Notch pathway inhibition depletes stem-like cells and blocks engraftment in embryonal brain tumors.
The Notch signaling pathway is required in both nonneoplastic neural stem cells and embryonal brain tumors, such as medulloblastoma, which are derived from such cells. We investigated the effects of Notch pathway inhibition on medulloblastoma growth using pharmacologic inhibitors of gamma-secretase. Notch blockade suppressed expression of the pathway target Hes1 and caused cell cycle exit, apoptosis, and differentiation in medulloblastoma cell lines. Interestingly, viable populations of better-differentiated cells continued to grow when Notch activation was inhibited but were unable to efficiently form soft-agar colonies or tumor xenografts, suggesting that a cell fraction required for tumor propagation had been depleted. It has recently been hypothesized that a small population of stem-like cells within brain tumors is required for the long-term propagation of neoplastic growth and that CD133 expression and Hoechst dye exclusion (side population) can be used to prospectively identify such tumor-forming cells. We found that Notch blockade reduced the CD133-positive cell fraction almost 5-fold and totally abolished the side population, suggesting that the loss of tumor-forming capacity could be due to the depletion of stem-like cells. Notch signaling levels were higher in the stem-like cell fraction, providing a potential mechanism for their increased sensitivity to inhibition of this pathway. We also observed that apoptotic rates following Notch blockade were almost 10-fold higher in primitive nestin-positive cells as compared with nestin-negative ones. Stem-like cells in brain tumors thus seem to be selectively vulnerable to agents inhibiting the Notch pathway.
Fan
Xing
X
Department of Pathology, Johns Hopkins University School of Medicine, 720 Rutland Avenue, Baltimore, MD 21205, USA.
Matsui
William
W
Khaki
Leila
L
Stearns
Duncan
D
Chun
Jiong
J
Li
Yue-Ming
YM
Eberhart
Charles G
CG
D053829:Amyloid Precursor Protein Secretases; D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D016282:Aspartic Acid Endopeptidases; D001932:Brain Neoplasms / Q000378:metabolism / Q000473:pathology* / Q000517:prevention & control; D002454:Cell Differentiation / Q000502:physiology; D048708:Cell Growth Processes / Q000502:physiology; D045744:Cell Line, Tumor; D010450:Endopeptidases / Q000378:metabolism; D006801:Humans; D007381:Intermediate Filament Proteins / Q000378:metabolism; D008527:Medulloblastoma / Q000378:metabolism / Q000473:pathology* / Q000517:prevention & control; D051379:Mice; D014411:Neoplastic Stem Cells / Q000378:metabolism / Q000473:pathology*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D064231:Nestin; D009474:Neurons / Q000473:pathology; D011480:Protease Inhibitors / Q000494:pharmacology; D051880:Receptors, Notch / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000187:drug effects; D014183:Transplantation, Heterologous
D007381:Intermediate Filament Proteins; C577484:NES protein, human; D009419:Nerve Tissue Proteins; C577485:Nes protein, mouse; D064231:Nestin; D011480:Protease Inhibitors; D051880:Receptors, Notch; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; D016282:Aspartic Acid Endopeptidases; C509280:BACE1 protein, human; C509282:Bace1 protein, mouse