Expression of PEA3 family members in HNSCC
The mRNA and protein expression of the PEA3 subfamily was investigated using the ONCOMINE and GEPIA datasets. As shown in Fig. 1A and 1B, the expression of ETV1 was higher in the normal tissues than in the cancer tissues. The expression of ETV4 and ETV5, on the contrary, was higher in the cancer tissues. The TNM plot dataset was also used to compare the PEA3 expression amongst cancer and normal tissues. The results indicated that ETV4/5 was significantly higher in HNSCC tissues than in normal tissues (p < 0.05, Fig. 1C).
Clinical subgroup analysis
A subgroup analysis of multiple clinical-pathological features was conducted using the TCGA database. Subgroup analysis by age, metastasis, status, gender subgroup, and cancer stages indicated that the transcriptional levels of ETV1 were lower in patients with HNSCC than in healthy individuals. Besides, subgroup analysis by age, cancer stages, metastasis status, HPV status, gender subgroup, and tumor grade demonstrated that the transcriptional levels of ETV4 and ETV5 were significantly higher in patients with HNSCC across all subgroups (Fig. 2).
Prognostic analysis
The prognostic significance, which was obtained from publicly available online datasets, of the PEA3 subfamily, was explored in patients with HNSCC. As shown in Fig. 3, the increased expression of ETV1 (HR = 0.73, 95% CI: 0.56–0.96, p = 0.021) was related to prolonged OS. The low expression levels of ETV4 (HR = 1.5, 95% CI: 1.14–1.96, p = 0.0031) and ETV5 (HR = 1.51, 95% CI: 1.15–1.99, p = 0.0026) were also related to prolonged OS. These results suggested that the levels of PEA3 may play an important role in HNSCC prognosis.
Predicted functions and pathways of PEA3 in HNSCC
The mutation patterns and functional networks of PEA3 were analyzed using cBioPortal and GeneMANIA further to explore the biological role of PEA3 in HNSCC. Amongst the 827 HNSCC tumor samples sequenced, genetic alterations were detected in 132 samples, with a mutation rate of 16%. ETV5 was ranked as the most mutated gene, with a mutation rate of 16%. The network for PEA3 and 22 most frequently altered neighboring genes was also shown (Fig. 4).
The functions of PEA3 and these 22 genes were analyzed using GO and KEGG enrichment (Fig. 5). GO analysis indicated that the changes in biological processes included aging, positive regulation of hair cycle, extracellular matrix disassembly, replicative senescence, and negative regulation of metallopeptidase activity. The molecular function was mainly enriched in metalloendopeptidase inhibitor activity, transcription coactivator binding, mitogen-activated protein kinase binding, protein serine/threonine kinase activity, and transcription cofactor binding. Changes in cell components were primarily enriched in secretory granule lumen, cytoplasmic vesicle lumen, vesicle lumen, protein-lipid complex, and specific granule lumen. According to KEGG analysis results, pathway enrichment analysis was mainly enriched in transcriptional misregulation in cancer, prostate cancer, cellular senescence, cholesterol metabolism, VEGF signaling pathway, MAPK signaling pathway, and FoxO signaling pathway.
Immune infiltrates in correlation with PEA3 in HNSCC
A statistically significant correlation was found between PEA3 expression in HNSCC and immune infiltrates (p < 0.05, Fig. 6). The expression levels of ETV1 and ETV5 were positively correlated with the immune infiltration levels in HNSCC, HNSCC-HPV-pos, and HNSCC-HPV-neg, whereas that of ETV4 was negatively correlated. We hypothesize that infiltration of immune cells significantly affect prognosis. Therefore, we explored the difference in cumulative survival between HNSCC, HNSCC-HPV-pos, and HNSCC-HPV-neg. The results showed that B cells, CD8+ T cells, and neutrophils of immune infiltrates statistically significant to PEA3 subfamily levels in HNSCC-HPV-pos subgroup, indicating that these immune cell infiltrations significantly affect prognosis. (Fig. 7).