| Summary: | <p>Abstract</p> <p>Background</p> <p>The Sonic hedgehog (Shh) signaling pathway is critical for cell growth and differentiation. Impairment of this pathway can result in both birth defects and cancer. Despite its importance in cancer development, the Shh pathway has not been thoroughly investigated in tumorigenesis of brain tumors. In this study, we sought to understand the regulatory roles of <it>GLI1</it>, the immediate downstream activator of the Shh signaling pathway on its downstream target genes <it>PTCH1</it>, <it>Cyclin D2</it>, <it>Plakoglobin</it>, <it>NKX2.2 </it>and <it>PAX6 </it>in medulloblastoma and astrocytic tumors.</p> <p>Methods</p> <p>We silenced <it>GLI1 </it>expression in medulloblastoma and astrocytic cell lines by transfection of siRNA against <it>GLI1</it>. Subsequently, we performed RT-PCR and quantitative real time RT-PCR (qRT-PCR) to assay the expression of downstream target genes <it>PTCH1, Cyclin D2, Plakoglobin, NKX2.2 </it>and <it>PAX6</it>. We also attempted to correlate the pattern of expression of <it>GLI1 </it>and its regulated genes in 14 cell lines and 41 primary medulloblastoma and astrocytoma tumor samples. We also assessed the methylation status of the <it>Cyclin D2 </it>and <it>PTCH1 </it>promoters in these 14 cell lines and 58 primary tumor samples.</p> <p>Results</p> <p>Silencing expression of <it>GLI1 </it>resulted up-regulation of all target genes in the medulloblastoma cell line, while only <it>PTCH1 </it>was up-regulated in astrocytoma. We also observed methylation of the <it>cyclin D2 </it>promoter in a significant number of astrocytoma cell lines (63%) and primary astrocytoma tumor samples (32%), but not at all in any medulloblastoma samples. <it>PTCH1 </it>promoter methylation was less frequently observed than <it>Cyclin D2 </it>promoter methylation in astrocytomas, and not at all in medulloblastomas.</p> <p>Conclusions</p> <p>Our results demonstrate different regulatory mechanisms of Shh-<it>GLI1 </it>signaling. These differences vary according to the downstream target gene affected, the origin of the tissue, as well as epigenetic regulation of some of these genes.</p>
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