EIF3B act as unfavorable prognostic marker in HNSCC
To investigate the expression of EIF3B in HNSCC, we first checked its expression in TCGA HNSCC dataset. As shown in Fig. 1A, elevated expression of EIF3B was observed HNSCC cancer samples, compared with control normal group. Then we analyzed the relations between EIF3B expressions with pathological parameters in HNSCC. As shown in Table 1 and Fig. 1B-1H, the expression of EIF3B was significantly correlated with gender, age, HPV infection, T stage, N stage, perineural invasion and survival status. At last, the prognostic significance of EIF3B expression was analyzed with univariate and multivariate Cox regression analysis (Fig. 1I and 1J), and shown with Kaplan-Meier plot (Fig. 1K). Patients with higher EIF3B expression showed significant lower survival rates, suggesting that EIF3B serve as an unfavorable prognostic marker in HNSCC.
Table 1
Correlation of EIF3B expression with clinical parameters in HNSCC.
| EIF3B |
Characteristics | Low (No. cases) | High (No. cases) | X2 | p value |
Age | | | 7.946 | 0.005 |
≥ 65 | 6 | 18 | | |
< 65 | 43 | 31 | | |
Gender | | | 5.288 | 0.021 |
male | 44 | 35 | | |
female | 5 | 14 | | |
Stage | | | 3.199 | 0.074 |
stage1-2 | 13 | 6 | | |
stage3-4 | 36 | 43 | | |
N | | | 0.742 | 0.389 |
N0 | 18 | 14 | | |
N1-3 | 31 | 35 | | |
T | | | 17.193 | 0 |
T1-2 | 29 | 9 | | |
T3-4 | 20 | 40 | | |
HPV | | | 14.154 | 0 |
negative | 26 | 43 | | |
positive | 23 | 6 | | |
Tobacco_smoking_history | | | 0.763 | 0.858 |
Lifelong Non-smoker | 11 | 8 | | |
Current smoker | 17 | 19 | | |
Current reformed smoker for > 15 years | 6 | 7 | | |
Current reformed smoker for ≤15 years | 13 | 15 | | |
Perineural_invasion | | | 7.167 | 0.007 |
NO | 23 | 16 | | |
YES | 12 | 29 | | |
Status | | | 3.967 | 0.046 |
live | 39 | 30 | | |
dead | 10 | 19 | | |
EIF3B promotes HNSCC proliferation and progression in vitro and in vivo
To explore the functional role of EIF3B in HNSCC, we first applied lentivirus mediated EIF3B knockdown (Fig. 2A) in Fadu and Cal27 cell lines. As shRNA2 shows the overall best performance of silencing efficiency, shRNAs was chosen for subsequent phenotype studies. As shown in Fig. 2B-2C, EIF3B silenced Fadu and Cal27 cells exhibits reduced cell number, compared with control cells, suggesting that EIF3B may contributes to cell growth in HNSCC. Then apoptosis rate in EIF3B knockdown and control cells were analyzed. As shown in Fig. 2D, Annexin V/PI staining assay indicated that EIF3B knockdown induced the apoptosis rate, in both cell lines, especially in Fadu cells. Next, transwell and wound healing assays were conducted to explore the impact of EIF3B silencing on cell invasion and migration. As a result, the EIF3B silenced cells demonstrated decreased invasion capability, as shown in Fig. 2E, in both cell lines. Similar to the transwell assay result, the migration distance of HNSCC cell lines showed wider gap, implying that EIF3B knockdown also inhibit cell migration (Fig. 2F). As Fadu cells showed more pronounced overall tumor behavior compared with Cal27 cells, we choose Fadu cells for subsequent in vivo and mechanism study. At last, we applied nude mice xenograft experiment to explore the function of EIF3B in vivo, using Fadu cells. As shown in Fig. 2G, the tumor volume in EIF3B knockdown group was significantly decreased, supporting the oncogenic role of EIF3B in HNSCC.
Integrated analysis reveals CEBPB as a target of EIF3B translation
To explore the molecular mechanism of the oncogenic role in HNSCC, first, we applied RNA sequencing and label-free proteomics for EIF3B knockdown and Control Fadu cells. The RNA sequencing screened 976 significantly deregulated mRNAs (Fold change>=2 or <=-2, P value<0.05), shown in Fig. 3A. Meanwhile, the quantitative proteomics identified 425 significantly deregulated proteins of all 5195 proteins (Fold change>=1.5 or <=-1.5, P value<0.-05), shown in Fig. 3B. Then genes and significant pathways of deregulated mRNAs and proteins were compared. As shown in Fig. 3C, only 14 genes (LAMB3, MYL9, NDRG1, FOSL1, ADAM8, SPRY4, HMOX1, RAB31, PIR, TGFB1, TEF, FAT2, ABR and GRB7) showed both deregulation in mRNA and protein level. In pathway level, there are 103 and 27 significant (P<0.05) pathways for mRNAs and proteins, respectively. For mRNAs, the top3 most significant pathways were pathways in cancer, proteoglycans in cancer, and transcriptional misregulation in cancer. For proteins, the top3 most significant pathways were Ribosome, RNA transport and Ferroptosis. As shown in Fig. 4C, there are 12 common significant pathways enriched in both levels. Based on enrichment score (log10 P value), the 12 significant pathways in both levels were shown in Fig. 3D. In addition to MAPK pathways, a well-recognized pathway in cell proliferation and apoptosis, other cell death items, like ferroptosis and necrosis, were significantly enriched, which explains the function of EIF3B regulating cell proliferation and cell death.
EIF3B is a translation initiation factor, and involved in gene translation by binding to mRNAs. Since EIF3B play an oncogenic role in HNSCC, the abnormal expression of EIF3B may influence target genes’ translation and protein expression. So we applied RNA immunoprecipitation and RNA sequencing(RIP-Seq) to identify potential EIF3B binding mRNAs. 354 mRNAs were identified. Then we compared the 354 mRNAs with 425 significantly deregulated proteins in EIF3B silencing group, and identified 8 genes, VIM, TEF, CALB2, MVD, ASS1, GDF15, NDRG1 and CEBPB (Fig. 4A), and their expression was shown in Fig. 4B. Then we look into studies about the oncogenic and tumor suppressing role of the 8 genes in HNSCC, and finally choose CEBPB as a target candidate. CEBPB is reported to confer radiation resistance of nasopharyngeal carcinoma [17]. As a transcription factor, CEBPB was reported to be translational regulated by EIF6 [18], and regulates MAPK pathway in cancer [19]. To validate the role of CEBPB in mRNA level, we applied ENCODE and ChEA Consensus Transcription factors prediction, and CEBPB was one of the most significant proteins (Fig. 4C). At last, the binding peaks of EIF3B with CEBPB mRNAs and conserved motif were shown in Fig. 4D. After EIF3B was silenced, the binding peaks were reduced, compared with control group. In sum, we identified CEBPB as a translational target of EIF3B, by which EIF3B regulates MAPK and other pathways, in HNSCC.
At last, we explored potential targets of EIF3B regulated CEBPB translation. Fifteen genes were identified by ENCODE and ChEA Consensus Transcription factors prediction, and their expression in EIF3B knockdown and control groups were shown in Fig. 5A. Then we used qRT-PCR to validate 11 genes in EIF3B knockdown and control Fadu cells. In Fig. 5B, 5 genes (SPRY4, NFKBIA, IL6R, CCNG2 and ARID5B) showed consistent significant differential expression. At last, we calculated the co-expression coefficient of EIF3B with the CEBPB and 5 genes. As shown in Fig. 5C, EIF3B showed significant positive correlation with CEBPB (R=0.23, P=3.1e-08), IL6R (R=0.27, P=6.2e-11) and SPYR4 (R=0.27, P=1.5e-10), while showed significant negative correlation with CCNG2 (R=-0.16, P=0.00013). At last, we propose the molecular mechanism of EIF3B in HNSCC: promotes CEBPB translation and regulating targets, like IL6R and CCNG2 (Fig. 5D).