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Desert Hedgehog Downregulation Mediates Proliferative Inhibition by γ-Glutamylcyclotransferase Knockdown in Murine Glioblastoma Stem Cells

ABSTRACT: Glioblastoma is the most frequent type of adult-onset malignant brain tumors and has a very poor prognosis. A cell population called glioblastoma stem cells has been shown to be one of the mechanisms by which glioblastoma acquires therapy resistance. Therefore, there is a need to establish novel therapeutic strategies useful for inhibiting the cell population. γ-glutamylcyclotransferase (GGCT) is an enzyme involved in the synthesis and metabolism of glutathione, which is highly expressed in a wide range of cancer types including glioblastoma, and inhibition of its expression has been reported to have antitumor effects on various cancer types. In this study, we searched for pathways affected by the growth-promoting effect of GGCT overexpression in mouse embryonic fibroblasts NIH3T3 by comprehensive gene expression analysis and found the hedgehog pathway. Knockdown of GGCT inhibited proliferation of glioblastoma stem cells derived from a mouse glioblastoma model and caused decreased expression of desert hedgehog (Dhh), a representative ligand of the pathway, and the downstream target Gli1. To analyze the contribution of reduced Dhh, we activated the hedgehog pathway by forced expression of Dhh. We found that Dhh overexpression significantly restored the growth suppressive effect of GGCT knockdown. The results of this study indicate that high GGCT expression is important for Dhh expression and activation of the hedgehog pathway, which is required to maintain glioblastoma stem cell proliferation. Therefore, inhibition of GGCT function may be useful in suppressing stemness of glioblastoma stem cells accompanied with activation of the hedgehog pathway.

ORGANISM(S): Mus musculus

PROVIDER: GSE266154 | GEO | 2024/05/20

REPOSITORIES: GEO

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Project description:Misactivation of the Hedgehog (Hh) pathway can cause cancers such as medulloblastomas, the most common malignant brain tumor in children, and basal cell carcinomas, the most common cancer in the United States. Hedgehog signals are transmitted through primary cilia, where Hedgehog ligands bind to Patched1 and activate Smoothened through interactions with cilia-associated sterol lipids. The gene expression programs driving cellular responses to ciliary Hh signals are incompletely understood. Thus, to define Hh target genes, we performed RNA sequencing of cells after treatment with Hh ligands (Shh, Dhh, Ihh), cilia-associated lipids (7b,27-dihydroxycholesterol, 24(S),25-epoxycholesterol), or synthetic lipids or small molecules that activate Smoothened (20(S)-hydroxycholesterol, SAG). Treatment with Hh pathway agonists identified a core gene expression program comprised of 155 genes driving lipid synthesis, metabolism, signaling, adhesion, or angiogenesis. These datasets were integrated with RNA sequencing of Hh-human medulloblastomas (n=?), a Math1-Cre SmoM2 mouse genetic model of Hh-associated medulloblastoma (n=?), and human basal cell carcinomas (n=10) to ascertain how malignant Hh signaling differs from canonical Hh signaling. We discover a conserved response to ciliary Hh signals in human or mouse medulloblastomas, including known target genes such as Gli1 or Ptch1, and novel target genes such as Hsd11b1 or Retnla. Importantly, mechanistic studies reveal Hsd11b1 to be a putative negative regulator of Hh signaling that is dysregulated in malignancies. We further demonstrate Retnla to be a positive regulator of Hh signaling that drives expression of Hsd11b2, a druggable dependency underlying Hedgehog-associated medulloblastoma. Orthotopic implantation of neuroepithelial stem cells that overexpress either Hsd11b1 and Retnla demonstrate that tumors derived Hsd11ß1 overexpression are more primitive and less aggressive whereas Retnla overexpression forms tumors that are more differentiated and behave more aggressively. In sum, we illuminate the first comprehensive transcriptome of Hh signaling and highlight the intricate interplay between Hh signaling and lipid metabolism that Hh-dependent malignancies dysregulate to drive tumor progression.

Project description:Sivakumar2011 - Hedgehog Signaling Pathway This is the current model for the Hedgehog signaling pathway. The best data for mechanism of signaling has been worked out in Drosophila, so this model is based largely on Drosophila data. Hedgehog target genes vary from tissue to tissue, so the identities of individual target genes have not been listed. The main difference between the Drosophila and mammalian Hedgehog signaling pathways is the fact that there are three mammalian homologs of Cubitus interruptus, Gli1 Gli2 and Gli3. Some or all of the mammalian homologs may be proteolytically processed, but the data are controversial. There are two mammalian Ptc genes and three mammalian Hedgehog genes as well. The pathway for Sonic Hedgehog appears to be most similar to the Drosophila hedgehog pathway. References: Hedgehog signaling in animal development: paradigms and principles. Sonic hedgehog in the nervous system: functions, modifications and mechanisms. Hedgehog signal transduction: recent findings. Hedgehog signaling: Costal-2 bridges the transduction gap. This model is described in the article: A systems biology approach to model neural stem cell regulation by notch, shh, wnt, and EGF signaling pathways. Sivakumar KC, Dhanesh SB, Shobana S, James J, Mundayoor S. Omics: a Journal of Integrative Biology. 2011; 15(10):729-737 Abstract: The Notch, Sonic Hedgehog (Shh), Wnt, and EGF pathways have long been known to influence cell fate specification in the developing nervous system. Here we attempted to evaluate the contemporary knowledge about neural stem cell differentiation promoted by various drug-based regulations through a systems biology approach. Our model showed the phenomenon of DAPT-mediated antagonism of Enhancer of split [E(spl)] genes and enhancement of Shh target genes by a SAG agonist that were effectively demonstrated computationally and were consistent with experimental studies. However, in the case of model simulation of Wnt and EGF pathways, the model network did not supply any concurrent results with experimental data despite the fact that drugs were added at the appropriate positions. This paves insight into the potential of crosstalks between pathways considered in our study. Therefore, we manually developed a map of signaling crosstalk, which included the species connected by representatives from Notch, Shh, Wnt, and EGF pathways and highlighted the regulation of a single target gene, Hes-1, based on drug-induced simulations. These simulations provided results that matched with experimental studies. Therefore, these signaling crosstalk models complement as a tool toward the discovery of novel regulatory processes involved in neural stem cell maintenance, proliferation, and differentiation during mammalian central nervous system development. To our knowledge, this is the first report of a simple crosstalk map that highlights the differential regulation of neural stem cell differentiation and underscores the flow of positive and negative regulatory signals modulated by drugs. This model is hosted on BioModels Database and identified by: BIOMD0000000395. To cite BioModels Database, please use: BioModels Database: An enhanced, curated and annotated resource for published quantitative kinetic models. To the extent possible under law, all copyright and related or neighbouring rights to this encoded model have been dedicated to the public domain worldwide. Please refer to CC0 Public Domain Dedication for more information.

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Desert Hedgehog Downregulation Mediates Proliferative Inhibition by γ-Glutamylcyclotransferase Knockdown in Murine Glioblastoma Stem Cells

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