Dissecting and Targeting the PUMA and OLIG2 Control Points of Tumors of Neuroectodermal Origin with Stapled Peptides

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Dissecting and Targeting the PUMA and OLIG2 Control Points of Tumors of Neuroectodermal Origin with Stapled Peptides

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Title: Dissecting and Targeting the PUMA and OLIG2 Control Points of Tumors of Neuroectodermal Origin with Stapled Peptides
Author: Edwards, Amanda Lee
Citation: Edwards, Amanda Lee. 2013. Dissecting and Targeting the PUMA and OLIG2 Control Points of Tumors of Neuroectodermal Origin with Stapled Peptides. Doctoral dissertation, Harvard University.
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Abstract: Tumors of neuroectodermal origin are among the most aggressive and treatment-refractory forms of human cancer. While such tumors arise from a variety of defects, two key targets are the transcription factors p53 and OLIG2. We have developed stabilized peptides to study and target deregulated p53 and OLIG2 pathways in neuroectodermal cancers. PUMA (p53-upregulated modulator of apoptosis) is a BH3-only member of the BCL-2 protein family that regulates apoptosis in response to p53-dependent and p53-independent stress signals. The specific interactions that mediate the pro-apoptotic activity of PUMA remain controversial. We generated stabilized alpha-helices of BCL-2 domains (SAHB) peptides modeled after the BH3 effector domain of PUMA. Structural analyses determined that PUMA SAHB contacts BAX at both the N-terminal \(\alpha1/\alpha6\) trigger site and the canonical BH3 binding pocket, binding events that functionally activate BAX. Notably, both PUMA SAHB and PUMA protein pull-downs identified anti- and pro-apoptotic binding partners in a cellular context. As PUMA has been implicated in driving apoptosis in multiple neural cell types, we further demonstrated that treatment of neuroblastoma cell lines with a cell-permeable PUMA SAHB analog triggered dose-dependent apoptosis. Together, we find that the PUMA BH3 domain activates apoptosis through multimodal interactions with BCL-2 family proteins, and its mimetics may serve as prototype therapeutics in tumors of neural origin. Whereas suppression of p53 signaling and apoptosis are features of diverse tumor types, the basic helix-loop-helix (bHLH) transcription factor OLIG2 is selectively overexpressed in gliomas. Early in development, OLIG2 is responsible for maintaining progenitor cells in a replication-competent state. Tumor stem cells are believed to co-opt this OLIG2 functionality to continually repopulate glial tumors. To achieve its transcriptional function, OLIG2 must dimerize via its bHLH domain. Stabilized alpha-helices of OLIG2 (SAH-OLIG2) peptides of the OLIG2 bHLH domain were generated in an effort to disrupt this pathologic dimerization. While helical stabilization of several SAH-OLIG2 peptides was achieved, specific engagement and disruption of the native bHLH dimer did not occur, informing alternative design strategies for future targeting efforts. These studies underscored the importance of interrogating the OLIG2 dimeric structure and catalyzed the discovery of candidate OLIG2 interaction partners for therapeutic targeting.
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Citable link to this page: http://nrs.harvard.edu/urn-3:HUL.InstRepos:11125005
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