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.

Download full-text


Available from: David B Sacks, Apr 29, 2015
  • Source
    • "). L1601PDP induced T-ALL in 30% of control mice but none of the Zmiz1-deleted mice (Figure 2D). When T-ALL was induced with the stronger DEGFDLNRDP allele (Chiang et al., 2006), deletion of Zmiz1 caused a significant 1.6- fold reduction in DP T cell frequency at 4 weeks after transplant (Figures 2E and 2F). The median survival was 55 days longer in Zmiz1-deleted mice than in controls (Figure 2G). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Pan-NOTCH inhibitors are poorly tolerated in clinical trials because NOTCH signals are crucial for intestinal homeostasis. These inhibitors might also promote cancer because NOTCH can act as a tumor suppressor. We previously reported that the PIAS-like coactivator ZMIZ1 is frequently co-expressed with activated NOTCH1 in T cell acute lymphoblastic leukemia (T-ALL). Here, we show that similar to Notch1, Zmiz1 was important for T cell development and controlled the expression of certain Notch target genes, such as Myc. However, unlike Notch, Zmiz1 had no major role in intestinal homeostasis or myeloid suppression. Deletion of Zmiz1 impaired the initiation and maintenance of Notch-induced T-ALL. Zmiz1 directly interacted with Notch1 via a tetratricopeptide repeat domain at a special class of Notch-regulatory sites. In contrast to the Notch cofactor Maml, which is nonselective, Zmiz1 was selective. Thus, targeting the NOTCH1-ZMIZ1 interaction might combat leukemic growth while avoiding the intolerable toxicities of NOTCH inhibitors.
    Full-text · Article · Nov 2015 · Immunity
  • Source
    • "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. "
    [Show abstract] [Hide abstract]
    ABSTRACT: T leukemogenesis is a multistep process, where the genetic errors during T cell maturation cause the healthy progenitor to convert into the leukemic precursor that lost its ability to differentiate but possesses high potential for proliferation, self-renewal, and migration. A new misdirecting " leukemogenic " signaling network appears, composed by three types of participants which are encoded by (1) genes implicated in determined stages of T cell development but deregulated by translocations or mutations, (2) genes which normally do not participate in T cell development but are upregulated, and (3) nondifferentially expressed genes which become highly interconnected with genes expressed differentially. It appears that each of three groups may contain genes coding ion channels. In T cells, ion channels are implicated in regulation of cell cycle progression, differentiation, activation, migration, and cell death. In the present review we are going to reveal a relationship between different genetic defects, which drive the T cell neoplasias, with calcium signaling and ion channels. We suggest that changes in regulation of various ion channels in different types of the T leukemias may provide the intracellular ion microenvironment favorable to maintain self-renewal capacity, arrest differentiation, induce proliferation, and enhance motility.
    Full-text · Article · Sep 2014 · BioMed Research International
  • Source
    • "Given that the TAD mutation does not appear to influence mRNA levels (Fig. 1C), this difference likely stems from post-transcriptional factors. Although the TAD deletion leaves intact PEST sequences that are known to influence Notch1 degradation, it is also believed that sequences in the TAD stimulate Notch1 protein turnover (Fryer et al. 2004; Chiang et al. 2006). We tested the relative stability of DTAD and wildtype Notch1 proteins by looking at the rate of disappearance of the activated forms of these proteins in cells treated with a g secretase inhibitor (GSI), which blocks the generation of active Notch1. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Notch1 is required to generate the earliest embryonic hematopoietic stem cells (HSCs); however since Notch-deficient embryos die early in gestation, additional functions for Notch in embryonic HSC biology have not been described. We used two complementary genetic models to address this important biological question. Unlike Notch1-deficient mice, mice lacking the conserved Notch1 transcriptional activation domain (TAD) show attenuated Notch1 function in vivo and survive until late gestation, succumbing to multiple cardiac abnormalities. Notch1 TAD-deficient HSCs emerge and successfully migrate to the fetal liver but are decreased in frequency by embryonic day 14.5. In addition, TAD-deficient fetal liver HSCs fail to compete with wild-type HSCs in bone marrow transplant experiments. This phenotype is independently recapitulated by conditional knockout of Rbpj, a core Notch pathway component. In vitro analysis of Notch1 TAD-deficient cells shows that the Notch1 TAD is important to properly assemble the Notch1/Rbpj/Maml trimolecular transcription complex. Together, these studies reveal an essential role for the Notch1 TAD in fetal development and identify important cell-autonomous functions for Notch1 signaling in fetal HSC homeostasis.
    Full-text · Article · Mar 2014 · Genes & development
Show more