Notch signaling is an evolutionarily conserved signal transduction pathway that is essential for metazoan development. Upon ligand binding, the Notch intracellular domain (NOTCH ICD) translocates into the nucleus and forms a complex with the transcription factor RBPJ (also known as CBF1 or CSL) to activate expression of Notch target genes. In the absence of a Notch signal, RBPJ acts as a transcriptional repressor. Using a proteomic approach, we identified L3MBTL3 (also known as MBT1) as a novel RBPJ interactor. L3MBTL3 competes with NOTCH ICD for binding to RBPJ. In the absence of NOTCH ICD, RBPJ recruits L3MBTL3 and the histone demethylase KDM1A (also known as LSD1) to the enhancers of Notch target genes, leading to H3K4me2 demethylation and to transcriptional repression. Importantly, in vivo analyses of the homologs of RBPJ and L3MBTL3 in Drosophila melanogaster and Caenorhabditis elegans demonstrate that the functional link between RBPJ and L3MBTL3 is evolutionarily conserved, thus identifying L3MBTL3 as a universal modulator of Notch signaling in metazoans.

Sixty‐four genomic loci and seven genes that contribute to heritable variation in a model quantitative trait—resistance to oxidative stress—are identified across three yeast strains. The high‐resolution understanding of this phenotype provides new insight into the genetic and molecular basis of quantitative traits.

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 these 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 postphosphorylation 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.

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.

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