RUNX3 and SHH in medulloblastoma

4310 Medulloblastoma is a highly malignant primary brain tumor that originates in the cerebellum. Morphologically, the presence of desmoplastic features. Desmoplastic Medulloblastoma (DMB, as opposed to the conventional type) is known to be associated with mutations of the sonic hedgehog (SHH) signaling pathway. Previously, we have reported RUNX3 overexpression in basal cell carcinoma (Oncogene 2006;25(58):7646-9), another SHH related disease model while, in general, RUNX3 is inactivated in most human cancers by protein mislocalization and promoter hypermethylation. Medulloblastoma clinical samples were screened for RUNX3 protein expression by immunohistochemistry. Western blot analysis was carried out on ATCC medulloblastoma cell lines (desmoplastic and conventional). Genomic DNA and total RNA was extracted from these cell lines. The genomic DNA was amplified by PCR and sequenced at the coding exons of RUNX3. Hypermethlyation of the RUNX3 promoter region was carried out. RUNX3 transcription was analysed by real-time PCR. The clinical DMB samples tested showed that RUNX3 protein is over-expressed in the nuclei of the cancer cells. This was concordant with the Western blot analysis of the desmoplastic medulloblastoma cell line, while the conventional cell line failed to show this overexpression. No mutation was detected in the coding exons of RUNX3 in these cell lines. Based on the immunohistochemistry staining, we have ruled out protein mislocalization for inactivation of RUNX3 in the conventional MB. Since promoter hypermethylation is a mechanism for gene and protein downregulation in other models, we explored the RUNX3 methylation in all the cell lines. While the cell lines showed unmethylated RUNX3 promoter region, the RUNX3 mRNA was actively transcribed. DMB is SHH related and, as in the BCC model, is associated with RUNX3 protein overexpression both in cell lines and clinical samples, a biological observation that may have important prognostic implications.