The Notch ligand, Delta-1, alters retinoic acid (RA)-induced neutrophilic differentiation into monocytic and reduces RA-induced apoptosis in NB4 cells

Regulation of glioblastoma stem cells by retinoic acid: role for Notch pathway inhibition

It is necessary to understand mechanisms by which differentiating agents influence tumor-initiating cancer stem cells. Toward this end, we investigated the cellular and molecular responses of glioblastoma stem-like cells (GBM-SCs) to all-trans retinoic acid (RA). GBM-SCs were grown as non-adherent neurospheres in growth factor supplemented serum-free medium. RA treatment rapidly induced morphology changes, induced growth arrest at G1/G0 to S transition, decreased cyclin D1 expression and increased p27 expression. Immunofluorescence and western blot analysis indicated that RA induced the expression of lineage-specific differentiation markers Tuj1 and GFAP and reduced the expression of neural stem cell markers such as CD133, Msi-1, nestin and Sox-2. RA treatment dramatically decreased neurosphere-forming capacity, inhibited the ability of neurospheres to form colonies in soft agar and inhibited their capacity to propagate subcutaneous and intracranial xenografts. Expression microarray analysis identified ∼350 genes that were altered within 48 h of RA treatment. Affected pathways included retinoid signaling and metabolism, cell-cycle regulation, lineage determination, cell adhesion, cell-matrix interaction and cytoskeleton remodeling. Notch signaling was the most prominent of these RA-responsive pathways. Notch pathway downregulation was confirmed based on the downregulation of HES and HEY family members. Constitutive activation of Notch signaling with the Notch intracellular domain rescued GBM neurospheres from the RA-induced differentiation and stem cell depletion. Our findings identify mechanisms by which RA targets GBM-derived stem-like tumor-initiating cells and novel targets applicable to differentiation therapies for glioblastoma.

Activating Notch signaling post-SCI modulates angiogenesis in penumbral vascular beds but does not improve hindlimb locomotor recovery

Manipulation of Notch signaling has led to significant tumor shrinkage as well as recovery from several traumatic and ischemic injury models indicating its potential clinical application. We have tested both an agonist and antagonist of Notch signaling to study the effects of Notch-mediated angiogenesis on spinal cord vascular pathology following traumatic injury. Initial neonatal retinal vascularization assays showed their respective bioactivities in vivo. Mice were treated with either the antagonist Jagged1-Fc chimera (Jag1-Fc) or agonist Notch1 antibody (N1 Ab) immediately following a mid-thoracic contusive injury through an initial jugular bolus and tail vein injections for 3 days post-injury. After 14 days, activating Notch signaling decreased the overall vascular density within the penumbral gray matter compared to controls while maintaining the density of perfused vessels. Inhibiting Notch signaling did not change the density or perfusion of microvessels within the lesion penumbra. Furthermore, neither activation nor inhibition of Notch signaling significantly altered inflammation, hypoxia, and lesion volume in the epicenter and penumbra. Importantly, neither treatment changed locomotor function. In postnatal retinal vascular assays, administration of Jag1-Fc and N1 Ab increased and decreased both tip cell numbers and branch points in each treatment, respectively. However, these agents did not modulate primary CNS EC proliferation in vitro in spite of sufficient Notch ligand expression. We conclude that Notch signaling, while an important part of developmental angiogenesis, may play a lesser role in mediating vascular recovery following traumatic injury to the CNS.

Notch signaling maintains proliferation and survival of the HL60 human promyelocytic leukemia cell line and promotes the phosphorylation of the Rb protein

The Notch signaling pathway has been implicated in the development of several leukemia and lymphoma. In order to investigate the relationship between Notch signaling and acute myeloid leukemia (AML), in this study, we expressed a recombinant Notch ligand protein, the DSL domain of the human Jagged1 fused with GST (GST-Jag1). GST-Jag1 could activate Notch signaling in the human promyelocytic leukemia cell line HL60, as shown by a reporter assay and the induced expression of Notch effector gene Hes1 and Hes5. However, GST-Jag1 had no effect on the proliferation and survival of HL60 cells. HL60 cells expressed both Notch ligands and receptors, and had a potential of reciprocal stimulation of Notch signaling between cells. We, therefore, blocked Notch signaling in cultured HL60 cells using a gamma-secretase inhibitor (GSI). We found that GSI inhibited the proliferation of HL60 cells significantly by blocking the cell-cycle progression in the G1 phase. Furthermore, GSI induced remarkably apoptosis of HL60 cells. These changes in GSI-treated HL60 cells correlated with the down-regulation of c-Myc and Bcl2, and the low phosphorylation of the Rb protein. These results suggested that reciprocal Notch signaling might be necessary for the proliferation and survival of AML cells, possibly through the maintenance of the expression of c-Myc and Bcl2, as well as the phosphorylation of the Rb protein.

Transcriptional activation of pref-1 by E2F1 in 3T3 L1 cells

The E2F gene family appears to regulate the proliferation and differentiation of events that are required for adipogenesis. Pref-1 is a transmembrane protein that inhibits adipocyte differentiation in 3T3-L1 cells. In this study, we found that the expression of pref-1 is regulated by the transcription factor E2F1. The expression of pref-1 and E2F1 was strongly induced in preadipocytes and at the late differentiation stage. Using luciferase reporter assay, ChIP assay and EMSA, we found that the -211/-194 region of the pref-1 promoter is essential for the binding of E2F1 as well as E2F1-dependent transcriptional activation. Knockdown of E2F1 reduced both pref-1 promoter activity and the level of pref-1 mRNA. Taken together, our data suggest that transcriptional activation of pref-1 is stimulated by E2F1 protein in adipocytes.

All-trans retinoic acid inhibits the differentiation, maturation, and function of human monocyte-derived dendritic cells

All-trans retinoic acid (ATRA) affects on the function of antigen presenting cells with somewhat controversies. We investigated the effects of ATRA on differentiation, maturation and function of human monocyte-derived dendritic cells (DCs). Low dose (10(-14)M) or high dose (10(-6)M) of ATRA was added either when monocytes were differentiated into immature DCs (imDCs) or mature DCs (mDCs) were induced. Apoptotic cell populations were dramatically increased in imDCs or mDCs with increasing concentration of ATRA. The productions of IL-12p40 and IL-12p70 were significantly suppressed in imDCs or mDCs induced by the addition of ATRA in the dose-dependent manner, whereas IL-10 was increased. DCs cultured with ATRA induced the differentiation of naïve T cells towards a helper T cell type 2 (Th2) response and expansion of CD4(+)CD25(+)Foxp3(+) regulatory T cells. Allostimulatory capacity of DCs was suppressed with increasing concentration of ATRA. These findings suggest that ATRA inhibits the effects on the differentiation, maturation and function of human monocyte-derived DCs in vitro and also enhance the differentiation of naïve T cell toward the Th2 type.

Apoptosis related protein 3, an ATRA-upregulated membrane protein arrests the cell cycle at G1/S phase by decreasing the expression of cyclin D1

Human Apr3 was first cloned from HL-60 cells treated by ATRA. In this study, we further demonstrated that Apr3 could be obviously upregulated by ATRA in many other ATRA sensitive cells, suggesting a common role of Apr3 in ATRA effects. Indirect immunofluorescence assay indicates that Apr3 is a membrane protein, while its truncated form without the predicted transmembrane and intracellular domain, was likely a secreted one. Furthermore, FACS analysis showed that Apr3 overexpression could cause an obvious G1/S phase arrest which might be induced by dramatic reduction of cyclin D1 expression. Strikingly, the truncated Apr3 antagonized the negative role of Apr3 on cell cycle and cyclin D1. Taken together, our data suggest that Apr3 should play an important role in ATRA signal pathway and the predicted transmembrane and/or the intracellular domain mediates Apr3 membrane localization and is vital for the negative regulation on cell cycle and cyclin D1.

Establishment of a novel B-cell lymphoma cell line with suppressed growth by gamma-secretase inhibitors

A novel lymphoma cell line, designated TMD8 was established from cells of a patient with diffuse large B-cell lymphoma. TMD8 cells expressed HES1 mRNA, suggesting constitutive activation of Notch signaling. TMD8 cells expressed normal-sized Notch1 protein, and showed no mutations in the NOTCH1 gene. Cell growth was suppressed by gamma-secretase inhibitors (GSI). It was reported that GSI suppressed growth of T-cell acute lymphoblastic leukemia (T-ALL) cell lines, which frequently had NOTCH1 mutations. In addition to T-ALL, TMD8 is another unique cell line sensitive to GSI, and is useful to study effects of GSI in molecular targeting therapy.

Diverse effects of the Notch ligands Jagged1 and Delta1 on the growth and differentiation of primary acute myeloblastic leukemia cells

OBJECTIVE

Notch signaling plays a role in regulating the self-renewal and differentiation of hematopoietic progenitors. Since acute myeloblastic leukemia (AML) originates from dysregulated hematopoietic progenitors, the Notch system may be involved in the abnormal growth. We previously reported that AML cells express Notch proteins. In this study, we examined the effects of recombinant human Notch ligand proteins, Jagged1 and Delta1, on the growth and differentiation of primary AML cells.

MATERIALS AND METHODS

AML cells separated from blood from 12 patients were cultured in wells coated with Jagged1, Delta1, or control IgG. The short-term growth was evaluated using a colorimetric assay. The self-renewal capacity was evaluated by the clonogenic cells recovered, which were obtained via a colony assay involving cells cultured with the ligands or control IgG. Differentiation was evaluated by the morphology of the cultured cells and flow cytometric analysis.

RESULTS

The ligand stimulation caused three types of response in the short-term growth of the primary AML cells, namely, promotion, suppression, or no significant effect. The self-renewal capacity was suppressed or not significantly affected by the ligands, even in cells showing short-term growth promotion. The ligand stimulation altered blast cells into macrophage-like cells from their morphology and increased the expression of differentiation markers such as CD13 or CD14 in some samples.

CONCLUSIONS

The Notch ligands had diverse effects on the short-term growth of primary AML cells. The ligands did not promote the self-renewal capacity of any of the cells examined and instead tended to induce differentiation under the conditions used.