GLI2-regulated transcription factors in basal cell carcinoma

Ligand-independent activation of the Hedgehog (Hh) signal transduction pathway in epidermal cells represents the initial event in the development of Basal Cell Carcinoma (BCC), the most common malignancy in the western world. Despite this clear understanding of the primary causes of BCC development, little is known about the downstream mechanisms underlying the tumorigenic conversion of epidermal cells induced by Hh-signalling. The zinc finger transcription factors GLI1 and GLI2 have been identified as bona fide mediator of Hh-signalling in BCC. Though the relative contribution of either transcription factor (TF) to Hh-induced tumorigenesis is unclear at present, evidence has accumulated suggesting that GLI2 rather than GLI1 acts as the primary mediator of the Hh- signal in the nucleus. Thus, identification and functional analysis of GLI2 target genes will be crucial for a detailed understanding of Hh-induced neoplastic conversion of epidermal cells. Using a combination of DNA-array technology and promoter analysis, we have identified two putative direct GLI2 target genes, GLI1 and FOXE1, which encode TFs highly overexpressed in BCC and are likely to play a decisive role in the oncogenic transcriptional programme downstream of GLI2. The aim of this project is the functional analysis of GLI1 and FOXE1 in GLI2-induced epidermal hyperproliferation and BCC development. Simulated loss-of-function mutations of GLI1 or FOXE1 will be introduced into GLI2-expressing human keratinocytes by retroviral siRNA technology. The resulting phenotypes will be analysed by cDNA array technology and by specifc assays addressing cell proliferation, tumorigenicity and epidermal differentiation capacity of manipulated cells. The results will shed light on the transcriptional networks regulated by Hh/Gli-signalling in human neoplasia and serve as a basis for the identification of putative drug targets required for the design of novel and efficient therapeutic strategies allowing specific modulation of Hh- signalling in BCC.

Ligand-independent activation of the Hedgehog (Hh) signal transduction pathway in epidermal cells represents the initial event in the development of Basal Cell Carcinoma (BCC), the most common malignancy in the western world. Despite this clear understanding of the primary causes of BCC development, little is known about the downstream mechanisms underlying the tumorigenic conversion of epidermal cells induced by Hh-signalling. The zinc finger transcription factors GLI1 and GLI2 have been identified as bona fide mediator of Hh-signalling in BCC. Though the relative contribution of either transcription factor (TF) to Hh-induced tumorigenesis is unclear at present, evidence has accumulated suggesting that GLI2 rather than GLI1 acts as the primary mediator of the Hh- signal in the nucleus. Thus, identification and functional analysis of GLI2 target genes will be crucial for a detailed understanding of Hh-induced neoplastic conversion of epidermal cells. Using a combination of DNA-array technology and promoter analysis, we have identified two putative direct GLI2 target genes, GLI1 and FOXE1, which encode TFs highly overexpressed in BCC and are likely to play a decisive role in the oncogenic transcriptional programme downstream of GLI2. The aim of this project is the functional analysis of GLI1 and FOXE1 in GLI2-induced epidermal hyperproliferation and BCC development. Simulated loss-of-function mutations of GLI1 or FOXE1 will be introduced into GLI2-expressing human keratinocytes by retroviral siRNA technology. The resulting phenotypes will be analysed by cDNA array technology and by specifc assays addressing cell proliferation, tumorigenicity and epidermal differentiation capacity of manipulated cells. The results will shed light on the transcriptional networks regulated by Hh/Gli-signalling in human neoplasia and serve as a basis for the identification of putative drug targets required for the design of novel and efficient therapeutic strategies allowing specific modulation of Hh- signalling in BCC.