Biological implications of somatic DDX41 p.R525H mutation in acute myeloid leukemia.

The DDX41 gene, encoding a DEAD-box type ATP-dependent RNA helicase, is rarely but reproducibly mutated in myeloid diseases. The acquired mutation in DDX41 is highly concentrated at c.G1574A (p.R525H) in the conserved motif VI located at the C-terminus of the helicase core domain where ATP interacts and is hydrolyzed. Therefore, it is likely that the p.R525H mutation perturbs ATPase activity in a dominant-negative manner. In this study, we screened for the DDX41 mutation of CD34-positive tumor cells based on mRNA sequencing and identified the p.R525H mutation in three cases among 23 patients. Intriguingly, these patients commonly exhibited acute myeloid leukemia (AML) with peripheral blood cytopenias and low blast counts, suggesting that the mutation inhibits the growth and differentiation of hematopoietic cells. Data from cord blood cells and leukemia cell lines suggest a role for DDX41 in preribosomal RNA processing, in which the expression of the p.R525H mutant causes a certain ribosomopathy phenotype in hematopoietic cells by suppressing MDM2-mediated RB degradation, thus triggering the inhibition of E2F activity. This study uncovered a pathogenic role of p.R525H DDX41 in the slow growth rate of tumor cells. Age-dependent epigenetic alterations or other somatic changes might collaborate with the mutation to cause AML.

Human Neutrophil Elastase Induce Interleukin-10 Expression in Peripheral Blood Mononuclear Cells through Protein Kinase C Theta/Delta and Phospholipase Pathways.

OBJECTIVE: Neutrophils have an important role in the rapid innate immune response, and the release or active secretion of elastase from neutrophils is linked to various inflammatory responses. Purpose of this study was to determine how the human neutrophil elastase affects the interleukin-10 (IL-10) response in peripheral blood mononuclear cells (PBMC). MATERIALS AND METHODS: In this prospective study, changes in IL-10 messenger RNA (mRNA) and protein expression levels in monocytes derived from human PBMCs were investigated after stimulation with human neutrophil elastase (HNE). A set of inhibitors was used for examining the pathways for IL-10 production induced by HNE. RESULTS: Reverse transcription polymerase chain reaction (RT-PCR) showed that stimulation with HNE upregulated IL-10 mRNA expression by monocytes, while the enzyme-linked immunosorbent assay (ELISA) revealed an increase of IL-10 protein level in the culture medium. A phospholipase C inhibitor (U73122) partially blunt- ed the induction of IL-10 mRNA expression by HNE, while IL-10 mRNA expression was significantly reduced by a protein kinase C (PKC) inhibitor (Rottlerin). A calcium chelator (3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester: TMB-8) inhibited the response of IL-10 mRNA to stimulation by HNE. In addition, pretreatment with a broad-spectrum PKC inhibitor (Ro-318425) partly blocked the response to HNE. Finally, an inhibitor of PKC theta/delta abolished the increased level of IL-10 mRNA expression. CONCLUSION: These results indicate that HNE mainly upregulates IL-10 mRNA ex- pression and protein production in moncytes via a novel PKC theta/delta, although partially via the conventional PKC pathway.

Mechanism of interferon-gamma production by monocytes stimulated with myeloperoxidase and neutrophil extracellular traps.

Neutrophil extracellular traps (NETs) have an important role in antimicrobial innate immunity and release substances that may modulate the immune response. We investigated the effects of soluble factors from NETs and neutrophil granule proteins on human monocyte function by using the Transwell system to prevent cell-cell contact. NET formation was induced by exposing human neutrophils to phorbol myristate acetate (PMA). When monocytes were incubated with PMA alone, expression of interleukin (IL)-4, IL-6, IL-8, and tumor necrosis factor (TNF)-alpha mRNA was upregulated, but IL-10, IL-12, and interferon (IFN)-gamma mRNA were not detected. Incubation of monocytes with NETs enhanced the expression of IL-10 and IFN-gamma mRNA, but not IL-12 mRNA. Myeloperoxidase stimulated IFN-gamma production by monocytes in a dose-dependent manner. Both a nuclear factor-kappaB inhibitor (PDTC) and an intracellular calcium antagonist (TMB-8) prevented upregulation of IFN-gamma production. Neither a combined p38alpha and p38beta inhibitor (SB203580) nor an extracellular signal-regulated kinase inhibitor (PD98059) suppressed IFN-gamma production. Interestingly, a combined p38gamma and p38delta inhibitor (BIRB796) significantly decreased IFN-gamma production. These findings suggest that myeloperoxidase induces IFN-gamma production by monocytes via p38gamma/delta mitogen-activated protein kinase.

Mechanism of tissue factor production by monocytes stimulated with neutrophil elastase.

BACKGROUND: Monocytes and neutrophils are activated during disseminated intravascular coagulation. Tissue factor, the main initiator of coagulation, is expressed by monocytes, while elastase is released by neutrophils. AIMS: This study investigated tissue factor production by peripheral monocytes after stimulation with human neutrophil elastase. METHODS: Tissue factor mRNA levels were investigated by the reverse transcriptase-polymerase chain reaction and tissue factor protein production was assessed by western blotting when monocytes were exposed to neutrophil elastase with or without preincubation using various inhibitors. RESULTS: Neutrophil elastase upregulated tissue factor mRNA and protein levels in monocytes. Both U73122 (phospholipase C inhibitor) and TMB-8 (intracellular calcium antagonist) prevented the upregulation of tissue factor mRNA. SB203580 (p38 mitogen-activated protein kinase inhibitor) suppressed this response, but PD98059 (extracellular signal-regulated kinase inhibitor) did not. Ro-318425 (ATP-competitive and selective protein kinase C (PKC) inhibitor) and Go 6976 (inhibitor of conventional PKCs and PKCµ) blocked the upregulation of tissue factor mRNA expression. Go 6983 (broad-spectrum PKC inhibitor) and CGP 4125 (staurosporine analog) partially attenuated it, as did a PKC theta/delta inhibitor. CONCLUSIONS: Neutrophil elastase mainly enhances tissue factor production by monocytes via the phospholipase C/conventional PKC/p38 MAPK pathway, although a novel PKC is also involved.

Adhesion of suspension cells on a coverslip in serum-free conditions.

Here, we present a rapid and damage-free fixation protocol for human cells cultured in suspension. Our results demonstrated that serum-free incubation of myeloid suspension cell lines HL-60, U937, and THP-1 for 10 min resulted in cell adhesion to coverslips, allowing simple and efficient fixation for microscopy. The fixed cells exhibited an intact morphology and were suitable for immunostaining. Such simplicity and cost effectiveness have not been achieved by any previously established fixation technique, and our newly developed method provides an additional fixation technique for researchers working with suspension cells.

Genomic DNAs in a human leukemia cell line unfold after cold shock, with formation of neutrophil extracellular trap-like structures.

Cells are generally stored at low temperature which slows their cellular metabolism. However, the stress induced by cold shock can lead to cell injury or death. Here, we found that exposing human leukemia HL-60 cells to cold shock followed by rewarming (CS/RW) increased the number of dead cells with remodeled genomic structures in which DNA fibers fully unfold and extrude into extracellular space, similar to neutrophil extracellular traps (NETs). The unfolded DNA was associated with NET marker proteins, such as neutrophil elastase and histone H3, and could trap significant numbers of Escherichia coli. We also found that reactive oxygen species-a requisite for NET generation-accumulated during CS/RW in HL-60 cells. This treatment of HL-60 cells to trigger global DNA structural alterations has not been reported before, and helps to elucidate the mechanisms of human cellular response to cold stress.