title: The Notch target Hes1 directly modulates Gli1 expression and Hedgehog signaling: a potential mechanism of therapeutic resistance.
abstract: OBJECTIVE
  Multiple developmental pathways including Notch, Hedgehog, and Wnt are active in malignant brain tumors such as medulloblastoma and glioblastoma (GBM). This raises the possibility that tumors might compensate for therapy directed against one pathway by upregulating a different one. We investigated whether brain tumors show resistance to therapies against Notch, and whether targeting multiple pathways simultaneously would kill brain tumor cells more effectively than monotherapy.
  
  
  METHODS
  We used GBM neurosphere lines to investigate the effects of a gamma-secretase inhibitor (MRK-003) on tumor growth, and chromatin immunoprecipitation to study the regulation of other genes by Notch targets. We also evaluated the effect of combined therapy with a Hedgehog inhibitor (cyclopamine) in GBM and medulloblastoma lines, and in primary human GBM cultures.
  
  
  RESULTS
  GBM cells are at least partially resistant to long-term MRK-003 treatment, despite ongoing Notch pathway suppression, and show concomitant upregulation of Wnt and Hedgehog activity. The Notch target Hes1, a repressive transcription factor, bound the Gli1 first intron, and may inhibit its expression. Similar results were observed in a melanoma-derived cell line. Targeting Notch and Hedgehog simultaneously induced apoptosis, decreased cell growth, and inhibited colony-forming ability more dramatically than monotherapy. Low-passage neurospheres isolated from freshly resected human GBMs were also highly susceptible to coinhibition of the two pathways, indicating that targeting multiple developmental pathways can be more effective than monotherapy at eliminating GBM-derived cells.
  
  
  CONCLUSIONS
  Notch may directly suppress Hedgehog via Hes1 mediated inhibition of Gli1 transcription, and targeting both pathways simultaneously may be more effective at eliminating GBMs cells.
authors.affiliation: Department of Neuroscience, Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
authors.forename: Karisa C
authors.initials: KC
authors.lastname: Schreck
authors.forename: Pete
authors.initials: P
authors.lastname: Taylor
authors.forename: Luigi
authors.initials: L
authors.lastname: Marchionni
authors.forename: Vidya
authors.initials: V
authors.lastname: Gopalakrishnan
authors.forename: Eli E
authors.initials: EE
authors.lastname: Bar
authors.forename: Nicholas
authors.initials: N
authors.lastname: Gaiano
authors.forename: Charles G
authors.initials: CG
authors.lastname: Eberhart
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism / Q000502:physiology*; D001932:Brain Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D003499:Cyclic S-Oxides / Q000008:administration & dosage; D004353:Drug Evaluation, Preclinical; D019008:Drug Resistance, Neoplasm / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic; D005909:Glioblastoma / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism*; D018398:Homeodomain Proteins / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D051880:Receptors, Notch / Q000378:metabolism / Q000502:physiology; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology; D013830:Thiadiazoles / Q000008:administration & dosage; D000072056:Transcription Factor HES-1; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D020298:U937 Cells; D014704:Veratrum Alkaloids / Q000008:administration & dosage; D000071676:Zinc Finger Protein GLI1
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D003499:Cyclic S-Oxides; D053823:Hedgehog Proteins; D018398:Homeodomain Proteins; D051880:Receptors, Notch; D013830:Thiadiazoles; D000072056:Transcription Factor HES-1; D014157:Transcription Factors; D014704:Veratrum Alkaloids; D000071676:Zinc Finger Protein GLI1; C400551:GLI1 protein, human; C523799:MRK 003; C078493:HES1 protein, human; C000541:cyclopamine