Effects of GSK-3 Inhibition on Cerebellar Development and Medulloblastoma Tumorigenesis

Activating mutations in either the Sonic Hedgehog (SHH) or the Wingless (WNT) signaling pathways gives rise to two of the major subgroups of medulloblastoma. Analysis of the gene expression profiles of the SHH and WNT medulloblastoma subgroups have revealed that they might be mutually exclusive. It is still not known, however, what the role of the WNT signaling pathway is in SHH-induced tumor growth. We hypothesize that constitutively activating the WNT signaling pathway through the inhibition of Glycogen Synthase Kinase 3 (GSK-3) will prevent SHH subgroup tumor growth. Cerebellar progenitors were treated with varying doses of CHIR-98014, a GSK-3 inhibitor, for 24 hours and collected for western blot analysis or immunofluorescence analysis. Wild-type cells were treated with SHH and CHIR-98014 for 24 hours and collected for FACS analysis. A decreasing trend in proliferation marker, pRb, and mitosis marker, pHH3, was seen, as well as an increasing trend in S phase inhibition marker, CDKN1A (p21), with increasing dosages of drug in tumor cells. Treatment with CHIR-98014 in the presence of SHH in cells cultured from wild-type mice showed a shift in cell cycle phase away from S phase. To elucidate the maximum tolerable dose of CHIR-98014, oral gavage of wild type mice with varying dosages of CHIR-98014 was then conducted and presented no significant change in weight during treatment. Increasing dosages of CHIR-98014 were shown to significantly decrease proliferation of tumor cells, revealing possible viability for use of CHIR-98014 targeting medulloblastoma. These findings support the hypothesis that constitutively activated WNT signaling through the inhibition of GSK-3 prevents SHH subgroup tumor growth. Understanding the role of the WNT signaling pathway in the context of SHH-induced medulloblastoma may lead to better management of the disease. Further characterization of CHIR-98014 and its effects on cerebellar development and tumorigenesis is necessary and provides significance in the treatment of SHH-induced medulloblastoma.Bachelor of Scienc