EGFR-co-amplified lncRNA ELDR drives glioblastoma tumorigenicity by enhancing BMI1 activity.
BACKGROUND: In glioblastoma (GBM), epidermal growth factor receptor (EGFR) amplification, one of the most prevalent genetic alterations, often occurs on extrachromosomal DNAs (ecDNAs) that contain amplified oncogenes and regulatory elements, driving tumor progression. Despite the central oncogenic role of EGFR amplification, therapeutic strategies targeting EGFR have demonstrated limited clinical efficacy, suggesting that additional mechanisms may underlie EGFR-driven GBM malignancy and treatment resistance. Long non-coding RNAs (lncRNAs) are critical regulators in cancer; however, the roles of EGFR-associated lncRNAs-particularly those localized on ecDNA-in GBM tumorigenicity and therapeutic resistance remain poorly understood. METHODS: Transcriptomic and genomic analyses were performed to identify lncRNAs co-amplified with EGFR. Biochemical and molecular biological studies were carried out to reveal the mechanisms. In vivo xenograft models were used to evaluate the tumorigenicity and the therapeutic efficacy of combination treatment strategies. RESULTS: The lncRNA EGFR long non-coding downstream RNA (ELDR) was co-amplified with EGFR on ecDNA and chromosomes and was associated with poor prognosis in glioma. ELDR promoted GBM tumorigenicity through a BMI1-dependent epigenetic mechanism operating in parallel with canonical EGFR signaling. Mechanistically, ELDR interacted with purine-rich element-binding protein A (PURA), disrupted the inhibitory PURA-BMI1 interaction, and thereby enhanced the activity of BMI1, a core component of Polycomb repressive complex 1 (PRC1). Therapeutically, combining a BMI1 inhibitor or ELDR-targeting antisense oligonucleotides (ASOs) with an EGFR inhibitor erlotinib significantly enhanced antitumor efficacy in preclinical models of  EGFR  -amplified GBM with high ELDR expression. CONCLUSION: EGFR co-amplified ELDR promotes GBM tumorigenicity by enhancing BMI1 activity. Targeting the ELDR-BMI1 axis in combination with EGFR inhibition represents a promising therapeutic strategy for a subset of  EGFR  -amplified GBMs with high ELDR expression.