A molecular cascade modulates MAP1B and confers resistance to mTOR inhibition in human glioblastoma

• Published in: Neuro-oncology (Charlottesville, Va.) Va.), 2018-05, Vol.20 (6), p.764-775
• Main Authors: Laks, Dan R, Oses-Prieto, Juan A, Alvarado, Alvaro G, Nakashima, Jonathan, Chand, Shreya, Azzam, Daniel B, Gholkar, Ankur A, Sperry, Jantzen, Ludwig, Kirsten, Condro, Michael C, Nazarian, Serli, Cardenas, Anjelica, Shih, Michelle Y S, Damoiseaux, Robert, France, Bryan, Orozco, Nicholas, Visnyei, Koppany, Crisman, Thomas J, Gao, Fuying, Torres, Jorge Z, Coppola, Giovanni, Burlingame, Alma L, Kornblum, Harley I
• Format: Article
• Language: English
• Subjects: Animals; Antibiotics, Antineoplastic - pharmacology; Apoptosis; Basic and Translational Investigations; Biomarkers, Tumor - genetics; Biomarkers, Tumor - metabolism; Cell Proliferation; Extracellular Signal-Regulated MAP Kinases - antagonists & inhibitors; Extracellular Signal-Regulated MAP Kinases - genetics; Extracellular Signal-Regulated MAP Kinases - metabolism; Gene Expression Regulation, Neoplastic - drug effects; Glioblastoma - drug therapy; Glioblastoma - genetics; Glioblastoma - pathology; Glycogen Synthase Kinase 3 beta - antagonists & inhibitors; Glycogen Synthase Kinase 3 beta - genetics; Glycogen Synthase Kinase 3 beta - metabolism; Humans; Male; Mice; Mice, Inbred NOD; Mice, SCID; Microtubule-Associated Proteins - antagonists & inhibitors; Microtubule-Associated Proteins - genetics; Microtubule-Associated Proteins - metabolism; Phosphatidylinositol 3-Kinases - genetics; Phosphatidylinositol 3-Kinases - metabolism; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Proto-Oncogene Proteins c-akt - antagonists & inhibitors; Proto-Oncogene Proteins c-akt - genetics; Proto-Oncogene Proteins c-akt - metabolism; RNA, Small Interfering - genetics; Signal Transduction; Sirolimus - pharmacology; TOR Serine-Threonine Kinases - antagonists & inhibitors; TOR Serine-Threonine Kinases - genetics; TOR Serine-Threonine Kinases - metabolism; Tumor Cells, Cultured; Xenograft Model Antitumor Assays
• ISSN: 1522-8517; 1523-5866
• DOI: 10.1093/neuonc/nox215

Clinical trials of therapies directed against nodes of the signaling axis of phosphatidylinositol-3 kinase/Akt/mammalian target of rapamycin (mTOR) in glioblastoma (GBM) have had disappointing results. Resistance to mTOR inhibitors limits their efficacy. To determine mechanisms of resistance to chronic mTOR inhibition, we performed tandem screens on patient-derived GBM cultures. An unbiased phosphoproteomic screen quantified phosphorylation changes associated with chronic exposure to the mTOR inhibitor rapamycin, and our analysis implicated a role for glycogen synthase kinase (GSK)3B attenuation in mediating resistance that was confirmed by functional studies. A targeted short hairpin RNA screen and further functional studies both in vitro and in vivo demonstrated that microtubule-associated protein (MAP)1B, previously associated predominantly with neurons, is a downstream effector of GSK3B-mediated resistance. Furthermore, we provide evidence that chronic rapamycin induces microtubule stability in a MAP1B-dependent manner in GBM cells. Additional experiments explicate a signaling pathway wherein combinatorial extracellular signal-regulated kinase (ERK)/mTOR targeting abrogates inhibitory phosphorylation of GSK3B, leads to phosphorylation of MAP1B, and confers sensitization. These data portray a compensatory molecular signaling network that imparts resistance to chronic mTOR inhibition in primary, human GBM cell cultures and points toward new therapeutic strategies.