and stage, on the OS of CMM. What’s more, the cumulative analysis also confirmed the stratification ability of risk score (Figure 8B). The survival outcomes of CMM patients were vividly presented and quantified using a nomogram plot (Figure 8D). The cumulative score from each covariate provides a valuable tool for predicting individual patient OS rates at 1, 3, and 5 years. Additionally, the calibration curve in Figure 8C showcased that the signature's performance was well-controlled to prevent overfitting. The decision curve analyses (DCAs) at 1 year (Figure 8E), 3 years (Figure 8F), and 5 years (Figure 8G) underscored that the nomogram yielded a substantially higher net clinical benefit, further affirming its prognostic value in CMM.