Identification of differently expressed RBPs in GC patients
In present study, we aimed to obtained the prognostic-associated RBPs in GC patients using bioinformatic analysis. The analysis steps were illustrated in Figure 1. The databases of GC were downloaded from TCGA, which included 375 GC samples and 32 normal samples. As Figure 2 showed, there were 79 differently expressed RBPs according to the criteria of |log2 fold change (FC)| ≥1 and false discovery rate (FDR)<0.05. Of these 79 RBPs, 39 RBPs were upregulated in GC samples, 40 RBPs were downregulated in GC samples (Table 1).
Table 1
The differently expressed RBPs
| Gene |
Up-regulated | TRIM71 L1TD1 CD3EAP RDM1 XPO5 HENMT1 BOP1 BOLL TDRD5 OAS3 RNASE1 APOBEC4 PUS7 IGF2BP1 IGF2BP2 IGF2BP3 MOV10L1 WARS RNF113B DNMT3B TDRD6 PIWIL1 PIWIL3 RNASE2 RNASE3 DKC1 EZH2 URB2 DDX4 BRCA1 PABPC1L MEX3A TERT DCAF13 POP1 ZNF239 RANBP17EXO1 PABPC5 |
Down-regulated | RBFOX3 ELAVL3 ELAVL4 DZIP1 APOBEC2 APOBEC1 MYEF2 ZCCHC24 SMAD9 ADAD2 ADARB1TDRD10 AFF3 RBM20 SIDT2 PAIP2B RNASE10 ANG LARP6 ZFP36 EIF1AY RBM24 RBPMSRBPMS2 RNASE11 ENDOU DDX3Y SNRPN TLR3 CELF2 CPEB1 CPEB2 CPEB3 PABPC1L2APABPC1L2B NR0B1 EIF4E3 NANOS1 NOVA1 |
GO and KEGG pathway enrichment analysis of the differently expressed RBPs
GO enrichment analysis was performed to investigate the function enrichment of the differently expressed RBPs in GC. As Figure 3A showed, the differently expressed RBPs were significantly enriched in regulation of translation, regulation of cellular amide metabolic process, and RNA catabolic process in biological process (BP) analysis. In the cellular component (CC) analysis, the differently expressed RBPs were mainly enriched in cytoplasmic ribonucleoprotein granule, ribonucleoprotein granule, and P granule (Figure 3A). In regard to the molecular function (MF), the differently expressed RBPs were notably enriched in mRNA 3'−UTR binding, catalytic activity, acting on RNA, and translation regulator activity (Figure 3A). KEGG pathway analysis was conducted, and suggested that the differently expressed RBPs were significantly enriched in MicroRNAs in cancer, RNA degradation, and mRNA surveillance pathway (Figure 3B).
Ppi Network Construction And Key Modules Selecting
We constructed the PPI network through STRING database and Cytoscape software to investigate the potential roles of the differently expressed RBPs in GC. As Figure 4A showed, there were 59 nodes and 276 edges in the network based on the data from STRING database. Furthermore, we analyzed the co-expression network to detect possible key modules by using plug-in MODE in Cytosacpe software, and obtained 44 nodes and 136 edges (Figure 4B).
Identification Of Prognostic-associated Rbps
A total of 59 key differently expressed RBPs were obtained from the PPI network. Subsequently, univariable and multivariable Cox regression was performed to determine the prognostic-associated RBPs form these hub candidate RBPs in GC. As Figure 5A showed, 9 prognostic-associated RBPs (ADARB1, RNASE3, RNASE2, RNASE1, BOLL, EZH2, ZFP36, LARP6, and PABPC5) were identified by univariable Cox regression. Furthermore, 4 RBPs (RNASE3, RNASE1, BOLL, and PABPC5) were identified as independent prognostic-associated predictors in GC (Figure 5B).
Validation of expression and prognostic value of these prognostic-associated RBPs
We examined the expressions of RNASE3, RNASE1, BOLL, and PABPC5 compared 375 GC samples with 32 healthy controls from TCGA database. Figure 6A showed that RNASE3, RNASE1, BOLL, and PABPC5 was significantly up-regulated in GC samples compared to the healthy controls (P=0.0012, P=0.0011, P<0.001, and P=0.028, respectively). Moreover, we found that the higher expressions of RNASE3, RNASE1, BOLL, and PABPC5 were associated with a poorer overall survival (OS) by Kaplan-Meier survival analysis (P=0.019, P=0.046, P=0.017, and P=0.022, respectively) (Figure 6B).
Construction And Analysis Of A Prognostic-associated Risk Score Model
A prognostic-associated risk score model was constructed based on the four independent prognostic-associated RBP. The risk score of each GC patient was computed according to the following formula: Risk score = 0.44*Exp RNASE3 + 0.25*Exp RNASE1 + 2.46*Exp BOLL + 1.63*Exp PABPC5.
Then, we performed a survival analysis to assess the predictive performance of the risk score model. A total of GC patients from TCGA were divided into training and testing datasets including 187 cases and 184 case, respectively. Subsequently, 184 GC patients in training dataset were divided into low- and high-risk groups based on the median risk score. We found that GC patients in the high-risk group were associated with poorer OS compared to GC patients in the low-risk group (Figure 7A). Moreover, the area under the ROC curves (AUCs) for 1 year OS was 0.706 according to the risk score model in the training datasets (Figure 7B). Furthermore, the Figure 7C showed that the GC patients with overexpression of these four prognostic-associated RBPs contributed to high-risk scores and poorer OS. Consistently, in test datasets, we also discovered that GC patients in the high-risk group were associated with poorer OS based on this prognostic-associated risk score model. The results were showed in Figure 7D, 7E and 7F. Therefore, these results revealed that the four prognostic-associated RBPs risk score model had a satisfactory sensitivity and specificity of prediction values for GC patients.
Construction of a nomogram based on the four prognostic-associated RBPs
We built a nomogram plot to construct a quantitative model and predict the survival probability of 1-, 2-, and 3- years OS for GC patients based on four prognostic-associated RBPs (Figure 8). A vertical line was draw to determine the points for each variable and summed the points of all variables to calculate the total points for each patient, and then normalized them to distribution of 0 to 100. Therefore, the survival rates of GC patients can be calculated through drawing a vertical line between the total points axis and each prognosis axis at 1-, 2-, and 3- years.
Assessment Of The Prognostic Value Of Clinical Parameters
We performed univariable and multivariable Cox regression to assess the prognostic value of different clinical characteristics for GC patients from TCGA databases. In training dataset, we found that patients age, stage and risk scores were associated with OS by univariable Cox regression (Figure 9A). Moreover, multivariable Cox regression showed that patients age, stage and risk scores were associated with OS (Figure 9B). However, in test dataset, we discovered that stage and risk scores were associated with OS by univariable and multivariable Cox regression (Figure 9C and 9D).
The Protein Levels Of The Four Prognostic-associated Rbps
We detected the protein levels of the four prognostic-associated RBPs using the immunohistochemistry results from HPA. The results revealed that the protein levels of RNASE3, RNASE1, and PABPC5 was significantly up-regulated in GC tissues compared with normal tissues, whereas the protein level of BOLL was not detected between GC tissues and normal tissues (Figure 10).