Carboxy-terminal truncated STAT5 is induced by interleukin-2 and GM-CSF in human neutrophils

Grass carp Il-2 promotes neutrophil extracellular traps formation via inducing ROS production and autophagy in vitro

Interleukin (IL)-2 has been reported to regulate neutrophil functions in humans, mice, pigs and chicken although it is a key regulator of T cells. Consistently, we found that grass carp (Ctenopharyngodon idellus) interleukin-2 (gcIl-2) is capable of modulating the antimicrobial activities of neutrophils via regulating granzyme B- and perforin-like gene expression in our previous study. In the present study, stimulation of gcIl-2 on neutrophil extracellular traps (NETs) formation in grass carp neutrophils was demonstrated by detecting free DNA release, histone H3 citrullination and morphological changes of the cells. Further investigation revealed that reactive oxygen species (ROS) production from NADPH oxidase but not mitochondria was involved in NETosis induced by gcIl-2. Aside from ROS, autophagy was disclosed to be indispensable for NETosis induced by gcIl-2. These converging lines of evidence suggested that fish Il-2 could induce NETs formation via NADPH oxidase-derived ROS- and autophagy-dependent pathways in fish species which is evolutionarily conserved with that in mammals. It is noteworthy that these two pathways did not interplay with each other in Il-2-stimulated NETosis. The mechanisms governing autophagy induced by Il-2 were also explored in the present study, showing that Il-2 modulated the action of high mobility group box 1 (HMGB1) protein to stimulate autophagy, leading to NETs formation in fish neutrophils. These results provided a new insight to the function of Il-2 in fish neutrophils, and a clue about the regulation of NETosis in the lower vertebrates.

RNA sequencing from human neutrophils reveals distinct transcriptional differences associated with chronic inflammatory states

BACKGROUND

The transcriptional complexity of mammalian cells suggests that they have broad abilities to respond to specific environmental stimuli and physiologic contexts. These abilities were not apparent a priori from the structure of mammalian genomes, but have been identified through detailed transcriptome analyses. In this study, we examined the transcriptomes of cells of the innate immune system, human neutrophils, using RNA sequencing (RNAseq).

METHODS

We sequenced poly-A RNA from nine individual samples corresponding to specific phenotypes: three children with active, untreated juvenile idiopathic arthritis (JIA)(AD), three children with the same disease whose disease was inactive on medication (CRM), and three children with cystic fibrosis (CF).

RESULTS

We demonstrate that transcriptomes of neutrophils, typically considered non-specific in their responses and functions, display considerable specificity in their transcriptional repertoires dependent on the pathologic context, and included genes, gene isoforms, and long non-coding RNA transcripts. Furthermore, despite the small sample numbers, these findings demonstrate the potential of RNAseq approaches to biomarker development in rheumatic diseases.

CONCLUSIONS

These data demonstrate the capacity of cells previously considered non-specific in function to adapt their transcriptomes to specific biologic contexts. These data also provide insight into previously unrecognized pathological pathways and show considerable promise for elucidating disease and disease-state specific regulatory networks.

Endothelium-derived GM-CSF influences expression of oncostatin M

During and after transendothelial migration, neutrophils undergo a number of phenotypic changes resulting from encounters with endothelium-derived factors. This report uses an in vitro model with human umbilical vein endothelial cells and isolated human neutrophils to examine the effects of two locally derived cytokines, granulocyte (G)-macrophage (M) colony-stimulating factor (GM-CSF) and G-CSF, on oncostatin M (OSM) expression. Neutrophils contacting activated HUVEC expressed and released increased amounts of oncostatin M (OSM), a proinflammatory cytokine known to induce polymorphonuclear neutrophil adhesion and chemotaxis. Neutrophil transendothelial migration resulted in threefold higher OSM expression and protein levels compared with nontransmigrated cells. Addition of anti-GM-CSF neutralizing antibody reduced OSM expression level but anti-G-CSF was without effect. GM-CSF but not G-CSF protein addition to cultures of isolated neutrophils resulted in a significant increase in OSM protein secretion. However, inhibition of β(2) integrins by neutralizing antibody significantly reduced GM-CSF-induced OSM production indicating this phenomenon is adhesion dependent. Thus cytokine-stimulated endothelial cells can produce sufficient quantities of GM-CSF to influence in an adhesion-dependent manner, the phenotypic characteristics of neutrophils resulting in the latter's transmigration. Both transmigration and adhesion phenomenon lead to increased production of OSM by neutrophils that then play a major role in inflammatory response.

Purification and identification of the STAT5 protease in myeloid cells

STAT (signal transducer and activator of transcription) proteins are critical regulators of cytokine-induced cell proliferation, differentiation and survival. STAT functional activity can be variably regulated by post-translational modifications, including phosphorylation, acetylation, methylation and sumoylation. Additionally, limited proteolytic digestion of full-length STAT proteins (STATalpha) generates C-terminally truncated forms (STATgamma) in different cell lineages, which have significantly reduced transcriptional activity due to the lack of the transactivation domain. Previously, it has been shown that STAT5gamma, generated by an unidentified nuclear serine protease, plays an important role in myeloid cell differentiation and is aberrantly expressed in acute myeloid leukaemia. To better understand this regulatory mechanism for STAT5 function, we have purified the STAT5 protease from the immature myeloid cell line 32D and identified it by MS analysis as the granule-derived serine protease, CatG (cathepsin G). We show that purified CatG can specifically cleave full-length STAT5 to generate STAT5gamma, and this activity can be inhibited by AEBSF [4-(2-aminoethyl)benzenesulfonyl fluoride] in an in vitro protease assay. Importantly, preparation of nuclear and cytoplasmic extracts from immature myeloid cell lines, 32D and FDC-P1, in the presence of a specific inhibitor for CatG results in the identification of STAT5alpha only. These studies indicate that nuclear STAT5gamma does not naturally exist in immature myeloid cells and is artificially generated from STAT5alpha during the preparation of extracts due to the abundance of CatG in these cells. Therefore in contrast with earlier studies, our data suggest that STAT5alpha, rather than STAT5gamma is the active form in immature myeloid cells.

Naturally occurring C-terminally truncated STAT5 is a negative regulator of HIV-1 expression

CD4(+) cells of most individuals infected with HIV-1 harbor a C-terminally truncated and constitutively activated form of signal transducer and activator of transcription-5 (STAT5 Delta). We report that the chronically HIV-infected U1 cell line expresses STAT5 Delta but not full-length STAT5. Granulocyte-macrophage colony-stimulating factor (GM-CSF) stimulation of U1 cells promoted early activation of STAT5 Delta and of extracellular signal regulated kinases (ERKs), followed by later activation of activator protein 1 (AP-1) and HIV expression. Inhibition of ERK/AP-1 by PD98,059 abolished, whereas either tyrphostin AG490 or a STAT5 small interfering RNA (siRNA) enhanced, virion production in GM-CSF-stimulated U1 cells. Chromatin immunoprecipitation demonstrated the induction of STAT5 Delta binding to STAT consensus sequences in the HIV-1 promoter together with a decreased recruitment of RNA polymerase II after 1 hour of GM-CSF stimulation of U1 cells. Down-regulation of STAT5 Delta by siRNA resulted in the up-regulation of both HIV-1 gag-pol RNA and p24 Gag antigen expression in CD8-depleted leukocytes of several HIV-positive individuals cultivated ex vivo in the presence of interleukin-2 but not of interleukin-7. Thus, the constitutively activated STAT5 Delta present in the leukocytes of most HIV-positive individuals acts as a negative regulator of HIV expression.

The G-CSF receptor carboxyl terminus, truncated in AML/SCN, is required for induction of a Stat5 protease activity

Granulocyte colony-stimulating factor (G-CSF) has been shown to stimulate the activation of the signal transducer and activator of transcription 5 (Stat5). We show here that G-CSF-stimulated activation of Stat5 was attenuated when myeloid cells were induced to differentiate with G-CSF. Attenuated activation of Stat5 correlated with reduced Stat5 protein levels, which was associated with upregulation of a Stat5 protease activity. Carboxyl terminal truncation of the G-CSF receptor or expression of leukemogenic proteins Bcr-Abl and Tel-Jak2 abolished the upregulation of the Stat5 protease activity by G-CSF. These data add to our understanding of the roles of G-CSF and Stat5 in normal granulopoiesis and leukemogenesis.

Regulation of STAT signalling by proteolytic processing

Interaction of cytokines with their cognate receptors leads to the activation of latent transcription factors, the signal transducer and activator of transcription (STAT) proteins. Numerous studies have identified the critical roles played by STAT proteins in regulating cell proliferation, differentiation and survival. Consequently, the activity of STAT proteins is negatively regulated by a variety of different mechanisms, which include alternative splicing, covalent modifications, protein-protein interactions with negative regulatory proteins and proteolytic processing by proteases. Cleavage of STAT proteins by proteases results in the generation of C-terminally truncated proteins, called STATgamma, which lack the transactivation domain and behave as functional dominant-negative proteins. Currently, STATgamma isoforms have been identified for Stat3, Stat5a, Stat5b and Stat6 in different cellular contexts and biological processes. Evidence is mounting for the role of as yet unidentified serine proteases in the proteolytic processing of STAT proteins, although at least one cysteine protease, calpain is also known to cleave these STATs in platelets and mast cells. Recently, studies of acute myeloid leukaemia and cutaneous T cell lymphoma patients have revealed important roles for the aberrant expression of Stat3gamma and Stat5gamma proteins in the pathology of these diseases. Together, these findings indicate that proteolytic processing is an important mechanism in the regulation of STAT protein biological activity and provides a fertile area for future studies.

Signal transducer and activator of transcription (STAT) signalling and T-cell lymphomas

Interaction of cytokines with their cognate receptors leads to the activation of latent transcription factors - the signal transducers and activators of transcription (STAT) proteins - whose biological activities ultimately regulate many critical aspects of cell growth, survival and differentiation. Dysregulation of the JAK-STAT pathway is frequently observed in many primary human tumours, reflecting the importance of this pathway in the maintenance of cellular integrity. Here we review the current progress in STAT structure and function, and the contribution of STAT signalling to the pathogenesis of T-cell lymphomas.

Human neutrophils produce interferon gamma upon stimulation by interleukin-12

Interferon gamma (IFNgamma) is a Th1 cytokine mainly produced by T cells, NK cells and macrophages in response to interleukin (IL)-12. As polymorphonuclear neutrophils (PMN) have been shown to produce and to release numerous cytokines, in particular upon IL-12 stimulation, we investigated the ability of highly purified PMN to secrete IFNgamma. We found that PMN contained a small store of IFNgamma, and that this store was rapidly secreted upon stimulation by degranulating agents such as formyl peptides. Moreover, after a few hours of stimulation with appropriate agents, PMN synthesized IFNgamma. The effect of IL-12 was time- and concentration-dependent, and IL-12 combinations with IL-2, IL-15, IL-18 or LPS were highly synergistic. Cycloheximide inhibited IFNgamma release in such optimal conditions, confirming the ability of PMN to synthesize IFNgamma. IFNgamma synthesis was associated with an increase in specific mRNA content, pointing to a transcriptional mechanism. The IFNgamma produced by PMN was biologically active, as demonstrated by its ability to induce TNFalpha synthesis by PMN themselves or to induce IL-10 synthesis by peripheral blood mononuclear cells. These findings reveal a novel pathway of autocrine and paracrine PMN activation. They also identified a new role for IFNgamma, bridging innate and adaptive immune responses.