title: Hedgehog/GLI1 regulates IGF dependent malignant behaviors in glioma stem cells.
abstract: A population of tumorigenic, chemoresistant, and radioresistant cancer stem cells is postulated to contribute to the aggressive and fatal clinical course of glioblastomas. Activation of the Hedgehog (HH) pathway and increased expression of its downstream effector GLI1 are driving factors of glioma tumorigenicity and glioma stem cell (GSC) biology. In this study, we describe a dependence of insulin-like growth factor (IGF) signaling on active HH/GLI1 in GSCs. Insulin receptor substrate 1 (IRS1) was identified as a target of the GLI1 transcription factor and inhibition of GLI1 was sufficient to obstruct IRS1 protein expression and IGF-I induced mitogen-activated protein kinase (MAPK) activation. Suppression of GLI1 activity decreased the responsiveness of GSCs to IGF-I stimulation and constrained IGF-I dependent GSC proliferation, clonogenicity, invasion, and angiogenesis. In addition, blockade of the HH/GLI1 and IGF pathways countered the intrinsic and acquired resistance of GSCs to temozolomide. These results provide further insight into the oncogenic mechanisms of the HH pathway in glioblastoma and demonstrate a cooperative signaling axis between the HH/GLI1 and IGF pathways to propagate malignant GSC phenotypes.
authors.affiliation: School of Medicine, Johns Hopkins University, Baltimore, Maryland, USA.
authors.forename: Antony
authors.initials: A
authors.lastname: Hsieh
authors.forename: Ron
authors.initials: R
authors.lastname: Ellsworth
authors.forename: David
authors.initials: D
authors.lastname: Hsieh
mesh_terms: D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D003606:Dacarbazine / Q000031:analogs & derivatives / Q000494:pharmacology; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D055785:Gene Knockdown Techniques; D020868:Gene Silencing / Q000187:drug effects; D005910:Glioma / Q000201:enzymology / Q000235:genetics / Q000473:pathology*; D053823:Hedgehog Proteins / Q000378:metabolism*; D006801:Humans; D055504:Insulin Receptor Substrate Proteins / Q000235:genetics / Q000378:metabolism; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D014411:Neoplastic Stem Cells / Q000201:enzymology / Q000473:pathology*; D034741:RNA, Small Interfering / Q000378:metabolism; D011836:Radiation Tolerance / Q000187:drug effects; D000077204:Temozolomide; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D015854:Up-Regulation / Q000187:drug effects; D000071676:Zinc Finger Protein GLI1
chemical_list: C400551:GLI1 protein, human; D053823:Hedgehog Proteins; D055504:Insulin Receptor Substrate Proteins; D034741:RNA, Small Interfering; D014157:Transcription Factors; D000071676:Zinc Finger Protein GLI1; D007334:Insulin-Like Growth Factor I; D003606:Dacarbazine; D000077204:Temozolomide