Structure of the mouse Stat 3/5 locus: evolution from Drosophila to zebrafish to mouse

Genomic Mutations of the STAT5 Transcription Factor Are Associated with Human Cancer and Immune Diseases

Signal transducer and activation of transcription 5 (STAT5) is a key transcription factor that regulates various biological processes in mammalian development. Aberrant regulation of STAT5 has also been causally linked to many diseases, including cancers and immune-related diseases. Although persistent activation of STAT5 due to dysregulation of the signaling cascade has been reported to be associated with the progression of solid tumors and leukemia, various genomic mutations of STAT5 have also been found to cause a wide range of diseases. The present review comprehensively summarizes results of recent studies evaluating the intrinsic function of STAT5 and the link between STAT5 mutations and human diseases. This review also describes the types of disease models useful for investigating the mechanism underlying STAT5-driven disease progression. These findings provide basic knowledge for understanding the regulatory mechanisms of STAT5 and the progression of various diseases resulting from aberrant regulation of STAT5. Moreover, this review may provide insights needed to create optimal disease models that reflect human disease associated STAT5 mutations and to design gene therapies to correct STAT5 mutations.

The Mammary Gland: Basic Structure and Molecular Signaling during Development

The mammary gland is a compound, branched tubuloalveolar structure and a major characteristic of mammals. The mammary gland has evolved from epidermal apocrine glands, the skin glands as an accessory reproductive organ to support postnatal survival of offspring by producing milk as a source of nutrition. The mammary gland development begins during embryogenesis as a rudimentary structure that grows into an elementary branched ductal tree and is embedded in one end of a larger mammary fat pad at birth. At the onset of ovarian function at puberty, the rudimentary ductal system undergoes dramatic morphogenetic change with ductal elongation and branching. During pregnancy, the alveolar differentiation and tertiary branching are completed, and during lactation, the mature milk-producing glands eventually develop. The early stages of mammary development are hormonal independent, whereas during puberty and pregnancy, mammary gland development is hormonal dependent. We highlight the current understanding of molecular regulators involved during different stages of mammary gland development.

Nipah Virus V Protein Binding Alters MDA5 Helicase Folding Dynamics

Nipah virus (NiV) is an emerging and deadly zoonotic paramyxovirus that is responsible for periodic epidemics of acute respiratory illness and encephalitis in humans. Previous studies have shown that the NiV V protein antagonizes host antiviral immunity, but the molecular mechanism is incompletely understood. To address this gap, we biochemically characterized NiV V binding to the host pattern recognition receptor MDA5. We find that the C-terminal domain of NiV V (V_CTD) is sufficient to bind the MDA5_SF2 domain when recombinantly co-expressed in bacteria. Analysis by hydrogen-deuterium exchange mass spectrometry (HDX-MS) studies revealed that NiV V_CTD is conformationally dynamic, and binding to MDA5 reduces the dynamics of V_CTD. Our results also suggest that the β-sheet region in between the MDA5 Hel1, Hel2, and Hel2i domains exhibits rapid HDX. Upon V_CTD binding, these β-sheet and adjacent residues show significant protection. Collectively, our findings suggest that NiV V binding disrupts the helicase fold and dynamics of MDA5 to antagonize host antiviral immunity.

A centric view of JAK/STAT5 in intestinal homeostasis, infection, and inflammation

Cytokines, growth factors or hormones take action through the JAK/STAT5 signaling pathway, which plays a critical role in regulating the intestinal response to infection and inflammation. However, the way in which STAT5 regulates intestinal epithelial compartment is largely ignored due to the lack of genetic tools for proper exploration and because the two STAT5 transcription factors (STAT5A and STAT5B) have some redundant but also distinct functions. In this review article, by focusing on STAT5 functions in the intestinal undifferentiated and differentiated epithelia, we discuss major advances of the growth factor/cytokine-JAK/STAT5 research in view of intestinal mucosal inflammation and immunity. We highlight the gap in the research of the intestinal STAT5 signaling to anticipate the gastrointestinal explorative insights. Furthermore, we address the critical questions to illuminate how STAT5 signaling influences intestinal epithelial cell differentiation and stem cell regeneration during homeostasis and injury. Overall, our article provides a centric view of the relevance of the relationship between chronic inflammatory diseases and JAK/STAT5 pathway and it also gives an example of how chronic infection and inflammation pirate STAT5 signaling to worsen intestinal injuries. Importantly, our review suggests how to protect a wound healing from gastrointestinal diseases by modulating intestinal STAT5.

Zika Virus-Encoded NS2A and NS4A Strongly Downregulate NF-κB Promoter Activity

Since Zika virus (ZIKV) was first detected in Uganda in 1947, serious outbreaks have occurred globally in Yap Island, French Polynesia and Brazil. Even though the number of infections and spread of ZIKV have risen sharply, the pathogenesis and replication mechanisms of ZIKV have not been well studied. ZIKV, a recently highlighted Flavivirus, is a mosquito-borne emerging virus causing microcephaly and the Guillain-Barre syndrome in fetuses and adults, respectively. ZIKV polyprotein consists of three structural proteins named C, prM and E and seven nonstructural proteins named NS1, NS2A, NS2B, NS3, NS4A, NS4B, and NS5 in an 11-kb single-stranded positive sense RNA genome. The function of individual ZIKV genes on the host innate immune response has barely been studied. In this study, we investigated the modulations of the NF-κB promoter activity induced by the MDA5/RIG-I signaling pathway. According to our results, two nonstructural proteins, NS2A and NS4A, dramatically suppressed the NF-κB promoter activity by inhibiting signaling factors involved in the MDA5/RIG-I signaling pathway. Interestingly, NS2A suppressed all components of MDA5/RIG-I signaling pathway, but NS4A inhibited most signaling molecules, except IKKε and IRF3-5D. In addition, both NS2A and NS4A downregulated MDA5-induced NF-κB promoter activity in a dosedependent manner. Taken together, our results suggest that NS2A and NS4A signifcantly antagonize MDA5/RIG-I-mediated NF-κB production, and these proteins seem to be controlled by different mechanisms. This study could help understand the mechanisms of how ZIKV controls innate immune responses and may also assist in the development of ZIKV-specific therapeutics.

Genome-wide identification, characterization of RLR genes in Yesso scallop (Patinopecten yessoensis) and functional regulations in responses to ocean acidification

Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs), are crucial sensors with a conserved structure in cytoplasm, inducing the production of cytokines, chemokines and host restriction factors which mediate a variety of intracellular activities to interfere with distinct PAMPs (pathogen-associated molecular patterns) for eliminating pathogens in innate immune system. Although RLR genes have been investigated in most vertebrates and some invertebrates, the systematic identification and characterization of RLR genes have not been reported in scallops. In this study, four RLR genes (PY-10413.4, PY-10413.5, PY-443.7 and PY-443.8, designated PyRLRs) were identified in Yesso scallop (Patinopecten yessoensis) through whole-genome scanning through in silico analysis, including two pairs of tandem duplicate genes located on the same scaffold (PY-10413.4 and PY-10413.5, PY-443.7 and PY-443.8, respectively). Phylogenetic and protein structural analyses were performed to determine the identities and evolutionary relationships of these genes. The expression profiles of PyRLRs were determined in all developmental stages, in healthy adult tissues, and in mantles that simulated ocean acidification (OA) exposure (pH = 6.5 and 7.5) at different time points (3, 6, 12 and 24 h). Spatiotemporal expression patterns suggested the functional roles of PyRLRs in all stages of development and growth of the scallop. Regulation expressions revealed PY-10413.4 and PY-10413.5 with one or two CARD(s) (caspase activation and recruitment domain) were up-regulated expressed at most time points, whereas PY-443.8 and PY-10413.4 without CARD were significantly down-regulated at each time points, suggesting functional differentiations in the two pairs of PyRLRs based on the structural differences in response to OA. Collectively, this study demonstrated gene duplication of RLR family genes and provide primary analysis for versatile roles in the response of the bivalve innate immune system to OA challenge.

Cnp Promoter-Driven Sustained ERK1/2 Activation Increases B-Cell Activation and Suppresses Experimental Autoimmune Encephalomyelitis

The ERK1/2 signaling pathway promotes myelin wrapping during development and remyelination, and sustained ERK1/2 activation in the oligodendrocyte (OL) lineage results in hypermyelination of the CNS. We therefore hypothesized that increased ERK1/2 signaling in the OL lineage would 1) protect against immune-mediated demyelination due to increased baseline myelin thickness and/or 2) promote enhanced remyelination and thus functional recovery after experimental autoimmune encephalomyelitis (EAE) induction. Cnp-Cre;Mek1DD-eGFP/+ mice that express a constitutively active form of MEK1 (the upstream activator of ERK1/2) in the OL lineage, exhibited a significant decrease in EAE clinical severity compared to controls. However, experiments using tamoxifen-inducible Plp-CreERT;Mek1DD-eGFP/+ or Pdgfrα-CreERT;Mek1DD-eGFP mice revealed this was not solely due to a protective or reparative effect resulting from MEK1DD expression specifically in the OL lineage. Because EAE is an immune-mediated disease, we examined Cnp-Cre;Mek1DD-eGFP/+ splenic immune cells for recombination. Surprisingly, GFP+ recombined CD19+ B-cells, CD11b+ monocytes, and CD3+ T-cells were noted when Cre expression was driven by the Cnp promoter. While ERK1/2 signaling in monocytes and T-cells is associated with proinflammatory activation, fewer studies have examined ERK1/2 signaling in B-cell populations. After in vitro stimulation, MEK1DD-expressing B-cells exhibited a 3-fold increase in CD138+ plasmablasts and a 5-fold increase in CD5+CD1dhi B-cells compared to controls. Stimulated MEK1DD-expressing B-cells also exhibited an upregulation of IL-10, known to suppress the initiation of EAE when produced by CD5+CD1dhi regulatory B-cells. Taken together, our data support the conclusion that sustained ERK1/2 activation in B-cells suppresses immune-mediated demyelination via increasing activation of regulatory B10 cells.

JAK/STAT Cytokine Signaling at the Crossroad of NK Cell Development and Maturation

Natural Killer (NK) cells are cytotoxic lymphocytes of the innate immune system and play a critical role in anti-viral and anti-tumor responses. NK cells develop in the bone marrow from hematopoietic stem cells (HSCs) that differentiate through common lymphoid progenitors (CLPs) to NK lineage-restricted progenitors (NKPs). The orchestrated action of multiple cytokines is crucial for NK cell development and maturation. Many of these cytokines such as IL-2, IL-7, IL-12, IL-15, IL-21, IL-27, and interferons (IFNs) signal via the Janus Kinase / Signal Transducer and Activator of Transcription (JAK/STAT) pathway. We here review the current knowledge about these cytokines and the downstream signaling involved in the development and maturation of conventional NK cells and their close relatives, innate lymphoid cells type 1 (ILC1). We further discuss the role of suppressor of cytokine signaling (SOCS) proteins in NK cells and highlight their potential for therapeutic application.

STAT5A and STAT5B-Twins with Different Personalities in Hematopoiesis and Leukemia

The transcription factors STAT5A and STAT5B have essential roles in survival and proliferation of hematopoietic cells-which have been considered largely redundant. Mutations of upstream kinases, copy number gains, or activating mutations in STAT5A, or more frequently in STAT5B, cause altered hematopoiesis and cancer. Interfering with their activity by pharmacological intervention is an up-and-coming therapeutic avenue. Precision medicine requests detailed knowledge of STAT5A's and STAT5B's individual functions. Recent evidence highlights the privileged role for STAT5B over STAT5A in normal and malignant hematopoiesis. Here, we provide an overview on their individual functions within the hematopoietic system.

STAT5-Driven Enhancers Tightly Control Temporal Expression of Mammary-Specific Genes

The de novo formation of milk-secreting mammary epithelium during pregnancy is regulated by prolactin through activation of the transcription factor STAT5, which stimulates the expression of several hundred mammary-specific genes. In addition to its key role in activating gene expression in mammary tissue, STAT5, which is ubiquitously expressed in most cell types, implements T cell-specific programs controlled by interleukins. However, the mechanisms by which STAT5 controls cell-specific genetic programs activated by distinct cytokines remain relatively unknown. Integration of data from genome-wide surveys of chromatin markers and transcription factor binding at regulatory elements may shed light on the mechanisms that drive cell-specific programs. Here, we have illustrated how STAT5 controls cell-specific gene expression through its concentration and an auto-regulatory enhancer supporting its high levels in mammary tissue. The unique genomic features of STAT5-driven enhancers or super-enhancers that regulate mammary-specific genes and their dynamic remodeling in response to pregnancy hormone levels are described. We have further provided biological evidence supporting the in vivo function of a STAT5-driven super-enhancer with the aid of CRISPR/Cas9 genome editing. Finally, we discuss how the functions of mammary-specific super-enhancers are confined by the zinc finger protein, CTCF, to allow exclusive activation of mammary-specific genes without affecting common neighboring genes. This review comprehensively summarizes the molecular pathways underlying differential control of cell-specific gene sets by STAT5 and provides novel insights into STAT5-dependent mammary physiology.

The detection and significance of cystic fibrosis transmembrane conductance regulator gene promoter mutations in Chinese patients with congenital bilateral absence of the vas deferens

OBJECTIVE

Mutations in the cystic fibrosis transmembrane conductance regulator gene (CFTR) gene can be involved in the development of congenital bilateral absence of the vas deferens (CBAVD). This study was aimed at investigating mutations in the promoter region of the CFTR gene and its associated effects on CFTR transcription in Chinese patients with CBAVD.

METHODS

To identify CFTR promoter region mutations in Chinese CBAVD patients, fragments 1.4 kb upstream of the ATG start codon of the CFTR gene were sequenced in 66 Chinese patients with CBAVD and compared to the corresponding sequences from 60 healthy subjects and sequence data present in the NCBI database. The relationship between the mutations and gene regulation was explored using Transfac analysis and a phylogenetic footprint method. Plasmids were constructed by incorporating statistically significant variant sequences. The effects of the mutations on CFTR transcription were investigated using a dual luciferase reporter gene assay.

RESULTS

a total of six point mutations, which included c.-150G > T, c.-205 T > C, c.-245C > T, c.-871G > T, c.-966 T > G and c.-1062G > C, and one deletion mutation, namely c.-861delT, were identified in the promoter region of the CFTR gene in Chinese CBAVD patients. Among them, c.-966 T > G had the highest frequency and presented in either a homozygous or heterozygous mutation state. The frequency of G/G genotype in the CBAVD group was 33/66 (50.00%), while the T/G and T/T genotypes had frequencies of 18/66 (27.27%) and 15/66 (22.73%), respectively. A significant difference was found between the CBAVD and control group (P < 0.01). The locus for this variant was found in a conserved sequence. The Transfac tool showed that transcription factors EHF and STAT3, which are closely associated with reproduction, can bind to the sequence containing the variant locus. Two types of plasmid vectors, one carrying the G/G variant and the other the wild type T/T sequences, were constructed and respectively transfected into human cervical cancer cells (HeLa), human renal epithelial cells (HEK-293), and human colon cancer cells (SW480). It was found that the homozygous c.-966 T > G mutation significantly reduced CFTR transcription efficiency by 18.75%-35.50%.

CONCLUSION

Mutations in the promoter region of the CFTR gene in Chinese CBAVD patients are different from those found in comparable Caucasian patients. The homozygous c.-966 T > G mutation state had the highest frequency, which reduced the CFTR transcriptional level and showed significant tissue-specificity.

17β-Estradiol and ICI182,780 Differentially Regulate STAT5 Isoforms in Female Mammary Epithelium, With Distinct Outcomes

Prolactin (PRL) and estrogen cooperate in lobuloalveolar development of the mammary gland and jointly regulate gene expression in breast cancer cells in vitro. Canonical PRL signaling activates STAT5A/B, homologous proteins that have different target genes and functions. Although STAT5A/B are important for physiological mammary function and tumor pathophysiology, little is known about regulation of their expression, particularly of STAT5B, and the consequences for hormone action. In this study, we examined the effect of two estrogenic ligands, 17β-estradiol (E2) and the clinical antiestrogen, ICI182,780 (ICI, fulvestrant) on expression of STAT5 isoforms and resulting crosstalk with PRL in normal and tumor murine mammary epithelial cell lines. In all cell lines, E2 and ICI significantly increased protein and corresponding nascent and mature transcripts for STAT5A and STAT5B, respectively. Transcriptional regulation of STAT5A and STAT5B by E2 and ICI, respectively, is associated with recruitment of estrogen receptor alpha and increased H3K27Ac at a common intronic enhancer 10 kb downstream of the Stat5a transcription start site. Further, E2 and ICI induced different transcripts associated with differentiation and tumor behavior. In tumor cells, E2 also significantly increased proliferation, invasion, and stem cell-like activity, whereas ICI had no effect. To evaluate the role of STAT5B in these responses, we reduced STAT5B expression using short hairpin (sh) RNA. shSTAT5B blocked ICI-induced transcripts associated with metastasis and the epithelial mesenchymal transition in both cell types. shSTAT5B also blocked E2-induced invasion of tumor epithelium without altering E2-induced transcripts. Together, these studies indicate that STAT5B mediates a subset of protumorigenic responses to both E2 and ICI, underscoring the need to understand regulation of its expression and suggesting exploration as a possible therapeutic target in breast cancer.

The Impact of the Interferon/TNF-Related Apoptosis-Inducing Ligand Signaling Axis on Disease Progression in Respiratory Viral Infection and Beyond

Interferons (IFNs) are well described to be rapidly induced upon pathogen-associated pattern recognition. After binding to their respective IFN receptors and activation of the cellular JAK/signal transducer and activator of transcription signaling cascade, they stimulate the transcription of a plethora of IFN-stimulated genes (ISGs) in infected as well as bystander cells such as the non-infected epithelium and cells of the immune system. ISGs may directly act on the invading pathogen or can either positively or negatively regulate the innate and adaptive immune response. However, IFNs and ISGs do not only play a key role in the limitation of pathogen spread but have also been recently found to provoke an unbalanced, overshooting inflammatory response causing tissue injury and hampering repair processes. A prominent regulator of disease outcome, especially in-but not limited to-respiratory viral infection, is the IFN-dependent mediator TRAIL (TNF-related apoptosis-inducing ligand) produced by several cell types including immune cells such as macrophages or T cells. First described as an apoptosis-inducing agent in transformed cells, it is now also well established to rapidly evoke cellular stress pathways in epithelial cells, finally leading to caspase-dependent or -independent cell death. Hereby, pathogen spread is limited; however in some cases, also the surrounding tissue is severely harmed, thus augmenting disease severity. Interestingly, the lack of a strictly controlled and well balanced IFN/TRAIL signaling response has not only been implicated in viral infection but might furthermore be an important determinant of disease progression in bacterial superinfections and in chronic respiratory illness. Conclusively, the IFN/TRAIL signaling axis is subjected to a complex modulation and might be exploited for the evaluation of new therapeutic concepts aiming at attenuation of tissue injury.

An autoregulatory enhancer controls mammary-specific STAT5 functions

Signal Transducers and Activators of Transcription (STATs) are principal transcription factors downstream of cytokine receptors. Although STAT5A is expressed in most tissues it remains to be understood why its premier, non-redundant functions are restricted to prolactin-induced mammary gland development and function. We report that the ubiquitously expressed Stat5a/b locus is subject to additional lineage-specific transcriptional control in mammary epithelium. Genome-wide surveys of epigenetic status and transcription factor occupancy uncovered a putative mammary-specific enhancer within the intergenic sequences separating the two Stat5 genes. This region exhibited several hallmarks of genomic enhancers, including DNaseI hypersensitivity, H3K27 acetylation and binding by GR, NFIB, ELF5 and MED1. Mammary-specific STAT5 binding was obtained at two canonical STAT5 binding motifs. CRISPR/Cas9-mediated genome editing was used to delete these sites in mice and determine their biological function. Mutant animals exhibited an 80% reduction of Stat5 levels in mammary epithelium and a concomitant reduction of STAT5-dependent gene expression. Transcriptome analysis identified a class of mammary-restricted genes that was particularly dependent on high STAT5 levels as a result of the intergenic enhancer. Taken together, the mammary-specific enhancer enables a positive feedback circuit that contributes to the remarkable abundance of STAT5 and, in turn, to the efficacy of STAT5-dependent mammary physiology.

The spectrum of STAT functions in mammary gland development

The signal transducer and activator of transcription (STAT) family of transcription factors have a spectrum of functions in mammary gland development. In some cases these roles parallel those of STATs in other organ systems, while in other instances the function of individual STATs in the mammary gland is specific to this tissue. In the immune system, STAT6 is associated with differentiation of T helper cells, while in the mammary gland, it has a fundamental role in the commitment of luminal epithelial cells to the alveolar lineage. STAT5A is required for the production of luminal progenitor cells from mammary stem cells and is essential for the differentiation of milk producing alveolar cells during pregnancy. By contrast, the initiation of regression following weaning heralds a dramatic and specific activation of STAT3, reflecting its pivotal role in the regulation of cell death and tissue remodeling during mammary involution. Although it has been demonstrated that STAT1 is regulated during a mammary developmental cycle, it is not yet determined whether it has a specific, non-redundant function. Thus, the mammary gland constitutes an unusual example of an adult organ in which different STATs are sequentially activated to orchestrate the processes of functional differentiation, cell death and tissue remodeling.

Evaluation of STAT5A Gene Expression in Aflatoxin B1 Treated Bovine Mammary Epithelial Cells

PURPOSE

Aflatoxin B1 (AFB1) is a potent mycotoxin which has been produced by fungi such as Aspergillus flavus and Aspergillus parasiticus as secondary metabolites due to their growth on food stuffs and induces hepatocellular carcinoma in many animal species, including humans. In the present study, the effect of AFB1 on STAT5A gene expression was investigated in bovine mammary epithelial cells using real time RT-PCR.

METHODS

Bovine mammary epithelial cells were seeded in a 24-well culture plate for three-dimensional (3D) culture in Matrigel matrix. After 21 days of 3D culture and reaching the required number of cells, cells were treated with AFB1 and incubated for 8 h. For real time PCR reaction, total RNA from the cultured and treated cells was extracted and used for complementary DNA synthesis.

RESULTS

The expression of STAT5A gene was significantly down regulated by AFB1 in dose- dependent manner and led to the reduction of proliferation and differentiation of epithelial cells, which has direct effect in milk protein quantity and quality.

CONCLUSION

According to the results, it seems that down regulation of STAT5A gene in AFB1-treated cells maybe due to DNA damage induced by AFB1 in bovine mammary epithelial cells.

Peroxisome proliferator-activated receptor gamma/signal transducers and activators of transcription 5A pathway plays a key factor in adipogenesis of human bone marrow-derived stromal cells and 3T3-L1 preadipocytes

Adipogenesis is largely dependent on the signal transducers and activators of transcription (STAT) pathway. However, the molecular mechanism of the STAT pathway in the adipogenesis of human bone marrow-derived stromal cells (hBMSCs) remains not well understood. The purpose of this research was to characterize the transcriptional regulation involved in expression of STAT5A and STAT5B during adipogenesis in hBMSCs and 3T3-L1 cells. The expression of STAT5A and STAT5B increases with the onset of adipogenesis in hBMSCs and 3T3-L1 cells. The PPAR response elements regulatory element of STAT5A exists at a promoter region ranging from -346 to -101, and the CCAAT/enhancer-binding protein (C/EBP) regulatory element is located at -196 to -118 of the STAT5B promoter. C/EBPβ and C/EBPα bound to the STAT5B promoter region, whereas peroxisome proliferator-activated receptor γ (PPARγ) bound to STAT5A. RNA interference of STAT5A completely blocked differentiation, whereas the inhibition of STAT5B only partially blocked differentiation. We propose that C/EBPα, C/EBPβ, and PPARγ control adipogenesis by regulating STAT5B and STAT5A and that STAT5A is necessary, whereas STAT5B plays a supplementary role during adipogenesis. Further, the regulation of PPARγ-STAT5 by C/EBPβ signaling seems to be the crucial adipogenesis pathway-initiating cascade of the various adipogenic genes.

Mechanisms regulating dendritic cell specification and development

Understanding the diversification of dendritic cell (DC) lineages is one of the last frontiers in mapping the developmental hierarchy of the hematopoietic system. DCs are a vital link between the innate and adaptive immune responses; thus, elucidating their developmental pathways is crucial for insight into the generation of natural immunity and for learning how to regulate DCs in clinical settings. DCs arise from hematopoietic stem cells through specialized progenitor subsets under the direction of FMS-like tyrosine kinase 3 ligand (Flt3L) and Flt3L receptor (Flt3) signaling. Recent studies have revealed important contributions from granulocyte-macrophage colony-stimulating factor (GM-CSF) and type I interferons (IFNs) in vivo. Furthermore, DC development is guided by lineage-restricted transcription factors such as IRF8, E2-2, and Batf3. A critical question centers on how cytokines and lineage-restricted transcription factors operate molecularly to direct DC diversification. Here, we review recent findings that provide new insight into the DC developmental process.

Ebolavirus VP35 uses a bimodal strategy to bind dsRNA for innate immune suppression

Ebolavirus causes a severe hemorrhagic fever and is divided into five distinct species, of which Reston ebolavirus is uniquely nonpathogenic to humans. Disease caused by ebolavirus is marked by early immunosuppression of innate immune signaling events, involving silencing and sequestration of double-stranded RNA (dsRNA) by the viral protein VP35. Here we present unbound and dsRNA-bound crystal structures of the dsRNA-binding domain of Reston ebolavirus VP35. The structures show that VP35 forms an unusual, asymmetric dimer on dsRNA binding, with each of the monomers binding dsRNA in a different way: one binds the backbone whereas the other caps the terminus. Additional SAXS, DXMS, and dsRNA-binding experiments presented here support a model of cooperative dsRNA recognition in which binding of the first monomer assists binding of the next monomer of the oligomeric VP35 protein. This work illustrates how ebolavirus VP35 could mask key recognition sites of molecules such as RIG-I, MDA-5, and Dicer to silence viral dsRNA in infection.

Leptin receptor signaling and the regulation of mammalian physiology

The adipocyte-derived hormone, leptin, signals the status of body energy stores to the central nervous system to regulate appetite and energy expenditure. A specific long-form leptin receptor (LepRb), a type I cytokine receptor, mediates leptin action on LepRb-expressing neurons in the brain. Leptin binding to LepRb activates the associated Janus kinase-2 (Jak2) tyrosine kinase to promote the phosphorylation of Jak2 and three residues on LepRb; each of these sites mediates a distinct aspect of downstream LepRb signaling, with differing physiologic functions. Tyr(1138) --> STAT3 signaling suppresses feeding, but is not required for a number of other leptin actions. Tyr(985) binds SH2-containing tyrosine phosphatase-2 and suppressor of cytokine signaling-3 and primarily mediates the attenuation of LepRb signaling in vivo. The role for Tyr(1077), the major regulator of signal transducer and activator of transcription-5 (STAT5) during leptin signaling, in the physiologic response to leptin remains unclear, although the obese phenotype of animals deleted for STAT5 in the brain suggests the potential importance of this signaling pathway. Leptin also modulates a number of other signaling pathways in the brain, including PI 3-kinase, mammalian target of rapamycin and AMP-dependent protein kinase; the pathways by which leptin controls these signals remain unclear, however, and may involve some indirect mechanisms. Important issues regarding leptin action and LepRb signaling in the future include not only the more thorough analysis of intracellular signaling pathways, but the neural substrate by which leptin acts, as most major populations of LepRb neurons remain poorly studied.

Inteferons pen the JAK-STAT pathway

Characterization of how interferons (IFNs) mediate their biological response led to identification of the JAK-STAT signaling cascade, where JAKs are receptor-associated kinases and STATs the transcription factors they activate. Today, 4 JAKs and 7 STATs are known to transduce pivotal signals for the over 50 members of the four-helix bundle family of cytokines. This review will provide an overview and historical perspective of the JAK-STAT paradigm.

STAT5 activity in pancreatic β-cells

Signal transducer and activator of transcription (STAT)5A and -5B are latent transcription factors activated by cytokines and hormones of the cytokine family. In pancreatic insulin-secreting β-cells, STAT5A and -5B are activated primarily by prolactin and growth hormone stimulation and are important mediators of the potent stimulation of proliferation and insulin production caused by these hormones. STAT5A and -5B are both expressed in β-cells and control the expression of a number of mRNAs implicated in cell replication control, insulin biosynthesis and secretion. In addition to STAT5A and -5B being transcriptional activators, they may also repress gene transcription. By these means, STAT5 proteins increase the levels of anti-apoptotic transcripts in β-cells and repress expression of pro-apoptotic genes. This review focuses on the anti-apoptotic role of STAT5 signaling, providing a mechanism for β-cell resistance to pro-apoptotic cytokines, Type 1 diabetes mellitus and obesity-associated β-cell stress. It is clear from studies of STAT5 signaling in pancreatic β-cells that STAT5 is important for postnatal β-cell compensatory growth (as in pregnancy or obesity) and in the defense against β-cell stress factors.

The long form of the leptin receptor regulates STAT5 and ribosomal protein S6 via alternate mechanisms

The action of leptin via the long form of its receptor (LepRb) is central to the control of body energy homeostasis and neuroendocrine function, but the mechanisms by which LepRb regulates intracellular signaling have remained incompletely understood. Here we demonstrate that leptin stimulates the phosphorylation of STAT5 and ribosomal protein S6 in the hypothalamic arcuate nucleus in mice. In cultured cells, we investigate the mechanisms by which leptin regulates each of these pathways. Our analysis reveals a dominant role for LepRb Tyr(1077) (which we demonstrate to be phosphorylated during receptor activation) and a secondary role for LepRb Tyr(1138) in the acute phosphorylation of STAT5a and STAT5b. Tyr(1138) and STAT3 attenuate STAT5-dependent transcription over the long-term, however. In contrast, Tyr(985) (the LepRb phosphorylation site required for ERK activation) mediates the phosphorylation of the ribosomal S6 kinase (RSK) and S6, as well as cap-dependent translation. Thus, these data demonstrate the phosphorylation of Tyr(1077) on LepRb during receptor activation, substantiate the hypothalamic regulation of STAT5 and S6 by leptin, and define the alternate LepRb signaling pathways that mediate each of these signals and their effects in cultured cells. Dissecting the contributions of these individual pathways to leptin action will be important for our ultimate understanding of the processes that regulate energy balance in vivo.

Socs 3 modulates the activity of the transcription factor Stat3 in mammary tissue and controls alveolar homeostasis

Signal transducer and activator of transcription 5 and 3 (Stat5 and Stat3) control pregnancy-mediated mammary development and involution-dependent remodeling, respectively. Suppressor of cytokine signaling 3 (Socs3) has been implicated in the modulation of both Stat3 and Stat5 activity. To explore the biology of Socs3 in mammary tissue, the gene was deleted using Cre-mediated recombination. Deletion of the Socs3 gene from mammary stem or early progenitor cells did not grossly alter pregnancy-mediated mammary development but resulted in impaired lactation due to attenuated proliferation. Loss of Socs3 from differentiated luminal cells did not interfere with glandular function during lactation, but resulted in accelerated tissue remodeling upon weaning. Loss of Socs3 led to enhanced and precocious Stat3 activation. Thus, Socs3 serves as a modulator of Stat3 activity to ensure controlled proliferation and apoptosis in pregnancy and involution, respectively.

Immunohistochemical evaluation of STAT3-p-tyr705 expression in feline mammary gland tumours and correlation with histologic grade

STAT3 (signal transducer and activator of transcription 3) is a cytoplasmic transcription factor that plays a role in the G1 to S phase cell-cycle transition and is induced by cytokines and growth factors. The expression of STAT3 phosphorylated on tyrosine 705 (STAT3-p-tyr705) in normal, hyperplastic and neoplastic feline mammary gland tissue was assessed by immunohistochemistry in 45 cats. The samples included 4 normal mammary non-lactating tissues, 9 hyperplastic tissues (5 fibroepithelial hyperplasia and 4 lobular epithelial hyperplasia), 2 benign tumours (1 complex adenoma, and 1 simple adenoma), and 30 carcinomas (18 simple tubular papillary, 6 simple tubular, 2 simple solid, 3 cribriform, and 1 adenosquamous carcinoma). For immunohistochemistry, tissue sections were incubated with an anti-STAT3-p-tyr705 monoclonal antibody and visualized with EnVision-DAB polymer. STAT3-p-tyr705 positivity was quantified in a semi-quantitative manner. All positive samples showed cytoplasmic and/or nuclear positivity. Normal non-lactating mammary tissue showed a low number of positive cells, similar to hyperplastic tissue. In neoplastic tissues, a high number of positive cells with a moderate to intense reaction was observed. Moreover, a correlation was observed between nuclear positivity for STAT3-p-tyr705 and histologic grade (P=0.013; r=0.447), tubular formation (P=0.043; r=0.820), and mitotic activity (P<0.0001; r=0.689). In contrast, no such correlations were observed for cytoplasmic reactivity of STAT3-p-tyr705. A significant difference was observed between malignant lesions and hyperplasia with regards to expression of STAT3-p-tyr 705 in the cytoplasm (P=0.008; U=59.00) and nuclei (P=0.002; U=47.00). These results confirm previous our data and reinforce the potential role of STAT3 in malignancy as reported for human breast cancer and other sporadic tumours.

STAT5A/B activity is required in the developing forebrain and spinal cord

Formation of the CNS requires the coordination and integration of processes such as cell proliferation, neuronal differentiation, neuronal migration, axon tract formation and synaptogenesis, all of which must occur at precise times and places during development. Although growth factors are known to play a role in regulating many of these processes, very little is known of the signaling events immediately downstream of ligand-receptor interactions in the developing CNS. Here we present evidence that STAT5, an important mediator of cytokine signaling, is required for some aspects of CNS development. We show that phosphorylated and hence activated forms of STAT5 (pSTAT5) are expressed in a temporally restricted manner in a subset of early-born telencephalic neurons and axons. Accordingly, Stat5 mutants have reduced numbers of interneurons in the cortical marginal zone, suggestive of migration defects. Moreover, corticofugal axons develop aberrantly in Stat5 mutants, indicative of a role for pSTAT5 in axon guidance. Notably, pSTAT5 is also expressed in commissural axons in the embryonic spinal cord, where it is also required for their guidance. Taken together, we provide the first evidence that STAT5 is a key effector molecule in the developing mammalian CNS.

Signal transducer and activator of transcription signals in allergic disease

Signal transducer and activator of transcription (STAT) proteins are a group of transcription factors that transmit signals from the extracellular milieu of cells to the nucleus. They are crucial for the signaling of many cytokines that are mediators of allergic inflammation and impact various cell types critical to allergy including epithelial cells, mast cells, lymphocytes, dendritic cells, and eosinophils. Dysregulation of STAT signaling has been implicated in allergic disease, highlighting the importance of these ubiquitous molecules in allergic inflammation and the potential of these pathways as a target for therapeutic intervention. This review will summarize the current understanding of the roles of STAT signaling in allergic disease and the potential of targeting STATs for the treatment of allergic disorders, emphasizing recent observations.

Regulation of hypocretin (orexin) expression in embryonic zebrafish

Hypocretins/orexins are neuropeptides involved in the regulation of sleep and energy balance in mammals. Conservation of gene sequence, hypothalamic localization of cell bodies, and projection patterns in adult zebrafish suggest that the architecture and function of the hypocretin system are conserved in fish. We report on the complete genomic structure of the zebrafish and Tetraodon hypocretin genes and the complete predicted hypocretin protein sequences from five teleosts. Using whole mount in situ hybridization, we have traced the development of hypocretin cells in zebrafish from onset of expression at 22 h post-fertilization through the first week of development. Promoter elements of similar size from zebrafish and Tetraodon were capable of driving efficient and specific expression of enhanced green fluorescent protein in developing zebrafish embryos, thus defining a minimal promoter region able to accurately mimic the native hypocretin pattern. This enhanced green fluorescent protein expression also revealed a complex pattern of projections within the hypothalamus, to the midbrain, and to the spinal cord. To further analyze the promoter, a series of deletion and substitution constructs were injected into embryos, and resulting promoter activity was monitored in the first week of development. A critical region of 250 base pairs was identified containing a core 13-base pair element essential for hypocretin expression.

Systemic evaluation of total Stat3 and Stat3 tyrosine phosphorylation in normal human tissues

Stat3 plays important roles in many biological phenomena including cell survival, growth, proliferation, differentiation and cancer malignancies. As Stat3 emerges as a new therapeutic target for treatment of cancers in which the Stat3 is constitutively activated, the overall evaluation of basal expression of Stat3 and phosphorylated Stat3 at tyrosine residue 705 in human tissues would be very important and informative. We took a pilot study to examine the expression patterns of total Stat3 and phosphorylated Stat3 protein (p-Stat3) using immunohistochemistry in 47 different adult normal human tissues of 10 organ systems. Immunohistochemistry showed that total Stat3 protein was almost universally detected in all tissues except peripheral nerve. Interestingly, majorities of tissues showed to have moderate to high expression levels of total Stat3 protein. Several heart tissues displayed a unique perinuclear immunostaining for both Stat3 and p-Stat3, most likely in Golgi complexes. Based on the cell types, the p-Stat3 was also expressed in glandular, secretory, mucosal epithelial, circulatory endothelial, lymphoid, proliferative, and reabsorption-active cells.

Shared and unique functions of the DExD/H-box helicases RIG-I, MDA5, and LGP2 in antiviral innate immunity

The cellular protein retinoic acid-inducible gene I (RIG-I) senses intracellular viral infection and triggers a signal for innate antiviral responses including the production of type I IFN. RIG-I contains a domain that belongs to a DExD/H-box helicase family and exhibits an N-terminal caspase recruitment domain (CARD) homology. There are three genes encoding RIG-I-related proteins in human and mouse genomes. Melanoma differentiation associated gene 5 (MDA5), which consists of CARD and a helicase domain, functions as a positive regulator, similarly to RIG-I. Both proteins sense viral RNA with a helicase domain and transmit a signal downstream by CARD; thus, these proteins share overlapping functions. Another protein, LGP2, lacks the CARD homology and functions as a negative regulator by interfering with the recognition of viral RNA by RIG-I and MDA5. The nonstructural protein 3/4A protein of hepatitis C virus blocks the signaling by RIG-I and MDA5; however, the V protein of the Sendai virus selectively abrogates the MDA5 function. These results highlight ingenious mechanisms for initiating antiviral innate immune responses and the action of virus-encoded inhibitors.

Conservation, duplication and divergence of the zebrafish stat5 genes

There are seven mammalian signal transducer and activator of transcription (Stat) proteins that act downstream of cytokine and growth factor receptors to mediate rapid changes in gene expression. The mammalian Stat5a and Stat5b genes show high sequence identity and lie adjacent in a head-to-head configuration next to the Stat3 gene, apparently the result of a relatively recent mammal-specific gene duplication event. We have identified and characterized two stat5 homologues that are expressed in zebrafish, named stat5.1 and stat5.2. The stat5.1 gene shows a high level of conservation with the single stat5 gene found in other teleosts and lies next to the stat3 gene, in the same relative orientation as the mammalian Stat5b gene. In contrast, the stat5.2 gene lies on a different chromosome to stat5.1 and stat3, and has diverged from the stat5 genes of other teleosts, with no apparent orthologue. Together, these data suggest that the ancestral Stat5 gene has undergone two independent gene duplication events to generate a stat5.2 paralogue in zebrafish and a Stat5a paralogue in mammals.

Inactivation of Stat5 in mouse mammary epithelium during pregnancy reveals distinct functions in cell proliferation, survival, and differentiation

This study explored the functions of the signal transducers and activators of transcription 5a and 5b (referred to as Stat5 here) during different stages of mouse mammary gland development by using conditional gene inactivation. Mammary gland morphogenesis includes cell specification, proliferation and differentiation during pregnancy, cell survival and maintenance of differentiation throughout lactation, and cell death during involution. Stat5 is activated by prolactin, and its presence is mandatory for the proliferation and differentiation of mammary epithelium during pregnancy. To address the question of whether Stat5 is also necessary for the maintenance and survival of the differentiated epithelium, the two genes were deleted at different time points. The 110-kb Stat5 locus in the mouse was bracketed with loxP sites, and its deletion was accomplished by using two Cre-expressing transgenic lines. Loss of Stat5 prior to pregnancy prevented epithelial proliferation and differentiation. Deletion of Stat5 during pregnancy, after mammary epithelium had entered Stat5-mediated differentiation, resulted in premature cell death, indicating that at this stage epithelial cell proliferation, differentiation, and survival require Stat5.

Stat5a is tyrosine phosphorylated and nuclear localized in a high proportion of human breast cancers

Signal transducers and activators of transcription (STATs) are latent cytoplasmic transcription factors that are activated and translocated into the nucleus after phosphorylation at a conserved tyrosine residue. Mouse model studies have demonstrated that activated Stat5a acts as a critical survival factor for normal, preneoplastic and malignant mammary epithelial cells. Very limited information is available, however, on the expression, tyrosine phosphorylation status and nuclear localization of Stat5a in human breast cancers. In our study, the pattern of Stat5a cellular localization was analyzed by immunohistochemistry in a series of 83 randomly selected primary human breast adenocarcinomas. Immunoprecipitation/Western blotting and immunohistochemistry assays employing different phospho-specific antibodies verified Stat5a tyrosine phosphorylation status. Stat5a was nuclear localized and tyrosine phosphorylated in 59 of 78 (76%) breast cancers examined; 38 of 78 (49%) demonstrated Stat5a nuclear localization in more than 25% of the breast cancer cells within the adenocarcinomas. Nuclear localized Stat5a was associated positively with increased levels of histologic differentiation (p = 0.03). A statistically significant positive association with p27 nuclear localization also was identified (p = 0.05). No relationship was found between nuclear localized Stat5a and menopausal status, tumor size, ploidy, percentage of cells in S-phase, lymph node metastases, ER, ErbB2, nuclear localized p21 or nuclear localized Stat5b/Stat3. As its role in human breast cancer progression and response to therapy is defined, Stat5a could become a new molecular target for breast cancer therapy.

Genomic structure, expression and characterization of a STAT5 homologue from pufferfish (Tetraodon fluviatilis)

The STAT5 (signal transducer and activator of transcription 5) gene was isolated and characterized from a round-spotted pufferfish genomic library. This gene is composed of 19 exons spanning 11 kb. The full-length cDNA of Tetraodon fluviatilis STAT5 (TfSTAT5) contains 2461 bp and encodes a protein of 785 amino acid residues. From the amino acid sequence comparison, TfSTAT5 is most similar to mouse STAT5a and STAT5b with an overall identity of 76% and 78%, respectively, and has < 35% identity with other mammalian STATs. The exon/intron junctions of the TfSTAT5 gene were almost identical to those of mouse STAT5a and STAT5b genes, indicating that these genes are highly conserved at the levels of amino acid sequence and genomic structure. To understand better the biochemical properties of TfSTAT5, a chimeric STAT5 was generated by fusion of the kinase-catalytic domain of carp Janus kinase 1 (JAK1) to the C-terminal end of TfSTAT5. The fusion protein was expressed and tyrosine-phosphorylated by its kinase domain. The fusion protein exhibits specific DNA-binding and transactivation potential toward an artificial fish promoter as well as authentic mammalian promoters such as the beta-casein promoter and cytokine inducible SH2 containing protein (CIS) promoter when expressed in both fish and mammalian cells. However, TfSTAT5 could not induce the transcription of beta-casein promoter via rat prolactin and Nb2 prolactin receptor. To our knowledge, this is the first report describing detailed biochemical characterization of a STAT protein from fish.

Stabilization of beta-catenin induces lesions reminiscent of prostatic intraepithelial neoplasia, but terminal squamous transdifferentiation of other secretory epithelia

The present study documents that stabilization of beta-catenin is sufficient to induce lesions reminiscent of prostate intraepithelial neoplasia (PIN). Such lesions were present in all compound mutant mice and all prostate acini expressing stabilized beta-catenin. High grade PIN-like lesions resembling early human prostate cancer were detected as early as 10 weeks of age. Surprisingly, stabilization of beta-catenin in other secretory epithelia including salivary, preputial, harderian, and mammary glands induced extensive squamous metaplasia and keratinization associated with terminal differentiation of the target cells, but failed to cause neoplastic transformation. Epidermal hyperplasia, hair follicle cysts, and odontomas were also observed. The prostatic lesions exhibited upregulation of c-myc, increased rate of cellular proliferation, loss of the Na-K-Cl co-transporter NKCC1, and expression of androgen receptor. Basal cell markers such as p63 and keratin 5 were not expressed by the masses of PIN-like lesions, but were present in small foci of proliferating beta-catenin expressing basal cells. Our observations indicate that beta-catenin stabilization is a crucial event for the initiation of PIN-like lesions, but induces squamous metaplasia rather than tumorigenesis in secretory epithelia other than the prostate.

Signaling through the JAK/STAT pathway, recent advances and future challenges

Investigation into the mechanism of cytokine signaling led to the discovery of the JAK/STAT pathway. Following the binding of cytokines to their cognate receptor, signal transducers and activators of transcription (STATs) are activated by members of the janus activated kinase (JAK) family of tyrosine kinases. Once activated, they dimerize and translocate to the nucleus and modulate the expression of target genes. During the past several years significant progress has been made in the characterization of the JAK/STAT signaling cascade, including the identification of multiple STATs and regulatory proteins. Seven STATs have been identified in mammals. The vital role these STATs play in the biological response to cytokines has been demonstrated through the generation of murine 'knockout' models. These mice will be invaluable in carefully elucidating the role STATs play in regulating the host response to various stresses. Similarly, the solution of the crystal structure of two STATs has and will continue to facilitate our understanding of how STATs function. This review will highlight these exciting developments in JAK/STAT signaling.

The structure of human STAT5A and B genes reveals two regions of nearly identical sequence and an alternative tissue specific STAT5B promoter

STAT5A and STAT5B genes belong to the signal transducer and activators of transcription (STAT) family of transcription factors. They show a high degree of sequence homology at levels of mRNA, however, in spite of their supposed redundancy, each STAT5 has distinct biological functions mainly related to the immune system, hematopoiesis, growth and mammary development. We isolated and sequenced both STAT5A and STAT5B encoding human genes finding that they are segmented in 20 and 19 exons, respectively, of comparable size except for the extreme 5' exons and the 3' exons. Two CpG islands, 23.2% CpG for STAT5A and 30.2% for STAT5B, are present at the 5' of both STAT5 genes covering the 5' untranslated regions. More surprisingly, the two genes share two major regions of almost identical sequence which diverge between the different species indicating an intra-species specific mechanism of preservation. Furthermore, we identified two alternative 5' exons in STAT5B genes and thus two alternative promoters. The second putative promoter is not embedded in a CpG island and it shows a tissue specific pattern of expression. Finally, the STAT5B gene was assessed as a candidate gene in a human disorder related to growth failure.

The Stat3/5 locus encodes novel endoplasmic reticulum and helicase-like proteins that are preferentially expressed in normal and neoplastic mammary tissue

The signal transducers and activators of transcription (STAT) 5 and 3 are critical for mammary alveolar development during pregnancy and remodeling during involution. In the mouse, STAT3, STAT5a, and STAT5b are encoded by adjacent genes on chromosome 11 (60.5 cM). To identify additional genes in the Stat3/5 locus that may participate in normal and neoplastic development of the mammary gland, we have cloned and sequenced 500 kb and searched for genes preferentially expressed in mammary tissue. We identified six known genes and cloned two new genes, termed D11Lgp1 and D11Lgp2. Both genes are most highly expressed in normal mammary tissue and mammary tumors from several transgenic mouse models. LGP1 consists of 532 and 530 amino acids in mouse and human, respectively (88% similarity). A region in the carboxy-terminal half of LGP1 has limited homology with Arabidopsis thaliana GH3-like proteins. Immunofluorescence studies demonstrated that LGP1 is located in the nuclear envelope and the endoplasmic reticulum. LGP2 is a cytoplasmic protein of 678 amino acids.

Comparative genomic sequence analysis of the FXR gene family: FMR1, FXR1, and FXR2

Mutations in the X-linked gene FMR1 cause fragile X syndrome, the leading cause of inherited mental retardation. Two autosomal paralogs of FMR1 have been identified, and are known as FXR1 and FXR2. Here we describe and compare the genomic structures of the mouse and human genes FMR1, FXR1, and FXR2. All three genes are very well conserved from mouse to human, with identical exon sizes for all but two FXR2 exons. In addition, the three genes share a conserved gene structure, suggesting they are derived from a common ancestral gene. As a first step towards exploring this hypothesis, we reexamined the Drosophila melanogaster gene Fmr1, and found it to have several of the same intron/exon junctions as the mammalian FXRs. Finally, we noted several regions of mouse/human homology in the noncoding portions of FMR1 and FXR1. Knowledge of the genomic structure and sequence of the FXR family of genes will facilitate further studies into the function of these proteins.