Abstract 4351: A mammalian mitochondrial ribosomal protein contributes to intrinsic and extrinsic pathways for apoptosis in high grade gliomas of childhood

Abstract

Abstract Background: High grade gliomas (HGG) of childhood represent approximately 7% of pediatric brain tumors. They are highly invasive tumors and respond poorly to conventional treatments. Although significant progress has been made in understanding the molecular pathways that lead to the development of HGG in adults, comparatively few data is available for gliomas of childhood. The death-associated protein 3 (DAP3) is localized on the chromosomal region 1q21-22 that has been previously described as a region of frequent chromosomal gain in pediatric HGG. It encodes a 46 kDa mitochondrial ribosomal GTP-binding pro-apoptotic protein. DAP3 has been reported to be overexpressed in glioblastomas and to protect glioblastoma cells from camptothecin-induced apoptosis. Methods: In the current study, to investigate the functional role of DAP3 in pediatric HGG we suppressed the endogenous DAP3 using DAP3-specific short hairpin RNA (shRNA) and analyzed the mitochondrial morphology by immunofluorescence in vitro. Results: We found that repression of DAP3 by shRNA induced mitochondrial fragmentation and apoptosis in pediatric glioma cell lines while in adult glioma cell lines it reduced proliferation. Protein kinase C (PKC) has been implicated in the proliferation and apoptosis of glial tumors and has been suggested to phosphorylate DAP3 in mitochondria. Western blot analysis showed that adult glioma cells expressed higher levels of PKCα and lower levels of PKCβ as compared with pediatric glioma cell lines. Specific inhibition of the two PKC isoforms (PKCα and PKCβ) reduced the expression of DAP3 protein in both pediatric and adult glioma cell lines without affecting the mitochondrial morphology. The inhibition of PKCα in adult glioma cells significantly suppressed proliferation as compared with pediatric glioma cell lines. The suppression of PKCβ rendered pediatric glioma cells more sensitive to the apoptotic effect of TRAIL through a caspase-dependent process as compared with adult glioma cells suggesting a possible implication of DAP3 in intrinsic and extrinsic pathways for apoptosis in pediatric HGG. Our findings confirmed the anti-apoptotic role of DAP3 in glioma cell biology and pointed out the specific functional role of this protein in mitochondrial maintenance. Conclusion: The results suggest that the phosphorylation of DAP3 which may result from differential activation of specific PKC isoforms in glioma cells is required for functional suppression of apoptosis by DAP3 in HGG. DAP3 may represent a novel target for the treatment of gliomas. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4351.