5,5′-dimethyloxazolidine-2,4-dione is a strong inducer of differentiation of human promyelocytic leukemia (HL-60) cells

5,5′-Dimethyloxazolidine-2,4-dione (DMO), a weak non-metabolizable acid, is commonly utilized for determining intracellular pH. In these studies, DMO was tested as an inducer of differentiation on the basis that its uptake and subsequent dissociation might transiently raise intracellular pH and activate ion-fluxes critical for triggering maturation. After 5 days of exposure to 40 mM DMO, >60% of HL-60 cells displayed phenotypic and functional changes characteristic of mature granulocytes. As with other inducers of HL-60 cell differentiation, commitment to differentiation required culture in the presence of DMO for more than 24 h, indicating that if transient effects on pH or ion-fluxes occurred, they were not sufficient to trigger this process.DMO was either weak or inactive as an inducer of murine erythroleukemia cell (FLC) differentiation. Although other weak acids and bases triggered differentiation of both HL-60 cells and FLC, the spectrum of response differed markedly between the two lines. These results suggest that: (1) a number of common buffering agents have the potential to alter cell phenotype, and (2) their effects must be evaluated for each individual cell type.     

α-Dystrobrevin distribution and association with other proteins in human promyelocytic NB4 cells treated for granulocytic differentiation

Dystrobrevins (DBs) bind directly to dystrophin and are prominent components of the dystrophin-associated protein complex (DAPC) that links the cytoskeleton to the extracellular matrix. They are involved in brain development, synapse formation and plasticity, as well as water and ion homeostasis. However, the role of DB in non-muscular cells is not clear. In this study, we show that different α-dystrobrevin isoforms are present in promyelocytic leukemia (NB4) cells. Only the biggest α-dystrobrevin isoform (DB-α), which can be important for its function, was expressed in the membrane fraction of NB4 cells; the other α-DB isoforms were found in the hydrophilic cell fractions. Employing the immunoprecipitation and mass spectrometry, we identified novel α-DB-interacting proteins involved in cytoskeleton reorganization (actin, tropomyosin, gelsolin, tubulin) and signal transduction process (stathmin, prohibitin, RIBA) during proliferation and differentiation of NB4 cells. Our results suggest that α-DB isoforms play a central role in cytoskeleton reorganization via their multiple interactions with actin and actin-associating proteins and may participate in signal transduction process during NB4 cell granulocytic differentiation via directly and non directly associated proteins.     

Phospholipases Dα and δ are involved in local and systemic wound responses of cotton (G. hirsutum)

Phospholipases D (PLDs) catabolize structural phospholipids to produce phosphatidic acid (PtdOH), a lipid playing central role in signalling pathways in animal, yeast and plant cells. In animal cells two PLD genes have been studied while in model plant Arabidopsis twelve genes exist, classified in six classes (α-ζ). This underlines the role of these enzymes in plant responses to environmental stresses. However, information concerning the PLD involvement in the widely cultivated and economically important cotton plant responses is very limited. The aim of this report was to study the activity of conventional cotton PLD and its participation in plant responses to mechanical wounding, which resembles both biotic and abiotic stresses. PLDα activity was identified and further characterized by transphosphatidylation reaction. Upon wounding, cotton leaf responses consist of an acute in vitro increase of PLDα activity in both wounded and systemic tissue. However, determination of the in vivo PtdOH levels under the same wounding conditions revealed a rapid PtdOH formation only in wounded leaves and a late response of a PtdOH increase in both tissues. Εxpression analysis of PLDα and PLDδ isoforms showed mRNA accumulation of both isoforms in the wounded tissue, but only PLDδ exerts a high and sustainable expression in systemic leaves, indicating that this isoform is mainly responsible for the systemic wound-induced PtdOH production. Therefore, our data suggest that PLDα and PLDδ isoforms are involved in different steps in cotton wound signalling.     

Protein phosphatase type 2Cα and 2Cβ are involved in fatty acid-induced apoptosis of neuronal and endothelial cells

Unsaturated fatty acids with special structural features have been shown to activate serine/threonine protein phosphatase type 2C (PP2C) isoforms α and β at physiological Mg²⁺-concentrations in vitro. These compounds also induce apoptosis in neuronal and endothelial cells. In this study we further analysed this striking correlation and tried to elucidate whether or not there is a causative relationship between activation of PP2C and induction of apoptosis. We employed RNA interference to simultaneously knock down PP2Cα and PP2Cβ in SH-SY5Y cells or HUVECs, respectively. This downregulation was transient. Treatment of SH-SY5Y cells or HUVECs with oleic acid (18:1,cis-Δ⁹) caused apoptosis in a time- and concentration-dependent manner. In both cases, cells with reduced PP2C-levels were less susceptible to oleic acid-induced cell damage. In conclusion, our results demonstrate that PP2C activation by unsaturated fatty acids actually causes apoptosis in neuronal and endothelial cells.     

Up-regulation of p21 and TNF-α is mediated in lycorine-induced death of HL-60 cells

Background  

Leukemia is one of the most life-threatening cancers today, and acute promyelogenous leukemia (APL) is a common type of leukemia. Many natural compounds have already been found to exhibit significant anti-tumor effects. Lycorine, a natural alkaloid extracted from Amaryllidaceae, exhibited anti-leukemia effects in vitro and in vivo. The survival rate of HL-60 cells exposed to lycorine was decreased, cell growth was slowed down, and cell regeneration potential was inhibited. HL-60 cells exhibited typical apoptotic characteristic. Lycorine can suppress leukemia growth and reduce cell survival and inducing apoptosis of tumor cells. The purpose of this work is to elucidate the mechanism by which lycorine induces APL cells.     

Dexamethasone-mediated regulation of death and differentiation of muscle cells. Is hydrogen peroxide involved in the process?

The hypothetical involvement of H2O2 in dexamethasone-mediated regulation of muscle cell differentiation and elimination was studied. Rat L6 myoblasts and mouse C2C12 satellite cells were chosen for acute (24 h) and chronic (5 or 10 day) experiments. Mitogenicity and anabolism were both affected by H2O2. Micromolar concentrations of H2O2 inhibited DNA while stimulating protein synthesis. At the millimolar level, H2O2 led to cell death by apoptosis.Synthetic glucocorticoi - dexamethasone (Dex) was shown to effect muscle cell fate similarly to H2O2. Chronic treatment with H2O2 or Dex dose-dependently accelerated either the formation of myotubes or cell elimination. Dex-induced cell death slightly differed from classical apoptosis and was featured by the symptoms of cell senescence such as extensive cytoplasm vacuolisation, accumulation of inclusion-bodies and lack of low molecular weight oligonucleosomal DNA fragmentation but chromatin condensation. Antioxidants (sodium ascorbate, N-acetyl-L-cysteine, catalase) abrogated Dex-dependent cell death. We conclude that H2O2 directly influences myogenesis and muscle cell elimination. Moreover, H2O2 can be considered as the potent mediator of glucocorticoid-dependent effects on muscle cells.     

Role of C/EBPβ-LAP and C/EBPβ-LIP in early adipogenic differentiation of human white adipose-derived progenitors and at later stages in immature adipocytes

We investigated the role of the major isoforms of CCAAT enhancer binding protein β (C/EBPβ), C/EBPβ-LAP and C/EBPβ-LIP, in adipogenesis of human white adipose-derived stromal/progenitor cells (ASC). C/EBPβ gene expression was transiently induced early in adipogenesis. At later stages, in immature adipocytes, the C/EBPβ mRNA and protein levels declined. The C/EBPβ-LIP protein steady-state level decreased considerably stronger than the C/EBPβ-LAP level and the C/EBPβ-LIP half-life was significantly shorter than the C/EBPβ-LAP half-life. The turn-over of both C/EBPβ-isoforms was regulated by ubiquitin/proteasome-dependent degradation. These data suggest that the protein stability of the C/EBPβ-isoforms is differentially regulated in the course of adipogenesis and in immature adipocytes. Constitutive overexpression of C/EBPβ-LIP had antiadipogenic activity in human ASC. C/EBPβ-LAP, which promotes adipogenesis in mouse 3T3-L1 preadipocytes by directly activating expression of the adipogenic keyregulator PPARγ2, induced the expression of PPARγ2 and of the adipocyte differentiation gene product FABP4 in confluent ASC in the absence of adipogenic hormones. At later stages after hormone cocktail-induced adipogenesis, in immature adipocytes, constitutive overexpression of C/EBPβ-LAP led to reduced expression of PPARγ2 and FABP4, C/EBPα expression was downregulated and the expression of the adipocyte differentiation gene products adiponectin and leptin was impaired. These findings suggest that constitutive overexpression of C/EBPβ-LAP induces adipogenesis in human ASC and negatively regulates the expression of adipogenic regulators and certain adipocyte differentiation gene products in immature adipocytes. We conclude the regulation of both C/EBPβ gene expression and C/EBPβ-LIP and C/EBPβ-LAP protein turn-over plays an important role for the expression of adipogenic regulators and/or adipocyte differentiation genes in early adipogenic differentiation of human ASC and at later stages in human immature adipocytes.