Glioblastoma multiforme (GBM), the most aggressive manifestation of malignant gliomas, are characterized by microvascular proliferation, necrosis, extreme resistance to all extant therapeutic modalities and a neurologically destructive course culminating in death often within 12 months of diagnosis. Major conceptual gaps remain on the mechanistic level including how the classical genetic lesions contribute to these phenotypic aspects. To address this issue, we performed oncogenomic analyses of a large panel of human GBMs by array-CGH and expression profiling in an effort to gain a more comprehensive view of the genetic events underlying GBM development. In the course of characterizing a region of gain on chromosome 19q, we identified Bcl2L12 (for Bcl2-Like-12) as a glioma oncogene that is over-expressed in virtually all GBM samples, yet low or absent in low-grade disease and normal tissue. Extensive biochemical studies have established that Bcl2L12 functions as an anti-apoptotic protein in primary astrocytic cultures by inhibiting post-mitochondrial caspase-3 and caspase-7 activation. Since inhibition of apoptosis at the post- mitochondrial level is known to block apoptosis but promotes necrosis, Bcl2L12 over-expression in GBM may provide a rational explanation for a prime paradox in the biology of this disease - apoptosis resistance yet florid necrosis - and points to Bcl2L12 up-regulation as a key progression event in malignant glioma. In addition to its cytosolic caspase-3/7 inhibitory activity, Bcl2L12 resides in the nucleoplasm where it interacts with p53 and blocks p53-mediated transactivation. To analyze Bcl2L12-modulated pathways in cell culture- based assays in more detail and to genetically validate these findings in vivo, this grant proposal aims to elucidate further the molecular basis of Bcl2L12's oncogenic activity through detailed structure-function analyses. We will employ cell culture-based assays and orthotopic SCID explant tumor models using genetically engineered neuronal stem cells and mature cortical astrocytes to dissect apoptosis- and p53 modulatory activities. Furthermore, we will characterize in depth the molecular mechanism of p53 inhibition that defines yet another oncogenic activity of Bcl2L12 through detailed studies of p53-mediated transcriptional regulation. Finally, the consequences of Bcl2L12 inactivation for the development of GBM will be assessed using conditional Bcl2L12 knockout mice that may serve as an in vivo platform on which to assess consequence of pharmacological inactivation of Bcl2L12 for malignant glioma therapy. ? ? The continued lack of success in treating high-grade gliomas has prompted a reevaluation of all aspects of glioma drug development. This grant proposal aims to specifically address the currently unmet needs in the development of effective glioma therapies by refining the molecular understanding of the disease and by developing more accurate in vitro and in vivo glioma model system. ? ? ?
| Stegh, Alexander H; Chin, Lynda; Louis, David N et al. (2008) What drives intense apoptosis resistance and propensity for necrosis in glioblastoma? A role for Bcl2L12 as a multifunctional cell death regulator. Cell Cycle 7:2833-9 |
| Stegh, Alexander H; Kesari, Santosh; Mahoney, John E et al. (2008) Bcl2L12-mediated inhibition of effector caspase-3 and caspase-7 via distinct mechanisms in glioblastoma. Proc Natl Acad Sci U S A 105:10703-8 |
