STAT5 is an ambivalent regulator of neutrophil homeostasis

The methylome of buccal epithelial cells is influenced by age, sex, and physiological properties

Epigenetic modifications, particularly DNA methylation, have emerged as regulators of gene expression and are implicated in various biological processes and disease states. Understanding the factors influencing the epigenome is essential for unraveling its complexity. In this study, we aimed to identify how the methylome of buccal epithelial cells, a noninvasive and easily accessible tissue, is associated with demographic and health-related variables commonly used in clinical settings, such as age, sex, blood immune composition, hemoglobin levels, and others. We developed a model to assess the association of multiple factors with the human methylome and identify the genomic loci significantly impacted by each trait. We demonstrated that DNA methylation variation is accurately modeled by several factors. We confirmed the well-known impact of age and sex and unveiled novel clinical factors associated with DNA methylation, such as blood neutrophils, hemoglobin, red blood cell distribution width, high-density lipoprotein cholesterol, and urea. Genomic regions significantly associated with these traits were enriched in relevant transcription factors, drugs, and diseases. Among our findings, we showed that neutrophil-impacted loci were involved in neutrophil functionality and maturation. Similarly, hemoglobin-influenced sites were associated with several diseases, including aplastic anemia, and the genomic loci affected by urea were related to congenital anomalies of the kidney and urinary tract. Our findings contribute to a better understanding of the human methylome plasticity and provide insights into novel factors shaping DNA methylation patterns, highlighting their potential clinical implications as biomarkers and the importance of considering these physiological traits in future medical epigenomic investigations.NEW & NOTEWORTHY We have developed a quantitative model to assess how the human methylome is associated with several factors and to identify the genomic loci significantly impacted by each trait. We reported novel health-related factors driving DNA methylation patterns and new site-specific regulations that further elucidate methylome dynamics. Our study contributes to a better understanding of the plasticity of the human methylome and unveils novel physiological traits with a potential role in future medical epigenomic investigations.

A review of granulocyte colony-stimulating factor receptor signaling and regulation with implications for cancer

Granulocyte colony-stimulating factor receptor (GCSFR) is a critical regulator of granulopoiesis. Studies have shown significant upregulation of GCSFR in a variety of cancers and cell types and have recognized GCSFR as a cytokine receptor capable of influencing both myeloid and non-myeloid immune cells, supporting pro-tumoral actions. This systematic review aims to summarize the available literature examining the mechanisms that control GCSFR signaling, regulation, and surface expression with emphasis on how these mechanisms may be dysregulated in cancer. Experiments with different cancer cell lines from breast cancer, bladder cancer, glioma, and neuroblastoma are used to review the biological function and underlying mechanisms of increased GCSFR expression with emphasis on actions related to tumor proliferation, migration, and metastasis, primarily acting through the JAK/STAT pathway. Evidence is also presented that demonstrates a differential physiological response to aberrant GCSFR signal transduction in different organs. The lifecycle of the receptor is also reviewed to support future work defining how this signaling axis becomes dysregulated in malignancies.

Scaffold compound L971 exhibits anti-inflammatory activities through inhibition of JAK/STAT and NFκB signalling pathways

JAK/STAT and NFκB signalling pathways play essential roles in regulating inflammatory responses, which are important pathogenic factors of various serious immune-related diseases, and function individually or synergistically. To find prodrugs that can treat inflammation, we performed a preliminary high-throughput screening of 18 840 small molecular compounds and identified scaffold compound L971 which significantly inhibited JAK/STAT and NFκB driven luciferase activities. L971 could inhibit the constitutive and stimuli-dependent activation of STAT1, STAT3 and IκBα and could significantly down-regulate the proinflammatory gene expression in mouse peritoneal macrophages stimulated by LPS. Gene expression profiles upon L971 treatment were determined using high-throughput RNA sequencing, and significant differentially up-regulated and down-regulated genes were identified by DESeq analysis. The bioinformatic studies confirmed the anti-inflammatory effects of L971. Finally, L971 anti-inflammatory character was further verified in LPS-induced sepsis shock mouse model in vivo. Taken together, these data indicated that L971 could down-regulate both JAK/STAT and NFκB signalling activities and has the potential to treat inflammatory diseases such as sepsis shock.

Neutrophils are mediators of metastatic prostate cancer progression in bone

Bone metastatic prostate cancer (BM-PCa) significantly reduces overall patient survival and is currently incurable. Current standard immunotherapy showed promising results for PCa patients with metastatic, but less advanced, disease (i.e., fewer than 20 bone lesions) suggesting that PCa growth in bone contributes to response to immunotherapy. We found that: (1) PCa stimulates recruitment of neutrophils, the most abundant immune cell in bone, and (2) that neutrophils heavily infiltrate regions of prostate tumor in bone of BM-PCa patients. Based on these findings, we examined the impact of direct neutrophil-prostate cancer interactions on prostate cancer growth. Bone marrow neutrophils directly induced apoptosis of PCa in vitro and in vivo, such that neutrophil depletion in bone metastasis models enhanced BM-PCa growth. Neutrophil-mediated PCa killing was found to be mediated by suppression of STAT5, a transcription factor shown to promote PCa progression. However, as the tumor progressed in bone over time, neutrophils from late-stage bone tumors failed to elicit cytotoxic effector responses to PCa. These findings are the first to demonstrate that bone-resident neutrophils inhibit PCa and that BM-PCa are able to progress via evasion of neutrophil-mediated killing. Enhancing neutrophil cytotoxicity in bone may present a novel therapeutic option for bone metastatic prostate cancer.

Revealing the Critical Regulators of Cell Identity in the Mouse Cell Atlas

Recent progress in single-cell technologies has enabled the identification of all major cell types in mouse. However, for most cell types, the regulatory mechanism underlying their identity remains poorly understood. By computational analysis of the recently published mouse cell atlas data, we have identified 202 regulons whose activities are highly variable across different cell types, and more importantly, predicted a small set of essential regulators for each major cell type in mouse. Systematic validation by automated literature and data mining provides strong additional support for our predictions. Thus, these predictions serve as a valuable resource that would be useful for the broad biological community. Finally, we have built a user-friendly, interactive web portal to enable users to navigate this mouse cell network atlas.

Dual-Specificity Phosphatase 4 Regulates STAT5 Protein Stability and Helper T Cell Polarization

Immune responses are critically regulated by the functions of CD4 helper T cells. Based on their secreted cytokines, helper T cells are further categorized into different subsets like Treg or Th17 cells, which suppress or promote inflammatory responses, respectively. Signals from IL-2 activate the transcription factor STAT5 to promote Treg but suppress Th17 cell differentiation. Our previous results found that the deficiency of a dual-specificity phosphatase, DUSP4, induced STAT5 hyper-activation, enhanced IL-2 signaling, and increased T cell proliferation. In this report, we examined the effects of DUSP4 deficiency on helper T cell differentiation and STAT5 regulation. Our in vivo data showed that DUSP4 mice were more resistant to the induction of autoimmune encephalitis, while in vitro differentiations revealed enhanced iTreg and reduced Th17 polarization in DUSP4-deficient T cells. To study the cause of this altered helper T cell polarization, we performed luciferase reporter assays and confirmed that, as predicted by our previous report, DUSP4 over-expression suppressed the transcription factor activity of STAT5. Surprisingly, we also found that DUSP4-deficient T but not B cells exhibited elevated STAT5 protein levels, and over-expressed DUSP4 destabilized STAT5 in vitro; moreover, this destabilization required the phosphatase activity of DUSP4, and was insensitive to MG132 treatment. Finally, domain-mapping results showed that both the substrate-interacting and the phosphatase domains of DUSP4 were required for its optimal interaction with STAT5, while the coiled-coil domain of STAT5 appeared to hinder this interaction. Our data thus provide the first genetic evidence that DUSP4 is important for helper T cell development. In addition, they also help uncover the novel, DUSP4-mediated regulation of STAT5 protein stability.

Central role of conventional dendritic cells in regulation of bone marrow release and survival of neutrophils

Neutrophils are the most abundant cell type in the immune system and play an important role in the innate immune response. Using a diverse range of mouse models with either defective dendritic cell (DC) development or conditional DC depletion, we provide in vivo evidence indicating that conventional DCs play an important role in the regulation of neutrophil homeostasis. Flk2, Flt3L, and Batf3 knockout mice, which have defects in DC development, have increased numbers of liver neutrophils in the steady state. Conversely, neutrophil frequency is reduced in DC-specific PTEN knockout mice, which have an expansion of CD8(+) and CD103(+) DCs. In chimeric CD11c-DTR mice, conventional DC depletion results in a systemic increase of neutrophils in peripheral organs in the absence of histological inflammation or an increase in proinflammatory cytokines. This effect is also present in splenectomized chimeric CD11c-DTR mice and is absent in chimeric mice with 50% normal bone marrow. In chimeric CD11c-DTR mice, diphtheria toxin treatment results in enhanced neutrophil trafficking from the bone marrow into circulation and increased neutrophil recruitment. Moreover, there is an increased expression of chemokines/cytokines involved in neutrophil homeostasis and reduced neutrophil apoptosis. These data underscore the role of the DC pool in regulating the neutrophil compartment in nonlymphoid organs.

Bortezomib inhibits STAT5-dependent degradation of LEF-1, inducing granulocytic differentiation in congenital neutropenia CD34(+) cells

The transcription factor lymphoid enhancer-binding factor 1 (LEF-1), which plays a definitive role in granulocyte colony-stimulating factor (G-CSF) receptor-triggered granulopoiesis, is downregulated in granulocytic progenitors of severe congenital neutropenia (CN) patients. However, the exact mechanism of LEF-1 downregulation is unclear. CN patients are responsive to therapeutically high doses of G-CSF and are at increased risk of developing acute myeloid leukemia. The normal expression of LEF-1 in monocytes and lymphocytes, whose differentiation is unaffected in CN, suggests the presence of a granulopoiesis-specific mechanism downstream of G-CSF receptor signaling that leads to LEF-1 downregulation. Signal transducer and activator of transcription 5 (STAT5) is activated by G-CSF and is hyperactivated in acute myeloid leukemia. Here, we investigated the effects of activated STAT5 on LEF-1 expression and functions in hematopoietic progenitor cells. We demonstrated that constitutively active STAT5a (caSTAT5a) inhibited LEF-1-dependent autoregulation of the LEF-1 gene promoter by binding to the LEF-1 protein, recruiting Nemo-like kinase and the E3 ubiquitin-ligase NARF to LEF-1, leading to LEF-1 ubiquitination and a reduction in LEF-1 protein levels. The proteasome inhibitor bortezomib reversed the defective G-CSF-triggered granulocytic differentiation of CD34(+) cells from CN patients in vitro, an effect that was accompanied by restoration of LEF-1 protein levels and LEF-1 messenger RNA autoregulation. Taken together, our data define a novel mechanism of LEF-1 downregulation in CN patients via enhanced ubiquitination and degradation of LEF-1 protein by hyperactivated STAT5.

Gain-of-function of Stat5 leads to excessive granulopoiesis and lethal extravasation of granulocytes to the lung

The Signal Transducer and Activator of Transcription 5 (Stat5) plays a significant role in normal hematopoiesis and a variety of hematopoietic malignancies. Deficiency in Stat5 causes impaired cytokine-mediated proliferation and survival of progenitors and their differentiated descendants along major hematopoietic lineages such as erythroid, lymphoid, and myeloid cells. Overexpression and persistent activation of Stat5 are sufficient for neoplastic transformation and development of multi-lineage leukemia in a transplant model. Little is known, however, whether a continuous activation of this signal transducer is essential for the maintenance of hematopoietic malignancies. To address this issue, we developed transgenic mice that express a hyperactive mutant of Stat5 in hematopoietic progenitors and derived lineages in a ligand-controlled manner. In contrast to the transplant model, expression of mutant Stat5 did not adversely affect normal hematopoiesis in the presence of endogenous wildtype Stat5 alleles. However, the gain-of-function of this signal transducer in mice that carry Stat5a/b hypomorphic alleles resulted in abnormally high numbers of circulating granulocytes that caused severe airway obstruction. Downregulation of hyperactive Stat5 in diseased animals restored normal granulopoiesis, which also resulted in a swift clearance of granulocytes from the lung. Moreover, we demonstrate that Stat5 promotes the initiation and maintenance of severe granulophilia in a cell autonomous manner. The results of this study show that the gain-of-function of Stat5 causes excessive granulopoiesis and prolonged survival of granulocytes in circulation. Collectively, our findings underline the critical importance of Stat5 in maintaining a normal balance between myeloid and lymphoid cells during hematopoiesis, and we provide direct evidence for a function of Stat5 in granulophilia–associated pulmonary dysfunction.

Computational identification of transcriptional regulators in human endotoxemia

One of the great challenges in the post-genomic era is to decipher the underlying principles governing the dynamics of biological responses. As modulating gene expression levels is among the key regulatory responses of an organism to changes in its environment, identifying biologically relevant transcriptional regulators and their putative regulatory interactions with target genes is an essential step towards studying the complex dynamics of transcriptional regulation. We present an analysis that integrates various computational and biological aspects to explore the transcriptional regulation of systemic inflammatory responses through a human endotoxemia model. Given a high-dimensional transcriptional profiling dataset from human blood leukocytes, an elementary set of temporal dynamic responses which capture the essence of a pro-inflammatory phase, a counter-regulatory response and a dysregulation in leukocyte bioenergetics has been extracted. Upon identification of these expression patterns, fourteen inflammation-specific gene batteries that represent groups of hypothetically ‘coregulated’ genes are proposed. Subsequently, statistically significant cis-regulatory modules (CRMs) are identified and decomposed into a list of critical transcription factors (34) that are validated largely on primary literature. Finally, our analysis further allows for the construction of a dynamic representation of the temporal transcriptional regulatory program across the host, deciphering possible combinatorial interactions among factors under which they might be active. Although much remains to be explored, this study has computationally identified key transcription factors and proposed a putative time-dependent transcriptional regulatory program associated with critical transcriptional inflammatory responses. These results provide a solid foundation for future investigations to elucidate the underlying transcriptional regulatory mechanisms under the host inflammatory response. Also, the assumption that coexpressed genes that are functionally relevant are more likely to share some common transcriptional regulatory mechanism seems to be promising, making the proposed framework become essential in unravelling context-specific transcriptional regulatory interactions underlying diverse mammalian biological processes.

The transcription factors STAT5A/B regulate GM-CSF-mediated granulopoiesis

Neutrophils play a vital role in the immune defense, which is evident by the severity of neutropenia causing life-threatening infections. Granulocyte macrophage-colony stimulating factor (GM-CSF) controls homeostatic and emergency development of granulocytes. However, little is known about the contribution of the downstream mediating transcription factors signal transducer and activator of transcription 5A and 5B (STAT5A/B). To elucidate the function of this pathway, we generated mice with complete deletion of both Stat5a/b genes in hematopoietic cells. In homeostasis, peripheral neutrophils were markedly decreased in these animals. Moreover, during emergency situations, such as myelosuppression, Stat5a/b-mutant mice failed to produce enhanced levels of neutrophils and were unable to respond to GM-CSF. Both the GM-CSF-permitted survival of mature neutrophils and the generation of granulocytes from granulocyte-macrophage progenitors (GMPs) were markedly reduced in Stat5a/b mutants. GMPs showed impaired colony-formation ability with reduced number and size of colonies on GM-CSF stimulation. Moreover, continuous cell fate analyses by time-lapse microscopy and single cell tracking revealed that Stat5a/b-null GMPs showed both delayed cell-cycle progression and increased cell death. Finally, transcriptome analysis indicated that STAT5A/B directs GM-CSF signaling through the regulation of proliferation and survival genes.

Genetic and molecular diagnosis of severe congenital neutropenia

PURPOSE OF REVIEW

Severe congenital neutropenia has been a well known hematological condition for over 50 years. Over this long period of time, the variable genetic causes and associated sequelae of the disease have been ascertained, and successful treatment strategies developed. Over the past 2 years, however, new studies have added greatly to our understanding of the molecular basis of the disease, details of which are presented in this review.

RECENT FINDINGS

Recent studies have elucidated a role for the unfolded protein response in mediating the pathogenic effects of ELA2 mutations, the most common mutation in severe congenital neutropenia (SCN) as well as cyclic neutropenia. Genetic lesions in HAX1 have also been identified in the original Kostmann pedigree representing the autosomal recessive form of SCN. An emerging theme is the convergence of these and other genetic lesions underlying SCN in enhancing neutrophil apoptosis. Other studies have revealed the importance of multiple independent mutations in these and other genes in SCN. Finally, the key role for signal transducer and activator of transcription 5 in mediating the effects of granulocyte colony-stimulating factor receptor truncation mutations in the development of myelodysplastic syndrome/acute myeloid leukemia following SCN has been elucidated.

SUMMARY

As the full spectrum of molecular mutations causing neutropenia emerges, it is becoming possible to differentiate patients into subtypes with different prognoses, for whom tailored therapies are indicated.

Profound functional and signaling changes in viable inflammatory neutrophils homing to cystic fibrosis airways

Blood neutrophils recruited to cystic fibrosis (CF) airways are believed to be rapidly killed by resident bacteria and to passively release elastase and other toxic by-products that promote disease progression. By single-cell analysis, we demonstrate that profound functional and signaling changes readily occur within viable neutrophils recruited to CF airways, compared with their blood counterparts. Airway neutrophils have undergone conventional activation, as shown by decreased intracellular glutathione, increased lipid raft assembly, surface mobilization of CD11b+ and CD66b+ granules, and increased levels of the cytoskeleton-associated phospho-Syk kinase. Unexpectedly, they also mobilize to the surface CD63+ elastase-rich granules, usually confined intracellularly, and lose surface expression of CD16 and CD14, both key receptors in phagocytosis. Furthermore, they express CD80, major histocompatibility complex type II, and the prostaglandin D2 receptor CD294, all normally associated with other lineages, which reflects functional reprogramming. This notion is reinforced by their decreased total phosphotyrosine levels, mirroring a postactivated stage, and increased levels of the phospho-S6 ribosomal protein, a key anabolic switch. Thus, we identified a subset of neutrophils within CF airways with a viable but dysfunctional phenotype. This subset provides a possible therapeutic target and indicates a need to revisit current paradigms of CF airway disease.

STAT5 requires the N-domain to maintain hematopoietic stem cell repopulating function and appropriate lymphoid-myeloid lineage output

OBJECTIVE

Signal transducer and activator of transcription 5 (STAT5) is a critical regulator of hematopoietic development and its impaired activation is associated with hematopoietic and immune cell defects. However, much of this information has been learned from knockout mice that still retain the potential for expression of STAT5 proteins that are N-terminally truncated due to alternative internal translation initiation codons. The goal of these studies was to use transplantation-based assays to analyze the degree of STAT5 deltaN activity in hematopoietic stem cells (HSC) and throughout lymphomyeloid development.

METHODS

We have directly compared E14.5 fetal liver cells from mice with potential to express STAT5ab deltaN (STAT5ab(deltaN/deltaN)) with mice completely lacking STAT5a and STAT5b (STAT5abnull/null). We have also utilized retroviral complementation of STAT5abnull/null fetal liver HSC to enforce expression of full-length STAT5a or STAT5a lacking the first 136 amino acids (STAT5a deltaN).

RESULTS

We report that STAT5 is required for HSC, lymphocyte, and erythrocyte development. We demonstrate that restored expression of STAT5a in STAT5abnull/null HSC provides a strong selective advantage, correcting T- and B-lymphocyte and erythrocyte development. Interestingly, Gr-1(+) blood cells were inversely correlated with B lymphocytes and both were normalized by STAT5a expression. In contrast, transduction of STAT5a deltaN only provided partial B-lymphocyte development.

CONCLUSIONS

These studies define the role of STAT5 in maintaining normal lymphoid vs myeloid balance during hematopoiesis and highlight a major role for the N-domain in HSC function. The platform of retroviral complementation described here will be particularly useful for future studies to subdefine the N-domain regions that are critical for hematopoiesis.