Jagged1-induced Notch signaling drives proliferation of multiple myeloma cells

Notch receptors expressed on hematopoietic stem cells interact with their ligands on bone marrow stromal cells and thereby control cell fate decisions and survival. We recently demonstrated that Notch signaling is involved in proliferation and survival of B cell-derived tumor cells of classic Hodgkin disease and described a novel mechanism for the oncogenic capacity of Notch. In this study we investigated whether Notch signaling is involved in the tight interactions between neoplastic plasma cells and their bone marrow microenvironment, which are essential for tumor cell growth in multiple myeloma (MM). Here we demonstrate that Notch receptors and their ligand Jagged1 are highly expressed in cultured and primary MM cells, whereas nonneoplastic counterparts show low to undetectable levels of Notch. Functional data indicate that ligand-induced Notch signaling is a growth factor for MM cells and suggest that these interactions contribute to myelomagenesis in vivo.     

Notch activation results in phenotypic and functional changes consistent with endothelial-to-mesenchymal transformation

Various studies have identified a critical role for Notch signaling in cardiovascular development. In this and other systems, Notch receptors and ligands are expressed in regions that undergo epithelial-to-mesenchymal transformation. However, there is no direct evidence that Notch activation can induce mesenchymal transdifferentiation. In this study we show that Notch activation in endothelial cells results in morphological, phenotypic, and functional changes consistent with mesenchymal transformation. These changes include downregulation of endothelial markers (vascular endothelial [VE]-cadherin, Tie1, Tie2, platelet-endothelial cell adhesion molecule-1, and endothelial NO synthase), upregulation of mesenchymal markers (alpha-smooth muscle actin, fibronectin, and platelet-derived growth factor receptors), and migration toward platelet-derived growth factor-BB. Notch-induced endothelial-to-mesenchymal transformation does not seem to require external regulation and is restricted to cells expressing activated Notch. Jagged1 stimulation of endothelial cells induces a similar mesenchymal transformation, and Jagged1, Notch1, and Notch4 are expressed in the ventricular outflow tract during stages of endocardial cushion formation. This is the first evidence that Jagged1-Notch interactions induce endothelial-to-mesenchymal transformation, and our findings suggest that Notch signaling may be required for proper endocardial cushion differentiation and/or vascular smooth muscle cell development.     

Jagged1-dependent Notch signaling is dispensable for hematopoietic stem cell self-renewal and differentiation

Jagged1-mediated Notch signaling has been suggested to be critically involved in hematopoietic stem cell (HSC) self-renewal. Unexpectedly, we report here that inducible Cre-loxP-mediated inactivation of the Jagged1 gene in bone marrow progenitors and/or bone marrow (BM) stromal cells does not impair HSC self-renewal or differentiation in all blood lineages. Mice with simultaneous inactivation of Jagged1 and Notch1 in the BM compartment survived normally following a 5FU-based in vivo challenge. In addition, Notch1-deficient HSCs were able to reconstitute mice with inactivated Jagged1 in the BM stroma even under competitive conditions. In contrast to earlier reports, these data exclude an essential role for Jagged1-mediated Notch signaling during hematopoiesis.     

Expression of Notch-1 and its ligand Jagged-1 in rat liver during liver regeneration

The Notch/Jagged signaling pathway is important for cellular differentiation and proliferation. Its dysfunction is associated with human pathologies in several tissues including liver. Point mutations in Jagged-1 gene are the cause for Alagille syndrome, associated with paucity of intrahepatic bile ducts. To determine the putative role of the trans-membrane receptor Notch and its ligand Jagged-1 in liver regeneration, we investigated the expression of Notch and Jagged-1 in rat liver following 2/3 partial hepatectomy. Immunohistochemical staining of normal rat liver showed that Notch was expressed in hepatocytes, bile duct cells and endothelial cells, whereas Jagged-1 was expressed in bile duct cells and hepatocytes. Both Notch-1 and Jagged-1 proteins were upregulated in hepatocytes after partial hepatectomy up to day 4. After partial hepatectomy, nuclear translocation of the intracellular cytoplasmic domain of Notch (NICD) increased and peaked within 15 minutes, indicating the activation of Notch. Expression of the Notch-dependent target gene (HES-1) expression increased within 30-60 minutes. Addition of recombinant Jagged-1 protein to primary cultures of hepatocytes stimulated hepatocyte DNA synthesis. Furthermore, injection of silencing RNA for Notch and Jagged-1 to livers 2 days before partial hepatectomy significantly suppressed proliferation of hepatocytes at days 2 to 4 of the regenerative response. In conclusion, Notch/Jagged signaling pathway is activated during liver regeneration and is potentially contributing to signals affecting cell growth and differentiation.     

Jagged2 acts as a Delta-like Notch ligand during early hematopoietic cell fate decisions

Notch signaling critically mediates various hematopoietic lineage decisions and is induced in mammals by Notch ligands that are classified into 2 families, Delta-like (Delta-like-1, -3 and -4) and Jagged (Jagged1 and Jagged2), based on structural homology with both Drosophila ligands Delta and Serrate, respectively. Because the functional differences between mammalian Notch ligands were still unclear, we have investigated their influence on early human hematopoiesis and show that Jagged2 affects hematopoietic lineage decisions very similarly as Delta-like-1 and -4, but very different from Jagged1. OP9 coculture experiments revealed that Jagged2, like Delta-like ligands, induces T-lineage differentiation and inhibits B-cell and myeloid development. However, dose-dependent Notch activation studies, gene expression analysis, and promoter activation assays indicated that Jagged2 is a weaker Notch1-activator compared with the Delta-like ligands, revealing a Notch1 specific signal strength hierarchy for mammalian Notch ligands. Strikingly, Lunatic-Fringe- mediated glycosylation of Notch1 potentiated Notch signaling through Delta-like ligands and also Jagged2, in contrast to Jagged1. Thus, our results reveal a unique role for Jagged1 in preventing the induction of T-lineage differentiation in hematopoietic stem cells and show an unexpected functional similarity between Jagged2 and the Delta-like ligands.     

Clonal relation in a case of CLL,ALCL, and Hodgkin composite lymphoma

Large cell lymphomas and Hodgkin disease may develop during the course of chronic lymphocytic leukemia (CLL). In some cases the transformed cells are Epstein-Barr virus (EBV)-positive and not clonally related to the CLL cells. In other cases the transformed cells have the same clonal rearrangements as the CLL cells. Here we describe a composite lymphoma in a patient with CLL that exhibits a combination of CLL/small lymphocytic lymphoma, large cell lymphoma with anaplastic morphology, and Hodgkin lymphoma (HL). Although the large cell lymphoma cells are CD45R0 and TIA-1-positive, suggesting a T- or 0-cell anaplastic large cell lymphoma (ALCL), the genetic analysis demonstrates immunoglobulin heavy chain (IgH) gene rearrangements for both alleles, carrying the same somatic mutations as observed in the CLL component. The Reed-Sternberg (R-S) cells in the Hodgkin component also strongly express TIA-1 but differ from the anaplastic large cells by the expression of CD15 and TARC and the presence of a prominent lymphocytic infiltrate. The ALCL and HL components both are EBV negative. Analysis of the IgH gene rearrangements in micromanipulated R-S cells revealed identical Ig gene rearrangements carrying the same somatic mutations as the CLL and the large cell components. The findings indicate transformation of the CLL cells into a large cell lymphoma with anaplastic morphology and a Hodgkin component.     

Constitutively activated Notch signaling is involved in survival and apoptosis resistance of B-CLL cells

Notch signaling is involved in tumorigenesis, but its role in B-chronic lymphocytic leukemia (B-CLL) pathogenesis is not completely defined. This study examined the expression and activation of Notch receptors in B-CLL cells and the role of Notch signaling in sustaining the survival of these cells. Our results show that B-CLL cells but not normal B cells constitutively express Notch1 and Notch2 proteins as well as their ligands Jagged1 and Jagged2. Notch signaling is constitutively activated in B-CLL cells, and its activation is further increased in B-CLL cells, which resist spontaneous apoptosis after 24-hour ex vivo culture. Notch stimulation by a soluble Jagged1 ligand increases B-CLL cell survival and is accompanied by increased nuclear factor-kappa B (NF-kappaB) activity and cellular inhibitor of apoptosis protein 2 (c-IAP2) and X-linked inhibitor of apoptosis protein (XIAP) expression. In contrast, Notch-signaling inhibition by the gamma-secretase inhibitor I (GSI; z-Leu-Leu-Nle-CHO) and the specific Notch2 down-regulation by small-interfering RNA accelerate spontaneous B-CLL cell apoptosis. Apoptotic activity of GSI is accompanied by reduction of NF-kappaB activity and c-IAP2 and XIAP expression. Overall, our findings show that Notch signaling plays a critical role in B-CLL cell survival and apoptosis resistance and suggest that it could be a novel potential therapeutic target.     

Jagged-mediated Notch signaling maintains proliferating neural progenitors and regulates cell diversity in the ventral spinal cord

Previous studies have shown that Delta-mediated Notch signaling regulates the number of early differentiating neurons. However, the role of Notch activation and Jagged-mediated signaling during late neurogenesis remains poorly defined. In the developing spinal cord of zebrafish, GABAergic Kolmer-Agduhr (KA') cells and motor neurons (MN) emerge sequentially from their progenitors in the p3 domain. Jagged2 is expressed uniformly in the pMN domain during late neurogenesis where Olig2 is required for its expression. We suggest that Jagged2 interacts ventrally with progenitors in the adjacent p3 domain, where it has a critical role in the maintenance of proliferating neural progenitors and in preventing differentiation of these progenitors as GABAergic KA' cells or secondary MN. This study identifies a critical role for Jagged-Notch signaling in the maintenance of proliferating neural precursors in a discrete compartment of the neural tube during the continuing growth and development of the vertebrate nervous system.     

吉西他滨对人胰腺癌SW1990和BxPC3细胞株Notch信号通路的诱导作用

目的 观察吉西他滨对人胰腺癌细胞(SW1990和BxPC3)Notch信号通路活性的影响,探讨其与胰腺癌对吉西他滨化疗耐药的关系.方法 不同浓度吉西他滨处理人胰腺癌SW1990和BxPC3细胞株48 h,实时定量PCR检测Notch信号通路受体Notch1、2、3、4,配体Jagged1、2和下游靶基因Hes1 mRNA的表达,Western blotting测定细胞Hes1蛋白表达.结果 2μmol/L吉西他滨作用胰腺癌细胞株48 h,SW1990细胞的Notch1、2、3、Jagged1、2和Hes1 mRNA表达量分别为8.26±0.48、39.12±4.87、0.84±0.06、105.8±17.92、6.59±0.32和17.30±2.96,均较未处理细胞的1.02±0.15、15.25±1.28、0.12±0.02、32.66±1.98、1.88±0.29和5.02±0.64明显升高(P<0.05或P<0.01);BxPC3细胞上述各项表达量分别为7.87±0.59、109.4±10.98、0.74±0.19、62.73±13.50、2.09±0.16和15.38±1.06,也均较未处理细胞的1.14±0.43、58.96±2.63、0.10±0.02、16.95±3.79、0.98±0.02和2.04±0.16,明显升高(P<0.05或P<0.01).1、2 μmol/L吉西他滨作用胰腺癌细胞株48 h,SW1990细胞Hes1蛋白表达量分别为0.30±0.03、0.42±0.03;BxPC3细胞分别为0.33±0.02、0.45±0.03,均较未处理细胞显著增高(0.13±0.01、F=33.71;0.09±0.02、F=38.54,P值均<0.01).结论 吉西他滨可明显激活SW1990和BxPC3细胞的Notch信号通路,这可能是胰腺癌细胞获得化疗耐受性的机制之一.     

Autocrine- and paracrine-activated receptor tyrosine kinases in classic Hodgkin lymphoma

The pathogenesis of Hodgkin lymphoma (HL) is still largely unknown. Based on a search for footprints of pathogenetic mechanisms in global RNA expression data of Hodgkin/Reed-Sternberg (HRS) cell lines, we analyzed the expression and activation of 6 receptor tyrosine kinases (RTKs) in classic HL. Immunohistochemistry revealed that the RTKs platelet-derived growth factor receptor A (PDGFRA), DDR2, EPHB1, RON, TRKB, and TRKA were each expressed in HRS cells in 30% to 75% of patients. These RTKs were not expressed in normal B cells, the origin of HRS cells, or in most B-cell non-Hodgkin lymphoma (NHL). In the majority of patients at least one RTK was expressed, and in most patients several RTKs were coexpressed, most prominently in Hodgkin lymphoma of the nodular sclerosis subtype. Phosphotyrosine-specific antibodies revealed exemplarily the activation of PDGFRA and TRKA/B and an elevation of cellular phosphotyrosine content. Immunohistochemistry for RTK ligands indicated that DDR2 and TRKA are likely activated in a paracrine fashion, whereas PDGFRA and EPHB1 seem to be activated by autocrine loops. Activating mutations were not detected in cDNA encoding the RTKs in HRS cell lines. These findings show the unprecedented coexpression of multiple RTKs in a tumor and indicate that aberrant RTK signaling is an important factor in HL pathogenesis and that it may be a novel therapeutic target.     

Liver-specific inactivation of Notch2, but not Notch1, compromises intrahepatic bile duct development in mice

The Notch pathway is an evolutionary conserved, intercellular signaling pathway that plays an important role in cell fate specification and the embryonic development of many organs, including the liver. In humans, mutations in the Notch receptor ligand Jagged1 gene result in defective intrahepatic bile duct (IHBD) development in Alagille syndrome. Developmental abnormalities of IHBD in mice doubly heterozygous for Jagged1 and Notch2 mutations propose that interactions of Jagged1 and its receptor Notch2 are crucial for normal IHBD development. Because different cell types in the liver are involved in IHBD development and morphogenesis, the cell-specific role of Notch signaling is not entirely understood. We investigated the effect of combined or single targeted disruption of Notch1 and Notch2 specifically in hepatoblasts and hepatoblast-derived lineage cells on liver development using AlbCre transgenic mice. Hepatocyte differentiation and homeostasis were not impaired in mice after combined deletion of Notch1 and Notch2 (N1N2(F/F)AlbCre). However, we detected irregular ductal plate structures in N1N2(F/F)AlbCre newborns, and further postnatal development of IHBD was severely impaired characterized by disorganized ductular structures accompanied by portal inflammation, portal fibrosis, and foci of hepatocyte feathery degeneration in adulthood. Further characterization of mutant mice with single deletion of Notch1 (N1(F/F)AlbCre) or Notch2 (N2(F/F)AlbCre) showed that Notch2 but not Notch1 is indispensable for normal perinatal and postnatal IHBD development. Further reduction of Notch2 gene dosage in Notch2 conditional/mutant (N2(F/LacZ)AlbCre) animals further enhanced IHBD abnormalities and concomitant liver pathology. CONCLUSION: Notch2 is required for proper IHBD development and morphogenesis.     

miR-155 regulates HGAL expression and increases lymphoma cell motility

HGAL, a prognostic biomarker in patients with diffuse large B-cell lymphoma and classic Hodgkin lymphoma, inhibits lymphocyte and lymphoma cell motility by activating the RhoA signaling cascade and interacting with actin and myosin proteins. Although HGAL expression is limited to germinal center (GC) lymphocytes and GC-derived lymphomas, little is known about its regulation. miR-155 is implicated in control of GC reaction and lymphomagenesis. We demonstrate that miR-155 directly down-regulates HGAL expression by binding to its 3'-untranslated region, leading to decreased RhoA activation and increased spontaneous and chemoattractant-induced lymphoma cell motility. The effects of miR-155 on RhoA activation and cell motility can be rescued by transfection of HGAL lacking the miR-155 binding site. This inhibitory effect of miR-155 suggests that it may have a key role in the loss of HGAL expression on differentiation of human GC B cells to plasma cell. Furthermore, this effect may contribute to lymphoma cell dissemination and aggressiveness, characteristic of activated B cell-like diffuse large B-cell lymphoma typically expressing high levels of miR-155 and lacking HGAL expression.     

Microfibril-associate glycoprotein-2 (MAGP-2) promotes angiogenic cell sprouting by blocking notch signaling in endothelial cells

Angiogenesis is highly sensitive to the composition of the vascular microenvironment, however, our understanding of the structural and matricellular components of the vascular microenvironment that regulate angiogenesis and the molecular mechanisms by which these molecules function remains incomplete. Our previous results described a novel pro-angiogenic activity for Microfibril-Associated Glycoprotein-2 (MAGP-2), but did not address the molecular mechanism(s) by which this is accomplished. We now demonstrate that MAGP-2 promotes angiogenic cell sprouting by antagonizing Notch signaling pathways in endothelial cells. MAGP-2 decreased basal and Jagged1 induced expression from the Notch sensitive Hes-1 promoter in ECs, and blocked Jagged1 stimulated Notch1 receptor processing in transiently transfected 293T cells. Interestingly, inhibition of Notch signaling by MAGP-2 seems to be restricted to ECs since MAGP-2 increased Hes-1 promoter activity and Notch1 receptor processing in heterologous cell types. Importantly, constitutive activation of the Notch signaling pathway blocked the ability of MAGP-2 to promote angiogenic cell sprouting, as well as morphological changes associated with angiogenesis. Collectively, these observations indicate that MAGP-2 promotes angiogenic cell spouting in vitro by antagonizing Notch signaling pathways in ECs.     

Notch1 engagement by Delta-like-1 promotes differentiation of B lymphocytes to antibody-secreting cells

Notch signaling regulates B and T lymphocyte development and T cell effector class decision. In this work, we tested whether Notch activity affects mature B cell activation and differentiation to antibody-secreting cells (ASC). We show increased frequency of ASC in cultures of splenic B cells activated with LPS or anti-CD40 when provided exogenous Notch ligand Delta-like-1 (Dll1). Our results indicate that Notch-Dll1 interaction releases a default pathway that otherwise inhibits Ig secretion upon B cell activation. Thus, Dll1 enhanced spontaneous Ig secretion by naturally activated marginal zone B and B1 cells and reversed the inhibition of ASC differentiation mediated by B cell receptor crosslinking during LPS. Moreover, suppression of Notch signaling in B cell expression of either a dominant-negative mutant form of Mastermind-like 1 or a null mutation of Notch1 not only prevented Dll1-mediated enhancement of ASC differentiation but also reduced dramatically LPS-induced Ig secretion. Finally, we show that Dll1 and Jagged-1 are differentially expressed in discrete areas of the spleen, and that the effect of Notch engagement on Ig secretion is ligand-specific. These results indicate that Notch ligands participate in the definition of the mature B cell microenvironment that influences their terminal differentiation.     

Notch signaling as an important mediator of cardiac repair and regeneration after myocardial infarction

Through local cell-cell interactions, the Notch signaling pathway controls tissue formation and homeostasis during embryonic and adult life. In the heart, Notch1 is expressed in a variety of cell types, such as cardiomyocytes, smooth muscle cells, and endothelial cells. In cardiomyocytes, Notch1 is activated in proliferating embryonic and immature cardiomyocytes, and it is downregulated in the myocardium during postnatal development. However, Notch signaling in the adult myocardium could be activated transiently in response to myocardial injury, suggesting that Notch signaling may contribute to cardiac repair. Indeed, activation of Notch1 intracellular domain blunts the severity of myocardial injury and improves myocardial hemodynamic function. Conversely, genetic ablation of the Notch1 gene, either systemically or in bone marrow-derived cells, leads to impaired cardiac repair following myocardial infarction. In this review, we discuss the complex mechanisms of Notch signaling and its role in cardiac repair and regeneration after myocardial infarction.