Abstract
Abstract Gadd45a protein is induced in medulloblastoma cell lines by treatment with ionizing radiation (IR), which requires p53 stabilization. The role of Gadd45a in IR-induced G2-M arrest of medulloblastoma cells is demonstrated by its increased binding to Cdc2, thereby inactivating Cdc2 kinase activity. Knockdown of Gadd45a alleviates G2-M blockage and results in decreased binding of Gadd45a to Cdc2. Further, the anti-tumorigenic role of Gadd45a is mediated by the negative regulation of β-catenin and its nuclear translocation, which might decrease the β-catenin/LEF-1-mediated transactivation of cell invasion proteins, such as MMP-9, examined in the present study. Overexpression of Gadd45a protein with IR treatment resulted in decreased nuclear levels of β-catenin, increased cytoplasmic levels of p-β-catenin, and increased distribution of β-catenin on membrane E and N-cadherins. The IR-treated control cells showed contrary results with demonstrated loss of E-cadherin, gain of N-cadherin, and inhibition of β-catenin binding to membrane cadherins as well as increased nuclear translocation of β-catenin. Zymography studies demonstrate the negative regulation of IR-induced MMP-9 activity by Gadd45a overexpression. Wound healing and Matrigel invasion assays confirmed the anti-tumorigenic and anti-metastatic role of Gadd45a in medulloblastoma cell lines. Furthermore, siRNA-mediated knockdown of MMP-9 results in prominent expression levels of Gadd45a protein in animal tumors. Thus, we confirm that overexpression of Gadd45a in combination with ionizing radiation has therapeutic implications by preventing recurrence of MMP-9-mediated cancer cell invasion and effectively containing cells in a static phase by maintaining CCA/CCI. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 576. doi:10.1158/1538-7445.AM2011-576
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