Hedgehog Signaling Pathway Is Active in GBM with GLI1 mRNA Expression Showing a Single Continuous Distribution Rather than Discrete High/Low Clusters

Abstract

Hedgehog (Hh) signaling pathway is a valid therapeutic target in a wide range of malignancies. We focus here on glioblastoma multiforme (GBM), a lethal malignancy of the central nervous system (CNS). By analyzing RNA-sequencing based transcriptomics data on 149 clinical cases of TCGA-GBM database we show here a strong correlation (r = 0.7) between GLI1 and PTCH1 mRNA expression—as a hallmark of the canonical Hh-pathway activity in this malignancy. GLI1 mRNA expression varied in 3 orders of magnitude among the GBM patients of the same cohort showing a single continuous distribution—unlike the discrete high/low-GLI1 mRNA expressing clusters of medulloblastoma (MB). When compared with MB as a reference, the median GLI1 mRNA expression in GBM appeared 14.8 fold lower than that of the “high-Hh” cluster of MB but 5.6 fold higher than that of the “low-Hh” cluster of MB. Next, we demonstrated statistically significant up- and down-regulation of GLI1 mRNA expressions in GBM patient-derived low-passage neurospheres in vitro by sonic hedgehog ligand-enriched conditioned media (shh-CM) and by Hh-inhibitor drug vismodegib respectively. We also showed clinically achievable dose (50 μM) of vismodegib alone to be sufficient to induce apoptosis and cell cycle arrest in these low-passage GBM neurospheres in vitro. Vismodegib showed an effect on the neurospheres, both by down-regulating GLI1 mRNA expression and by inducing apoptosis/cell cycle arrest, irrespective of their relative endogenous levels of GLI1 mRNA expression. We conclude from our study that this single continuous distribution pattern of GLI1 mRNA expression technically puts almost all GBM patients in a single group rather than discrete high- or low-clusters in terms of Hh-pathway activity. That is suggestive of therapies with Hh-pathway inhibitor drugs in this malignancy without a need for further stratification of patients on the basis of relative levels of Hh-pathway activity among them.

Upregulation of microRNA-129-5p inhibits cell invasion, migration and tumor angiogenesis by inhibiting ZIC2 via downregulation of the Hedgehog signaling pathway in cervical cancer

“…Since the overexpression of Gli1 and Gli2 implicated in the activation of the Hedgehog signaling pathway, we subsequently deduced that the Hedgehog signaling pathway was activated in CC. 18 The results of our study were in line with observations by Zhang et al in that miR-129-5p was depleted as CC develops. Likewise, consistent findings of the present study and evidence reported by Chan et al in that ZIC2 and Gli1 are overexpressed in CC cell lines including Hela and C-33A.…”

WNT signaling in glioblastoma and therapeutic opportunities

“…For instance, blockade of SHH signaling with the chemical inhibitor Vismodegib induced cell cycle arrest and apoptosis, and downregulated GLI1 expression in patient-derived GBM cells. 136 Several studies have suggested that SHH signaling has a suppressive effect on WNT signaling. 129,137,138 For example, it was reported that GLI1 binds to the sFRP1 promoter and increases Figure 3 Cross-talk with other signaling pathways.…”

Radiation-agent combinations for glioblastoma: challenges in drug development and future considerations

“…Whether Vismodegib has clinical activity in prospective glioblastoma clinical trials remains to be tested. Retrospective data indicates that Hedgehog signaling is an active and important pathway in glioblastoma [40]. …”