Rolling-translated EGFR variants sustain EGFR signaling and promote glioblastoma tumorigenicity

Neuro Oncol. 2021 May 5;23(5):743-756. doi: 10.1093/neuonc/noaa279.

Abstract

Background: Aberrant epidermal growth factor receptor (EGFR) activation is observed in over 50% of cases of adult glioblastoma (GBM). Nevertheless, EGFR antibodies are ineffective in clinical GBM treatment, suggesting the existence of redundant EGFR activation mechanisms. Whether circular RNA (circRNA) encodes a protein involved in EGFR-driven GBM remains unclear. We reported an unexpected mechanism in which circular EGFR RNA (circ-EGFR) encodes a novel EGFR variant to sustained EGFR activation.

Method: We used RNA-seq, Northern blot, and Sanger sequencing to confirm the existence of circ-EGFR. Antibodies and a liquid chromatograph tandem mass spectrometer were used to identify circ-EGFR protein products. Lentivirus-transfected stable cell lines were used to assess the biological functions of the novel protein in vitro and in vivo. Clinical implications of circ-EGFR were assessed using 97 pathologically diagnosed GBM patient samples.

Results: The infinite open reading frame (iORF) in circ-EGFR translated repeating amino acid sequences via rolling translation and programmed -1 ribosomal frameshifting (-1PRF) induced out-of-frame stop codon (OSC), forming a polymetric novel protein-complex, which we termed rolling-translated EGFR (rtEGFR). rtEGFR directly interacted with EGFR, maintained EGFR membrane localization and attenuated EGFR endocytosis and degradation. Importantly, circ-EGFR levels correlated with the EGFR signature and predicted the poor prognosis of GBM patients. Deprivation of rtEGFR in brain tumor-initiating cells (BTICs) attenuated tumorigenicity and enhanced the anti-GBM effect.

Conclusion: Our findings identified the endogenous rolling-translated protein and provided strong clinical evidence that targeting rtEGFR could improve the efficiency of EGFR-targeting therapies in GBM.

Keywords: CircRNA; EGFR; glioblastoma; iORF; rolling translation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Brain Neoplasms* / genetics
  • Cell Line, Tumor
  • Cell Proliferation
  • ErbB Receptors / genetics*
  • ErbB Receptors / metabolism
  • Glioblastoma* / genetics
  • Humans
  • RNA, Circular
  • Signal Transduction*

Substances

  • RNA, Circular
  • EGFR protein, human
  • ErbB Receptors