The Notch Target Hes1 Directly Modulates Gli1 Expression and Hedgehog Signaling: A Potential Mechanism of Therapeutic Resistance

• Published in: Clinical cancer research 2010-12, Vol.16 (24), p.6060-6070
• Main Authors: SCHRECK, Karisa C, TAYLOR, Pete, MARCHIONNI, Luigi, GOPALAKRISHNAN, Vidya, BAR, Eli E, GAIANO, Nicholas, EBERHART, Charles G
• Format: Article
• Language: English
• Subjects: Antineoplastic agents; Antineoplastic Combined Chemotherapy Protocols - therapeutic use; Basic Helix-Loop-Helix Transcription Factors - metabolism; Basic Helix-Loop-Helix Transcription Factors - physiology; Biological and medical sciences; Brain Neoplasms - drug therapy; Brain Neoplasms - genetics; Brain Neoplasms - metabolism; Brain Neoplasms - pathology; Cell Line, Tumor; Cyclic S-Oxides - administration & dosage; Drug Evaluation, Preclinical; Drug Resistance, Neoplasm - genetics; Gene Expression Regulation, Neoplastic; Glioblastoma - drug therapy; Glioblastoma - genetics; Glioblastoma - metabolism; Glioblastoma - pathology; Hedgehog Proteins - genetics; Hedgehog Proteins - metabolism; Homeodomain Proteins - metabolism; Homeodomain Proteins - physiology; Humans; Medical sciences; Pharmacology. Drug treatments; Receptors, Notch - metabolism; Receptors, Notch - physiology; Signal Transduction - genetics; Signal Transduction - physiology; Thiadiazoles - administration & dosage; Transcription Factor HES-1; Transcription Factors - genetics; Transcription Factors - metabolism; U937 Cells; Veratrum Alkaloids - administration & dosage; Zinc Finger Protein GLI1
• ISSN: 1078-0432; 1557-3265
• DOI: 10.1158/1078-0432.ccr-10-1624

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. 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. 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. 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.