Interferon-gamma (IFN-gamma) coordinates a diverse array of cellular programs through transcriptional regulation of immunologically relevant genes. This article reviews the current understanding of IFN-gamma ligand, receptor, signal transduction, and cellular effects with a focus on macrophage responses and to a lesser extent, responses from other cell types that influence macrophage function during infection. The current model for IFN-gamma signal transduction is discussed, as well as signal regulation and factors conferring signal specificity. Cellular effects of IFN-gamma are described, including up-regulation of pathogen recognition, antigen processing and presentation, the antiviral state, inhibition of cellular proliferation and effects on apoptosis, activation of microbicidal effector functions, immunomodulation, and leukocyte trafficking. In addition, integration of signaling and response with other cytokines and pathogen-associated molecular patterns, such as tumor necrosis factor-alpha, interleukin-4, type I IFNs, and lipopolysaccharide are discussed.

https://jlb.onlinelibrary.wiley.com/doi/epdf/10.1189/jlb.0603252

Interferon-γ: an overview of signals, mechanisms and functions

In the three decades since pluripotent mouse embryonic stem (ES) cells were first described they have been derived and maintained by using various empirical combinations of feeder cells, conditioned media, cytokines, growth factors, hormones, fetal calf serum, and serum extracts. Consequently ES-cell self-renewal is generally considered to be dependent on multifactorial stimulation of dedicated transcriptional circuitries, pre-eminent among which is the activation of STAT3 by cytokines (ref. 8). Here we show, however, that extrinsic stimuli are dispensable for the derivation, propagation and pluripotency of ES cells. Self-renewal is enabled by the elimination of differentiation-inducing signalling from mitogen-activated protein kinase. Additional inhibition of glycogen synthase kinase 3 consolidates biosynthetic capacity and suppresses residual differentiation. Complete bypass of cytokine signalling is confirmed by isolating ES cells genetically devoid of STAT3. These findings reveal that ES cells have an innate programme for self-replication that does not require extrinsic instruction. This property may account for their latent tumorigenicity. The delineation of minimal requirements for self-renewal now provides a defined platform for the precise description and dissection of the pluripotent state.

/pdf/the-ground-state-of-embryonic-stem-cell-self-renewal-41xqrmi7s8.pdf

The ground state of embryonic stem cell self-renewal

The IL (interleukin)-6-type cytokines IL-6, IL-11, LIF (leukaemia inhibitory factor), OSM (oncostatin M), ciliary neurotrophic factor, cardiotrophin-1 and cardiotrophin-like cytokine are an important family of mediators involved in the regulation of the acute-phase response to injury and infection. Besides their functions in inflammation and the immune response, these cytokines play also a crucial role in haematopoiesis, liver and neuronal regeneration, embryonal development and fertility. Dysregulation of IL-6-type cytokine signalling contributes to the onset and maintenance of several diseases, such as rheumatoid arthritis, inflammatory bowel disease, osteoporosis, multiple sclerosis and various types of cancer (e.g. multiple myeloma and prostate cancer). IL-6-type cytokines exert their action via the signal transducers gp (glycoprotein) 130, LIF receptor and OSM receptor leading to the activation of the JAK/STAT (Janus kinase/signal transducer and activator of transcription) and MAPK (mitogen-activated protein kinase) cascades. This review focuses on recent progress in the understanding of the molecular mechanisms of IL-6-type cytokine signal transduction. Emphasis is put on the termination and modulation of the JAK/STAT signalling pathway mediated by tyrosine phosphatases, the SOCS (suppressor of cytokine signalling) feedback inhibitors and PIAS (protein inhibitor of activated STAT) proteins. Also the cross-talk between the JAK/STAT pathway with other signalling cascades is discussed.

/pdf/principles-of-interleukin-il-6-type-cytokine-signalling-and-1tgjc4ttsu.pdf

Principles of interleukin (IL)-6-type cytokine signalling and its regulation.

Master Transcription Factors and Mediator Establish Super-Enhancers at Key Cell Identity Genes

The application of human embryonic stem (ES) cells in medicine and biology has an inherent reliance on understanding the starting cell population. Human ES cells differ from mouse ES cells and the specific embryonic origin of both cell types is unclear. Previous work suggested that mouse ES cells could only be obtained from the embryo before implantation in the uterus. Here we show that cell lines can be derived from the epiblast, a tissue of the post-implantation embryo that generates the embryo proper. These cells, which we refer to as EpiSCs (post-implantation epiblast-derived stem cells), express transcription factors known to regulate pluripotency, maintain their genomic integrity, and robustly differentiate into the major somatic cell types as well as primordial germ cells. The EpiSC lines are distinct from mouse ES cells in their epigenetic state and the signals controlling their differentiation. Furthermore, EpiSC and human ES cells share patterns of gene expression and signalling responses that normally function in the epiblast. These results show that epiblast cells can be maintained as stable cell lines and interrogated to understand how pluripotent cells generate distinct fates during early development.

New cell lines from mouse epiblast share defining features with human embryonic stem cells

The Janus family of protein tyrosine kinases (JAKs) regulate cellular processes involved in cell growth, differentiation and transformation through their association with cytokine receptors. However, compared with other kinases, little is known about cellular regulators of the JAKs. We have recently identified a JAK-binding protein (JAB) that inhibits JAK signaling in cells. In the studies presented here we demonstrate that JAB specifically binds to the tyrosine residue (Y1007) in the activation loop of JAK2, whose phosphorylation is required for activation of kinase activity. Binding to the phosphorylated activation loop requires the JAB SH2 domain and an additional N-terminal 12 amino acids (extended SH2 subdomain) containing two residues (Ile68 and Leu75) that are conserved in JAB-related proteins. An additional N-terminal 12-amino-acid region (kinase inhibitory region) of JAB also contributes to high-affinity binding to the JAK2 tyrosine kinase domain and is required for inhibition of JAK2 signaling and kinase activity. Our studies define a novel type of regulation of tyrosine kinases and might provide a basis for the design of specific tyrosine kinase inhibitors.

/pdf/the-jak-binding-protein-jab-inhibits-janus-tyrosine-kinase-4cm68cu94z.pdf

The JAK‐binding protein JAB inhibits Janus tyrosine kinase activity through binding in the activation loop

https://www.cell.com/cell-stem-cell/pdf/S1934-5909(12)00370-0.pdf

Esrrb is a pivotal target of the Gsk3/Tcf3 axis regulating embryonic stem cell self-renewal.

MDM2 interacts with MDMX through their RING finger domains

The STAT (signal transducers and activators of transcription) proteins are cytosolic latent transcription factors that are rapidly activated by interferons (IFNs), cytokines, and growth factors (4, 9, 26). A total of seven different STAT proteins, many of which play highly specific roles in innate and acquired immunity, have been identified. Mice with STAT1, STAT4, and STAT6 gene knockouts are viable but lack functions that are mediated by IFNs, interleukin 12 (IL-12), or IL-4/IL-13, respectively (5, 13, 20, 29, 33). In contrast, STAT3 knockout mice exhibit fetal lethality (34), a finding consistent with the activation of STAT3 by many cytokines that are important for development, such as leukemia inhibitory factor (LIF), cardiotrophin-1, and IL-6 (4, 9). The highly related proteins STAT5a and STAT5b are activated by various cytokines, including growth hormone (GH), prolactin (PRL), erythropoietin (EPO), IL-2, IL-3, granulocyte-macrophage colony-stimulating factor (GM-CSF), and thrombopoietin. The phenotypes of STAT5a and STAT5b single-gene knockout mice and double-knockout mice revealed important roles of STAT5 in PRL and GH signaling as well as in IL-2-dependent T-cell functions (7, 11, 17, 23, 35, 36). STAT5a is critical in PRL signaling (17), GM-CSF signaling (7), or IL-2 signaling (23), while STAT5b is necessary to maintain the sexual dimorphism of body growth rates and liver gene expression (36), IL-2-mediated T-cell proliferation, and NK cell development (11, 21).

The regulation of the Janus kinases (JAKs) and STATs is a central component in the control of cytokine signaling. Because of the critical role of cytokines in mediating inflammation and immunity, it could be proposed that the constitutive activation of JAKs could contribute to hematopoietic disorders, autoimmunity, and inflammatory diseases. However, the mechanisms that terminate or down-modulate the JAK-STAT pathway have not been fully understood. Considerable evidence suggests that one mechanism involves the recruitment of a tyrosine phosphatase containing the SH2 domain (SHP-1) to receptor complexes, resulting in the dephosphorylation of JAKs (12, 14). The potential importance of this mechanism is strongly suggested by the phenotype of motheaten (me/me) mice lacking SHP-1, which die from a disease with components of autoimmunity and inflammation (30). However, it has also been suggested that a family of small SH2 domain-containing proteins may be involved in the relatively specific regulation of cytokine signaling.

The CIS (cytokine-inducible SH2-containing protein) family of proteins, also referred to as the SOCS (suppressors of cytokine signaling) or SSI (STAT-induced STAT inhibitor) family, has been implicated in regulating signal transduction by a variety of cytokines (1, 31, 43). The gene encoding first member of this family, CIS1, was cloned as an immediate-early gene responding to a number of cytokines, including EPO, IL-2, IL-3, and GM-CSF (41), and is regulated by STAT5 (19). CIS1 binds to the tyrosine-phosphorylated IL-3 and EPO receptors and negatively regulates their signals (41). The second family member was independently cloned by three groups and is termed JAB (JAK-binding protein), SOCS-1, or SSI-1 (6, 22, 31). JAB is induced by IFN-γ and inhibits IFN as well as IL-6 signaling (28, 32). JAB and CIS3 directly bind to the kinase domain of JAKs, thereby inhibiting the kinase activity (32). This family now contains eight members, although most of them have not been well characterized except for CIS1, CIS3, and JAB (18, 43).

The CIS1 promoter contains two pairs of tandem TTCNNNGAA motifs that are capable of binding to STAT5 (19). The essential role of STAT5 in CIS1 expression was confirmed by the observation that CIS1 expression was not observed in the ovaries of STAT5a and -b double-gene knockout mice (35). In addition to STAT5-dependent expression of CIS1, it was interesting that CIS1 could negatively modulate STAT5 activation (19); forced expression of CIS1 partially suppressed EPO-dependent STAT5 activation in 293 and Ba/F3 cells. Thus, we hypothesized that CIS1 acts as a kind of negative feedback regulator of the JAK-STAT5 pathway.

To elucidate the physiological function of CIS1 and to find the relationship of the dysregulated expression of the CIS1 gene to human diseases, we created CIS1 transgenic mice. A striking similarity of phenotypes was found between CIS1 transgenic mice and STAT5 knockout mice. The CIS1 transgenic mice exhibited growth retardation and defects in mammary gland development as well as in T-cell and NK cell development. In addition, we found that helper T cells of CIS1 transgenic mice tend to differentiate into Th2 cells, suggesting an important role of CIS1 in T-cell differentiation. We also showed a decrease in STAT5 activation in response to GH, PRL, and IL-2 in transgenic mice. This study suggests an important regulatory role of CIS1 and STAT5 in T-cell development and differentiation, in addition to PRL and GH functions.

Suppression of STAT5 functions in liver, mammary glands, and T cells in cytokine-inducible SH2-containing protein 1 transgenic mice.

POU transcription factor Pou5f1 (Oct3/4) is required to maintain ES cells in an undifferentiated state. Here we show that global expression profiling of Oct3/4-manipulated ES cells delineates the downstream target genes of Oct3/4. Combined with data from genome-wide chromatin-immunoprecipitation (ChIP) assays, this analysis identifies not only primary downstream targets of Oct3/4, but also secondary or tertiary targets. Furthermore, the analysis also reveals that downstream target genes are regulated either positively or negatively by Oct3/4. Identification of a group of genes that show both activation and repression depending on Oct3/4 expression levels provides a possible mechanism for the requirement of appropriate Oct3/4 expression to maintain undifferentiated ES cells. As a proof-of-principle study, one of the downstream genes, Tcl1, has been analyzed in detail. We show that Oct3/4 binds to the promoter region of Tcl1 and activates its transcription. We also show that Tcl1 is involved in the regulation of proliferation, but not differentiation, in ES cells. These findings suggest that the global expression profiling of gene-manipulated ES cells can help to delineate the structure and dynamics of gene regulatory networks.

Satoshi Ohtsuka

Papers

The JAK‐binding protein JAB inhibits Janus tyrosine kinase activity through binding in the activation loop

Esrrb is a pivotal target of the Gsk3/Tcf3 axis regulating embryonic stem cell self-renewal.

MDM2 interacts with MDMX through their RING finger domains

Suppression of STAT5 functions in liver, mammary glands, and T cells in cytokine-inducible SH2-containing protein 1 transgenic mice.

Dissecting Oct3/4-Regulated Gene Networks in Embryonic Stem Cells by Expression Profiling