MELK‐Dependent FOXM1 Phosphorylation is Essential for Proliferation of Glioma Stem Cells

• Published in: Stem cells (Dayton, Ohio) Ohio), 2013-06, Vol.31 (6), p.1051-1063
• Main Authors: Joshi, Kaushal, Banasavadi‐Siddegowda, Yeshavanth, Mo, Xiaokui, Kim, Sung‐Hak, Mao, Ping, Kig, Cenk, Nardini, Diana, Sobol, Robert W., Chow, Lionel M.L., Kornblum, Harley I., Waclaw, Ronald, Beullens, Monique, Nakano, Ichiro
• Format: Article
• Language: English
• Subjects: Animals; Brain Neoplasms - drug therapy; Brain Neoplasms - genetics; Brain Neoplasms - metabolism; Brain Neoplasms - pathology; Cancer stem cell; Cancer Stem Cells; Cell Cycle Proteins - genetics; Cell Cycle Proteins - metabolism; Cell Proliferation - drug effects; Cells, Cultured; Dacarbazine - analogs & derivatives; Dacarbazine - pharmacology; Forkhead Transcription Factors - genetics; Forkhead Transcription Factors - metabolism; Glioblastoma; Glioblastoma - drug therapy; Glioblastoma - genetics; Glioblastoma - metabolism; Glioblastoma - pathology; Glioblastoma stem cell; HEK293 Cells; Humans; Kinases; Mice; Mitosis - drug effects; Mitosis - genetics; Mitosis - physiology; Neoplastic Stem Cells - drug effects; Neoplastic Stem Cells - metabolism; Neoplastic Stem Cells - pathology; Neural stem cell; Neural Stem Cells - drug effects; Neural Stem Cells - metabolism; Neural Stem Cells - pathology; Peptides - pharmacology; Phosphorylation; PLK1; Polo-Like Kinase 1; Protein Serine-Threonine Kinases - genetics; Protein Serine-Threonine Kinases - metabolism; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Stem cells; Temozolomide; Up-Regulation - drug effects
• ISSN: 1066-5099; 1549-4918
• DOI: 10.1002/stem.1358

Glioblastoma multiforme (GBM) is a life‐threatening brain tumor. Accumulating evidence suggests that eradication of glioma stem‐like cells (GSCs) in GBM is essential to achieve cure. The transcription factor FOXM1 has recently gained attention as a master regulator of mitotic progression of cancer cells in various organs. Here, we demonstrate that FOXM1 forms a protein complex with the mitotic kinase MELK in GSCs, leading to phosphorylation and activation of FOXM1 in a MELK kinase‐dependent manner. This MELK‐dependent activation of FOXM1 results in a subsequent increase in mitotic regulatory genes in GSCs. MELK‐driven FOXM1 activation is regulated by the binding and subsequent trans‐phosphorylation of FOXM1 by another kinase PLK1. Using mouse neural progenitor cells (NPCs), we found that transgenic expression of FOXM1 enhances, while siRNA‐mediated gene silencing diminishes neurosphere formation, suggesting that FOXM1 is required for NPC growth. During tumorigenesis, FOXM1 expression sequentially increases as cells progress from NPCs, to pretumorigenic progenitors and GSCs. The antibiotic Siomycin A disrupts MELK‐mediated FOXM1 signaling with a greater sensitivity in GSC compared to neural stem cell. Treatment with the first‐line chemotherapy agent for GBM, Temozolomide, paradoxically enriches for both FOXM1 (+) and MELK (+) cells in GBM cells, and addition of Siomycin A to Temozolomide treatment in mice harboring GSC‐derived intracranial tumors enhances the effects of the latter. Collectively, our data indicate that FOXM1 signaling through its direct interaction with MELK regulates key mitotic genes in GSCs in a PLK1‐dependent manner and thus, this protein complex is a potential therapeutic target for GBM. STEM Cells 2013;31:1051–1063