Novel SEC61G–EGFR Fusion Gene in Pediatric Ependymomas Discovered by Clonal Expansion of Stem Cells in Absence of Exogenous Mitogens

Abstract

The basis for molecular and cellular heterogeneity in ependymomas of the central nervous system is not understood. This study suggests a basis for this phenomenon in the selection for mitogen-independent (MI) stem-like cells with impaired proliferation but increased intracranial tumorigenicity. MI ependymoma cell lines created by selection for EGF/FGF2-independent proliferation exhibited constitutive activation of EGFR, AKT, and STAT3 and sensitization to the antiproliferative effects of EGFR tyrosine kinase inhibitors (TKI). One highly tumorigenic MI line harbored membrane-bound, constitutively active, truncated EGFR. Two EGFR mutants (ΔN566 and ΔN599) were identified as products of intrachromosomal rearrangements fusing the 3' coding portion of the gene to the 5'-UTR of the, yielding products lacking the entire extracellular ligand-binding domain of the receptor while retaining the transmembrane and tyrosine kinase domains. EGFR TKI efficiently targeted ΔN566/ΔN599-mutant-mediated signaling and prolonged the survival of mice bearing intracranial xenografts of MI cells harboring these mutations. RT-PCR sequencing of 16 childhood ependymoma samples identified chimeric mRNAs in one infratentorial ependymoma WHO III, arguing that this fusion occurs in a small proportion of these tumors. Our findings demonstrate how culture selections applied to genetically heterogeneous tumors can help identify focal mutations that are potentially pharmaceutically actionable in rare cancers. .

Structure and evolution of double minutes in diagnosis and relapse brain tumors

“…Notably, exon 16 codes for a segment of the extracellular domain close to the dimerization of the EGFR receptors, a process important for auto-inhibition of EGFR signaling pathway. Interestingly, an SEC61G - EGFR fusion gene that consists of the first exon of SEC61G and exon 16 skipping versions of EGFR (MF434546: exon14, 15, 17–28; and MF434547: exon15, 17–28) was reported in pediatric ependymomas recently [ 23 ]. Taken together, the EGFR isoform skipping exon 16 deserves further functional characterization in the future.…”

Discovery of New Fusion Transcripts in a Cohort of Pediatric Solid Cancers at Relapse and Relevance for Personalized Medicine

“…EGFR-containing gene fusions have been reported in a subset of ependymomas. 56 Given the therapeutic potential of a TK-containing fusion, we selected these 5 fusion oncogenes for validation and sequencing. The only in-frame transcript that we confirmed by sequencing was CCM2L-HCK transcript in patient 30 with medulloblastoma, who lacked aberrations in TP53 and genes of WNT and SHH pathways.…”

Honokiol Eliminates Glioma/Glioblastoma Stem Cell-Like Cells Via JAK-STAT3 Signaling and Inhibits Tumor Progression by Targeting Epidermal Growth Factor Receptor

“…An important mediator of tumor progression is EGFR, whose expression correlates positively with malignancy and contributes to poor prognosis [25]. EGFR is involved in Jak/STAT, nfb, mTOR and MAPK signaling pathways, thereby influencing cancer cell self-renewal, proliferation, differentiation and migration [26,27,28]. Honokiol can induce mitochondria-dependent and death receptor-mediated apoptosis in multi-drug resistant KB cells by inhibition of EGFR-STAT3 signaling and down-regulation of STAT3 target genes [29].…”