title: RRAD promotes EGFR-mediated STAT3 activation and induces temozolomide resistance of malignant glioblastoma.
abstract: Glioblastoma multiforme (GBM) is an extremely aggressive brain cancer with a median survival of less than 2 years. GBM is characterized by abnormal activation of receptor tyrosine kinase and constitutively activated STAT3. Although EGFR phosphorylation and STAT3 activation are essential for the maintenance of GBM cancer stem cells, the molecular mechanism underlying endosome-mediated STAT3 activation is not fully understood. In the current study, we showed that GTP-binding protein RRAD (RAS associated with diabetes, RAD) physically associates with EGFR, and EEA1, enhancing the stability and endosome-associated nuclear translocation of EGFR. Functionally, RRAD contributes to the activation of STAT3 and expression of the stem cell factors OCT4, NANOG, and SOX2, thereby enhancing self-renewing ability, tumor sphere formation, EMT, and in vivo tumorigenesis. Most importantly, RRAD contributes to poor survival in patients with GBM. RRAD expression is correlated with temozolomide resistance, and, conversely, depletion of RRAD leads to sensitization of highly temozolomide-resistant GBM cells. Our data collectively support a novel function of RRAD in STAT3 activation and provide evidence that RRAD acts as a positive regulator in the EGFR signaling pathway. These results demonstrate a critical role for RRAD in GBM tumorigenesis and provide a rationale for the development of pharmacologic inhibitors of RRAD in GBM.
authors.affiliation: Research Institute for Future Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Seon-Yong
authors.initials: SY
authors.lastname: Yeom
authors.affiliation: Department of Neurosurgery, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
authors.forename: Do-Hyun
authors.initials: DH
authors.lastname: Nam
authors.affiliation: Research Institute for Future Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea. cpark@skku.edu.
authors.forename: Chaehwa
authors.initials: C
authors.lastname: Park
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002471:Cell Transformation, Neoplastic / Q000235:genetics / Q000378:metabolism; D003606:Dacarbazine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D011992:Endosomes / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D005909:Glioblastoma / Q000235:genetics / Q000378:metabolism* / Q000401:mortality / Q000473:pathology; D006801:Humans; D011379:Prognosis; D055550:Protein Stability; D021381:Protein Transport; D050796:STAT3 Transcription Factor / Q000378:metabolism*; D018874:Spheroids, Cellular; D000077204:Temozolomide; D014407:Tumor Cells, Cultured; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
chemical_list: D018906:Antineoplastic Agents, Alkylating; C084355:RRAD protein, human; D050796:STAT3 Transcription Factor; D003606:Dacarbazine; D066246:ErbB Receptors; D018631:ras Proteins; D000077204:Temozolomide