Identification of a Conserved Negative Regulatory Sequence That Influences the Leukemogenic Activity of NOTCH1

Department of Hematology/Oncology, Abramson Family Cancer Research Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
Molecular and Cellular Biology (Impact Factor: 4.78). 09/2006; 26(16):6261-71. DOI: 10.1128/MCB.02478-05
Source: PubMed


NOTCH1 is a large type I transmembrane receptor that regulates normal T-cell development via a signaling pathway that relies
on regulated proteolysis. Ligand binding induces proteolytic cleavages in NOTCH1 that release its intracellular domain (ICN1),
which translocates to the nucleus and activates target genes by forming a short-lived nuclear complex with two other proteins,
the DNA-binding factor CSL and a Mastermind-like (MAML) coactivator. Recent work has shown that human T-ALL is frequently
associated with C-terminal NOTCH1 truncations, which uniformly remove sequences lying between residues 2524 and 2556. This
region includes the highly conserved sequence WSSSSP (S4), which based on its amino acid content appeared to be a likely site
for regulatory serine phosphorylation events. We show here that the mutation of the S4 sequence leads to hypophosphorylation
of ICN1; increased NOTCH1 signaling; and the stabilization of complexes containing ICN1, CSL, and MAML1. Consistent with these
in vitro studies, mutation of the WSSSSP sequence converts nonleukemogenic weak gain-of-function NOTCH1 alleles into alleles that cause aggressive T-ALLs in a murine bone marrow transplant model. These studies indicate that S4
is an important negative regulatory sequence and that the deletion of S4 likely contributes to the development of human T-ALL.

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Available from: David B Sacks, Apr 29, 2015
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    • "The question whether Notch aberrant expression is sufficient to induce T-ALL on its own was addressed. For this, different human gain-of-function Notch1 alleles were tested for their ability to drive an ectopic T cell development and to induce leukemia, when expressed in murine bone marrow progenitors [40] [50]. It was shown that the induction of the T cell leukemia is dependent on the Notch1 signal strength. "
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    BioMed Research International 09/2014; 2015. DOI:10.1155/2015/750203 · 2.71 Impact Factor
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    • "It is well established that the recipient animals develop T-ALL following this procedure. The first abnormal, GFP-positive CD4 + CD8 + cells appear in the peripheral blood after $2 weeks, mice develop multiple T cell tumors after 6 weeks, leading to the animals' death within 10–12 weeks (Li et al., 2008b; Chiang et al., 2006). Two weeks after bone marrow transplantation (BMT), when abnormal GFP + cells appeared in the peripheral blood, we challenged the recipient mice with pI-pC to ablate cyclin D3 expression in the transplanted cells. "
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    • "CDK8 is a kinase that is recruited by MAML1 to phosphorylate Notch, which facilitates Notch proteosomal degradation (18), so CDK8 could be involved in phosphorylating MAML1. So far, phosphorylation of Notch proteins has been correlated with Notch nuclear translocation (36,37), cellular transformation (38,39), and both activation (34) and inhibition (33) of Notch activity. A previous study demonstrated that GSK3β phosphorylates Notch1 ICD in vitro, Notch1 signaling is reduced in GSK3β deficient fibroblasts, and inhibition of endogenous GSK3β reduces the stability of Notch (34). "
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    ABSTRACT: Glycogen synthase kinase 3beta (GSK3beta) is involved in several cellular signaling systems through regulation of the activity of diverse transcription factors such as Notch, p53 and beta-catenin. Mastermind-like 1 (MAML1) was originally identified as a Notch coactivator, but has also been reported to function as a transcriptional coregulator of p53, beta-catenin and MEF2C. In this report, we show that active GSK3beta directly interacts with the MAML1 N-terminus and decreases MAML1 transcriptional activity, suggesting that GSK3beta might target a coactivator in its regulation of gene expression. We have previously shown that MAML1 increases global acetylation of histones, and here we show that the GSK3 inhibitor SB41, further enhances MAML1-dependent histone acetylation in cells. Finally, MAML1 translocates GSK3beta to nuclear bodies; this function requires full-length MAML1 protein.
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