The role of c-Myc on granulocyte colony-stimulating factor-dependent neutrophilic proliferation and differentiation of HL-60 cells

Mir-34c affects the proliferation and pluripotency of porcine induced pluripotent stem cell (piPSC)-like cells by targeting c-Myc

MicroRNAs are important regulators in stem cells, which involve in gene regulation, including cell proliferation, differentiation and apoptosis. As an important one, miR-34c participates in various processes by targeting protein-coding genes. It is generally considered as a tumor suppressor and cell adhesion inhibitor. However, whether miR-34c has effects on pluripotent stem cells is not clear. Here, by mir-34c mimics transfection, the function of miR-34c on porcine induced pluripotent stem cell (piPSC)-like cells was investigated. Bioinformatics analyses showed that c-Myc is miR-34c's candidate target, which was confirmed by dual Luciferase assay. The knockout of miR-34c indicated that mir-34c affects the proliferation and pluripotency of piPSC-like cells by targeting c-Myc. Our study explored the regulatory mechanism of miR-34c on piPSC-like cells, providing a reference for the establishment of true porcine PSCs.

Translational control of c-MYC by rapamycin promotes terminal myeloid differentiation

c-MYC inhibits differentiation and regulates the process by which cells acquire biomass, cell growth. Down-regulation of c-MYC, reduced cell growth, and decreased activity of the PI3K/AKT/mTORC1 signal transduction pathway are features of the terminal differentiation of committed myeloid precursors to polymorphonuclear neutrophils. Since mTORC1 regulates growth, we hypothesized that pharmacological inhibition of mTORC1 by rapamycin may reverse the phenotypic effects of c-MYC. Here we show that granulocytes blocked in their ability to differentiate by enforced expression of c-MYC can be induced to differentiate by reducing exogenous c-MYC expression through rapamycin treatment. Rapamycin also reduced expression of endogenous c-MYC and resulted in enhanced retinoid-induced differentiation. Total cellular c-Myc mRNA and c-MYC protein stability were unchanged by rapamycin, however the amount of c-Myc mRNA associated with polysomes was reduced. Therefore rapamycin limited expression of c-MYC by inhibiting c-Myc mRNA translation. These findings suggest that mTORC1 could be targeted to promote terminal differentiation in myeloid malignancies characterized by dysregulated expression of c-MYC.

Granulocyte colony-stimulating factor promotes the translocation of protein kinase Ciota in neutrophilic differentiation cells

Previously, we suggested that the phosphatidylinositol 3-kinase (PI3K)-p70 S6 kinase (p70 S6K) pathway plays an important role in granulocyte colony-stimulating factor (G-CSF)-dependent enhancement of the neutrophilic differentiation and proliferation of HL-60 cells. While atypical protein kinase C (PKC) has been reported to be a regulator of p70 S6K, abundant expression of PKCiota was observed in myeloid and lymphoid cells. Therefore, we analyzed the participation of PKCiota in G-CSF-dependent proliferation. The maximum stimulation of PKCiota was observed from 15 to 30 min after the addition of G-CSF. From 5 to 15 min into this lag time, PKCiota was found to translocate from the nucleus to the membrane. At 30 min it re-translocated to the cytosol. This dynamic translocation of PKCiota was also observed in G-CSF-stimulated myeloperoxidase-positive cells differentiated from cord blood cells. Small interfering RNA for PKCiota inhibited G-CSF-induced proliferation and the promotion of neutrophilic differentiation of HL-60 cells. These data indicate that the G-CSF-induced dynamic translocation and activation processes of PKCiota are important to neutrophilic proliferation.

α-melanocyte-stimulating hormone down-regulates CXC receptors through activation of neutrophil elastase

Considering the role of interleukin-8 (IL-8) in a large number of acute and chronic inflammatory diseases, the regulation of IL-8-mediated biological responses is important. Alpha-melanocyte-stimulating hormone (alpha-MSH), a tridecapeptide, inhibits most forms of inflammation by an unknown mechanism. In the present study, we have found that alpha-MSH interacts predominantly with melanocortin-1 receptors and inhibits several IL-8-induced biological responses in macrophages and neutrophils. It down-regulated receptors for IL-8 but not for TNF, IL-4, IL-13 or TNF-related apoptosis-inducing ligand (TRAIL) in neutrophils. It down-regulated CXCR type 1 and 2 but not mRNA levels. alpha-MSH did not inhibit IL-8 binding in purified cell membrane or affinity-purified CXCR. IL-8 or anti-CXCR Ab protected against alpha-MSH-mediated inhibition of IL-8 binding. The level of neutrophil elastase, a specific serine protease, but not cathepsin G or proteinase 3 increased in alpha-MSH-treated cells, and restoration of CXCR by specific neutrophil elastase or serine protease inhibitors indicates the involvement of elastase in alpha-MSH-induced down-regulation of CXCR. These studies suggest that alpha-MSH inhibits IL-8-mediated biological responses by down-regulating CXCR through induction of serine protease and that alpha-MSH acts as a potent immunomodulator in neutrophil-driven inflammatory distress.

Antisense c-myc fragments induce normal differentiation cycles in HL-60 cells

BACKGROUND

We have investigated the potential for using antisense technology as a means of delivering treatment for acute myeloblastic leukaemia (FAB-M2) by gene therapy.

MATERIALS AND METHODS

A test recombinant adenovirus vector was constructed containing human c-myc antisense fragments to study the effects of altering c-myc overexpression in the human HL-60 cell line. Control vector contained the human LacZ gene. Transfection efficiency in HL-60 cells was determined using control vector in the presence of protamine sulphate and multiplicity of infection of 100. Morphological and mechanistic changes were assessed using immunohistochemical analysis, flow cytometry and reverse transcription-polymerase chain reaction.

RESULTS

Transfection efficiency of control vector was 79.8% and morphological differences were observed after 72 h in culture. The rate of proliferation of HL-60 cells infected with test vector was inhibited by 73% compared with control following 6 days in culture. Normal terminal differentiation leading to apoptosis was only evident in test vector infected cells. Peak apoptosis (34.7%) was detected at day 6 and cell cycle arrest at days 2, 4 and 6. Expression of c-fos protein was significantly increased in test vector treated cells with a noticeable down-regulation of c-myc expression.

CONCLUSIONS

These data suggest that transfection of a human HL-60 cell line with vector containing c-myc antisense fragments could inhibit proliferation, but induce differentiation and apoptosis. Thus, we believe that further study of this construct is warranted as a potential gene therapy reagent for treatment of acute myeloblastic leukaemia.

Cardiac glycoside inhibits IL-8-induced biological responses by downregulating IL-8 receptors through altering membrane fluidity

Considering the potential role of interleukin-8 (IL-8) in inflammation, angiogenesis, tumorogenesis, and metastasis, and the involvement of different cell types especially neutrophils and macrophages in those processes, the regulation of IL-8-mediated biological responses is important. In this report we provide evidences that oleandrin, a cardiac glycoside potentially inhibited IL-8-, formyl peptide (FMLP)-, EGF-, or nerve growth factor (NGF)-, but not IL-1- or TNF-induced NF-kappaB activation in macrophages. Oleandrin inhibited IL-8-, but not TNF-induced NF-kappaB-dependent genes expression. Oleandrin inhibited the binding of IL-8, EGF, or NGF, but not IL-1 or TNF. It decreased almost 79% IL-8 binding without altering affinity towards IL-8 receptors and this inhibition of IL-8 binding was observed in isolated membrane. The IL-8, anti-IL-8Rs antibodies, or protease inhibitors were unable to protect oleandrin-mediated inhibition of IL-8 binding. Phospholipids significantly protected oleandrin-mediated inhibition of IL-8 binding thereby restoring IL-8-induced NF-kappaB activation. Oleandrin altered the membrane fluidity as detected by microviscosity parameter and a decrease in diphenylhexatriene, a lipid binding fluorophore binding in a dose-dependent manner. Overall, our results suggest that oleandrin inhibits IL-8-mediated biological responses in diverse cell types by modulating IL-8Rs through altering membrane fluidity and microviscosity. The study might help to regulate IL-8-mediated biological responses involved in inflammation, metastasis, and neovascularization.

Differential regulation of smooth muscle markers in human bone marrow-derived mesenchymal stem cells

OBJECTIVE

To study smooth-muscle differentiation and de-differentiation of human bone marrow-derived mesenchymal stem cells (MSCs), which have been shown to enter the circulation and to contribute to vascular repair and atherosclerosis.

DESIGN

Human MSCs from bone marrow were cultured with 20% fetal calf serum (FCS) or with 10% FCS and various concentrations of dimethyl sulfoxide (DMSO). Expression of smooth muscle markers was determined by Western blot analysis and immunofluorescence. For signalling studies, involvement of the mammalian target of rapamycin (mTOR) pathway was tested by treatment with rapamycin.

RESULTS

MSCs cultured with 20% FCS acquired a smooth muscle-like appearance and expressed the smooth muscle (sm) markers sm-alpha-actin, desmin, sm-calponin and myosin light chain kinase (MLCK). DMSO induced a spindle-like morphology with marked reduction of stress fibers. As judged by Western blot analysis, treatment with 2.5% DMSO strongly downregulated expression of sm-calponin (-85%), short MLCK (-98%) and sm-alpha-actin expression (-51%). Reduced calponin expression was detected by day 2 of treatment with 0.5-2.5% DMSO. After withdrawal of DMSO, MSCs regained high expression of sm-calponin. Treatment with 6 nmol/l rapamycin partly antagonized the effect of DMSO, indicating the involvement of mTOR in regulation of the smooth muscle phenotype of MSCs.

CONCLUSIONS

DMSO strongly downregulates the smooth muscle markers sm-calponin, short MLCK and sm-alpha-actin in human MSCs, indicating a transition from a smooth muscle-like phenotype to an undifferentiated state by an mTOR-dependent mechanism. Regulating the phenotype of human MSCs may be of relevance for novel therapeutic approaches in atherosclerosis and intimal hyperplasia after vascular injury.

HX531, a retinoid X receptor antagonist, inhibited the 9-cis retinoic acid-induced binding with steroid receptor coactivator-1 as detected by surface plasmon resonance

HX531 is a retinoid X receptor (RXR) antagonist that inhibits 9-cis retinoic acid-induced neutrophilic differentiation of HL-60 cells. In order to elucidate the inhibitory mechanism of HX531, we have developed a novel ligand sensor assay for RXR in which the receptor-coactivator interaction is directly monitored using surface plasmon resonance (SPR) biosensor technology. A 20-mer peptide from steroid receptor coactivator-1 (SRC-1), containing nuclear receptor interaction motif LXXLL was immobilized on the surface of a BIAcore sensor chip. Injection of human recombinant RXR with or without 9-cis retinoic acid resulted in ligand-dependent interaction with the SRC-1 peptide. Kinetic analysis revealed dissociation constants (KD) of 9-cis RA-preincubated RXR to SRC-1 was 5.92 x 10(-8)M. Using this technique, we found that 1 microM HX531 reduced the ka value of liganded-RXR with SRC-1, suggesting that HX531 reduced the affinity of RXR to SRC-1. This SPR assay system was applied to obtain quantitative kinetic data of RXR ligand binding to the SRC-1 peptide and the alteration of these data by antagonists.

Ribosomal p70S6K basal activity increases upon induction of differentiation of myelomonocytic leukemic cell lines HL60, AML14 and MPD

The role of ribosomal p70S6K in the cell cycle has been studied extensively, and it is known that this enzyme is crucial for cell advancement through G(1). Conversely, the participation of p70S6K in cell differentiation is not well understood. We have studied the response of p70S6K to the cytokine granulocyte-macrophage colony stimulating factor (GM-CSF) in three differentiation-capable leukemic cell lines (MPD, AML-14 and HL-60) and in normal mature neutrophils. Immature leukemic cells starved for 16 h showed a robust ( approximately 3.5-fold over controls) p70S6K phosphorylation on T(421)/S(424) residues in response to an acute (5 min) 10 nM GM-CSF stimulation. On the other hand, cells that had been induced to differentiate and express granulocytic phenotypes, showed an increased ( approximately 6-fold) basal level of p70S6K T(421)/S(424) phosphorylation over immature cells, as well as an increased baseline tyrosyl phosphorylation of the GM-CSF receptor beta subunit (GM-CSF.Rbeta). However, the differentiated cells displayed a weak ( approximately 1.4-fold over controls) response to GM-CSF even at prolonged incubation times (20 min). In vitro p70S6K enzymatic activity paralleled p70S6K T(421)/S(424) phosphorylation in both high basal, unstimulated, levels in immature cells and a low degree of response to GM-CSF. Lastly, peripheral blood mature neutrophils had low basal GM-CSF.Rbeta and p70S6K activity, with both parameters being robustly stimulated following addition of GM-CSF, a situation in contrast with the cell lines, indicative perhaps of their incomplete terminal differentiation. In summary, these findings show the increase in basal phosphorylation of p70S6K upon granulocytic differentiation of myeloid leukemic cells and their responses to GM-CSF that are closely paralleled with tyrosyl phosphorylation of its receptor, and help in pointing to specific cell signaling molecules that are different in leukemic blasts from normal leukocytes.