Up-regulation of human deoxyribonuclease II gene expression during myelomonocytic differentiation of HL-60 and THP-1 cells

Deficiency and haploinsufficiency of histone macroH2A1.1 in mice recapitulate hematopoietic defects of human myelodysplastic syndrome

BACKGROUND

Epigenetic regulation is important in hematopoiesis, but the involvement of histone variants is poorly understood. Myelodysplastic syndromes (MDS) are heterogeneous clonal hematopoietic stem cell (HSC) disorders characterized by ineffective hematopoiesis. MacroH2A1.1 is a histone H2A variant that negatively correlates with the self-renewal capacity of embryonic, adult, and cancer stem cells. MacroH2A1.1 is a target of the frequent U2AF1 S34F mutation in MDS. The role of macroH2A1.1 in hematopoiesis is unclear.

RESULTS

MacroH2A1.1 mRNA levels are significantly decreased in patients with low-risk MDS presenting with chromosomal 5q deletion and myeloid cytopenias and tend to be decreased in MDS patients carrying the U2AF1 S34F mutation. Using an innovative mouse allele lacking the macroH2A1.1 alternatively spliced exon, we investigated whether macroH2A1.1 regulates HSC homeostasis and differentiation. The lack of macroH2A1.1 decreased while macroH2A1.1 haploinsufficiency increased HSC frequency upon irradiation. Moreover, bone marrow transplantation experiments showed that both deficiency and haploinsufficiency of macroH2A1.1 resulted in enhanced HSC differentiation along the myeloid lineage. Finally, RNA-sequencing analysis implicated macroH2A1.1-mediated regulation of ribosomal gene expression in HSC homeostasis.

CONCLUSIONS

Together, our findings suggest a new epigenetic process contributing to hematopoiesis regulation. By combining clinical data with a discrete mutant mouse model and in vitro studies of human and mouse cells, we identify macroH2A1.1 as a key player in the cellular and molecular features of MDS. These data justify the exploration of macroH2A1.1 and associated proteins as therapeutic targets in hematological malignancies.

LPS-Induced G-CSF Expression in Macrophages Is Mediated by ERK2, but Not ERK1

Granulocyte colony-stimulating factor (G-CSF) selectively stimulates proliferation and differentiation of neutrophil progenitors which play important roles in host defense against infectious agents. However, persistent G-CSF production often leads to neutrophilia and excessive inflammatory reactions. There is therefore a need to understand the mechanism regulating G-CSF expression. In this study, we showed that U0126, a MEK1/2 inhibitor, decreases lipopolysaccharide (LPS)-stimulated G-CSF promoter activity, mRNA expression and protein secretion. Using short hairpin RNA knockdown, we demonstrated that ERK2, and not ERK1, involves in LPS-induced G-CSF expression, but not LPS-regulated expression of TNF-α. Reporter assays showed that ERK2 and C/EBPβ synergistically activate G-CSF promoter activity. Further chromatin immunoprecipitation (ChIP) assays revealed that U0126 inhibits LPS-induced binding of NF-κB (p50/p65) and C/EBPβ to the G-CSF promoter, but not their nuclear protein levels. Knockdown of ERK2 inhibits LPS-induced accessibility of the G-CSF promoter region to DNase I, suggesting that chromatin remodeling may occur. These findings clarify that ERK2, rather than ERK1, mediates LPS-induced G-CSF expression in macrophages by remodeling chromatin, and stimulates C/EBPβ-dependent activation of the G-CSF promoter. This study provides a potential target for regulating G-CSF expression.

Biogenesis and proteolytic processing of lysosomal DNase II

Deoxyribonuclease II (DNase II) is a key enzyme in the phagocytic digestion of DNA from apoptotic nuclei. To understand the molecular properties of DNase II, particularly the processing, we prepared a polyclonal antibody against carboxyl-terminal sequences of mouse DNase II. In the present study, partial purification of DNase II using Con A Sepharose enabled the detection of endogenous DNase II by Western blotting. It was interesting that two forms of endogenous DNase II were detected--a 30 kDa form and a 23 kDa form. Neither of those forms carried the expected molecular weight of 45 kDa. Subcellular fractionation showed that the 23 kDa and 30 kDa proteins were localized in lysosomes. The processing of DNase II in vivo was also greatly altered in the liver of mice lacking cathepsin L. DNase II that was extracellularly secreted from cells overexpressing DNase II was detected as a pro-form, which was activated under acidic conditions. These results indicate that DNase II is processed and activated in lysosomes, while cathepsin L is involved in the processing of the enzyme.

Rapamycin inhibits lipopolysaccharide induction of granulocyte-colony stimulating factor and inducible nitric oxide synthase expression in macrophages by reducing the levels of octamer-binding factor-2

This article reports an inhibitory effect of rapamycin on the lipopolysaccharide (LPS)-induced expression of both inducible nitric oxide synthase (iNOS) and granulocyte-colony stimulating factor (G-CSF) in macrophages and its underlying mechanism. The study arose from an observation that rapamycin inhibited the LPS-induced increase in octamer-binding factor-2 (Oct-2) protein levels through a mammalian target of rapamycin (mTOR)-dependent pathway in mouse RAW264.7 macrophages. As both iNOS and G-CSF are potential Oct-2 target genes, we tested the effect of rapamycin on their expression and found that it reduced the LPS-induced increase in iNOS and G-CSF mRNA levels and iNOS and G-CSF protein levels. Blocking of mTOR-signaling using a dominant-negative mTOR expression plasmid resulted in inhibition of the LPS-induced increase in iNOS and G-CSF protein levels, supporting the essential role of mTOR. Forced expression of Oct-2 using the pCG-Oct-2 plasmid overcame the inhibitory effect of rapamycin on the LPS-induced increase in iNOS and G-CSF mRNA levels. Chromatin immunoprecipitation assays showed that LPS enhanced the binding of Oct-2 to the iNOS and G-CSF promoters and that this effect was inhibited by pretreatment with rapamycin. Moreover, RNA interference knockdown of Oct-2 reduced iNOS and G-CSF expression in LPS-treated cells. The inhibitory effect of rapamycin on the LPS-induced increase in Oct-2 protein levels and on the iNOS and G-CSF mRNA levels was also detected in human THP-1 monocyte-derived macrophages. This study demonstrates that rapamycin reduces iNOS and G-CSF expression at the transcription level in LPS-treated macrophages by inhibiting Oct-2 expression.

Whole genomic expression analysis of octachlorostyrene-induced chronic toxicity in Caenorhabditis elegans

In recent years, microarray technology has enabled the investigation of possible mechanisms the expression of genes related to toxic compounds. We used a C. elegans whole genome microarray to observe and evaluate the chronic toxicity of the free-living nematode Caenorhabditis elegans (C. elegans) after exposure to octachlorostyrene, (OCS), a by-product in the manufacture of many chlorinated hydrocarbons. In this study, we examined sublethal toxicity, egg hatching, and movement of octachlorostyrene over three generations using a nematode growth medium (NGM) agar plate. In the third generation, OCS affected the fecundity rate of C. elegans. Specifically, the number of worm and eggs decreased significantly to about 50% of control (p < 0.05). In microarray experiments, total RNA was isolated at 0, 2 and 3 generations following treatment of OCS, and hybridized to the microarray containing about 22,000 C. elegans genes. Dye swaps were performed. After data analysis, we identified a total of 1,294 genes that were differentially expressed through generations.

Lethal anemia caused by interferon-beta produced in mouse embryos carrying undigested DNA

The livers of DNase II-deficient mouse embryos contain many macrophages carrying undigested DNA, and the embryos die in utero. Here we report that erythroid precursor cells underwent apoptosis in the livers of DNase II-deficient embryos and that in the liver, interferon-beta mRNA was expressed by the resident macrophages. When the DNase II-deficient mice were crossed with mice deficient in type I interferon receptor, the resultant 'double-mutant' mice were born healthy. The double-mutant embryos expressed interferon-beta mRNA, but the expression of a subset of the interferon-responsive genes dysregulated in DNase II-deficient embryos was restored to normal. These results indicate that the inability to degrade DNA derived from erythroid precursors results in interferon-beta production that induces expression of a specific set of interferon-responsive genes associated with embryonic lethality in DNase II-deficient mice.

Galectin-9 in physiological and pathological conditions

We first cloned galectin-9 (Gal-9)/ecalectin as a T cell-derived eosinophil chemoattractant. Gal-9 plays a role in not only accumulation but also activation of eosinophils in experimental allergic models and human allergic patients, because Gal-9 induces eosinophil chemoattraction in vitro and in vivo and activates eosinophils in many aspects. Gal-9 requires divalent galactoside-binding activity but not the linker peptide of Gal-9 to exhibit its biological functions, and an unidentified matrix metalloproteinase is involved in the release of Gal-9. Our recent studies also showed that Gal-9 has other functions, such as cell differentiation, aggregation, adhesion, and death. Now, we and other groups are on the way of investigating the regulation and function of Gal-9 in a variety of physiological and pathological conditions. In this article, we will show the possible role of Gal-9 in physiological and pathological conditions by using our recent findings.

Association of ABCA1 with syntaxin 13 and flotillin-1 and enhanced phagocytosis in tangier cells

The ATP-binding cassette transporter A1 (ABCA1) facilitates the cellular release of cholesterol and choline-phospholipids to apolipoprotein A-I (apoA-I) and several studies indicate that vesicular transport is associated with ABCA1 function. Syntaxins play a major role in vesicular fusion and have also been demonstrated to interact with members of the ABC-transporter family. Therefore, we focused on the identification of syntaxins that directly interact with ABCA1. The expression of syntaxins and ABCA1 in cultured human monocytes during M-CSF differentiation and cholesterol loading was investigated and syntaxins 3, 6, and 13 were found induced in foam cells together with ABCA1. Immunoprecipitation experiments revealed a direct association of syntaxin 13 and full-length ABCA1, whereas syntaxin 3 and 6 failed to interact with ABCA1. The colocalization of ABCA1 and syntaxin 13 was also shown by immunofluorescence microscopy. Silencing of syntaxin 13 by small interfering RNA (siRNA) led to reduced ABCA1 protein levels and hence to a significant decrease in apoA-I-dependent choline-phospholipid efflux. ABCA1 is localized in Lubrol WX-insoluble raft microdomains in macrophages and syntaxin 13 and flotillin-1 were also detected in these detergent resistant microdomains along with ABCA1. Syntaxin 13, flotillin-1, and ABCA1 were identified as phagosomal proteins, indicating the involvement of the phagosomal compartment in ABCA1-mediated lipid efflux. In addition, the uptake of latex phagobeads by fibroblasts with mutated ABCA1 was enhanced when compared with control cells and the recombinant expression of functional ABCA1 normalized the phagocytosis rate in Tangier fibroblasts. It is concluded that ABCA1 forms a complex with syntaxin 13 and flotillin-1, residing at the plasma membrane and in phagosomes that are partially located in raft microdomains.

Structural requirements of human DNase II alpha for formation of the active enzyme: the role of the signal peptide, N-glycosylation, and disulphide bridging

DNase II alpha (EC 3.1.22.1) is an endonuclease, which is active at low pH, that cleaves double-stranded DNA to short 3'-phosphoryl oligonucleotides. Although its biochemistry is well understood, its structure-activity relationship has been largely unexamined. Recently, we demonstrated that active DNase II alpha consists of one contiguous polypeptide, heavily glycosylated, and containing at least one intrachain disulphide linkage [MacLea, Krieser and Eastman (2002) Biochem. Biophys. Res. Commun. 292, 415-421]. The present paper describes further work to examine the elements of DNase II alpha protein required for activity. Truncated forms and site-specific mutants were expressed in DNase II alpha-null mouse cells. Results indicate that the signal-peptide leader sequence is required for correct glycosylation and that N-glycosylation is important for formation of the active enzyme. Despite this, enzymic deglycosylation of wild-type protein with peptide N-glycosidase F reveals that glycosylation is not intrinsically required for DNase activity. DNase II alpha contains six evolutionarily conserved cysteine residues, and mutations in any one of these cysteines completely ablated enzymic activity, consistent with the importance of disulphide bridging in maintaining correct protein structure. We also demonstrate that a mutant form of DNase II alpha that lacks the purported active-site His(295) can still bind DNA, indicating that this histidine residue is not simply involved in DNA binding, but may have a direct role in catalysis. These results provide a more complete model of the DNase II alpha protein structure, which is important for three-dimensional structural analysis and for production of DNase II alpha as a potential protein therapeutic for cystic fibrosis or other disorders.

Sp1 and Sp3 are involved in up-regulation of human deoxyribonuclease II transcription during differentiation of HL-60 cells

Expression of DNase II in macrophages is potentially crucially important in the removal of unwanted DNA. We have previously shown that DNase II expression is up-regulated at the transcriptional level during the phorbol 12-myristate-13-acetate (PMA)-induced differentiation of HL-60 and THP-1 cells. In this study, we investigated the cis-regulatory elements and transcription factors involved in this process in HL-60 cells. cis-Regulatory elements in the DNase II promoter were located by 5' deletion and site-directed mutagenesis of promoter-luciferase constructs and transient transfection of HL-60 cells. Furthermore, the binding proteins were identified by electrophoretic mobility shift assay (EMSA) in the presence of specific antibodies. In the DNase II promoter, 249 base pairs upstream of the transcription start site were essential for maximal promoter activity in both untreated and PMA-treated HL-60 cells and, within this region, three Sp1 and Sp3 binding sites were identified as essential for transcriptional regulation and PMA induction. Western blot analysis showed that PMA treatment resulted in increased levels of Sp1 and Sp3 proteins. Furthermore, cotransfection analysis in Drosophila SL2 cells showed that Sp1 was more potent than Sp3 in activating the DNase II promoter. We therefore conclude that Sp1 and/or Sp3 are involved in the up-regulation of DNase II expression during the differentiation of HL-60 cells.