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1.  Regulated Proteolysis of NOTCH2 and NOTCH3 Receptors by ADAM10 and Presenilins 
Molecular and Cellular Biology  2014;34(15):2822-2832.
In mammals, there are four NOTCH receptors and five Delta-Jagged-type ligands regulating many aspects of embryonic development and adult tissue homeostasis. NOTCH proteins are type I transmembrane receptors that interact with ligands on adjacent cells and are activated by regulated intramembrane proteolysis (RIP). The activation mechanism of NOTCH1 receptors upon ligand binding is well understood and requires cleavage by ADAM10 metalloproteases prior to intramembranous cleavage by γ-secretase. How the other human NOTCH receptor homologues are activated upon ligand binding is not known. Here, we dissect the proteolytic activation mechanism of the NOTCH2 and NOTCH3 receptors. We show that NOTCH2 and NOTCH3 signaling can be triggered by both Delta-Jagged-type ligands and requires ADAM10 and presenilin-1 or -2. Importantly, we did not find any role for the highly related ADAM17/TACE (tumor necrosis factor alpha-converting enzyme) protease in ligand-induced NOTCH2 or NOTCH3 signaling. These results demonstrate that canonical ligand-induced proteolysis of the NOTCH1, -2, and -3 receptors strictly depends on consecutive cleavage of these receptors by ADAM10 and the presenilin-containing γ-secretase complex, leading to transcriptional activation.
PMCID: PMC4135574  PMID: 24842903
2.  Crucial role of the Rap G protein signal in Notch activation and leukemogenicity of T-cell acute lymphoblastic leukemia 
Scientific Reports  2015;5:7978.
The Rap G protein signal regulates Notch activation in early thymic progenitor cells, and deregulated Rap activation (Raphigh) results in the development of Notch-dependent T-cell acute lymphoblastic leukemia (T-ALL). We demonstrate that the Rap signal is required for the proliferation and leukemogenesis of established Notch-dependent T-ALL cell lines. Attenuation of the Rap signal by the expression of a dominant-negative Rap1A17 or Rap1GAP, Sipa1, in a T-ALL cell line resulted in the reduced Notch processing at site 2 due to impaired maturation of Adam10. Inhibition of the Rap1 prenylation with a geranylgeranyl transferase inhibitor abrogated its membrane-anchoring to Golgi-network and caused reduced proprotein convertase activity required for Adam10 maturation. Exogenous expression of a mature form of Adam10 overcame the Sipa1-induced inhibition of T-ALL cell proliferation. T-ALL cell lines expressed Notch ligands in a Notch-signal dependent manner, which contributed to the cell-autonomous Notch activation. Although the initial thymic blast cells barely expressed Notch ligands during the T-ALL development from Raphigh hematopoietic progenitors in vivo, the ligands were clearly expressed in the T-ALL cells invading extrathymic vital organs. These results reveal a crucial role of the Rap signal in the Notch-dependent T-ALL development and the progression.
PMCID: PMC4303867  PMID: 25613394
3.  Notch: Architect, Landscaper, and Guardian of the Intestine 
Gastroenterology  2011;141(2):448-459.
In the past decade, enormous progress has been made in understanding the role of stem cells in physiologic tissue renewal and in pathologic processes such as cancer. These findings have shed light on the identity and biological properties of such cells and the intrinsic and extrinsic signals that balance stem cell self-renewal with differentiation. With its astonishing self-renewal capacity, the intestinal epithelium has provided a unique model to study stem cell biology, lineage specification, and cancer. Here we review the role of Notch signaling in physiologic cell renewal and differentiation in the intestine as well as during its malignant transformation.
PMCID: PMC4050496  PMID: 21689653
Intestine; Stem Cells; Homeostasis; Notch; Colon Cancer
4.  The Role of Adams in Notch Signaling 
Regulated intramembrane proteolysis (RIP) is a highly conserved signaling paradigm whereby membrane-bound signaling proteins are cleaved in their transmembrane region and then released into the cytoplasm to act as signaling molecules. In most if not all cases intramembrane cleavage is preceded and regulated by a membrane proximal cleavage step called “ectodomain shedding”. Here we will review the role of ectodomain shedding in RIP of the NOTCH signaling pathway, a highly conserved cell-cell communication pathway that mediates cell fate decisions during development and in adult tissues.
PMCID: PMC4050497  PMID: 22399336
5.  Cleavage of Notch1 by granzyme B disables its transcriptional activity 
The Biochemical journal  2011;437(2):313-322.
Granzyme-mediated cell death is the main pathway for cytotoxic lymphocytes to kill virus-infected and tumour cells. A major player in this process is GrB (granzyme B), which triggers apoptosis in both caspase-dependent and caspase-independent pathways. A caspase-independent substrate of GrB is the highly conserved transmembrane receptor Notch1. The GrB cleavage sites in Notch1 and functional consequences of Notch1 cleavage by GrB were unknown. In the present study, we confirmed that Notch1 is a direct and caspase-independent substrate of GrB. We demonstrate that GrB cleaved the intracellular Notch1 domain at least twice at two distinct aspartic acids, Asp1860 and Asp1961. GrB cleavage of Notch1 can occur in all subcellular compartments, during maturation of the receptor, at the membrane, and in the nucleus. GrB also displayed perforin-independent functions by cleaving the extracellular domain of Notch1. Overall, cleavage of Notch1 by GrB resulted in a loss of transcriptional activity, independent of Notch1 activation. We conclude that GrB disables Notch1 function, probably resulting in anti-cellular proliferation and cell death signals.
PMCID: PMC4050498  PMID: 21548883
cleavage; granzyme B; Notch signalling; proteolysis; γ-secretase; serine protease
7.  Alternative promoter usage at the Notch1 locus supports ligand-independent signaling in T cell development and leukemogenesis 
Immunity  2010;33(5):685-698.
Loss of Ikaros has been correlated with Notch activation in T cell acute lymphoblastic leukemia (T-ALL), however, the mechanism remains unknown. We identified promoters in Notch1 that drive expression of Notch1 proteins active in the absence of ligand. Ikaros bound to both canonical and alternative Notch1 promoters and its loss increased permissive chromatin, facilitating recruitment of transcription regulators. At early stages of leukemogenesis, increased basal expression from the canonical and 5’-alternative promoters initiated a feed-back loop, progressively augmenting Notch1 signaling. Ikaros also repressed intragenic promoters that are cryptic in wild-type, poised in pre-leukemic, and active in leukemic cells and which also produced ligand-independent Notch1 proteins. Only ligand-independent Notch1 isoforms were required for Ikaros-mediated leukemogenesis. Notch1 alternative-promoter usage was observed at stages of T cell development dependent on Notch signaling and during T-ALL progression. These studies identify a network of epigenetic and transcriptional regulators that control conventional and unconventional Notch signaling during normal development and leukemogenesis.
PMCID: PMC3072037  PMID: 21093322
Notch1; Ikaros; leukemogenesis; epigenetic regulation; ligand-independent; promoters; chromatin accessibility
8.  COMMD1 disrupts HIF-1α/β dimerization and inhibits human tumor cell invasion 
The Journal of Clinical Investigation  2010;120(6):2119-2130.
The gene encoding COMM domain–containing 1 (COMMD1) is a prototypical member of the COMMD gene family that has been shown to inhibit both NF-κB– and HIF-mediated gene expression. NF-κB and HIF are transcription factors that have been shown to play a role in promoting tumor growth, survival, and invasion. In this study, we demonstrate that COMMD1 expression is frequently suppressed in human cancer and that decreased COMMD1 expression correlates with a more invasive tumor phenotype. We found that direct repression of COMMD1 in human cell lines led to increased tumor invasion in a chick xenograft model, while increased COMMD1 expression in mouse melanoma cells led to decreased lung metastasis in a mouse model. Decreased COMMD1 expression also correlated with increased expression of genes known to promote cancer cell invasiveness, including direct targets of HIF. Mechanistically, our studies show that COMMD1 inhibits HIF-mediated gene expression by binding directly to the amino terminus of HIF-1α, preventing its dimerization with HIF-1β and subsequent DNA binding and transcriptional activation. Altogether, our findings demonstrate a role for COMMD1 in tumor invasion and provide a detailed mechanism of how this factor regulates the HIF pathway in cancer cells.
PMCID: PMC2877941  PMID: 20458141
9.  COMMD1 Promotes pVHL and O2-Independent Proteolysis of HIF-1α via HSP90/70 
PLoS ONE  2009;4(10):e7332.
The Copper Metabolism MURR1 Domain containing 1 protein COMMD1 has been associated with copper homeostasis, NF-κB signaling, and sodium transport. Recently, we identified COMMD1 as a novel protein in HIF-1 signaling. Mouse embryos deficient for Commd1 have increased expression of hypoxia/HIF-regulated genes i.e. VEGF, PGK and Bnip3. Hypoxia-inducible factors (HIFs) are master regulators of oxygen homeostasis, which control angiogenesis, erythropoiesis, glycolysis and cell survival/proliferation under normal and pathologic conditions. Although HIF activity is mainly controlled by ubiquitination and protein degradation by the von Hippel Lindau (pVHL) tumor suppressor gene other mechanisms have recently been identified that regulate HIF signaling independently of pVHL.
Principal Findings
Here we characterized the mechanism by which COMMD1 regulates HIF-1α protein degradation. We show that COMMD1 competes with the chaperone heat shock protein HSP90β for binding to the NH2-terminal DNA-binding and heterodimerization domain of HIF-1α to regulate HIF-1α stability together with HSP70. Inhibition of HSP90 activity with 17-Allylamino-17-demethoxygeldanamycin (17-AAG) increased COMMD1-mediated HIF-1α degradation independent of ubiquitin and pVHL.
These data reveal a novel role for COMMD1 in conjunction with HSP90β/HSP70 in the ubiquitin and O2-independent regulation of HIF-1α.
PMCID: PMC2750754  PMID: 19802386
10.  Mapping the consequence of Notch1 proteolysis in vivo with NIP-CRE 
Development (Cambridge, England)  2007;134(3):535-544.
The four highly conserved Notch (N) receptors receive short-range signals that control many biological processes during development and in adult vertebrate tissues. The involvement of Notch1 signaling in tissue self-renewal is less clear, however. We developed a novel genetic approach N1IP-CRE (Notch1 Intramembrane Proteolysis) to follow, at high resolution, the descendents of cells experiencing Notch1 activation in the mouse. By combining N1IP-CRE with loss of function analysis, Notch activation patterns were correlated with function during development, self-renewal, and malignancy in selected tissues. Identification of many known functions of Notch1 throughout development validated the utility of this approach. Importantly, novel roles for Notch1 signaling were identified in heart, vasculature, retina and in the stem cell compartments of self-renewing epithelia. We find that the probability of Notch1 activation in different tissues does not always indicate a requirement for this receptor and that gradients of Notch1 activation are evident within one organ. These findings highlight an underappreciated layer of complexity of Notch signaling in vivo. Moreover, NIP-CRE represents a general strategy applicable for monitoring proteolysis-dependent signaling in vivo.
PMCID: PMC2583343  PMID: 17215306
Notch; regulated intramembrane proteolysis (RIP); Cre recombinase; fate mapping; stem cells

Results 1-10 (10)