The EWS/FLI1 oncogenic transcription factor deregulates GLI1

Abstract

Ewing family tumors (EFT), classically Ewing's sarcoma and peripheral primitive neuroectodermal tumor, share a common class of tumor-specific fusion genes thought to be key mediators of tumor biology. Here we demonstrate that the most common Ewing's fusion, EWS/FLI1, produces transcriptional upregulation of GLI1 and its direct transcriptional target PATCHED1 in a model transformation system. This deregulation of GLI1 is common to other EWS/ets chimera and depends on the functional transcriptional regulatory domains. Inhibition of GLI1 via RNAi or via overexpression of endogenous inhibitors results in a reduction of EWS/FLI1 transformation activity. Activation of GLI1 appears to occur in a Hedgehog-independent fashion as blockade of Hedgehog signaling has only a modest effect on EFT cells. We present evidence that EWS/FLI1 upregulation of cMYC may play a role in the upregulation of GLI1 in EWS/ FLI1-transformed NIH3T3 cells. Finally, we demonstrate that observations made in a model transformation system translate to an Ewing cellular background. EFT cell lines express GLI1 and PATCHED and this expression is EWS/FLI1 dependent. Inhibition of GLI1 expression via RNAi results in reduced anchorage-independent growth in an EFT cell line. GLI1 appears to be a transcriptionally deregulated target of EWS/FLI1 that mediates a portion of its tumorigenic phenotype.

Arsenic antagonizes the Hedgehog pathway by preventing ciliary accumulation and reducing stability of the Gli2 transcriptional effector

“…Cyclopamine mimics are currently in wide development in the pharmaceutical industry (36,37,63,64) but are not expected to be effective in diseases in which pathway activation involves mutations in components downstream of Smo (13)(14)(15)41) or in which pathway activity results from increased expression or activity of the Gli1 proteins (16)(17)(18)(19)25). In addition, mutations that cause constitutive Smo activity can render Smo resistant to the action of cyclopamine mimics (11,30), or resistance can arise in the setting of treatment with a cyclopamine mimic, as has been documented for a human medulloblastoma patient (38,40).…”

“…Activating mutations of Smo also have been reported in sporadic basal cell carcinoma (11,12), and mutations in the intracellular regulator Suppressor of fused (Sufu) are associated with an increased prevalence of medulloblastoma and rhabdomyosarcoma (13)(14)(15). In addition, the Gli1 gene is amplified in many sarcomas (16,17) and is expressed at high level in association with the EWS/FLI fusion oncogene that causes Ewing sarcoma (18,19), thus causing activation of Hh pathway targets. Hh pathway activity also appears to be required for the maintenance of cancer stem cells in multiple myeloma (20), chronic myeloid leukemia (21,22), and perhaps other hematologic malignancies (23).…”

“…In addition, a metastatic medulloblastoma patient who initially responded well to GDC-0449 treatment subsequently succumbed to the disease that relapsed in association with a spontaneous mutation in Smo that did not affect its activity but impaired its binding to the drug (40). In addition, cancer-associated pathway activation in some cases is mediated by effects on components downstream of Smo, be it loss-of-function mutations in the intracellular regulator Sufu (13)(14)(15)41) or non-Hh pathway-mediated increase of Gli1 expression (16)(17)(18)(19)25).…”

Noncanonical Regulation of the Hedgehog Mediator GLI1 by c-MYC in Burkitt Lymphoma

“…Recent reports suggest that c-MYC activates GLI1 in vitro and enhances Hedgehog-induced medulloblastoma formation (9,10). Previously, we identified putative c-MYCbinding elements (E-boxes) in the 5 0 -regulatory region of GLI1 (11,12).…”

Activation of the hedgehog-signaling pathway in human cancer and the clinical implications

“…Koga et al, 2008;Kasperczyk et al, 2009). Expression of Gli1 is reported to be regulated by TGFb, Ras, JUN, SCL/TAL1 and EWS-FLI1 oncoprotein (Ji et al, 2007;Kasai et al, 2008;Zwerner et al, 2008;Beauchamp et al, 2009;Laner-Plamberger et al, 2009;NolanStevaux et al, 2009). The interaction between PKC and hedgehog signaling varies depending on PKC isoforms and cell types.…”