Title:Essential Role of Gli Proteins in Glioblastoma Multiforme
Volume: 14
Issue: 2
Author(s): Matteo Santoni, Luciano Burattini, Massimo Nabissi, Maria Beatrice Morelli, Rossana Berardi, Giorgio Santoni and Stefano Cascinu
Affiliation:
Keywords:
Gli proteins, Glioblastoma, Glioma stem cells, Hedgehog signaling pathway, Temozolomide
Abstract: Glioblastoma multiforme (GBM) is the most common and malignant primary brain tumor in adults. Despite
several advances, little is known about GBM–specific aberrant signalling processes. The hedgehog (Hh) signalling pathway
plays a central role in GBM pathogenesis and tumor progression. Its activation is mediated by sonic hedgehog (Shh),
which binds to its receptor patched, PTCH, promoting Gli1 activation. Gli1 is a member of the Kruppel family of zinc
finger transcription factors. Hh⁄Gli1 axis controls glioma stem cells (GSCs) behaviour, which is essential to GBM chemoand
radioresistance. Thus, Gli1 modulates the expression of stemness genes and the self–renewal of CD133+ GSCs. The
activation of Hh⁄Gli1 in GSCs seems to be dependent on the insulin–like growth factor (IGF) signaling, which also contributes
to intrinsic and acquired resistance of GSCs to temozolomide (TMZ). Beyond Hh signals, Gli1 activity is also
regulated by several elements, including Ras, Myc, Akt, p53 and PTEN. Recently, a truncated variant of Gli1 (tGli1) has
been demonstrated to gain the ability to regulate expression of genes that are not modulated by Gli1, such as the
migration⁄invasion–associated CD24 or the human vascular endothelial growth factor–A (VEGF–A), leading to their
upregulation. This review will summarize the role of Gli proteins in GBM tumorigenesis and their potential impact on
GBM therapy and treatment resistance.
