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, 17 (2), 165-72

HEDGEHOG-GLI1 Signaling Regulates Human Glioma Growth, Cancer Stem Cell Self-Renewal, and Tumorigenicity


HEDGEHOG-GLI1 Signaling Regulates Human Glioma Growth, Cancer Stem Cell Self-Renewal, and Tumorigenicity

Virginie Clement et al. Curr Biol.

Erratum in

  • Curr Biol. 2007 Jan 23;17(2):192


Cancer stem cells are rare tumor cells characterized by their ability to self-renew and to induce tumorigenesis. They are present in gliomas and may be responsible for the lethality of these incurable brain tumors. In the most aggressive and invasive type, glioblastoma multiforme (GBM), an average of about one year spans the period between detection and death [1]. The resistence of gliomas to current therapies may be related to the existence of cancer stem cells [2-6]. We find that human gliomas display a stemness signature and demonstrate that HEDGEHOG (HH)-GLI signaling regulates the expression of stemness genes in and the self-renewal of CD133(+) glioma cancer stem cells. HH-GLI signaling is also required for sustained glioma growth and survival. It displays additive and synergistic effects with temozolomide (TMZ), the current chemotherapeutic agent of choice. TMZ, however, does not block glioma stem cell self-renewal. Finally, interference of HH-GLI signaling with cyclopamine or through lentiviral-mediated silencing demonstrates that the tumorigenicity of human gliomas in mice requires an active pathway. Our results reveal the essential role of HH-GLI signaling in controlling the behavior of human glioma cancer stem cells and offer new therapeutic possibilities.


Figure 1
Figure 1. Gene expression in human gliomas and requirement of HH-GLI signaling
A) Diagram of expression levels using white for expression within normal range, red for overexpression and blue for underexpression. Normal expression ranges and thresholds were established by quantifying the expression level of the 22 markers used in three samples of normal cortex (Fig.S2). Gliomas are ranked by grade and by gene expression pattern as GBM (glioblastoma mulitforme or grade IV astrocytomas; all primary GBMs), A: astrocytoma, OG: oligodendroglioma, AG: Anaplastic glioma. The roman numeral denotes WHO grade and the arabic numeral the tumor number within our series. Two medulloblastomas (MB) are used as controls for HH-GLI pathway activity (7). Domains of consistent (>50% of cases) GLI1 activity and of the stemness signature are boxed and the names of the genes are highlighted. B) In situ hybridization of fresh-frozen OG-III-2 samples as indicated with an H&E stain (right) as control. Arrows point to expression in vessels (asterisks). C,D) Inhibition of glioma cell proliferation in primary adherent cultures (passages 1–3) of fresh tumors. Percent reduction in BrdU incorporation as a measure of cell division is shown as the ratio of the result of treatment with cyclopamine over the result of treatment with tomatidine used as control (C), or as the ratio of treatment with each specified GLI siRNA over an unrelated siRNA control (siC; D). Error bars are not shown for histograms denoting ratios but significance is provided by asterisks (p<0.05). PC: pineocytoma; NC: neurocytoma. E,F) Rescue of the effects of cyclopamine by siRNA GLI3. The incompleteness of the effect is likely due to partial siRNA lipofection compared with the ubiquitous effects of the drug. GLI1 or GLI2 siRNAs did not rescue the effects of cyclopamine (not shown). Asterisks denote significative (p<0.05) changes. Scale bar = 200μm for (B).
Figure 2
Figure 2. Requirement of HH-GLI function in glioma stem cell cultures and combined effects with temozolomide
A,B) Phase-contrast and fluorescent images after immunolabeling with GFAP (green) and Nestin (red) antibodies, respectively, of GBM-8 gliomaspheres. C–E) Decrease in cell proliferation as measured by BrdU incorporation C,E) or increase in apoptosis measured by activated Caspase-3+ (D) in gliomaspheres treated with cyclopamine (Cyc) or tomatidine (Tom) (C,D) or transduced with LV-control or LV-shSMOH (E). F,G) Synergistic or additive effects of intermediate doses of cyclopamine and TMZ on inhibition of cell proliferation and apoptosis as measured by phospho-Histone3+ (F) or Caspase3+ labeling (G), respectively. All combinations are significantly more effective (p<0.05; asterisks) as compared with cyclopamine alone and all but OG-III-1 as compared with TMZ alone (p<0.05). Scale bar = 140μm (A,B).
Figure 3
Figure 3. Inhibition of human glioma xenograft growth in vivo by interference with HH-GLI signaling
A) Development of invasive gliomas after intracerebral implantation of gliomaspheres transduced with a lentiviral vector expressing LacZ ±1 month after implantation of 105 cells (n=7 mice for GBM-8; n=7 mice for GBM-7 and n=7 mice for OG-III-1, not shown). Glioma stem cell-derived tumor cells infiltrate into the parenchyma (cells are blue after X-Gal cytochemistry). B,C) Inhibition of intracraneal tumor growth after treatment with cyclopamine (n=3 mice for OG-III-1, n=3 mice for GBM-8, not shown) but not carrier alone (n=3 mice for OG-III-1, n=3 mice for GBM-8, not shown). Tumor volume (B) or BrdU+ cell number (C) were monitored in section reconstructions. D) Tumor volume was also decreased after LV-shSMOH transduction (n=3 mice) but not after LV-control transduction (n=3 mice). E) Infection with GBM-8 gliomasphere cells with LV-shSMOH and LV-tTR-KRAB (see supplemental information) reduced tumor volume only after induction by DOX (n=3 mice with DOX treatment and 3 mice without). F,G) Representative examples of intracraneal gliomas ±1 month after implantation of 104 GFP+ gliomapsheres treated as described. The asterisk denotes the injection site. Note the strong migration of tumor cells contralaterally along the corpus callosum (cc, arrow) in control (G) but not LV-shSMOH-expressing cases (G). H) Survival of mice harboring LV-control (n=4) or LV-shSMOH-transduced (n=4) cells. Mice were sacrificed at the first signs of terminal disease before extreme pain was apparent. I-M). Inhibition of subcutaneous U87 gliomas by injection of cyclopamine (I, L; n=8 tumors) or interference with SMOH (LV-shSMOH; J,K,M; n=6 tumors), but not in U87 tumors treated with carrier alone (I and not shown; n=8 tumors) or infected with LV-control (J,M; n=6 tumors). Asterisks denote significative changes (p<0.05). Scale bar= 0.25cm (A), 0.8mm (F,G) and 8mm for (J–L).
Figure 4
Figure 4. Effects of HH-GLI signaling on self-renewal and on CD133+ glioma cancer stem cells
A) Profile of the expression of selected genes in 7 gliomasphere stem cell cultures. White denotes normal expression within 2-fold up and 50% down from the average of all values per gene without counting the outliers; red >2-fold overexpression and light blue <2-fold underexpression (Fig. S8). Boxed and highlighted are stemness genes that show normalcy in all samples, or enhanced expression like GLI1 and PTCH1. B) Representative image of gliomaspheres (GBM-8) treated with cyclopamine (top), tomatidine (middle) or SHH (bottom) for 7 days in a cloning assay. C,D) Reduction of the number of secondary gliomaspheres, as a measure of self-renewal, after interference with SMOH function through treatment with cyclopamine (C) or RNA interference (D). Ratios are shown as percentage of reduction. Asterisks denote significant changes (p<0.05) over controls as indicated. E) Schematic diagram of the dissociation, FACS analyses, treatment and cloning methods used to determine the self-renewal properties and expression profile of CD133+ cells (see F–H). F) Inhibition of clonogenicity of CD133+ cells isolated from three glioma stem cell cultures and one fresh tumor. Ratios are cyc/tom and asterisks denote significant changes (p<0.05). G) Gene expression changes in gliomaspheres derived from CD133+ cells treated for 7d with cyclopamine or tomatidine used in (F). Changes are shown as cyc/tom ratios and columns show the decrease in gene expression. E.g. in GMB-7 GLI1 is reduced to 5% of its normal expression. Note that the expression of GFAP, NCAM, EGFR, DOUBLECORIN (DCX) and BCAN is not altered. Scale bar = 80μm for (B).

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