Medulloblastoma is the most common malignant brain tumor of childhood. Therapeutic approaches to medulloblastoma have led to significant improvements, but are achieved at a high cost to quality of life. Aberrant upregulation of the hedgehog (Hh) pathway drives cerebellar tumorigenesis in ∼30% of medulloblastoma patients. Hh pathway inhibitors such as the SMO antagonist Vismodegib are currently being tested in Hh-activated medulloblastoma and the preliminary results are encouraging. However, resistance to SMO inhibition can be acquired, leading to relapse. Alternative therapeutic approaches are needed. We aim to uncover novel Hh signal modulators that are essential in medulloblastoma to maintain tumorigenic potential. Using our proteomic platform for systematic protein interaction mapping, we discovered a novel interaction between GLI1, a key transcription factor for the mediation of Hh signals, and PIN1, a peptidylprolyl cis/trans isomerase that regulates the post-phosphorylation conformation of its substrates. Our results support a molecular model in which PIN1 protects GLI1 from proteasomal degradation, thus contributing to the positive regulation of Hh signals. Most importantly, our in vivo functional analyses of PIN1 in mouse models of Hh-driven medulloblastoma demonstrate that the loss-of-PIN1 impairs tumor development and increases survival by 3 fold, from 57 to 158 days (P < 0.0001), establishing PIN1 as a key factor in Hh-driven medulloblastoma tumorigenesis. Finally, in human medulloblastoma tumor samples, the GLI1 and PIN1 proteins are correlated in their expression, supporting the relevance of the GLI1/PIN1 interaction in this disease context. In summary, the discovery of the GLI1/PIN1 interaction uncovers PIN1 as a novel therapeutic target in medulloblastoma tumorigenesis. If our hypothesis is validated, i.e., PIN1 inhibitors can improve survival in mouse models of Hh-driven medulloblastoma, our project will strongly justify testing the clinical relevance of PIN1 blockade in medulloblastoma patients. Citation Format: Jean-Francois M. Rual, Tao Xu, Honglai Zhang, Sung-Soo Park, Sriram Venneti, Rork Kuick, Kimberly Ha, Lowell Michael, Mariarita Santi, Chiyoko Uchida, Takafumi Uchida, Ashok Srinivasan, Andrzej Dlugosz, Sandra Camelo-Piragua. PIN1 protects GLI1 from ubiquitination and promotes Hedgehog-driven medulloblastoma tumorigenesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2447.
Medulloblastoma is the most common malignant brain tumor of childhood. Therapeutic approaches to medulloblastoma have led to significant improvements but are achieved at a high cost to quality of life. The Notch pathway governs cell proliferation in many biological contexts, including medulloblastoma tumorigenesis. Using our proteomic platform, we discovered an interaction between RBPJ, a key co-factor of Notch for the mediation of Notch signals, and L3MBTL3, a methyllysine reader for which deletions are observed in medulloblastoma. We demonstrated that L3MBTL3 is part of a molecular mechanism linking the KDM1A demethylase to Notch signal modulation. We hypothesize that malfunction of this molecular mechanism may contribute to the previously suggested tumor suppressor role of L3MBTL3 in medulloblastoma. In a survival analysis using our L3mbtl3 KO mouse in combination with a genetically engineered mouse model of medulloblastoma, we validated our hypothesis that L3mbtl3 is a tumor suppressor in this disease context. Our discovery provides insights into the role of the L3MBTL3 in medulloblastoma that could be harnessed in the future for the therapeutic benefit of medulloblastoma patients. Citation Format: Honglai Zhang, Ester Calvo Fernandez, Claire Peabody, Rork Kuick, Sung-Soo Park, Thomas Saunders, Sandra Camelo-Piragua, Jean-Francois M. Rual. Characterization of the role of L3MBTL3 in medulloblastoma tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3658.
Medulloblastoma is the most common malignant brain tumor in children. Therapeutic approaches to medulloblastoma (combination of surgery, radiotherapy and chemotherapy) have led to significant improvements, but are achieved at a high cost to quality of life. Alternative therapeutic approaches are needed. Genetic mutations leading to the activation of the Hedgehog pathway drive tumorigenesis in ~30% of medulloblastoma. In a yeast two-hybrid proteomic screen, we discovered a novel interaction between GLI1, a key transcription factor for the mediation of Hedgehog signals, and PIN1, a peptidylprolyl cis/trans isomerase that regulates the post-phosphorylation fate of its targets. The GLI1/PIN1 interaction was validated by reciprocal pulldowns using epitope-tagged proteins in HEK293T cells as well as by co-immunoprecipiations of the endogenous proteins in a medulloblastoma cell line. Our results support a molecular model in which PIN1 promotes GLI1 protein abundance, thus contributing to the positive regulation of Hedgehog signals. Most importantly, in vivo functional analyses of Pin1 in the GFAP-tTA;TRE-SmoA1 mouse model of Hedgehog-driven medulloblastoma demonstrate that the loss of Pin1 impairs tumor development and dramatically increases survival. In summary, the discovery of the GLI1/PIN1 interaction uncovers PIN1 as a novel therapeutic target in Hedgehog-driven medulloblastoma tumorigenesis. Citation Format: Jean-Francois M. Rual. Loss of Pin1 suppresses Hedgehog-driven medulloblastoma tumorigenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5821. doi:10.1158/1538-7445.AM2017-5821
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