Hierarchical phosphorylation within the ankyrin repeat domain defines a phosphoregulatory loop that regulates Notch transcriptional activity.
ABSTRACT The Notch signal transduction pathway mediates important cellular functions through direct cell-to-cell contact. Deregulation of Notch activity can lead to an altered cell proliferation and has been linked to many human cancers. Casein kinase 2 (CK2), a ubiquitous kinase, regulates several cellular processes by phosphorylating proteins involved in signal transduction, gene expression, and protein synthesis. In this report we identify Notch(ICD) as a novel target of phosphorylation by CK2. Using mapping and mutational studies, we identified serine 1901, located in the ankyrin domain of Notch, as the target amino acid. Interestingly, phosphorylation of serine 1901 by CK2 appears to generate a second phosphorylation site at threonine 1898. Furthermore, threonine 1898 phosphorylation only occurs when Notch forms a complex with Mastermind and CSL. Phosphorylation of both threonine 1898 and serine 1901 resulted in decreased binding of the Notch-Mastermind-CSL ternary complex to DNA and consequently lower transcriptional activity. These data indicate that the phosphorylation of serine 1901 and threonine 1898 negatively regulates Notch function by dissociating the complex from DNA. This study identifies a new component involved in regulation of Notch(ICD) transcriptional activity, reinforcing the notion that a precise and tight regulation is required for this essential signaling pathway.
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ABSTRACT: Notch signaling releases the Notch receptor intracellular domain (ICD), which complexes with CBF1 and Mastermind (MAM) to activate responsive genes. We previously reported that MAM interacts with CBP/p300 and promotes hyperphosphorylation and degradation of the Notch ICD in vivo. Here we show that CycC:CDK8 and CycT1:CDK9/P-TEFb are recruited with Notch and associated coactivators (MAM, SKIP) to the HES1 promoter in signaling cells. MAM interacts directly with CDK8 and can cause it to localize to subnuclear foci. Purified recombinant CycC:CDK8 phosphorylates the Notch ICD within the TAD and PEST domains, and expression of CycC:CDK8 strongly enhances Notch ICD hyperphosphorylation and PEST-dependent degradation by the Fbw7/Sel10 ubiquitin ligase in vivo. Point mutations affecting conserved Ser residues within the ICD PEST motif prevent hyperphosphorylation by CycC:CDK8 and stabilize the ICD in vivo. These findings suggest a role for MAM and CycC:CDK8 in the turnover of the Notch enhancer complex at target genes.Molecular Cell 12/2004; 16(4):509-20. · 15.28 Impact Factor
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ABSTRACT: The int-3 oncogene was identified as a frequent target in Mouse Mammary Tumor Virus (MMTV)-induced mammary carcinomas and encodes the intracellular domain of a novel mouse Notch gene. To investigate the role of the int-3 proto-oncogene in mouse development and carcinogenesis, we isolated cDNA clones corresponding to the entire coding potential of the int-3 proto-oncogene. We propose to name this gene Notch4 and reserve the int-3 nomenclature for references to the oncogenic form. The deduced amino acid sequence of Notch4 contains conserved motifs found in Notch proteins; however Notch4 has fewer epidermal growth factor (EGF)-like repeats and a shorter intracellular domain than other mouse Notch homologues. Comparison of the coding potential of the int-3 gene to that of Notch4 suggests that loss of the extracellular domain of Notch4 leads to constitutive activation of this murine Notch protein. In situ hybridization revealed that Notch4 transcripts are primarily restricted to endothelial cells in embryonic and adult life. Truncated Notch4 transcripts were detected in post-meiotic male germ cells. The distinct Notch4 protein features and its restricted expression pattern suggests a specific role for Notch4 during development of vertebrate endothelium.Development 08/1996; 122(7):2251-9. · 6.21 Impact Factor
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ABSTRACT: The Notch intracellular region (RAMIC) interacts with a DNA binding protein RBP-J to activate transcription of genes that inhibit cell differentiation. The RAM domain and ankyrin (ANK) repeats of mouse Notch1 RAMIC were shown to be responsible for RBP-J binding and necessary for transactivation. The C-terminal portion of Notch1 RAMIC has also been suggested to be important for transactivation. Using GAL4 fusion constructs, we identified a novel transactivation domain (TAD) between the ANK repeats and the PEST sequence of mouse Notch1. The C-terminal half of mouse Notch2 RAMIC also exhibited TAD activity. Unexpectedly, the RBP-J chimeric protein with the Notch1 TAD failed to activate transcription but the activity was recovered by addition of either the RAM domain or ANK repeats. The results suggest that the activity of Notch1 TAD is repressed by fusion with RBP-J because of the presence of a RBP-J-associated co-repressor(s), which could be displaced by either the RAM domain or ANK repeats. Taken together, mouse Notch1 RAMIC can experimentally be separated into three functional domains: the RAM domain and ANK repeats for RBP-J binding and co-repressor displacement and the C-terminal TAD.Nucleic Acids Research 01/1999; 26(23):5448-55. · 8.28 Impact Factor