title: RNA-binding protein Musashi1 modulates glioma cell growth through the post-transcriptional regulation of Notch and PI3 kinase/Akt signaling pathways.
abstract: Musashi1 (MSI1) is an RNA-binding protein that plays critical roles in nervous-system development and stem-cell self-renewal. Here, we examined its role in the progression of glioma. Short hairpin RNA (shRNA)-based MSI1-knock down (KD) in glioblastoma and medulloblastoma cells resulted in a significantly lower number of self renewing colony on day 30 (a 65% reduction), compared with non-silencing shRNA-treated control cells, indicative of an inhibitory effect of MSI1-KD on tumor cell growth and survival. Immunocytochemical staining of the MSI1-KD glioblastoma cells indicated that they ectopically expressed metaphase markers. In addition, a 2.2-fold increase in the number of MSI1-KD cells in the G2/M phase was observed. Thus, MSI1-KD caused the prolongation of mitosis and reduced the cell survival, although the expression of activated Caspase-3 was unaltered. We further showed that MSI1-KD glioblastoma cells xenografted into the brains of NOD/SCID mice formed tumors that were 96.6% smaller, as measured by a bioluminescence imaging system (BLI), than non-KD cells, and the host survival was longer (49.3±6.1 days vs. 33.6±3.6 days; P<0.01). These findings and other cell biological analyses suggested that the reduction of MSI1 in glioma cells prolonged the cell cycle by inducing the accumulation of Cyclin B1. Furthermore, MSI1-KD reduced the activities of the Notch and PI(3) kinase-Akt signaling pathways, through the up-regulation of Numb and PTEN, respectively. Exposure of glioma cells to chemical inhibitors of these pathways reduced the number of spheres and living cells, as did MSI1-KD. These results suggest that MSI1 increases the growth and/or survival of certain types of glioma cells by promoting the activation of both Notch and PI(3) kinase/Akt signaling.
authors.affiliation: Department of Physiology, Keio University School of Medicine, Shinjuku, Tokyo, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Muto
authors.forename: Takao
authors.initials: T
authors.lastname: Imai
authors.forename: Daisuke
authors.initials: D
authors.lastname: Ogawa
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Nishimoto
authors.forename: Yohei
authors.initials: Y
authors.lastname: Okada
authors.forename: Yo
authors.initials: Y
authors.lastname: Mabuchi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Kawase
authors.forename: Akio
authors.initials: A
authors.lastname: Iwanami
authors.forename: Paul S
authors.initials: PS
authors.lastname: Mischel
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Saya
authors.forename: Kazunari
authors.initials: K
authors.lastname: Yoshida
authors.forename: Yumi
authors.initials: Y
authors.lastname: Matsuzaki
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Okano
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000502:physiology; D045744:Cell Line, Tumor; D019926:Cyclin B / Q000378:metabolism; D055785:Gene Knockdown Techniques; D005910:Glioma / Q000378:metabolism* / Q000503:physiopathology*; D007150:Immunohistochemistry; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034622:RNA Interference / Q000502:physiology; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051880:Receptors, Notch / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*
chemical_list: D019926:Cyclin B; C104786:Msi1h protein, mouse; D009419:Nerve Tissue Proteins; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D051880:Receptors, Notch; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt