Transcriptomic analysis of EGFR co-expression and activation in glioblastoma reveals associations with its ligands

Background. Approximately half of the isocitrate dehydrogenase (IDH)-wildtype glioblastomas (GBMs) exhibit EGFR amplification. Additionally, genomic changes that occur in the extracellular domain of EGFR can lead to ligand-hypersensitivity (R108K/A289V/G598V) or ligand-independence (EGFRvIII). Unlike in lung adenocarcinoma (LUAD), clinical trials with epidermal growth factor receptor (EGFR) inhibitors showed no survival benefit for GBM and it remains unclear why. We aimed to elucidate differences in molecular mechanisms of EGFR activation and regulation between GBM and LUAD. Methods. We used RNA-sequencing (RNA-seq) data to find EGFR co-regulated genes and pathways in GBM and compare EGFR signaling patterns between GBM and LUAD. Cellular origins of expression signals were determined by analyzing single-cell RNA-seq data. Results. We identified 2 ligands (BTC/EREG) among the significant EGFR predictor genes (TCGA-GBM: n = 169, Intellance-2: n = 166). Their expression was inversely correlated with EGFR amplification and incidence of ligand-sensitive mutations. Ligands were expressed by nonmalignant cells and differed in their primary source of expression (BTC: neurons, EREG: myeloid). High expression of MDM2 and CDK4 was less common in EGFR-amplified GBMs with ligand-sensitive mutations compared with those without these mutations. Our analyses revealed distinct transcriptional profiles between GBM and LUAD when comparing tumors carrying activating mutations. Conclusions.BTC and EREG are negatively associated with EGFR expression in GBM. These findings emphasize the role of ligands in regulating EGFR, where EGFR activation seems to be modulated by the highly varying levels of EGFR amplification, the sensitivity of the receptor toward ligands, and ligand expression levels. Ligand expression levels and EGFR mutations could refine patient stratification for EGFR-targeted therapies in GBM.