Upregulation of p21 RAS levels in HL-60 cells during differentiation induction with DMSO, all-trans-retinoic acid and TPA

Intracellular Accumulation and Secretion of YKL-40 (CHI3L1) in the Course of DMSO-Induced HL-60 Cell Differentiation

YKL-40 (CHI3L1) is a matrix glycoprotein stored in human neutrophil-specific granules and released upon activation. While it is implicated in inflammation, cancer progression, and cell differentiation, its exact physiological role remains unclear. This study investigated the intracellular expression and secretion of YKL-40 by untreated and DMSO-treated HL-60 cells in association with surface expression of CD11b and CD66b throughout the differentiation process (up to 120 h). Secreted YKL-40 protein and mRNA levels of YKL-40, CD66b, and CD11b were measured by ELISA and quantitative RT-PCR, respectively. The intracellular YKL-40 and surface CD11b and CD66b expression were assessed by flow cytometry. A significant increase in CD11b expression confirmed DMSO-induced differentiation of HL-60 cells. Upon DMSO stimulation, YKL-40 mRNA expression increased in a time-dependent manner, unlike CD66b. The lack of CD66b (a granulocyte maturation and activation marker) on the surface of HL-60 cells might suggest that DMSO treatment did not induce full maturation or activation. The intracellular YKL-40 protein expression was increasing up to 96 h of DMSO treatment and then declined. YKL-40 secretion into the culture medium was detectable only at later time points (96 and 120 h), which was correlated with a decreased proliferation of DMSO-treated HL-60 cells. These findings suggest sequential changes in YKL-40 production and secretion during DMSO-induced differentiation of HL-60 cells and might contribute to a better understanding of YKL-40's involvement in both physiological processes and disease development, including multiple sclerosis.

Novel Insights into the Role of Kras in Myeloid Differentiation: Engaging with Wnt/β-Catenin Signaling

Cells of the HL-60 myeloid leukemia cell line can be differentiated into neutrophil-like cells by treatment with dimethyl sulfoxide (DMSO). The molecular mechanisms involved in this differentiation process, however, remain unclear. This review focuses on the differentiation of HL-60 cells. Although the Ras proteins, a group of small GTP-binding proteins, are ubiquitously expressed and highly homologous, each has specific molecular functions. Kras was shown to be essential for normal mouse development, whereas Hras and Nras are not. Kras knockout mice develop profound hematopoietic defects, indicating that Kras is required for hematopoiesis in adults. The Wnt/β-catenin signaling pathway plays a crucial role in regulating the homeostasis of hematopoietic cells. The protein β-catenin is a key player in the Wnt/β-catenin signaling pathway. A great deal of evidence shows that the Wnt/β-catenin signaling pathway is deregulated in malignant tumors, including hematological malignancies. Wild-type Kras acts as a tumor suppressor during DMSO-induced differentiation of HL-60 cells. Upon DMSO treatment, Kras translocates to the plasma membrane, and its activity is enhanced. Inhibition of Kras attenuates CD11b expression. DMSO also elevates levels of GSK3β phosphorylation, resulting in the release of unphosphorylated β-catenin from the β-catenin destruction complex and its accumulation in the cytoplasm. The accumulated β-catenin subsequently translocates into the nucleus. Inhibition of Kras attenuates Lef/Tcf-sensitive transcription activity. Thus, upon treatment of HL-60 cells with DMSO, wild-type Kras reacts with the Wnt/β-catenin pathway, thereby regulating the granulocytic differentiation of HL-60 cells. Wild-type Kras and the Wnt/β-catenin signaling pathway are activated sequentially, increasing the levels of expression of C/EBPα, C/EBPε, and granulocyte colony-stimulating factor (G-CSF) receptor.

Studying Neutrophil Function in vitro: Cell Models and Environmental Factors

Neutrophils are the most abundant immune cell type in the blood and constitute the first line of defense against invading pathogens. Despite their important role in many diseases, they are challenging to study due to their short life span and the inability to cryopreserve or expand them in vitro. Thus, research into neutrophils has to rely on cells freshly isolated from peripheral blood of human donors, introducing donor-dependent variation in the experimental data. To counteract these problems, researchers tried to develop adequate cell models, such as cell lines. For those functional studies that cannot rely on cell models, a standardization of protocols regarding neutrophil purification and culturing could be a solution. In this review, we provide an overview of the most commonly used models for neutrophil function (HL-60, PLB-985, NB4, Kasumi-1 and induced pluripotent stem cells). In addition, we describe the effects of glucose concentration, pH, oxygen tension and temperature on neutrophil function.

Kras promotes myeloid differentiation through Wnt/β-catenin signaling

Wild-type Kras, a small GTPase, inactivates Ras growth-promoting signaling. However, the role of Kras in differentiation of myeloid cells remains unclear. This study showed the involvement of Kras in a novel regulatory mechanism underlying the dimethyl sulfoxide (DMSO)-induced differentiation of human acute myeloid leukemia HL-60 cells. Kras was found to positively regulate DMSO-induced differentiation, with the activity of Kras increasing upon DMSO. Inhibition of Kras attenuated CD11b expression in differentiated HL-60 cells. GSK3β, an important component of Wnt signaling, was found to be a downstream signal of Kras. Phosphorylation of GSK3β was markedly enhanced by DMSO treatment. Moreover, inhibition of GSK3β enhanced CD11b expression and triggered the accumulation in the nucleus of β-catenin and Tcf in response to DMSO. Inhibitors of β-catenin-mediated pathways blocked CD11b expression, further indicating that β-catenin is involved in the differentiation of HL-60 cells. Elevated expression of C/EBPα and C/EBPɛ accompanied by the expression of granulocyte colony-stimulating factor (G-CSF) receptor was observed during differentiation. Taken together, these findings suggest that Kras engages in cross talk with the Wnt/β-catenin pathway upon DMSO treatment of HL-60 cells, thereby regulating the granulocytic differentiation of HL-60 cells. These results indicate that Kras acts as a tumor suppressor during the differentiation of myeloid cells.

Regulation of the cell cycle in response to inhibition of mitochondrial generated energy

Cell cycle control is regulated through the temporal action of both cyclin-dependent kinases and cyclin binding partners. Previously, we have demonstrated that low doses of oligomycin result in a cell cycle arrest of HL-60 cells in G(1) [S. Sweet, G. Singh, Accumulation of human promyelocytic leukemic (HL-60) cells at two energetic cell cycle checkpoints, Cancer Res. 55 (1995) 5164-5167]. In this study, we provide the molecular mechanisms for the observed G(1) arrest following mitochondrial ATPase inhibition. Protein expression of cyclin E and CDK2, the kinase activity of complexed cyclin E/CDK2, and protein expression of p16, p21, and p27 were all unaffected by oligomycin administration. While CDK4 levels were unchanged following oligomycin treatment, a dramatic reduction in cyclin D(1) was observed. Moreover, increased amounts of hypo-phosphorylated retinoblastoma protein (Rbp) and Rbp bound E2F were observed following mitochondrial ATP synthase inhibition. These data provide further evidence that surveillance of available energy occurs during G(1) and ATP deprivation results in cell cycle arrest via a reduction in cyclin D.

Expression level of inositol trisphosphate and inositol tetrakisphosphate receptors and their influence on Ca2+ release in permeabilized HL-60 and T15 cells

To try to further define the mechanism of action of the putative second messenger inositol 1,3,4,5-tetrakisphosphate (InsP4), we have studied its effects in permeabilized cells expressing different levels of inositol trisphosphate receptor (InsP3R) types I and III and of the GTPase-activating protein GAP1IP4BP. During the growth curve of human HL-60 cells and mouse T15 cells there was an increase in these proteins, which was further increased by differentiation (HL-60) and, marginally, by transformation (T15). T15 cells entering the stationary phase showed much lower concentrations of these proteins and expression was below detection in apoptotic HL-60 cells. Rasp21 showed a different pattern of expression. The ratios of InsP3R subtypes seem to affect the dose-response curve for inositol 2,4,5-trisphosphate Ins(2,4,5)P3. In permeabilized T15 cells the curve was approximately 5-fold to the right of that obtained using HL-60 cells. However, permeabilized untreated and differentiated HL-60 cells and T15 cells all showed a comparable synergistic effect of InsP4 on Ca2+ release stimulated by a concentration of Ins(2,4,5)P3, releasing approximately 20% of the Ins(1,4,5)P3 sensitive Ca2+ pool. The data indicate that under these conditions InsP4 is acting independently of cell type, of the ratio of inositol trisphosphate receptor subtypes, and of the concentration of GAP1IP4BP.

Factors involved in the cell density-dependent regulation of nuclear/cytoplasmic distribution of the 11.5-kDa Zn(2+)-binding protein (parathymosin-alpha) in rat hepatocytes

Although the 11.5 kDa Zn(2+)-binding protein (ZnBP, parathymosin-alpha) possesses a functional bipartite nuclear localization signal it was found in most tissues in the cytoplasm. The cultivation of freshly isolated rat hepatocytes for 24 hours under standard conditions was associated with an almost complete translocation of ZnBP from the cytoplasm to the nuclei. Here we demonstrate, that this translocation is negatively correlated with cell density. The translocation of ZnBP to the nucleus can be inhibited or abolished by inhibitors of protein synthesis (cycloheximide) or transcription (actinomycin D). Moreover, cycloheximide can induce a relocation of ZnBP to the cytoplasm when applied after the appearance of ZnBP in the nuclei. DMSO, an inhibitor of dedifferentiation of cultured hepatocytes, abolishes also the translocation of ZnBP into the nucleus. Thinly seeded cells keep their ZnBP in the cytoplasm if they are co-cultured with plasma membranes from Morris MH7777 hepatoma cells or antibodies against E-cadherin indicating the involvement of cell adhesion proteins. We have enriched a protein from the cytosol of fresh hepatocytes which inhibits the translocation of ZnBP, but not that of albumin-NLS into the nucleus in a permeabilized cell system. Such an activity could not be found in the cytoplasm of permanent cell lines which harbor ZnBP only in the nucleus. A model for the regulation of the nuclear import of ZnBP is proposed.

Oncogenic RAS genes impair erythroid differentiation of erythroleukaemia cells

RAS mutations occur frequently in acute myeloid leukaemia and myelodysplasia, suggesting a functional role for this oncogene in leukaemogenesis. We show here, for the first time, that both N-RAS and H-RAS can impair erythroid differentiation of erythroleukaemia cells induced with hexamethylene bisacetamide. Transformation by RAS allowed extended proliferation in the presence of inducer and also inhibited maturation as measured by impaired haemoglobinization and reduction in cell size. These data provide an interesting counterpoint to the effect of mutant RAS on monocytic cells, where it has a potentiating effect on differentiation and may indicate a causal link between the activation of RAS and erythroid lineage dysplasia in preleukaemia.

Differentiation of human trophoblast cells in vitro is inhibited by dimethylsulfoxide

Dimethyl sulfoxide (DMSO) exerts a number of biological effects, the most frequently cited being induction of cell differentiation. The compound also increases invasiveness and metastatic potential. In contrast to the many reports of DMSO-induced cell differentiation, we report here that DMSO inhibits the morphological differentiation of human cytotrophoblast cells to syncytiotrophoblast, as revealed by immunofluorescence staining for desmosomal protein and nuclei. Cytotrophoblast cells treated with DMSO under differentiation-inducing conditions remained mononucleated with intense desmosomals staining. The effect was dose dependent, with a maximal effect seen at 1.5% DMSO. Concentrations of < or = 0.5% had no effect and concentrations > 2% were cytotoxic. In addition to these morphological changes, DMSO inhibited secretion of human chorionic gonadotropin in a dose-dependent manner. At a concentration of 1.5%, DMSO inhibited secretion by 70%. If cytotrophoblast cells were cultured in the presence of DMSO and then switched to DMSO-free medium, they proceeded to differentiate normally. While the precise mechanism of action remains unknown, judicious use of DMSO may be a useful tool for studying and manipulating the differentiation of human trophoblast cells in vitro. The findings also indicate that care should be used in interpreting results obtained using DMSO as a carrier in drug and inhibitor studies.

Changes in the levels of glycerophosphoinositols during differentiation of hepatic and neuronal cells

Glycerophosphoinositols are metabolites formed by a phosholipase A2 and a lysolipase specifically acting on membrane phosphoinositol lipids. High levels of these compounds characterize epithelial cells and fibroblasts transformed by ras and other cellular oncogenes. Here we have analyzed the glycerophosphoinositol levels in cells that are considered models of cell differentiation. Using rat hepatocytes at different stages of liver development we have shown that the glycerophosphoinositol basal levels of fetal cells were up to fourfold higher than in adult hepatocytes. No changes in glycerophosphoinositol were observed in regenerating rat liver, a model of differentiated cells proliferating in a synchronous manner, where only glycerophosphoinositol 4-phosphate increased by 80%. Similarly to fetal hepatocytes, a modest but significant increase (30%) in the levels of glycerophosphoinositols was observed in undifferentiated NG-108-15 cells as compared to the same cells induced to differentiate by cAMP. In a different neuronal cell line, PC12 cells, increased glycerophosphoinositol levels characterized the differentiated cells. Based on these observations we suggest that high glycerophosphoinositol levels characterize cellular phenomena associated with the activation of ras/mitogen-activated protein kinase pathways.