Extracellular signal-regulated kinase/90-KDA ribosomal S6 kinase/nuclear factor-kappa B pathway mediates phorbol 12-myristate 13-acetate-induced megakaryocytic differentiation of K562 cells

Bioinformatics of Differentially Expressed Genes in Phorbol 12-Myristate 13-Acetate-Induced Megakaryocytic Differentiation of K562 Cells by Microarray Analysis

Megakaryocytes are large hematopoietic cells present in the bone marrow cavity, comprising less than 0.1% of all bone marrow cells. Despite their small number, megakaryocytes play important roles in blood coagulation, inflammatory responses, and platelet production. However, little is known about changes in gene expression during megakaryocyte maturation. Here we identified the genes whose expression was changed during K562 leukemia cell differentiation into megakaryocytes using an Affymetrix GeneChip microarray to determine the multifunctionality of megakaryocytes. K562 cells were differentiated into mature megakaryocytes by treatment for 7 days with phorbol 12-myristate 13-acetate, and a microarray was performed using RNA obtained from both types of cells. The expression of 44,629 genes was compared between K562 cells and mature megakaryocytes, and 954 differentially expressed genes (DEGs) were selected based on a p-value < 0.05 and a fold change >2. The DEGs was further functionally classified using five major megakaryocyte function-associated clusters—inflammatory response, angiogenesis, cell migration, extracellular matrix, and secretion. Furthermore, interaction analysis based on the STRING database was used to generate interactions between the proteins translated from the DEGs. This study provides information on the bioinformatics of the DEGs in mature megakaryocytes after K562 cell differentiation.

Replication of Dengue Virus in K562-Megakaryocytes Induces Suppression in the Accumulation of Reactive Oxygen Species

Dengue virus can infect human megakaryocytes leading to decreased platelet biogenesis. In this article, we report a study of Dengue replication in human K562 cells undergoing PMA-induced differentiation into megakaryocytes. PMA-induced differentiation in these cells recapitulates steps of megakaryopoiesis including gene activation, expression of CD41/61 and CD61 platelet surface markers and accumulation of intracellular reactive oxygen species (ROS). Our results show differentiating megakaryocyte cells to support higher viral replication without any apparent increase in virus entry. Further, Dengue replication suppresses the accumulation of ROS in differentiating cells, probably by only augmenting the activity of the transcription factor NFE2L2 without influencing the expression of the coding gene. Interestingly pharmacological modulation of NFE2L2 activity showed a simultaneous but opposite effect on intracellular ROS and virus replication suggesting the former to have an inhibitory effect on the later. Also cells that differentiated while supporting intracellular virus replication showed reduced level of surface markers compared to uninfected differentiated cells.

Cabozantinib promotes erythroid differentiation in K562 erythroleukemia cells through global changes in gene expression and JNK activation

Cabozantinib is a potent tyrosine kinase inhibitor with multiple targets including MET, VEGFR2, RET, KIT, and FLT3. Cabozantinib is widely used for the treatment of medullary thyroid cancer and renal cell carcinoma. We recently suggested cabozantinib as a potential therapeutic alternative for acute myeloid leukemia (AML) patients with FLT3-internal tandem duplication (FLT3-ITD). Here, we report that cabozantinib can promote differentiation in erythroid leukemia cells. We found that K562 erythroid leukemia cells treated with 1 μM cabozantinib for 72 h underwent erythroid lineage differentiation. Transcriptomic analysis revealed that various pathways associated with heme biosynthesis, hemoglobin production, and GATA1 targets were upregulated, whereas cell survival pathways were downregulated. Further examination revealed that cabozantinib-induced erythroid differentiation is at least in part regulated by JNK activation and phosphorylation. Levels of phosphorylated BCR-ABL, AKT, STAT5, ERK, and p38 also decreased following cabozantinib treatment. Therefore, we indicate that cabozantinib has dual functions. First, it induces K562 cell differentiation toward the erythroid lineage by upregulating heme biosynthesis, globin synthesis, and erythroid-associated reactions. Second, cabozantinib inhibits K562 cell proliferation by inhibiting the phosphorylation of BCR-ABL and the downstream MAPK, PI3K-AKT, and JAK-STAT signaling pathways.

Analyzing Signaling Pathways Using Antibody Arrays

Cell signaling is comprised of complex networks that regulate homeostasis and human diseases. The analyses of such pathways would improve our understanding of disease pathology and direct drug development. However, it remains a great challenge to study pathways using traditional methods. We developed a high-throughput sandwich-based antibody array technology for the simultaneous detection of multiple targets, capable of identifying the relative expression levels or phosphorylation levels of major signaling pathway proteins. This array-based system features a nitrocellulose membrane or glass slide solid support, spotted with antibodies targeting key proteins of major signaling pathways, including RTK, EGFR, MAPK, AKT, apoptosis, TGFb, JAK/STAT, NFkB, and insulin receptor pathways. We employed these antibody arrays to investigate how the anti-cancer drugs, camptothecin and phorbol 12-myristate 13-acetate (PMA), alter protein phosphorylation in Jurkat and HeLa cells, respectively. Our array data suggest that camptothecin treatment induced DNA double-strand breaks in Jurkat cells and activated the DNA damage pathways ATM and Chk2, which then further induced apoptosis through caspase 3 and PARP. PMA induced the MAPK pathway in HeLa cells through the activation of ERK, CREB, and RSK1. These array results are consistent with previous studies using traditional methods and were validated with Western blotting. Our studies demonstrate that pathway antibody arrays provide a rapid, efficient, and multiplexed approach for profiling phosphorylated proteins.

Natural Coumarin Derivative Esculetin Regulates Platelet Activation via Modulating NF-κB Signaling in Cyclic Nucleotide-Independent Manner

Esculetin, a natural coumarin derivative, shows exciting biological activities in a variety of cell and animal models. Our recent study demonstrated that esculetin exhibits antiplatelet effects by obstructing the phospholipase C γ2/protein kinase C cascade, hydroxyl radical formation, and Akt activation. In this study, we further examined the involvement of cyclic 3′-5′adenosine monophosphate/, vasodilator-stimulated phosphoprotein (VASP), integrin αIIbβ3, and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), since cyclic nucleotides reduce the phosphorylation of VASP and activate NF-κB, subsequently inducing αIIbβ3 activation that significantly involves the platelet inhibitory pathways. We found that esculetin (50 and 80 µM) did not significantly affect fibrinogen-induced aggregation of elastase-treated platelets; however, it markedly blocked integrin αIIbβ3 activation by interrupting the binding of fluorescein isothiocyanate-labeled PAC-1. In addition, neither ODQ nor SQ22536 significantly reversed esculetin-mediated antiplatelet activity stimulated by collagen. Nitroglycerin and prostaglandin E1 significantly increased VASP phosphorylation, but esculetin had no effect in this reaction, the values being almost identical with those of normal platelets. Furthermore, esculetin, at its maximum concentration of 80 μM significantly reduced the phosphorylation of IκBα and p65 and reversed IκBα degradation in collagen-induced platelets. These results suggest that the NF-κB-dependent αIIbβ3 inhibition of esculetin might represent a novel feedback inhibitory mechanism to regulate platelet functions.

De novo UBE2A mutations are recurrently acquired during chronic myeloid leukemia progression and interfere with myeloid differentiation pathways

Despite the advent of tyrosine kinase inhibitors, a proportion of chronic myeloid leukemia patients in chronic phase fail to respond to imatinib or to second-generation inhibitors and progress to blast crisis. Until now, improvements in the understanding of the molecular mechanisms responsible for chronic myeloid leukemia transformation from chronic phase to the aggressive blast crisis remain limited. Here we present a large parallel sequencing analysis of 10 blast crisis samples and of the corresponding autologous chronic phase controls that reveals, for the first time, recurrent mutations affecting the ubiquitin-conjugating enzyme E2A gene (UBE2A, formerly RAD6A). Additional analyses on a cohort of 24 blast crisis, 41 chronic phase as well as 40 acute myeloid leukemia and 38 atypical chronic myeloid leukemia patients at onset confirmed that UBE2A mutations are specifically acquired during chronic myeloid leukemia progression, with a frequency of 16.7% in advanced phases. In vitro studies show that the mutations here described cause a decrease in UBE2A activity, leading to an impairment of myeloid differentiation in chronic myeloid leukemia cells.

Nuclear factor-κB regulates expression of platelet phospholipase C-β2 (PLCB2)

Phospholipase C (PLC)-β2 (gene PLCB2) is a critical regulator of platelet responses upon activation. Mechanisms regulating of PLC-β2 expression in platelets/MKs are unknown. Our studies in a patient with platelet PLC-β2 deficiency revealed the PLCB2 coding sequence to be normal and decreased platelet PLC-β2 mRNA, suggesting a defect in transcriptional regulation. PLCB2 5'- upstream region of the patient revealed a heterozygous 13 bp deletion (-1645/-1633 bp) encompassing a consensus sequence for nuclear factor-κB (NF-κB). This was subsequently detected in three of 50 healthy subjects. To understand the mechanisms regulating PLC-β2, we studied the effect of this variation in the PLCB2. Gel-shift studies using nuclear extracts from human erythroleukaemia (HEL) cells or recombinant p65 showed NF-κB binding to oligonucleotide with NF-κB site; in luciferase reporter studies its deletion reduced PLCB2 promoter activity. PLCB2 expression was decreased by siRNA knockdown of NF-κB p65 subunit and increased by p65 overexpression. By immunoblotting platelet PLC-β2 in 17 healthy subjects correlated with p65 (r=0.76, p=0.0005). These studies provide the first evidence that NF-κB regulates MK/platelet PLC-β2 expression. This interaction is important because of the major role of PLC-β2 in platelet activation and of NF-κB in processes, including inflammation and atherosclerosis, where both are intimately involved.

Nuclear Translocation of p65 is Controlled by Sec6 via the Degradation of IκBα

Nuclear factor-κB (NF-κB) is an inducible transcription factor that mediates immune and inflammatory responses. NF-κB pathways are also involved in cell adhesion, differentiation, proliferation, autophagy, senescence, and protection against apoptosis. The deregulation of NF-κB activity is found in a number of disease states, including cancer, arthritis, chronic inflammation, asthma, neurodegenerative diseases, and heart disease. The 90 kDa ribosomal S6 kinase (p90RSK) family, which is serine/threonine kinases, is phosphorylated by extracellular signal-regulated kinase1/2 (ERK1/2) and is related to NF-κB pathways. Our previous studies revealed that Sec6, a component of the exocyst complex, plays specific roles in cell-cell adhesion and cell cycle arrest. However, the mechanism by which Sec6 regulates the NF-κB signaling pathway is unknown. We demonstrated that Sec6 knockdown inhibited the degradation of IκBα and delayed the nucleus-cytoplasm translocation of p65 in HeLa cells transfected with Sec6 siRNAs after treatment with tumor necrosis factor alpha (TNF-α). Furthermore, the binding of p65 and cAMP response element binding protein (CREB) binding protein (CBP) or p300 decreased and NF-κB related genes which were inhibitors of NF-κB alpha (IκBα), A20, B cell lymphoma protein 2 (Bcl-2), and monocyte chemoattractant protein-1 (MCP-1) were low in cells transfected with Sec6 siRNAs in response to TNF-α stimulation. Sec6 knockdown decreased the expression of p90RSKs and the phosphorylation of ERK or p90RSK1 at Ser380 or IκBα at Ser32. The present study suggests that Sec6 regulates NF-κB transcriptional activity via the control of the phosphorylation of IκBα, p90RSK1, and ERK.

Hemin induces mitophagy in a leukemic erythroblast cell line

BACKGROUND INFORMATION

In eukaryotic cells, autophagy is considered a lysosomal catabolic process which participates in the degradation of intracellular components in a vacuolar structure termed autolysosome. This pathway plays a significant role in the erythropoiesis process, contributing to the clearance of some organelles (such as mitochondria) that are not necessary in the mature red blood cells. Nevertheless, the role of autophagy in erythrocyte maturation has not been fully established.

RESULTS

Here, we have demonstrated that hemin (a physiological erythroid maturation stimulator) is able to induce the expression of critical autophagic genes (i.e., Map1a1b (LC3), Beclin-1 gen, Atg5) in an erythroleukemia cell type. We have also shown that hemin increased the size of autophagic vacuoles which were labelled with LC3 and the degradative lysosomal marker dye quenched-bovine serum albumin. In addition, we have determined by Western blot a rise in the lipidated form of the autophagic protein LC3 (i.e., LC3-II) upon hemin treatment. Moreover, we provide evidence that hemin induces mitochondrial membrane depolarisation and that mitochondria sequestration by autophagy requires the active form of the NIX protein.

CONCLUSIONS

We have found that the physiological erythroid maturation stimulator hemin is able to induce mitophagy in K562 cells, and that the autophagy adaptor NIX is necessary for mitophagy progression. K562 cells have been used as a relevant model to determine the possible therapeutic role of new differentiating compounds.

SIGNIFICANCE

It has been proposed that autophagy induction is a feasible new therapeutic key in fighting cancer. Our results suggest that hemin is favoring erythroid maturation by inducing an autophagic response in K562 cells, being a possible therapeutic candidate that may help in the chronic myelogenous leukemia (CML) treatment.

ERK2-Pyruvate Kinase Axis Permits Phorbol 12-Myristate 13-Acetate-induced Megakaryocyte Differentiation in K562 Cells

Metabolic changes that contribute to differentiation are not well understood. Overwhelming evidence shows the critical role of glycolytic enzyme pyruvate kinase (PK) in directing metabolism of proliferating cells. However, its role in metabolism of differentiating cells is unclear. Here we studied the role of PK in phorbol 12-myristate 13-acetate (PMA)-induced megakaryocytic differentiation in human leukemia K562 cells. We observed that PMA treatment decreased cancer-type anabolic metabolism but increased ATP production, along with up-regulated expression of two PK isoforms (PKM2 and PKR) in an ERK2-dependent manner. Interestingly, silencing of PK (PKM2 and PKR) inhibited PMA-induced megakaryocytic differentiation, as revealed by decreased expression of megakaryocytic differentiation marker CD61 and cell cycle behavior. Further, PMA-induced ATP production reduced greatly upon PK silencing, suggesting that PK is required for ATP synthesis. In addition to metabolic effects, PMA treatment also translocated PKM2, but not PKR, into nucleus. ERK1/2 knockdowns independently and together suggested the role of ERK2 in the up-regulation of both the isoforms of PK, proposing a role of ERK2-PK isoform axis in differentiation. Collectively, our findings unravel ERK2 guided PK-dependent metabolic changes during PMA induction, which are important in megakaryocytic differentiation.

Regulation of STIM1/Orai1-dependent Ca2+ signalling in platelets

Platelet secretion and aggregation as well as thrombus formation of blood platelets critically depend on increase of cytosolic Ca2+ concentration ([Ca2+]i) mainly resulting from intracellular Ca2+ release followed by store operated Ca2+ entry (SOCE) through Ca2+ release activated channels (CRAC). SOCE is in part accomplished by the pore forming unit Orai and its regulator stromal interaction molecule (STIM). Orai1 and STIM1 transcription is stimulated by NF-κB (nuclear factor kappa B). Serum- and glucocorticoid-inducible kinase 1 (SGK1) up-regulates NF-κB-activity in megakaryocytes and thus Orai1-expression and SOCE in platelets. SGK1 is thus a powerful regulator of platelet Ca2+-signalling and thrombus formation and presumably participates in the regulation of platelet activation by a variety of hormones as well as clinical conditions (e.g. type 2 diabetes or metabolic syndrome) associated with platelet hyperaggregability and increased risk of thromboocclusive events. SOCE in platelets is further regulated by scaffolding protein Homer and chaperone protein cyclophilin A (CyPA). Additional potential regulators of Orai1/STIM1 and thus SOCE in platelets include AMP activated kinase (AMPK), protein kinase A (PKA), reactive oxygen species, lipid rafts, pH and mitochondrial Ca2+ buffering. Future studies are required defining the significance of those mechanisms for platelet Orai1 abundance and function, for SOCE into platelets and for platelet function in cardiovascular diseases.

Effects of radiation on the maturation of megakaryocytes

Megakaryocytes are generated by the differentiation of megakaryocytic progenitors; however, little information has been reported regarding how ionizing radiation affects the differentiation pathway and cellular responses. Human leukemia K562 cells have been used as a model to study megakaryocytic differentiation. In the present study, to investigate the effects of radiation on phorbol 12-myristate 13-acetate (PMA)-induced megakaryocytic differentiation of K562 cells, the cellular processes responsible for the expression of CD41 antigen (GPIIb/IIIa), which is reported to be expressed early in megakaryocyte maturation, were analyzed. The expression of CD41 antigens was significantly increased 72 h after treatment with both 4 Gy X-irradiation and PMA. In this fraction, two populations, CD41(low) and CD41(high) cells, were detected by flow cytometry. The CD41(high) cells sustained intracellular ROS at the initial level for up to 72 h, but CD41(low) cells had reduced ROS by 48 h. The maximum suppressive effect on CD41 expression was observed when N-acetyl cysteine, which is known to act as a ROS scavenger, was administered 48 h after PMA stimulation. When K562 cells were pretreated with mitogen-activated protein kinase (MAPK) pathway inhibitors, an ERK1/2 inhibitor and a p38 MAPK inhibitor, followed by X-irradiation and PMA stimulation, the reactivity profiles of both inhibitors showed the involvement of MAPK pathway. There is a possibility that the K562 cell population contains at least two types of radiosensitive megakaryocytic progenitors with respect to ROS production mechanisms, and intracellular ROS levels determine the extent of CD41 expression.

The serum- and glucocorticoid-inducible kinase 1 (SGK1) influences platelet calcium signaling and function by regulation of Orai1 expression in megakaryocytes

Platelets are activated on increase of cytosolic Ca2+ activity ([Ca2+]i), accomplished by store-operated Ca2+ entry (SOCE) involving the pore-forming ion channel subunit Orai1. Here, we show, for the first time, that the serum- and glucocorticoid-inducible kinase 1 (SGK1) is expressed in platelets and megakaryocytes. SOCE and agonist-induced [Ca2+]i increase are significantly blunted in platelets from SGK1 knockout mice (sgk1−/−). Similarly, Ca2+-dependent degranulation, integrin αIIbβ3 activation, phosphatidylserine exposure, aggregation, and in vitro thrombus formation were significantly impaired in sgk1−/− platelets, whereas tail bleeding time was not significantly enhanced. Platelet and megakaryocyte Orai1 transcript levels and membrane protein abundance were significantly reduced in sgk1−/− mice. In human megakaryoblastic cells (MEG-01), transfection with constitutively active S422DSGK1 but not with inactive K127NSGK1 significantly enhanced Orai1 expression and SOCE, while effects reversed by the SGK1 inhibitor GSK650394 (1μM). Transfection of MEG-01 cells with S422DSGK1 significantly increased phosphorylation of IκB kinase α/β and IκBα resulting in nuclear translocation of NF-κB subunit p65. Treatment of S422DSGK1-transfected MEG-01 cells with the IκB kinase inhibitor BMS-345541 (10μM) abolished SGK1-induced increase of Orai1 expression and SOCE. The present observations unravel SGK1 as novel regulator of platelet function, effective at least in part by NF-κB–dependent transcriptional up-regulation of Orai1 in megakaryocytes and increasing platelet SOCE.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) impairs the regulation of apoptosis in megakaryocytes by activating NF-κB: a proteomic study

We previously showed that the Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) and its receptor VPAC1 are negative regulators of megakaryopoiesis and platelet function, but their downstream signaling pathway that inhibits this process still remained unknown. A combined proteomic, transcriptomic, and bioinformatic approach was here used to elucidate the molecular mechanisms underlying PACAP signaling via VPAC1 in megakaryocytes. Two-dimensional difference gel electrophoresis and tandem MS were applied to detect differentially expressed proteins in megakaryocytic CHRF cells stimulated with PACAP. The majority of the 120 proteins modulated by PACAP belong to the class of "cell cycle and apoptosis" proteins. The up- or down-regulated expression of some proteins was confirmed by immunoblot and immunohistochemical analysis. A meta-analysis of our data and 12 other published studies was performed to evaluate signaling pathways involved in different cellular models of PACAP response. From 2384 differentially expressed genes/proteins, 83 were modulated by PACAP in at least three independent studies and Ingenuity Pathway Analysis further identified apoptosis as the highest scored network with NF-κB as a key-player. PACAP inhibited serum depletion-induced apoptosis of CHRF cells via VPAC1 stimulation. In addition, PACAP switched on NF-κB dependent gene expression since higher nuclear levels of the active NF-κB p50/p65 heterodimer were found in CHRF cells treated with PACAP. Finally, a quantitative real time PCR apoptosis array was used to study RNA from in vitro differentiated megakaryocytes from a PACAP overexpressing patient, leading to the identification of 15 apoptotic genes with a 4-fold change in expression and Ingenuity Pathway Analysis again revealed NF-κB as the central player. In conclusion, our findings suggest that PACAP interferes with the regulation of apoptosis in megakaryocytes, probably via stimulation of the NF-κB pathway.

Small Rab GTPase Rab7b promotes megakaryocytic differentiation by enhancing IL-6 production and STAT3-GATA-1 association

Induction of the differentiation of human leukemia cells is a useful strategy in treatment of human leukemia. However, the molecular mechanisms involved in leukemia cell differentiation have not been fully elucidated. Interleukin 6 (IL-6) is a pleiotropic cytokine acting on a variety of cell types, and plays important roles in hematopoiesis. GATA binding protein 1 (GATA-1) is an important transcription factor involved in either megakaryocytic or erythrocytic differentiation. Herein we report that Rab7b, a late endosome/lysosome-localized myeloid small GTPase, promotes phorbol-12-myristate-13-acetate (PMA)-induced megakaryocytic differentiation by increasing nuclear factor κB (NF-κB)-dependent IL-6 production and subsequently enhancing the association of activated signal transducer and activator of transcription 3 (STAT3) with GATA-1. By using PMA-induced megakaryocytic differentiation of leukemia cells as a model, we investigated the roles of Rab7b in megakaryocytic differentiation. We find that Rab7b can potentiate PMA-induced upregulation of megakaryocytic markers, production of IL-6, and activation of NF-κB. Inhibitor of NF-κB and neutralizing antibodies for IL-6 or the IL-6 signaling receptor gp130 can block the effects of Rab7b in megakaryocytic differentiation. In Rab7b-silenced cells, PMA-induced activation of NF-κB, IL-6 production, and megakaryocytic differentiation are impaired. Furthermore, we demonstrate that IL-6-induced activation of STAT3 and the subsequent association of STAT3 with GATA-1 may contribute to PMA-induced and Rab7b-mediated transcriptional upregulation of megakaryocytic differentiation markers. Therefore, our data suggest that Rab7b may play important roles in megakaryopoiesis by activating NF-κB and promoting IL-6 production. Our study also indicates that the IL-6-induced association of STAT3 with GATA-1 may regulate megakaryocytic differentiation.

Induction of erythroid differentiation in human erythroleukemia cells by depletion of malic enzyme 2

Malic enzyme 2 (ME2) is a mitochondrial enzyme that catalyzes the conversion of malate to pyruvate and CO2 and uses NAD as a cofactor. Higher expression of this enzyme correlates with the degree of cell de-differentiation. We found that ME2 is expressed in K562 erythroleukemia cells, in which a number of agents have been found to induce differentiation either along the erythroid or the myeloid lineage. We found that knockdown of ME2 led to diminished proliferation of tumor cells and increased apoptosis in vitro. These findings were accompanied by differentiation of K562 cells along the erythroid lineage, as confirmed by staining for glycophorin A and hemoglobin production. ME2 knockdown also totally abolished growth of K562 cells in nude mice. Increased ROS levels, likely reflecting increased mitochondrial production, and a decreased NADPH/NADP+ ratio were noted but use of a free radical scavenger to decrease inhibition of ROS levels did not reverse the differentiation or apoptotic phenotype, suggesting that ROS production is not causally involved in the resultant phenotype. As might be expected, depletion of ME2 induced an increase in the NAD+/NADH ratio and ATP levels fell significantly. Inhibition of the malate-aspartate shuttle was insufficient to induce K562 differentiation. We also examined several intracellular signaling pathways and expression of transcription factors and intermediate filament proteins whose expression is known to be modulated during erythroid differentiation in K562 cells. We found that silencing of ME2 leads to phospho-ERK1/2 inhibition, phospho-AKT activation, increased GATA-1 expression and diminished vimentin expression. Metabolomic analysis, conducted to gain insight into intermediary metabolic pathways that ME2 knockdown might affect, showed that ME2 depletion resulted in high orotate levels, suggesting potential impairment of pyrimidine metabolism. Collectively our data point to ME2 as a potentially novel metabolic target for leukemia therapy.

Thrombin and collagen induce a feedback inhibitory signaling pathway in platelets involving dissociation of the catalytic subunit of protein kinase A from an NFkappaB-IkappaB complex

Protein kinase A (PKA) activation by cAMP phosphorylates multiple target proteins in numerous platelet inhibitory pathways that have a very important role in maintaining circulating platelets in a resting state. Here we show that in thrombin- and collagen-stimulated platelets, PKA is activated by cAMP-independent mechanisms involving dissociation of the catalytic subunit of PKA (PKAc) from an NFkappaB-IkappaBalpha-PKAc complex. We demonstrate mRNA and protein expression for most of the NFkappaB family members in platelets. From resting platelets, PKAc was co-immunoprecipitated with IkappaBalpha, and conversely, IkappaBalpha was also co-immunoprecipitated with PKAc. This interaction was significantly reduced in thrombin- and collagen-stimulated platelets. Stimulation of platelets with thrombin- or collagen-activated IKK, at least partly by PI3 kinase-dependent pathways, leading to phosphorylation of IkappaBalpha, disruption of an IkappaBalpha-PKAc complex, and release of free, active PKAc, which phosphorylated VASP and other PKA substrates. IKK inhibitor inhibited thrombin-stimulated IkBalpha phosphorylation, PKA-IkBalpha dissociation, and VASP phosphorylation, and potentiated integrin alphaIIbbeta3 activation and the early phase of platelet aggregation. We conclude that thrombin and collagen not only cause platelet activation but also appear to fine-tune this response by initiating downstream NFkappaB-dependent PKAc activation, as a novel feedback inhibitory signaling mechanism for preventing undesired platelet activation.

MicroRNA-34a inhibits cell proliferation by repressing mitogen-activated protein kinase kinase 1 during megakaryocytic differentiation of K562 cells

Phorbol 12-myristate 13-acetate (PMA) induces megakaryocytic differentiation of the human chronic myelocytic leukemia cell line K562. We examined the potential regulatory role of microRNAs (miRNAs) in this process. Genome-wide expression profiling identified 21 miRNAs (miRs) that were induced by the treatment of K562 cells with PMA. Among them, the expression of miR-34a, miR-221, and miR-222 was induced in the early stages and maintained throughout the late stages of differentiation. Cell signaling analysis showed that the activation of extracellular signal-regulated protein kinase (ERK) in response to PMA strongly induced miR-34a expression by transactivation via the activator protein-1 binding site in the upstream region of the miR-34a gene. Reporter gene assays identified mitogen-activated protein kinase kinase 1 (MEK1) as a direct target of miR-34a and c-fos as a direct target of miR-221/222. Although overexpression of the three miRNAs had little effect on cell differentiation, overexpression of miR-34a significantly repressed the proliferation of K562 cells with a concomitant reduction in MEK1 protein expression. Conversely, a locked nucleic acid probe against miR-34a significantly enhanced the proliferation of PMA-treated K562 cells. Taken together, the results show that PMA activates the MEK-ERK pathway and strongly induces miRNA-34a expression, which in turn inhibits cell proliferation by repressing the expression of MEK1. Thus, the results highlight an important regulatory role for miR-34a in the process of megakaryocytic differentiation, especially in the arrest of cell growth, which is a prerequisite for cells to enter differentiation.

The mitogen-activated protein kinase signaling pathways: role in megakaryocyte differentiation

Megakaryopoiesis is a process by which bone marrow progenitor cells develop into mature megakaryocytes (MKs), which in turn produce platelets required for normal hemostasis. The mitogen-activated protein kinases (MAPKs) family comprises four main groups of proteins: extracellular signal-related kinases (ERKs) (ERK1/2 or p44/p42), ERK5, p38MAPKs (alpha, beta, gamma, delta) and c-Jun amino-terminal kinases (JNKs) (JNK 1, 2, 3). These intracellular signaling pathways play a pivotal role in many essential cellular processes including proliferation and differentiation. The purpose of this review is to summarize our current knowledge on the role of MAPKs in MKs, specifically regarding differentiation in immortalized cell lines and primary MKs. A critical role of the MEK (MAPK kinase)-ERK1/2 pathway in MK development has been demonstrated although the details remain controversial. There is at present no functional evidence for a role of p38MAPKs whereas the role of JNKs and ERK5 in MK development is not known. Characterization of these molecular event cascades remains crucial for the understanding of the megakaryopoiesis process.

miR-34a contributes to megakaryocytic differentiation of K562 cells independently of p53

The role of miRNAs in regulating megakaryocyte differentiation was examined using bipotent K562 human leukemia cells. miR-34a is strongly up-regulated during phorbol ester–induced megakaryocyte differentiation, but not during hemin-induced erythrocyte differentiation. Enforced expression of miR-34a in K562 cells inhibits cell proliferation, induces cell-cycle arrest in G1 phase, and promotes megakaryocyte differentiation as measured by CD41 induction. miR-34a expression is also up-regulated during thrombopoietin-induced differentiation of CD34+ hematopoietic precursors, and its enforced expression in these cells significantly increases the number of megakaryocyte colonies. miR-34a directly regulates expression of MYB, facilitating megakaryocyte differentiation, and of CDK4 and CDK6, to inhibit the G1/S transition. However, these miR-34a target genes are down-regulated rapidly after inducing megakaryocyte differentiation before miR-34a is induced. This suggests that miR-34a is not responsible for the initial down-regulation but may contribute to maintaining their suppression later on. Previous studies have implicated miR-34a as a tumor suppressor gene whose transcription is activated by p53. However, in p53-null K562 cells, phorbol esters induce miR-34a expression independently of p53 by activating an alternative phorbol ester-responsive promoter to produce a longer pri-miR-34a transcript.

Essential involvement of cross-talk between IFN-gamma and TNF-alpha in CXCL10 production in human THP-1 monocytes

Interferon (IFN)-gamma-induced protein 10 (IP-10/CXCL10), a CXC chemokine, has been documented in several inflammatory and autoimmune disorders including atopic dermatitis and bronchial asthma. Although CXCL10 could be induced by IFN-gamma depending on cell type, the mechanisms regulating CXCL10 production following treatment with combination of IFN-gamma and TNF-alpha have not been adequately elucidated in human monocytes. In this study, we showed that TNF-alpha had more potential than IFN-gamma to induce CXCL10 production in THP-1 monocytes. Furthermore, IFN-gamma synergistically enhanced the production of CXCL10 in parallel with the activation of NF-kappaB in TNF-alpha-stimulated THP-1 cells. Blockage of STAT1 or NF-kappaB suppressed CXCL10 production. JAKs inhibitors suppressed IFN-gamma plus TNF-alpha-induced production of CXCL10 in parallel with activation of STAT1 and NF-kappaB, while ERK inhibitor suppressed production of CXCL10 as well as activation of NF-kappaB, but not that of STAT1. IFN-gamma-induced phosphorylation of JAK1 and JAK2, whereas TNF-alpha induced phosphorylation of ERK1/2. Interestingly, IFN-gamma alone had no effect on phosphorylation and degradation of IkappaB-alpha, whereas it significantly promoted TNF-alpha-induced phosphorylation and degradation of IkappaB-alpha. These results suggest that TNF-alpha induces CXCL10 production by activating NF-kappaB through ERK and that IFN-gamma induces CXCL10 production by increasing the activation of STAT1 through JAKs pathways. Of note, TNF-alpha-induced NF-kappaB may be the primary pathway contributing to CXCL10 production in THP-1 cells. IFN-gamma potentiates TNF-alpha-induced CXCL10 production in THP-1 cells by increasing the activation of STAT1 and NF-kappaB through JAK1 and JAK2.

HIF-1alpha regulates epithelial inflammation by cell autonomous NFkappaB activation and paracrine stromal remodeling

Hypoxia inducible factor-1 (HIF-1) is a master regulatory transcription factor controlling multiple cell-autonomous and non-cell-autonomous processes, such as metabolism, angiogenesis, matrix invasion, and cancer metastasis. Here we used a new line of transgenic mice with constitutive gain of HIF-1 function in basal keratinocytes and demonstrated a signaling pathway from HIF-1 to nuclear factor kappa B (NFkappaB) activation to enhanced epithelial chemokine and cytokine elaboration. This pathway was responsible for a phenotypically silent accumulation of stromal inflammatory cells and a marked inflammatory hypersensitivity to a single 12-O-tetradecanoylphorbol-13-acetate (TPA) challenge. HIF-1-induced NFkappaB activation was composed of 2 elements, IkappaB hyperphosphorylation and phosphorylation of Ser276 on p65, enhancing p65 nuclear localization and transcriptional activity, respectively. NFkappaB transcriptional targets macrophage inflammatory protein-2 (MIP-2/CXCL2/3), keratinocyte chemokine (KC/CXCL1), and tumor necrosis factor [alfa] (TNFalpha) were constitutively up-regulated and further increased after TPA challenge both in cultured keratinocytes and in transgenic mice. Whole animal KC, MIP-2, or TNFalpha immunodepletion each abrogated TPA-induced inflammation, whereas blockade of either VEGF or placenta growth factor (PlGF) signaling did not affect transgenic inflammatory hyper-responsiveness. Thus, epithelial HIF-1 gain of function remodels the local environment by cell-autonomous NFkappaB-mediated chemokine and cytokine secretion, which may be another mechanism by which HIF-1 facilitates either inflammatory diseases or malignant progression.

Leukotriene B4enhances tumour necrosis factor-?-induced CCL27 production in human keratinocytes

BACKGROUND

A chemokine CCL27 recruits skin-homing T cells. CCL27 production by epidermal keratinocytes is dependent on nuclear factor-kappaB (NF-kappaB) activity and is enhanced in lesions with atopic dermatitis or allergic contact dermatitis. A lipid mediator leukotriene B(4) (LTB(4)) may be involved in the development of these allergic dermatoses. LTB(4) acts on cell surface G-protein-coupled receptors, BLT1 and BLT2.

OBJECTIVE

The aim of this study was to investigate the in vitro effects of LTB(4) on CCL27 production in human keratinocytes.

METHODS

Keratinocytes were incubated with TNF-alpha and LTB(4). CCL27 secretion and mRNA levels were analysed by ELISA and RT-PCR, respectively. NF-kappaB activities were analysed by luciferase assays. Protein levels or phosphorylation status were analysed by cell-based ELISA.

RESULTS

LTB(4) alone did not enhance CCL27 production and modestly enhanced NF-kappaB activity in human keratinocytes. However, LTB(4) potently enhanced TNF-alpha-induced CCL27 secretion and mRNA expression and NF-kappaB activity. LTB(4) alone or together with TNF-alpha, induced phosphorylation and degradation of inhibitory NF-kappaB alpha (IkappaBalpha) and phosphorylation of NF-kappaB p65. These effects of LTB(4) were suppressed by BLT1 antagonist U75302, pertussis toxin, phosphoinositide-3 kinase (PI3K) inhibitor LY294002 and extracellular signal-regulated kinase (ERK) kinase inhibitor U0126, but not by BLT2 antagonist LY255283. LTB(4) induced phosphorylation of ERK and Akt, downstream kinase of PI3K; LY294002 suppressed phosphorylation of both kinases while U0126 suppressed only the former.

CONCLUSION

These results suggest that LTB(4) may enhance TNF-alpha-induced CCL27 production by activating NF-kappaB via the BLT1/G(i/o)/PI3K/ERK pathway in human keratinocytes. LTB(4) may contribute to the enhanced CCL27 production of keratinocytes in lesions with atopic dermatitis or allergic contact dermatitis.

IL-18 enhances IFN-gamma-induced production of CXCL9, CXCL10, and CXCL11 in human keratinocytes

IL-18 is involved in the pathogenesis of atopic dermatitis, psoriasis, and allergic contact dermatitis. CXCL9, CXCL10, and CXCL11 recruit type 1 T cells, and the production of these chemokines by keratinocytes is enhanced in these dermatoses. We examined the in vitro effects of IL-18 on IFN-gamma-induced CXCL9, CXCL10, and CXCL11 production in human keratinocytes. IL-18 enhanced the IFN-gamma-induced secretion and mRNA expression of CXCL9, CXCL10, and CXCL11 in parallel to the activation of NF-kappaB, STAT1, and IFN-regulatory factor (IRF)-1. Antisense oligonucleotides against NF-kappaB p50, p65, or STAT1 suppressed CXCL9, CXCL10, and CXCL11 production, and antisense IRF-1 suppressed CXCL11 production. Inhibitors of PI3 K, p38 MAPK, and MEK suppressed IL-18 plus IFN-gamma-induced CXCL9, CXCL10, and CXCL11 production and NF-kappaB, STAT1, and IRF-1 activities. IL-18 induced phosphorylation of ERK and Akt, while IFN-gamma induced phosphorylation of p38 MAPK. These results suggest that IL-18 may potentiate IFN-gamma-induced CXCL9, CXCL10, and CXCL11 production in keratinocytes by activating NF-kappaB, STAT1, or IRF-1 through PI3 K/Akt and MEK/ERK pathways. These effects of IL-18 may promote the infiltration of type 1 T cells into lesions with inflammatory dermatoses and amplify the skin inflammation. IL-18 may act as a pro-inflammatory cytokine in these dermatoses and thus is a candidate therapeutic target.

Differential expression changes in K562 cells during the hemin-induced erythroid differentiation and the phorbol myristate acetate (PMA)-induced megakaryocytic differentiation

K562 cell line has been used as a model of common progenitor of erythroblasts and magakaryocytes and can be differentiated into erythroid and megakaryocytic lineages by hemin and phorbol myristate acetate (PMA) respectively. We analyzed mRNA expression in un-induced, hemin-induced and PMA-induced K562 cells by differential display reverse transcription polymerase chain reaction (DDRT-PCR) method. 314 differential expression sequence tags (ESTs) were obtained. Among them, 201 ESTs displayed up-regulation and 85 ESTs down-regulation after hemin induction, 186 ESTs showed up-regulation and 72 ESTs down-regulation after PMA induction. The differentially expressed genes included those encoding transcription factors, signaling factors, apoptosis-associated factors and others. 45 of these ESTs stand for genes whose open reading frames were found but whose functions remain unknown. 4 ESTs represent possibly new genes. Furthermore we compared differences of gene expression during hemin-induced erythroid differentiation and PMA-induced megakaryocytic differentiation and found that the expressional changes of some transcription factors and metabolism proteins are the common but the expressional changes of some signal pathways in these two differentiation processes are different. These results suggested that erythroid differentiation and megakaryocytic differentiation are associated in activation and repression of different signal pathways.

1Alpha,25-dihydroxyvitamin D3-mediated stimulation of steroid sulphatase activity in myeloid leukaemic cell lines requires VDRnuc-mediated activation of the RAS/RAF/ERK-MAP kinase signalling pathway

1Alpha,25-dihydroxyvitamin D(3) (1alpha,25(OH)(2)D(3)) stimulates the activity of steroid sulphatase (STS) in myeloid cells [Hughes et al., 2001, 2005]. This was attenuated by inhibitors of phospholipase D (PLD) (n-butanol, 2,3-diphosphoglyceric acid, C(2)-ceramide) and phosphatidate phosphohydrolase (PAP) (propranolol and chlorpromazine), but was unaffected by inhibitors of phospholipase C. The 1alpha,25(OH)(2)D(3)-induced STS activity was also attenuated by inhibitors of protein kinase Calpha and protein kinase Cdelta (Go 6976, HBDDE and rottlerin), but not by an inhibitor of protein kinase Cbeta (LY379196). Additionally, 1alpha,25(OH)(2)D(3)-induced STS activity was attenuated by inhibitors of RAS (manumycin A), RAF (GW5074), MEK (PD098059 and U1026) and JNK (SP600125), but not p38 (PD169316). 1alpha,25(OH)(2)D(3) produced a rapid and long lasting stimulation of the ERK-MAP kinase signalling cascade in HL60 myeloid leukaemic cells. This 'non-genomic' effect of 1alpha,25(OH)(2)D(3) blocked by pharmacological antagonists of nuclear vitamin D receptors (VDR(nuc)) and does not appear to require hetero-dimerisation with the retinoid-X receptor (RXR). Inhibitors of the Src tyrosine kinase (PP1), RAS (manumycin A), RAS-RAF interactions (sulindac sulphide and RAS inhibitory peptide), RAF (GW5074 or chloroquine), and protein kinase Calpha (HBDDE) abrogated the 1alpha,25(OH)(2)D(3)-stimulated increase in ERK-MAP kinase activity. Taken together, these results show that 1alpha,25(OH)(2)D(3)/VDR(nuc) activation of the RAS/RAF/ERK-MAP kinase signalling pathway plays an important role in augmenting STS activity in human myeloid leukaemic cell lines.

A survey of the signaling pathways involved in megakaryocytic differentiation of the human K562 leukemia cell line by molecular and c-DNA array analysis

The K562 cell line serves as a model to study the molecular mechanisms associated with leukemia differentiation. We show here that cotreatment of K562 cells with PMA and low doses of SB202190 (SB), an inhibitor of the p38 MAPK pathway, induced a majority of cells to differentiate towards the megakaryocytic lineage. Electronic microscopy analysis showed that K562 cells treated with PMA+SB exhibited characteristic features of physiological megakaryocytic differentiation including the presence of vacuoles and demarcation membranes. Differentiation was also accompanied by a net increase in megakaryocytic markers and a reduction of erythroid markers, especially when both effectors were present. PMA effect was selectively mediated by new PKC isoforms. Differentiation of K562 cells by the combination of PMA and SB required Erk1/2 activation, a threshold of JNK activation and p38 MAPK inhibition. Interestingly, higher concentrations of SB, which drastically activated JNK, blocked megakaryocytic differentiation, and considerably increased cell death in the presence of PMA. c-DNA microarray membranes and PCR analysis allow us to identify a set of genes modulated during PMA-induced K562 cell differentiation. Several gene families identified in our screening, including ephrins receptors and some angiogenic factors, had never been reported so far to be regulated during megakaryocytic differentiation.

Transcriptional regulation of human CC chemokine CCL15 gene by NF-kappaB and AP-1 elements in PMA-stimulated U937 monocytoid cells

CCL15 exerts biological effects on a variety of cells, including monocytes. NF-kappaB has been reported to be involved in the transcription of the CCL15 gene. In this study, we have identified an AP-1 element located at -76/-65, which appears to regulate the transcription of the CCL15 gene. We also confirmed that the AP-1 factor binds to the element. Specific inhibitors for MAPK pathways and expression of dominant negative MKK4 or JNK1 reduced PMA-induced transcriptional activation of CCL15. Our findings indicate that transcription of the CCL15 gene is regulated by AP-1 and NF-kappaB through MEK and JNK MAPK pathways in monocytoid cells.

A new cellular signaling mechanism for angiotensin II activation of NF-kappaB: An IkappaB-independent, RSK-mediated phosphorylation of p65

OBJECTIVE

Angiotensin II (Ang II) promotes vascular inflammation and remodeling via activation of nuclear factor kappaB (NF-kappaB)-mediated transcription of proinflammatory genes such as interleukin-6 (IL-6). We examined the signaling mechanism whereby Ang II activates NF-kappaB in vascular smooth muscle cells (VSMCs).

METHODS AND RESULTS

Ang II treatment did not increase phosphorylation of inhibitor of kappaBalpha (IkappaBalpha) or IkappaBbeta or decrease their levels. In contrast, mitogen-activated protein kinase kinase-1 (MEK1) inhibition (dominant-negative MEK1 adenovirus or inhibitor U0126) suppressed Ang II-induced NF-kappaB promoter activity, NF-kappaB DNA-binding activity, p65 phosphorylation, and led to 70% reduction in IL-6 transcription/production. The mechanism involved Ang II activation of Ras and MEK1. Signaling distal to MEK1 involved extracellular signal-regulated kinase (ERK) because inhibition of MEK1 suppressed the Ang II-induced activation of ribosomal S6 kinase (RSK), a substrate of ERK. Downregulation of RSK by small interfering RNA (SiRNA) in VSMCs was found to suppress Ang II-induced activation of NF-kappaB and p65 phosphorylation. Immunopurified RSK from Ang II-treated VSMCs phosphorylated recombinant glutathione S-transferase-p65 in vitro.

CONCLUSIONS

We uncovered a nonclassical signaling pathway (Ras/MEK1/ERK/RSK) from Ang II to activation of NF-kappaB, a mechanism by which Ang II stimulates RSK-mediated phosphorylation of p65 to participate in vascular inflammation.

Prostaglandin E2 induces MUC8 gene expression via a mechanism involving ERK MAPK/RSK1/cAMP response element binding protein activation in human airway epithelial cells

MUC8 gene expression is overexpressed in nasal polyp epithelium and is also increased by treatment with inflammatory mediators in nasal epithelial cells. These data suggest that MUC8 may be one of important mucin genes expressed in human airway. However, the mechanisms of various inflammatory mediator-induced MUC8 gene expression in normal nasal epithelial cells remain unclear. We examined the mechanism by which prostaglandin E(2) (PGE2), an arachidonic acid metabolite, increases MUC8 gene expression levels. Here, we show that ERK mitogen-activated protein kinase is essential for PGE2-induced MUC8 gene expression in normal human nasal epithelial cells and that p90 ribosomal S 6 protein kinase 1 (RSK1) mediates the PGE2-induced phosphorylation of cAMP-response element binding protein. Our results also indicate that cAMP-response element at the -803 region of the MUC8 promoter is an important site of PGE2-induced MUC8 gene expression. In conclusion, this study gives insights into the molecular mechanism of PGE2-induced MUC8 gene expression in human airway epithelial cells.

Hemozoin Induces Macrophage Chemokine Expression through Oxidative Stress-Dependent and -Independent Mechanisms

Chemokine production has been associated with the immunopathology related to malaria. Previous findings indicated that hemozoin (HZ), a parasite metabolite released during schizogeny, might be an important source of these proinflammatory mediators. In this study we investigated the molecular mechanisms underlying HZ-inducible macrophage (Mphi) chemokine mRNA expression. We found that both Plasmodium falciparum HZ and synthetic HZ increase mRNA levels of various chemokine transcripts (MIP-1alpha/CCL3, MIP-1beta/CCL4, MIP-2/CXCL2, and MCP-1/CCL2) in murine B10R Mphi. The cellular response to HZ involved ERK1/2 phosphorylation, NF-kappaB activation, reactive oxygen species (ROS) generation, and ROS-dependent protein-tyrosine phosphatase down-regulation. Selective inhibition of either IkappaBalpha or the ERK1/2 pathway abolished both NF-kappaB activation and chemokine up-regulation. Similarly, blockage of HZ-inducible Mphi ROS with superoxide dismutase suppressed chemokine induction, strongly reduced NF-kappaB activation, and restored HZ-mediated Mphi protein-tyrosine phosphatase inactivation. In contrast, superoxide dismutase had no effect on EKR1/2 phosphorylation by HZ. Collectively, these data indicate that HZ triggers ROS-dependent and -independent signals, leading to increased chemokine mRNA expression in Mphi. Overall, our findings may help to better understand the molecular mechanisms through which parasite components, such as HZ, modulate the immune response during malaria infection.

Signaling Events Involved in Macrophage Chemokine Expression in Response to Monosodium Urate Crystals

Chemokine production has been associated with leukocyte infiltration into the joint during gouty arthritis, and monosodium urate (MSU) crystals, the causative agent of this arthropathy, have been shown to modulate their expression. In the present study, we investigated the transductional mechanisms underlying this cellular regulation in the murine macrophage cell line B10R. We report that MSU crystals rapidly and transiently increase mRNA levels of various chemokines in a concentration-dependent manner. Examination of second messenger activation revealed that macrophage exposure to MSU crystals led to MEK1/2, ERK1/2, and inhibitory protein kappaBalpha phosphorylation as well as to NF-kappaB and AP-1 nuclear translocation. Of interest, specific blockage of the ERK1/2 pathway drastically reduced up-modulation of MSU crystal-mediated chemokine production and activation of nuclear factors. Similarly, selective inhibition of NF-kappaB suppressed NF-kappaB DNA binding activity and the induction of all chemokine transcripts. These findings indicate that ERK1/2-dependent signals seem to be required for AP-1 and NF-kappaB activation and subsequent mRNA expression of the various macrophage chemokines. In addition, transcription and stability assays performed in presence of actinomycin D showed that MSU crystal-mediated MIP-1beta mRNA up-regulation resulted solely from transcriptional control, whereas that of MIP-1alpha, MIP-2, and MCP-1 was due to both gene transcription activation and mRNA posttranscriptional stabilization. Overall, the results of this study help to define the molecular events that govern macrophage chemokine regulation in response to MSU crystals, which is of paramount importance to better understand, and eventually to tame, the inflammatory response during acute gout.

Phorbol ester treatment of K562 cells regulates the transcriptional activity of AML1c through phosphorylation

We find that phorbol ester (PE) treatment of K562 cells greatly stimulates promoters (T cell receptor beta, myeloperoxidase, macrophage colony-stimulating factor receptor, and granulocyte macrophage colony-stimulating factor receptor) containing AML1 transcription factor binding sites. This stimulation of AML1c transcriptional activity is mediated by direct phosphorylation of the AML1c molecule on multiple phosphorylation sites. Eleven AML1c (S/T)P sites in the transcriptional activating domain are phosphorylated at a basal level in untreated K562 cells; treatment of the K562 cells with PE results in increased phosphorylation at five of these sites (serines 276, 293, 303, 462, and threonine 300). Mutation of these five sites to alanine inhibits PE-induced transcriptional activity; mutation of the sites to an acidic amino acid, aspartic acid, stimulates constitutive activity. Single mutations in four amino acids or double mutations (serines 276 and 293 or threonine 300 and serine 303) have little effect on AML1c transcriptional activity. Inhibitor assays suggest that the ERK family of protein kinases is activated by PEs to phosphorylate the (S/T)P sites within the AML1c molecule and markedly enhance the transcriptional activity of AML1c.

90-kDa ribosomal S6 kinase is a direct target for the nuclear fibroblast growth factor receptor 1 (FGFR1): role in FGFR1 signaling

Fibroblast growth factor receptor 1 (FGFR1) is a transmembrane protein capable of transducing stimulation by secreted FGFs. In addition, newly synthesized FGFR1 enters the nucleus in response to cellular stimulation and during development. Nuclear FGFR1 can transactivate CRE (cAMP responsive element), activate CRE-binding protein (CREB)-binding protein (CBP) and gene activities causing cellular growth and differentiation. Here, a yeast two-hybrid assay was performed to identify FGFR1-binding proteins and the mechanism of nuclear FGFR1 action. Ten FGFR1-binding proteins were identified. Among the proteins detected with the intracellular FGFR1 domain was a 90-kDa ribosomal S6 kinase (RSK1), a regulator of CREB, CBP, and histone phosphorylation. FGFR1 bound to the N-terminal region of RSK1. The FGFR1-RSK1 interaction was confirmed by co-immunoprecipitation and colocalization in the nucleus and cytoplasm of mammalian cells. Predominantly nuclear FGFR1-RSK1 interaction was observed in the rat brain during neurogenesis and in cAMP-stimulated cultured neural cells. In TE671 cells, transfected FGFR1 colocalized and coimmunoprecipitated, almost exclusively, with nuclear RSK1. Nuclear RSK1 kinase activity and RSK1 activation of CREB were enhanced by transfected FGFR1. In contrast, kinase-deleted FGFR1 (TK-), which did not bind to RSK1 failed to stimulate nuclear RSK1 activity or RSK1 activation of CREB. Kinase inactive FGFR1 (K514A) bound effectively to nuclear RSK1, but it failed to stimulate RSK1. Thus, active FGFR1 kinase regulates the functions of nuclear RSK1. The interaction of nuclear FGFR1 with pluripotent RSK1 offers a new mechanism through which FGFR1 may control fundamental cellular processes.

Alpha5beta1 integrin as a cellular coreceptor for human parvovirus B19: requirement of functional activation of beta1 integrin for viral entry

Replication of the pathogenic human parvovirus B19 is restricted to erythroid progenitor cells. Although blood group P antigen has been reported to be the cell surface receptor for parvovirus B19, a number of nonerythroid cells, which express P antigen, are not permissive for parvovirus B19 infection. We have documented that P antigen is necessary for parvovirus B19 binding but not sufficient for virus entry into cells. To test whether parvovirus B19 utilizes a cell surface coreceptor for entry, we used human erythroleukemia cells (K562), which allow parvovirus B19 binding but not entry. We report here that upon treatment with phorbol esters, K562 cells become adherent and permissive for parvovirus B19 entry, which is mediated by alpha 5 beta 1 integrins, but only in their high-affinity conformation. Mature human red blood cells (RBCs), which express high levels of P antigen, but not alpha 5 beta 1 integrins, bind parvovirus B19 but do not allow viral entry. In contrast, primary human erythroid progenitor cells express high levels of both P antigen and alpha 5 beta 1 integrins and allow beta1 integrin-mediated entry of parvovirus B19. Thus, in a natural course of infection, RBCs are likely exploited for a highly efficient systemic dissemination of parvovirus B19.

Induction of MUC8 gene expression by interleukin-1 beta is mediated by a sequential ERK MAPK/RSK1/CREB cascade pathway in human airway epithelial cells

Mucins are the major components of the mucus layer that covers and protects the respiratory, digestive, and reproductive tracts. Our previous studies showed that MUC8 gene expression was overexpressed in in vivo polyp epithelium in chronic sinusitis and was also increased by treatment with inflammatory mediators in an in vitro culture condition. However, the mechanisms by which the inflammatory mediators-induced MUC8 gene expression in normal nasal epithelial cells evolved remain unclear. We examined the mechanism by which the important proinflammatory mediator, interleukin (IL)-1 beta, increases MUC8 gene expression levels. We found that pharmacologic and genetic inhibition of ERK MAPK pathway abolished IL-1 beta-induced MUC8 gene expression in normal human nasal epithelial cells. Moreover, the overexpression of wide-type or of the dominant-negative mutant of p90 ribosomal S6 protein kinase 1 (RSK1) enhanced or suppressed, respectively, IL-1 beta-induced MUC8 gene expression. RSK1 was found to directly phosphorylate cAMP-response element-binding protein (CREB), and this event led to the stimulation of subsequent CRE-mediated gene transcription. In conclusion, IL-1 beta was found to induce MUC8 gene expression via a sequential ERK/RSK1/CREB pathway in human airway epithelial cells.

Demonstration of an activation regulated NF-kappaB/I-kappaBalpha complex in human platelets

In eukaryotic cells, the ubiquity of the signaling system of transcription factor nuclear factor-kappa B (NF-kappaB)/I-kappa B (I-kappaB) is undisputed. Numerous studies have reported that the NF-kappaB/I-kappaB complex plays a pivotal role in regulating gene expression controlling cell differentiation, cell proliferation, inflammation, oncogenesis, and apoptosis. Here we show that NF-kappaB/I-kappaB families exist in human platelets, natural anuclear corpuscles derived from megakaryocytes. Moreover, the I-kappaB kinase (IKK) is present and may phosphorylate I-kappaB during platelet activation. Coupled with intracellular calcium flux, this leads to I-kappaB dissociation from the NF-kappaB/I-kappaB complex and proteolysis. The NF-kappaB/I-kappaB proteins may have function independent of gene regulation in platelets.

Induced dendritic cell differentiation of chronic myeloid leukemia blasts is associated with down-regulation of BCR-ABL

Although differentiation of leukemic blasts to dendritic cells (DC) has promise in vaccine strategies, the mechanisms underlying this differentiation and the differences between leukemia and normal progenitor-derived DC are largely undescribed. In the case of chronic myeloid leukemia (CML), understanding the relationship between the induction of DC differentiation and the expression of the BCR-ABL oncogene has direct relevance to CML biology as well as the development of new therapeutic approaches. We now report that direct activation of protein kinase C (PKC) by the phorbol ester PMA in the BCR-ABL(+) CML cell line K562 and primary CML blasts induced nonterminal differentiation into cells with typical DC morphology (cytoplasmic dendrites), characteristic surface markers (MHC class I, MHC class II, CD86, CD40), chemokine and transcription factor expression, and ability to stimulate T cell proliferation (equivalent to normal monocyte-derived DC). PKC-induced differentiation was associated with down-regulation of BCR-ABL mRNA expression, protein levels, and kinase activity. This down-regulation appeared to be signaled through the mitogen-activated protein kinase pathway. Therefore, PKC-driven differentiation of CML blasts into DC-like cells suggests a potentially novel strategy to down-regulate BCR-ABL activity, yet raises the possibility that CML-derived DC vaccines will be less effective in presenting leukemia-specific Ags.

Relaxin, a pregnancy hormone, is a functional endothelin-1 antagonist: attenuation of endothelin-1-mediated vasoconstriction by stimulation of endothelin type-B receptor expression via ERK-1/2 and nuclear factor-kappaB

We have recently demonstrated that relaxin (RLX) acts as compensatory mediator in human heart failure. RLX inhibits the stimulation of endothelin-1, the most potent vasoconstrictor in heart failure. Upregulation of the endothelin type-B receptor (ET(B)), which mediates endothelin-1 clearance and endothelial release of NO, represents a pivotal mode of RLX action. However, signal transduction and abundance of this phenomenon are unknown. Therefore, we investigated RLX-induced regulation of ET(B) in human umbilical vein endothelial, epithelial (HeLa), and vascular smooth muscle cells. In human umbilical vein endothelial cells and HeLa cells, but not in human vascular smooth muscle cells, RLX upregulated ET(B) expression and activated extracellular signal-regulated kinase-1/2 (ERK-1/2) and nuclear factor-kappaB (NF-kappaB), a transcription factor. PD-98059, a selective inhibitor of the mitogen-activated protein kinase kinase-1 (MEK-1)-ERK-1/2 pathway, abolished ERK-1/2 and NF-kappaB activation and ET(B) upregulation. NF-kappaB inhibition also prevented RLX-mediated ET(B) stimulation. In NF-kappaB-luciferase reporter assays, we demonstrated complete inhibition of RLX-induced NF-kappaB activation in cells transfected with dominant-negative Raf-1, MEK-1, or ERK-1/2 constructs, whereas dominant-negative Ras had no effect. In rat aorta and mesenteric artery, RLX pretreatment, in an ET(B)-dependent fashion, mitigated the maximum contractile response to endothelin-1, by 38+/-4% and 43+/-6%, and the endothelin-1 sensitivity (-log[EC(50)]: aorta, 8.2+/-0.2 for vehicle versus 7.2+/-0.2 for RLX; mesenteric artery, 8.0+/-0.2 for vehicle versus 7.1+/-0.1 for RLX). RLX pretreatment augmented the dilator effect of the ET(B) agonist endothelin-3 by 100+/-8% and 133+/-13%. In conclusion, RLX stimulates endothelial and epithelial ET(B) via a Ras-independent Raf-1-MEK-1-ERK-1/2 pathway that activates NF-kappaB. On vascular smooth muscle cells, ET(B), a contributor to endothelin-mediated vasoconstriction, remains unaffected. This renders RLX a functional endothelin-1 antagonist.

Potential roles of extracellular signal-regulated kinase but not p38 during myeloid differentiation of U937 cells stimulated by cytokines: augmentation of differentiation via prolonged activation of extracellular signal-regulated kinase

OBJECTIVE

To clarify the signaling mechanism of human myeloid differentiation by hematopoietic growth factors and cytokines, we investigated the role of extracellular signal-regulated kinase (ERK) during the differentiation of human monoblastic U937 cells stimulated by granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumor necrosis factor (TNF).

MATERIALS AND METHODS

Myeloid differentiation was evaluated by morphology, function (respiratory burst activity), and cell surface expression of adhesion molecule (CD11b), and activation of ERK and/or p38 was determined by Western blotting and/or in vitro kinase assay. Inhibition of the ERK pathway was performed using PD98059, a specific inhibitor of this pathway.

RESULTS

U937 cells were induced to be differentiated by the combination of GM-CSF and TNF, but only minimally by either cytokine alone. Transient phosphorylation and activation of ERK was induced by both GM-CSF alone and combination of the two cytokines, whereas sustained phosphorylation and activation was induced only by the combination. In addition, PD98059, a specific inhibitor of ERK pathway, almost completely abolished this prolonged phosphorylation of ERK and completely blocked differentiation. In contrast, both TNF alone and cytokine combination equivalently phosphorylated p38 in U937 cells, which was dissociated from differentiation, and a specific inhibitor of p38 (SB203580) did not inhibit differentiation.

CONCLUSIONS

The results indicate potential roles of sustained activation of ERK but not of p38 in the signaling pathways for human myeloid differentiation in U937 cells synergistically stimulated by the two physiologic cytokines GM-CSF and TNF.

p65-NFκB synergizes with Notch to activate transcription by triggering cytoplasmic translocation of the nuclear receptor corepressor N-CoR

Notch/RBP-Jκ and nuclear factor-κB (NFκB) complexes are key mediators of the progression of many cellular events through the activation of specific target gene transcription. Independent observations have shown that activation of Notch-dependent transcription generally correlates with inhibition of differentiation. In contrast, activated NFκB complexes are required for progression of differentiation in several systems. Although some interactions between both pathways have been observed, the physiological significance of their connection is unclear. We have now demonstrated that the increase in p65-NFκB protein levels enhances Notch-mediated activation of the Hes1 promoter up to three-fold. This effect does not require NFκB transcriptional activity, and it is independent of the previously described interaction between Notch and p50-NFκB. Furthermore, we show that p65-NFκB can modulate subcellular localization of the transcriptional corepressor N-CoR, abrogating N-CoR mediated repression of the Hes1 promoter. In addition, p65-NFκB is able to upregulate not only the Hes1 but also other promoters containing SRE and AP-1 sites, which are repressed by N-CoR. Thus, we conclude that p65-NFκB can regulate gene expression by a general mechanism that involves cytoplasmic translocation of the transcriptional corepressor protein N-CoR.