• Tiffany A Doucette, Yuhui Yang, Carolyn Pedone, John Y H Kim, Adrian Dubuc, Paul D Northcott, Michael D Taylor, Daniel W Fults, and Ganesh Rao.
• Department of Neurosurgery, The University of Texas MD Anderson Cancer Center, Houston, Texas 77030, USA.
• Neurosurgery. 2012 Apr 1;70(4):1003-10; discussion 1010.

BackgroundA significant number of medulloblastomas (MBs) originate from abnormal activation of the sonic hedgehog/patched (SHH/PTC) signaling pathway. Although p53 deficiency enhances tumor formation in mice, inactivation of the p53 gene is seen in a minority of MBs. Wild-type p53-induced phosphatase 1 (WIP1) downregulates p53 expression and has been shown to be overexpressed in MBs.ObjectiveWe tested the hypothesis that overexpression of WIP1 enhances tumor formation in an SHH-dependent model of MB.MethodsWe used the RCAS/Ntv-a system to study the effect of WIP1 in vitro and in vivo. We transfected A375-TVA cells with RCAS-WIP1 and then exposed these cells to cisplatin to determine the effect on p53 expression. We modeled ectopic WIP1 expression independently and in combination with SHH in the cerebella of newborn mice to assess the effect on tumor formation. Mice were observed for 12 weeks or until neurological symptoms developed. The brains were examined for tumor formation.ResultsA375-TVA cells infected with RCAS-WIP1 demonstrated reduced p53 expression after exposure to cisplatin compared with controls. We detected tumors in 12 of 35 mice (34%) injected with RCAS-WIP1 and RCAS-SHH. Tumors were detected in 3 of 40 mice (8%) injected with RCAS-SHH alone. The difference in tumor formation rates was significant (χ(2) test, P = < .01). Tumors did not form in mice injected with RCAS-WIP1 alone.ConclusionWe show that ectopic expression of WIP1 cooperates with SHH to enhance formation of MB, although it is insufficient to induce tumors independently. Our results verify the role of WIP1 in MB formation and provide a crucial link to the inactivation of p53 in MBs.

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