3.4 Construction and validation of prognostic model in TCGA cohort
To further investigate the role of ferroptosis-related genes in HCC, we established a prognostic model using 44 ferroptosis-related genes associated with OS in HCC by LASSO Cox regression analysis method. The introduction of the variable λ value determines which variables can optimize the model, and cross-validation can be used to find the optimal λ value (Fig. S1). We identified 12 genes for constructing the prognostic model of OS risk score which was calculated as follows:
risk scores = (0.0911) * G6PD+(0.0124) * KEAP1 + (0.0833) * ATG3 + (0.0469) * MAPK1 + (0.0487) * ATG13 + (0.2367) * MYB + (-0.3434) * FLT3 + (0.0174) * SLC1A5 + (0.0782) * SLC7A11 + (0.0359) * LONP1 + (0.1901) * HILPDA + (0.2949) * PRDX6
Patients were divided into high-risk groups (n = 185) and low-risk groups (n = 185) according to the median cut-off value (Fig. 4a). The Kaplan-Meier curve indicated that the OS of patients in the high-risk group was significantly lower than that in the low-risk group (Fig. 4b, P < 0.001). The survival rate of patients in the high-risk group was lower than that in the low-risk group (Fig. 4c). The predictive performance of the OS risk score was assessed by time-dependent ROC curves. The area under the curve (AUC) reaching 0.829 at 1 year, 0.768 at 3 years, and 0.768 at 5 years (Fig. 4d).
Then we used the ICGC database to verify the prognostic model of 12 genes. The results showed that patients in the high-risk group had a higher risk of survival than those in the low-risk group (Fig. 5a, 5b), and the survival time was shortened (Fig. 5c, P < 0.001). In addition, the AUC of the 12-gene signature was 0.775 at 1 year, 0.748 at 2 year, 0.763 at 3 year, and 0.743 at 4 year (Fig. 5d).
3.5 Independent prognostic analysis of the risk score and 12 genes
We then used univariate and multivariate Cox regression analysis to verify whether the risk score and 12 genes were independent prognostic predictors. Univariate Cox regression analysis showed that the risk score (HR = 3.750, 95% CI = 2.783 − 5.052 ,P < 0.0001) and 12 genes (P < 0.05) were significantly positively correlated with OS in HCC patients (Fig. 6a). We used multivariate Cox regression analysis after adjusting for other confounding factors. FLT3 (HR = 0.541, 95% CI = 0.302–0.970, P = 0.039), MYB (HR = 1.671, 95% CI = 1.075–2.599, P = 0.023) ), PRDX6 (HR = 1.887, 95% CI = 1.338–2.662, P = 0.0003) were still shown to be independent predictors of protective factor for OS in HCC patients (Fig. 6b).
3.6 Functional enrichment analysis of ferroptosis-related gene FLT3
When investigating the role of ferroptosis-related genes in HCC, we found that FLT3 gene was significantly under expressed in HCC tissues (Fig. 7a). Patients with high expression of FLT3 had good prognosis (P < 0.05) (Fig. 7b). The coefficients regression analysis showed that the role of FLT3 was prominent (Fig. S2). We conducted in-depth research on the FLT3 gene. The pan-cancer correlation analysis of FLT3 was performed by the “forestplot” package. FLT3 gene was significantly associated with prognosis of Breast invasive carcinoma (BRCA, HR = 0.67559, CI95% [0.49144, 0.92875], P = 0.0157), Head and Neck squamous cell carcinoma (HNSC, HR = 0.54985, CI 95%[0.41833, 0.72272], P < 0.0001), Kidney renal clear cell carcinoma (KIRC), Acute Myeloid Leukemia (LAML, HR = 1.68519, CI 95% [1.10071, 2.58002], P = 0.0163), Lung adenocarcinoma (LUAD, HR = 0.64355, CI 95% [0.47824, 0.866], P = 0.0036), Sarcoma (SARC, HR = 0.54636, CI 95% [0.36392, 0.82028], P = 0.0036) and other ten types of cancer (P < 0.05), as shown in Fig. 7c.
There was a significant difference in the abundance of immune cells between HCC tissues with high expression of FLT3 gene and HCC tissues with low expression of FLT3 gene by TIMER Scors analysis. In HCC tissues with high expression of FLT3 gene, the abundance of immune cells such as B cell, T cell CD4+, T cell CD8+, Neutrophil, Macrophag, Myeloid dendritic cell was higher than that in HCC tissues with low expression of FLT3 (Fig. 8).
To further explore the biological role of FLT3 gene in HCC tissues, we performed pathway enrichment analysis on FLT3 gene (Fig. 9). The results indicated that the FLT3 gene was associated with multiple pathways in HCC tissues. FLT3 gene was significantly associated with Tumor Inflammation Signature ( loge(S) = 15.02, P = 1.11e − 38, ρSpearman = 0.61, CI95% [0.54, 0.67], npairs = 371), Collagen formation (loge(S) = 15.48, P = 2.92e − 14, ρSpearman = 0.38, CI95% [0.29, 0.47], npairs = 371), EMT markers (loge(S) = 15.59, P = 2.16e − 09, ρSpearman = 0.30, CI95% [0.21, 0.40], npairs = 371), Apoptosis (loge(S) = 15.02, P = 7.84e − 39, ρSpearman = 0.61, CI95% [0.54, 0.67], npairs = 371), Degradation of ECM (loge(S) = 15.44, P = 3.7e − 16, ρSpearman = 0.41, CI95% [0.31, 0.49], npairs = 371]), ECM − relatted genes(loge(S) = 15.31, P = 1.66e − 22, ρSpearman = 0.48, CI95% [0.39, 0.55], npairs = 371) and other pathways. Especially, FLT3 showed a high positive correlation with Tumor Inflammation Signature and a high negative correlation with Tumor Proliferation Signature.