Additional NOTCH1 cofactors beyond CSL and MAML are required for NOTCH1 target activation.

  • Major finding: Additional NOTCH1 co-factors beyond CSL and MAML are required for NOTCH1 target activation.

  • Concept: LSD1 and PHF8 histone demethylase activity is required for expression of NOTCH1 target genes.

  • Impact: Histone demethylase–targeted therapies may be effective in Notch-dependent cancers.

The Notch signaling pathway is a key determinant of developmental programs and is deregulated in human cancers. Upon ligand binding, Notch receptors undergo proteolytic cleavage and the intracellular domain of Notch (ICN) translocates to the nucleus, where it converts CSL from a repressor to an activator and forms a complex with CSL and Mastermind-like (MAML) coactivators to induce target gene expression. To gain insight into the regulation and function of the ICN–CSL–MAML complex, Yatim and colleagues purified epitope-tagged ICN and identified interacting proteins by mass spectrometry. As expected, CSL and MAML1 were stoichiometric binding partners, but over 100 other NOTCH1-interacting proteins were also identified. ICN, CSL, and MAML were found to assemble into a complex with the transcriptional activator AF4p12, the histone demethylases LSD1 and PHF8, and the SWI/SNF nucleosome remodeling complex subunits BRG1 and PB1, all of which were required for expression of Notch target genes. In the presence of ICN, PHF8 removed the repressive histone H3 lysine-27 dimethylation (H3K27me2) mark and LSD1 removed the repressive H3K9me2 mark from Notch targets to promote gene expression. However, LSD1 was also associated with the CSL repressor in the absence of ICN and contributed to CSL-mediated Notch target repression by removing the activating H3K4me2 mark, suggesting that LSD1 plays a dual role in Notch signaling regulation. To determine whether histone demethylases play a role in oncogenic Notch signaling, the authors knocked down PHF8 and LSD1 in NOTCH1-mutant T-cell acute lymphoblastic leukemia (T-ALL) cell lines and observed decreased cell proliferation and complete abrogation of T-ALL xenograft tumor growth. These data thus underscore the importance of histone demethylases in transcriptional regulation of Notch target genes and implicate PHF8 and LSD1 as potential therapeutic targets in Notch-dependent cancers.

Yatim A, Benne C, Sobhian B, Laurent-Chabalier S, Deas O, Judde JG, et al. NOTCH1 nuclear interactome reveals key regulators of its transcriptional activity and oncogenic function. Mol Cell 2012 Sept 27 [Epub ahead of print].

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