Medulloblastoma is the most common malignant brain tumor in childhood and it is the main cause of morbidity and mortality in pediatric oncolology. Recent studies revelead 4 molecular subgroups of Medulloblastomas based on the transcriptional, mutational and cytogenetic profiles, these subgroups are: WNT, SHH, Group 3 and Group 4. The SHH molecular subgrupous which bears mutation in TP53 gene shows primary resistance to SMO inhibitor (Vismodegib) and poor prognosis,however, little is known about the molecular mechanism that underlie this agressive phenotype. The molecular pathways TGF-B and Hippo are aberrantly activated in various types of tumors and can perform cross-talks with other pathways causing resistance to chemotherapy and low survival rate. The Smad2/3-YAP complex was recently described and it is considered a key effector and molecular node bewtween TGF-B and Hippo pathway. It can promotes amplification of many transcriptional factors like GLI-2, a key protein of Sonic Hedgehog pathway and it is envolved in primary resistance of TP53 mutant SHH tumor to Vismodegib. This projects aims to develop a double Knockout model of Smad2/3 and YAP using CRISPR/Cas9 technology in MB cell lines TP53 mutant and Wild type. After assessing GLI2 expressions the cells will be treated with Vismodegib. After, apoptosis, proliferation and invasion will be measured. The second phase is to perform the orthotopic injection of these KO Cell lines in mice and treatment with the same inhibitor to assess loss of resistance and survival. We expect to elucidate the mechanism of chemoresistance indentified in MB SHH TP53 mutant tumors and provide informations that will be used for enhancement of disease treatment and prognosis.
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