The Hedgehog (Hh) pathway is activated in some human cancers, including medulloblastoma. The gliomaassociated oncogene homolog (GLI) transcription factors are critical mediators of the activated Hh pathway, and their expression may be elevated in some tumors independent of upstream Hh signaling. Thus, therapies targeting GLI transcription factors may benefit a wide spectrum of patients with mutations at different nodal points of the Hh pathway. In this study, we present evidence that arsenic trioxide (ATO) suppresses human cancer cell growth and tumor development in mice by inhibiting GLI1. Mechanistically, ATO directly bound to GLI1 protein, inhibited its transcriptional activity, and decreased expression of endogenous GLI target genes. Consistent with this, ATO inhibited the growth of human cancer cell lines that depended on upregulated GLI expression in vitro and in vivo in

Ewing sarcoma family of tumors (ESFT) is an undifferentiated neoplasm of the bone and soft tissue. ESFT is characterized by a specific chromosomal translocation occurring between chromosome 22 and (in most cases) chromosome 11, which generates an aberrant transcription factor, EWS-FLI1. The function of EWS-FLI1 is essential for the maintenance of ESFT cell survival and tumorigenesis. The Hedgehog pathway is activated in several cancers. Oncogenic potential of the Hedgehog pathway is mediated by increasing the activity of the GLI family of transcription factors. Recent evidence suggests that EWS-FLI1 increases expression of GLI1 by an unknown mechanism. Our data from chromatin immunoprecipitation and promoter reporter studies indicated GLI1 as a direct transcriptional target of EWS-FLI1. Expression of EWS-FLI1 in non-ESFT cells increased GLI1 expression and GLI-dependent transcription. We also detected high levels of GLI1 protein in ESFT cell lines. Pharmacological inhibition of GLI1 protein function decreased proliferation and soft agar colony formation of ESFT cells. Our results establish GLI1 as a direct transcriptional target of EWS-FLI1 and suggest a potential role for GLI1 in ESFT tumorigenesis. Ewing Sarcoma Family of Tumors (ESFT)2 affects patients between the ages of 3 and 40 with most cases occurring during the second decade of life. It is an undifferentiated small round cell tumor of the bone and soft tissue with an unknown cell of origin. Currently, the cure rate for patients with localized disease is only 70%, and is less than 30% for patients showing metastatic disease despite intensive multimodal treatment strategies (1). There is a need for more effective therapies to treat ESFT, especially in patients with metastases. ESFT is characterized by chromosomal translocations occurring between the genes for the TET (TAF15, EWS, and TLS) family member protein EWS and members of the ETS family of DNA-binding transcription factors. In ϳ90% of the cases, the translocation occurs between chromosome 22 and chromosome 11 (2). This results in expression of a fusion protein EWS-FLI1, which acts as an aberrant transcription factor whose persistent expression is necessary to maintain the viability of ESFT cells (3-5). The ability of EWS-FLI1 to alter transcription of several target genes such as PTPL1, ID2, and TGF␤-RII is very important to its function in tumor formation and progression (6 -9).The Hedgehog (Hh) pathway is activated in several cancers such as basal cell carcinoma, medulloblastoma, rhabdomyosarcoma, and cancers of the pancreas, lung, colon, stomach, and prostate (10 -18). The pathway is composed of three Hh ligands (Sonic, Indian, and Desert Hh) that all bind to the Patched1 receptor. In the absence of Hh ligand, Patched inhibits another transmembrane protein, Smoothened. When Patched is engaged by the Hh ligand, Smoothened is activated because of diminished inhibitory signal from Patched. The signal is then transduced to the important downstream effectors GLI1, GLI2, and GLI3, which act as transcr...

The contribution of the Wnt signaling pathway to HPV-induced carcinogenesis is poorly understood. In high-grade dysplastic lesions that are caused by high-risk human papilloma viruses (HR-HPVs), β-catenin is often located in the cell nucleus, which suggests that Wnt pathway may be involved in the development of HPV-related carcinomas. Most of the oncogenic potential of HR-HPVs resides on the E6 protein’s PDZ-binding domain. We hypothesized that the PDZ-binding domain of the HPV16-E6 oncoprotein induces the nuclear accumulation of β-catenin due to its capacity to degrade PDZ-containing cellular targets. To test this hypothesis, we evaluated the staining pattern of β-catenin in the skin epidermis of transgenic mice expressing the full-length E6 oncoprotein (K14E6 mice) and measured LacZ gene expression in K14E6 mice that were crossed with a strain expressing LacZ that was knocked into the Axin2 locus (Axin2+/LacZ mice). Here, we show that the E6 oncoprotein enhances the nuclear accumulation of β-catenin, the accumulation of cellularβ-catenin-responsive genes and the expression of LacZ. None of these effects were observed when a truncated E6 oncoprotein that lacks the PDZ-binding domain was expressed alone (K14E6ΔPDZ mice) or in combination with Axin2+/LacZ. Conversely, co-transfection with either E6 or E6ΔPDZ similarly enhanced canonical Wnt signaling in short-term in vitro assays that utilized a luciferase Wnt/β-catenin/TCF-dependent promoter. We propose that the activation of canonical Wnt signaling could be induced by the HPV16-E6 oncoprotein; however, the participation of the E6 PDZ-binding domain seems to be important in in vivo models only.