Distribution of the mammalian Stat gene family in mouse chromosomes

STAT signaling in the pathogenesis and therapy of acute myeloid leukemia and myelodysplastic syndromes

Acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) represent complex hematopoietic malignancies characterized by ineffective hematopoiesis and dysregulated myeloid differentiation. Recent research has underscored the critical role of aberrant STAT signaling pathways, particularly involving STAT3 and STAT5, in the pathogenesis of these disorders. Aberrant activation of STAT proteins has been implicated as a mediator of oncogenesis in several malignancies. In this review, we discuss the role of STAT proteins in both regulated and dysregulated hematopoiesis, the consequences of dysregulation in acute myeloid leukemia and myelodysplastic syndromes, therapeutic strategies, and recent advancements in STAT-targeted therapy. By integrating findings from recent preclinical and clinical studies, this review provides insights into the evolving landscape of STAT-targeted therapies, highlighting the promise of these approaches in enhancing treatment efficacy and improving patient outcomes in high-risk hematologic malignancies.

Tyrosine phosphorylation of both STAT5A and STAT5B is necessary for maximal IL-2 signaling and T cell proliferation

Cytokine-mediated STAT5 protein activation is vital for lymphocyte development and function. In vitro tyrosine phosphorylation of a C-terminal tyrosine is critical for activation of STAT5A and STAT5B; however, the importance of STAT5 tyrosine phosphorylation in vivo has not been assessed. Here we generate Stat5a and Stat5b tyrosine-to-phenylalanine mutant knockin mice and find they have greatly reduced CD8+ T-cell numbers and profoundly diminished IL-2-induced proliferation of these cells, and this correlates with reduced induction of Myc, pRB, a range of cyclins and CDKs, and a partial G1→S phase-transition block. These mutant CD8+ T cells also exhibit decreased IL-2-mediated activation of pERK and pAKT, which we attribute in part to diminished expression of IL-2Rβ and IL-2Rγ. Our findings thus demonstrate that tyrosine phosphorylation of both STAT5A and STAT5B is essential for maximal IL-2 signaling. Moreover, our transcriptomic and proteomic analyses elucidate the molecular basis of the IL-2-induced proliferation of CD8+ T cells.

Therapeutic advances of targeting receptor tyrosine kinases in cancer

Receptor tyrosine kinases (RTKs), a category of transmembrane receptors, have gained significant clinical attention in oncology due to their central role in cancer pathogenesis. Genetic alterations, including mutations, amplifications, and overexpression of certain RTKs, are critical in creating environments conducive to tumor development. Following their discovery, extensive research has revealed how RTK dysregulation contributes to oncogenesis, with many cancer subtypes showing dependency on aberrant RTK signaling for their proliferation, survival and progression. These findings paved the way for targeted therapies that aim to inhibit crucial biological pathways in cancer. As a result, RTKs have emerged as primary targets in anticancer therapeutic development. Over the past two decades, this has led to the synthesis and clinical validation of numerous small molecule tyrosine kinase inhibitors (TKIs), now effectively utilized in treating various cancer types. In this manuscript we aim to provide a comprehensive understanding of the RTKs in the context of cancer. We explored the various alterations and overexpression of specific receptors across different malignancies, with special attention dedicated to the examination of current RTK inhibitors, highlighting their role as potential targeted therapies. By integrating the latest research findings and clinical evidence, we seek to elucidate the pivotal role of RTKs in cancer biology and the therapeutic efficacy of RTK inhibition with promising treatment outcomes.

STAT signaling pathways in immune cells and their associated mechanisms in cancer pathogenesis

Introduction

Signal transducer and activator of transcriptions (STATs) factors as critical proteins in cell signaling regulate diverse biological processes such as differentiation and proliferation of cells. STATs have been shown to play distinct roles in modulating immune responses mediated by innate and adaptive immune cell subsets due to their significant roles in cytokine signaling.

Methods

In the current study, we review recent studies on the contribution of individual STAT proteins to cytokine signaling, development, and activity of diverse immune cells that constitute the whole immune system and help its performance against endogenous or exogenous agents with a particular focus on meaningful STAT factor in each of innate and adaptive immune cells' subsets to clarify their function in favor of the tumor or against it.

Results

Dysregulation of signaling pathways in the immune cells is associated with various immune disorders, such as the inability of immune system cells in the effective destruction of cancerous cells. Increase of knowledge about these pathways' functions is essential to understand how they can be effectively targeted to eliminate tumors.

Conclusion

The majority of immune cells use the Jak/STAT signaling pathway, which is one of the most important signaling pathways with a role in induction of proper immune responses. Since each of the STAT factors has a specific role in diverse immune cells' subsets, appropriate targeting of them can be a promising strategy for patients who suffer from immune system disorders; specifically it can be beneficial as an approach for cancer immunotherapy.

Protective Role of the Podocyte IL-15 / STAT5 Pathway in Focal Segmental Glomerulosclerosis

Introduction

During glomerular diseases, podocyte-specific pathways can modulate the intensity of histological disease and prognosis. The therapeutic targeting of these pathways could thus improve the management and prognosis of kidney diseases. The Janus Kinase/Signal Transducer and Activator of Transcription (JAK/STAT) pathway, classically described in immune cells, has been recently described in detail in intrinsic kidney cells.

Methods

We describe STAT5 expression in human kidney biopsies from patients with focal segmental glomerulosclerosis (FSGS) and studied mice with a podocyte-specific Stat5 deletion in experimental glomerular diseases.

Results

Here, we show, for the first time, that STAT5 is activated in human podocytes in FSGS. In addition, podocyte-specific Stat5 inactivation aggravates the structural and functional alterations in a mouse model of FSGS. This could be due, at least in part, to an inhibition of autophagic flux. Finally, interleukin 15 (IL-15), a classical activator of STAT5 in immune cells, increases STAT5 phosphorylation in human podocytes, and its administration alleviates glomerular injury in vivo by maintaining autophagic flux in podocytes.

Conclusion

Activating podocyte STAT5 with commercially available IL-15 represents a potential new therapeutic avenue for FSGS.

Genome-wide identification of STATs and analysis of their role in sex determination in Pacific oysters (Crassostrea gigas)

STAT (signal transducer and activator of the transcription) proteins, are a group of highly conserved transcription factors and fundamental components of the JAK-STAT signaling pathway. They play crucial roles in a variety of biological processes, such as immunity, proliferation, differentiation, and growth. However, little information is known regarding their role in gonad development and sex determination in mollusks. In this study, we identified 3 STAT genes in Pacific Oyster Crassostrea gigas. Phylogenetic analysis showed that STATs from mollusks were highly conserved, and most of them had four identical motif regions, except for the STAT1 and STAT3 predicted sequences from Crassostrea hongkongensis. Tissue expression analysis indicated CgSTAT1 had a high expression level in most tissues, while CgSTAT3 had a low expression level in most tissues. Expression analysis of early developmental stages showed CgSTAT1 had a higher expression level from egg to D shaped larva and a lower expression level in subsequent stages. In contrast CgSTAT1, CgSTAT2 had a reverse expression pattern. Expression analysis of different developmental stages of diploid gonads indicated that CgSTAT1 had a higher expression level at the S1 and S3 stages relative to the S2 stage in females, while in males the S3 stage had a higher expression than than the S2 stage. The expression level of CgSTAT1 between diploids and triploids in females differed significantly, but there were no significant differences in males. Expression of CgSTAT2 differed significantly between diploid and triploid males. These data suggest an important role for STATs in sex differentiation in diploid and triploid oysters. Our study is the first to explore the role of STATs in sex differentiation and gonadal development in oysters, and will help us better understand the molecular mechanisms of sex differentiation in shellfish.

SARS-CoV-2 Evasion of the Interferon System: Can We Restore Its Effectiveness?

Type I and III Interferons (IFNs) are the first lines of defense in microbial infections. They critically block early animal virus infection, replication, spread, and tropism to promote the adaptive immune response. Type I IFNs induce a systemic response that impacts nearly every cell in the host, while type III IFNs' susceptibility is restricted to anatomic barriers and selected immune cells. Both IFN types are critical cytokines for the antiviral response against epithelium-tropic viruses being effectors of innate immunity and regulators of the development of the adaptive immune response. Indeed, the innate antiviral immune response is essential to limit virus replication at the early stages of infection, thus reducing viral spread and pathogenesis. However, many animal viruses have evolved strategies to evade the antiviral immune response. The Coronaviridae are viruses with the largest genome among the RNA viruses. Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) caused the coronavirus disease 2019 (COVID-19) pandemic. The virus has evolved numerous strategies to contrast the IFN system immunity. We intend to describe the virus-mediated evasion of the IFN responses by going through the main phases: First, the molecular mechanisms involved; second, the role of the genetic background of IFN production during SARS-CoV-2 infection; and third, the potential novel approaches to contrast viral pathogenesis by restoring endogenous type I and III IFNs production and sensitivity at the sites of infection.

STAT1 Controls the Functionality of Influenza-Primed CD4 T Cells but Therapeutic STAT4 Engagement Maximizes Their Antiviral Impact

It is generally accepted that influenza A virus (IAV) infection promotes a Th1-like CD4 T cell response and that this effector program underlies its protective impact. Canonical Th1 polarization requires cytokine-mediated activation of the transcription factors STAT1 and STAT4 that synergize to maximize the induction of the "master regulator" Th1 transcription factor, T-bet. Here, we determine the individual requirements for these transcription factors in directing the Th1 imprint primed by influenza infection in mice by tracking virus-specific wild-type or T-bet-deficient CD4 T cells in which STAT1 or STAT4 is knocked out. We find that STAT1 is required to protect influenza-primed CD4 T cells from NK cell-mediated deletion and for their expression of hallmark Th1 attributes. STAT1 is also required to prevent type I IFN signals from inhibiting the induction of the Th17 master regulator, Rorγt, in Th17-prone T-bet-/- cells responding to IAV. In contrast, STAT4 expression does not appreciably impact the phenotypic or functional attributes of wild-type or T-bet-/- CD4 T cell responses. However, cytokine-mediated STAT4 activation in virus-specific CD4 T cells enhances their Th1 identity in a T-bet-dependent manner, indicating that influenza infection does not promote maximal Th1 induction. Finally, we show that the T-bet-dependent protective capacity of CD4 T cell effectors against IAV is optimized by engaging both STAT1 and STAT4 during Th1 priming, with important implications for vaccine strategies aiming to generate T cell immunity.

Hsa-miR-323a-3p functions as a tumor suppressor and targets STAT3 in neuroblastoma cells

Background

Studies conducted in the last decades have revealed a role for the non-coding microRNAs (miRNAs) in cancer development and progression. Several miRNAs within the chromosome region 14q32, a region commonly deleted in cancers, are associated with poor clinical outcome in the childhood cancer neuroblastoma. We have previously identified miR-323a-3p from this region to be downregulated in chemotherapy treated neuroblastoma cells compared to pre-treatment cells from the same patients. Furthermore, in neuroblastoma tumors, this miRNA is downregulated in advanced stage 4 disease compared to stage 1-2. In this study, we attempt to delineate the unknown functional roles of miR-323a-3p in neuroblastoma.

Methods

Synthetic miRNA mimics were used to overexpress miR-323a-3p in neuroblastoma cell lines. To investigate the functional roles of miR-323a-3p, cell viability assay, flow cytometry, reverse transcription-quantitative polymerase chain reaction, luciferase reporter assay and western blot were conducted on the neuroblastoma cell lines Kelly, SH-SY5Y and SK-N-BE(2)-C.

Results

Ectopic expression of miR-323a-3p resulted in marked reduction of cell viability in Kelly, SH-SY5Y and SK-N-BE(2)-C by causing G1-cell cycle arrest in Kelly and SH-SY5Y and apoptosis in all the cell lines tested. Furthermore, mRNA and protein levels of signal transducer and activator of transcription 3 (STAT3) were reduced upon miR-323a-3p overexpression. A direct binding of the miR-323a-3p to the 3'UTR of STAT3 was experimentally validated by luciferase reporter assay, where miR-323a-3p reduced luminescent signal from full length STAT3 3'UTR luciferase reporter, but not from a reporter with mutation in the predicted seed sequence.

Conclusions

miR-323a-3p inhibits growth of neuroblastoma cell lines through G1-cell cycle arrest and apoptosis, and the well-known oncogene STAT3 is a direct target of this miRNA.

STAT family of transcription factors in breast cancer: Pathogenesis and therapeutic opportunities and challenges

Breast cancer is the most commonly diagnosed cancer and second-leading cause of cancer deaths in women. Breast cancer stem cells (BCSCs) promote metastasis and therapeutic resistance contributing to tumor relapse. Through activating genes important for BCSCs, transcription factors contribute to breast cancer metastasis and therapeutic resistance, including the signal transducer and activator of transcription (STAT) family of transcription factors. The STAT family consists of six major isoforms, STAT1, STAT2, STAT3, STAT4, STAT5, and STAT6. Canonical STAT signaling is activated by the binding of an extracellular ligand to a cell-surface receptor followed by STAT phosphorylation, leading to STAT nuclear translocation and transactivation of target genes. It is important to note that STAT transcription factors exhibit diverse effects in breast cancer; some are either pro- or anti-tumorigenic while others maintain dual, context-dependent roles. Among the STAT transcription factors, STAT3 is the most widely studied STAT protein in breast cancer for its critical roles in promoting BCSCs, breast cancer cell proliferation, invasion, angiogenesis, metastasis, and immune evasion. Consequently, there have been substantial efforts in developing cancer therapeutics to target breast cancer with dysregulated STAT3 signaling. In this comprehensive review, we will summarize the diverse roles that each STAT family member plays in breast cancer pathobiology, as well as, the opportunities and challenges in pharmacologically targeting STAT proteins and their upstream activators in the context of breast cancer treatment.

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.

Immunomodulatory Effect of Hispolon on LPS-Induced RAW264.7 Cells and Mitogen/Alloantigen-Stimulated Spleen Lymphocytes of Mice

Hispolon is a potent anticancer, anti-inflammatory, antioxidant, and antidiabetic agent isolated from Phellinus linteus, an oriental medicinal mushroom. However, the immunomodulatory mechanisms by which hispolon affects macrophages and lymphocytes remain poorly characterized. We investigated the immunomodulatory effects of hispolon on oxidative stress, inflammatory responses, and lymphocyte proliferation using lipopolysaccharide (LPS)-treated RAW264.7 macrophages or mitogen/alloantigen-treated mouse splenocytes. Hispolon inhibited LPS-induced reactive oxygen and nitrogen species (ROS/RNS) generation and decreased total sulfhydryl (SH) levels in a cell-free system and RAW264.7 cells. Hispolon exerted significant anti-inflammatory effects by inhibiting production of the proinflammatory cytokines interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) and activation of nuclear factor kappa B (NF-κB) and signal transducer and activator of transcription 3 (STAT3) in LPS-treated RAW264.7 cells. Hispolon also modulated NF-κB and STAT3 activation by suppressing the NF-κB p65 interaction with phospho-IκBα and the STAT3 interaction with JAK1, as determined via coimmunoprecipitation analysis. Additionally, hispolon significantly decreased lymphocyte proliferation, T cell responses and T helper type 1 (Th1)/type 2 (Th2) cytokines production in mitogen/alloantigen-treated splenocytes. We conclude that hispolon exerts immunomodulatory effects on LPS-treated macrophages or mitogen/alloantigen-treated splenocytes through antioxidant, anti-inflammatory, and antiproliferative activities. Thus, hispolon may be a therapeutic agent for treating immune-mediated inflammatory diseases.

The Effects of Sesquiterpene Lactones on the Differentiation of Human or Animal Cells Cultured In-Vitro: A Critical Systematic Review

Cellular differentiation is pivotal in health and disease. Interfering with the process of differentiation, such as inhibiting the differentiation of adipocytes and inducing the differentiation of cancer cells, is considered a therapeutic approach. Sesquiterpene lactones, primarily found in plants, have been attracted attention as differentiating/dedifferentiating agents tested on various human or animal cells. However, a consensus on sesquiterpene lactones’ effects and their mechanism of action is required. In this sense, through a systematic review, we have investigated the differentiating/dedifferentiating effects of sesquiterpene lactones on human or animal cells. 13 different cell lines originated from humans, mice, and rats, in addition to the effects of a total of 21 sesquiterpene lactones, were evaluated in the included studies. These components had either inducing, inhibiting, or no effect on the cells, mediating their effects through JAK-STAT, PI3K-Akt, mitogen-activated protein kinases, NFκB, PPARγ pathways. Although nearly all inducing and inhibiting effects were attributed to cancerous and normal cells, respectively, this is likely a result of a biased study design. Few studies reported negative results along with others, and no study was found reporting only negative results. As a result, not only are the effects and mechanism of action of sesquiterpene lactones not vivid but our knowledge and decisions are also misconducted. Moreover, there is a significant knowledge gap regarding the type of evaluated cells, other sesquiterpene lactones, and the involved signaling pathways. In conclusion, sesquiterpene lactones possess significant effects on differentiation status, leading to potentially efficient therapy of obesity, osteoporosis, and cancer. However, reporting negative results and further investigations on other cells, sesquiterpene lactones, and signaling pathways are highly suggested to pave the path of sesquiterpene lactones to the clinic more consciously.

STAT proteins: a kaleidoscope of canonical and non-canonical functions in immunity and cancer

STAT proteins represent an important family of evolutionarily conserved transcription factors that play key roles in diverse biological processes, notably including blood and immune cell development and function. Classically, STAT proteins have been viewed as inducible activators of transcription that mediate cellular responses to extracellular signals, particularly cytokines. In this 'canonical' paradigm, latent STAT proteins become tyrosine phosphorylated following receptor activation, typically via downstream JAK proteins, facilitating their dimerization and translocation into the nucleus where they bind to specific sequences in the regulatory region of target genes to activate transcription. However, growing evidence has challenged this paradigm and identified alternate 'non-canonical' functions, such as transcriptional repression and roles outside the nucleus, with both phosphorylated and unphosphorylated STATs involved. This review provides a revised framework for understanding the diverse kaleidoscope of STAT protein functional modalities. It further discusses the implications of this framework for our understanding of STAT proteins in normal blood and immune cell biology and diseases such as cancer, and also provides an evolutionary context to place the origins of these alternative functional modalities.

SOCS Proteins in Immunity, Inflammatory Diseases, and Immune-Related Cancer

Cytokine signaling represents one of the cornerstones of the immune system, mediating the complex responses required to facilitate appropriate immune cell development and function that supports robust immunity. It is crucial that these signals be tightly regulated, with dysregulation underpinning immune defects, including excessive inflammation, as well as contributing to various immune-related malignancies. A specialized family of proteins called suppressors of cytokine signaling (SOCS) participate in negative feedback regulation of cytokine signaling, ensuring it is appropriately restrained. The eight SOCS proteins identified regulate cytokine and other signaling pathways in unique ways. SOCS1–3 and CISH are most closely involved in the regulation of immune-related signaling, influencing processes such polarization of lymphocytes and the activation of myeloid cells by controlling signaling downstream of essential cytokines such as IL-4, IL-6, and IFN-γ. SOCS protein perturbation disrupts these processes resulting in the development of inflammatory and autoimmune conditions as well as malignancies. As a consequence, SOCS proteins are garnering increased interest as a unique avenue to treat these disorders.

Comprehensive analyses of potential key genes in active tuberculosis: A systematic review

BACKGROUND

Tuberculosis (TB) is a global health problem that brings us numerous difficulties. Diverse genetic factors play a significant role in the progress of TB disease. However, still no key genes for TB susceptibility have been reported. This study aimed to identify the key genes of TB through comprehensive bioinformatics analysis.

METHODS

The series microarray datasets from the gene expression omnibus (GEO) database were analyzed. We used the online tool GEO2R to filtrate differentially expressed genes (DEGs) between TB and health control. Database for annotation can complete gene ontology function analysis as well as Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis. Protein-protein interaction (PPI) networks of DEGs were established by STRING online tool and visualized by Cytoscape software. Molecular Complex Detection can complete the analysis of modules in the PPI networks. Finally, the significant hub genes were confirmed by plug-in Genemania of Cytoscape, and verified by the verification cohort and protein test.

RESULTS

There are a total of 143 genes were confirmed as DEGs, containing 48 up-regulated genes and 50 down-regulated genes. The gene ontology and Kyoto Encyclopedia of Genes and Genomes analysis show that upregulated DEGs were associated with cancer and phylogenetic, whereas downregulated DEGs mainly concentrate on inflammatory immunity. PPI networks show that signal transducer and activator of transcription 1 (STAT1), guanylate binding protein 5 (GBP5), 2'-5'-oligoadenylate synthetase 1 (OAS1), catenin beta 1 (CTNNB1), and guanylate binding protein 1 (GBP1) were identified as significantly different hub genes.

CONCLUSION

We conclude that these genes, including TAT1, GBP5, OAS1, CTNNB1, GBP1 are a candidate as potential core genes in TB and treatment of TB in the future.

The repertoire of vertebrate STAT transcription factors: Origin and variations in fish

The stat gene family diversified during early vertebrate evolution thanks to two rounds of whole genome duplication (WGD) to produce a typical repertoire composed of 6 STAT factors (named 1-6). In contrast, only one or two stat genes have been reported in C. elegans and in D. melanogaster. The main types of STAT found from bony fish to mammals are present in Agnathan genomes, but a typical STAT1-6 repertoire is only observed in jawed vertebrates. Comparative syntenies showed that STAT6 was the closest to the ancestor of the family. An extensive survey of stat genes across fish including polyploid species showed that whole genome duplications did not lead to a uniform expansion of stat genes. While 2 to 5 stat1 are present in salmonids, whose genome duplicated about 35My ago, only one copy of stat2 and stat6 is retained. In contrast, common carp, with a recent whole genome duplication (5-10My), possesses a doubled stat repertoire indicating that the elimination of stat2 and stat6 additional copies is not immediate. Altogether our data shed light on the multiplicity of evolutionary pathways followed by key components of the canonical cytokine receptor signalling pathway, and point to differential selective constraints exerted on these factors.

Expression of STAT1 is positively correlated with PD-L1 in human ovarian cancer

Signal transducer and activator of transcription 1 (STAT1) is related to the immune microenvironment of tumorigenesis. The programmed cell death 1 (PD-1) and its ligand (PD-L1) have been reported to be important in immunotherapy by mediating tumor immune evasion. Blocking the PD-1/PD-L1 pathway can restore the endogenous anti-tumor immune response. This study aimed to examine the expression of STAT1, PD-1, and PD-L1 and the correlation between selected markers in human epithelial ovarian cancer (EOC). The results showed that malignant tumors contained more STAT1, PD-1, and PD-L1 positive cells. The expression of STAT1 and PD-L1 was associated with age, whereas PD-1 and PD-L1 associated with histopathological type, in patients with ovarian tumors. Moreover, the expression of STAT1 was found to be associated with disease stages and the grade of serous carcinoma. STAT1 expression was higher in OC cells than normal ovarian surface epithelial cells and was positively correlated with PD-L1 expression. The knockdown of STAT1 decreased PD-L1 expression, whereas overexpression of STAT1 increased PD-L1 expression. Furthermore, the expression of STAT1, PD-1, and PD-L1 was lower in paclitaxel-resistant cells than sensitive cells. Finally, STAT1 affected the overall survival and progression-free survival of patients with EOC. These findings suggest that STAT1, PD-1, and PD-L1 are the tissue markers of EOC and imply the possibility that the high level of STAT1, PD-1, and PD-L1 may favor the checkpoint immunotherapy in patients with EOC, but may have a limit in paclitaxel-resistant patients because of the low expression of STAT1, PD-1, and PD-L1 in paclitaxel-resistant cells.

STAT1 determines aggressiveness of glioblastoma both in vivo and in vitro through wnt/β-catenin signalling pathway

Glioblastoma is one of the most malignant tumors and causes the high mortality in cancer patients. Currently, there is no highly efficient therapy against glioblastoma. Therefore, searching for a new molecular target to anti-glioblastoma therapy is urgent and necessary. In this study, we elucidated the role of Signal transducer and activator of transcription 1 (STAT1) in proliferation, migration and apoptosis of glioblastoma cells. We found that STAT1 downregulation could weaken the aggressiveness of glioblastoma cells. Besides, the glioblastoma growth in vivo was also inhibited with the STAT1 downregulation by shRNA as well as by pharmacological stimulation withSTAT1inhibitors. This negative regulation of tumor growth was accompanied by the inhibition in epithelial-mesenchymal transition (EMT), whereas the STAT1 overexpression promoted EMT. Furthermore, the involvement of wnt/β-catenin was observed in STAT1 downregulation mediated weakness in glioblastoma aggressiveness since application of activator wnt agonist 1 could counteract the inhibitory effect induced by STAT1 downregulation. Collectively, this work provided the evidence to support the conclusion that STAT1 can regulate the glioblastoma growth and migration, potentially serving as a therapeutic target against glioblastoma. SIGNIFICANCE OF THE STUDY: Glioblastoma is one of the most malignant tumors with very high mortality. Until now, there is no efficient therapy against glioblastoma. In this study, we found downregulation of Signal transducer and activator of transcription 1 (STAT1) could weaken the aggressiveness of glioblastoma cells through inhibition in epithelial-mesenchymal transition, mediated through wnt/β-catenin signalling pathway. Thus, this work supported the regulatory role of STAT1 in glioblastoma growth and migration. This potentially serves as a new therapeutic target against glioblastoma.

Downregulation of STAT1 induces the differentiation of neural stem cells through JNK pathway

Neural stem cells (NSCs) generated neurons and glial cells. Thus, it is a preferable candidate to the cell replacement-based therapy against neural disorders. The signaling pathways that regulate differentiation of NSCs are widely studied. In the current study, we used in vitro culture system to elucidate the role of signal transducer and activator of transcription 1 (STAT1) in NSCs' differentiation. Downregulation of STAT1 inhibited the proliferation of NSCs. Meanwhile, we also found STAT1 regulation could control the differentiation of NSCs. More neurons and glia cells were generated from NSCs with STAT1 silencing. This process was mediated by the JNK/STAT1 signaling. STAT1 inhibitor promoted differentiation of NSCs. After transplantation, we observed more neurons generated from NSCs with shRNA-STAT1 treatment. Collectively, this work showed an efficient way to regulate neuronal differentiation of NSCs through regulating the STAT1 expression. This is likely to provide source and theoretical support to cell replacement based theory.

On the Way to Become a Natural Killer Cell

Natural Killer (NK) cells are innate lymphocytes playing pivotal roles in host defense and immune-surveillance. The homeostatic modulation of germ-line encoded/non-rearranged activating and inhibitory NK cell receptors (NKRs) determines the capability of these innate lymphocytes to either spare "self" cells or to kill viral-infected, tumor-transformed and heterologous cell targets. However, despite being discovered more than 40 years ago, several aspects of NK cell biology remain unknown or are still being debated. In particular, our knowledge of human NK cell ontogenesis and differentiation is still in its infancy as the majority of our experimental evidence on this topic mainly comes from findings obtained in vitro or with animal models in vivo. Although both the generation and the maintenance of human NK cells are sustained by hematopoietic stem cells (HSCs), the precise site(s) of NK cell development are still poorly defined. Indeed, HSCs and hematopoietic precursors are localized in different anatomical compartments that also change their ontogenic commitments before and after birth as well as in aging. Currently, the main site of NK cell generation and maturation in adulthood is considered the bone marrow, where their interactions with stromal cells, cytokines, growth factors, and other soluble molecules support and drive maturation. Different sequential stages of NK cell development have been identified on the basis of the differential expression of specific markers and NKRs as well as on the acquisition of specific effector-functions. All these phenotypic and functional features are key in inducing and regulating homing, activation and tissue-residency of NK cells in different human anatomic sites, where different homeostatic mechanisms ensure a perfect balance between immune tolerance and immune-surveillance. The present review summarizes our current knowledge on human NK cell ontogenesis and on the related pathways orchestrating a proper maturation, functions, and distributions.

The molecular details of cytokine signaling via the JAK/STAT pathway

More than 50 cytokines signal via the JAK/STAT pathway to orchestrate hematopoiesis, induce inflammation and control the immune response. Cytokines are secreted glycoproteins that act as intercellular messengers, inducing proliferation, differentiation, growth, or apoptosis of their target cells. They act by binding to specific receptors on the surface of target cells and switching on a phosphotyrosine-based intracellular signaling cascade initiated by kinases then propagated and effected by SH2 domain-containing transcription factors. As cytokine signaling is proliferative and often inflammatory, it is tightly regulated in terms of both amplitude and duration. Here we review molecular details of the cytokine-induced signaling cascade and describe the architectures of the proteins involved, including the receptors, kinases, and transcription factors that initiate and propagate signaling and the regulatory proteins that control it.

Prolactin Receptor Isoforms as the Basis of Tissue-Specific Action of Prolactin in the Norm and Pathology

The review describes functional and structural features of different isoforms of prolactin receptor, mechanisms of signaling pathway activation, and molecular messengers involved in the transmission and termination of signal from the prolactin receptor isoforms. Changes in the ratio between prolactin receptor isoforms, key mediators of prolactin signal transduction and termination in various organs and tissues, are analyzed. Special attention is given to the role of molecular mediators and the ratio between the isoforms in normal physiological functions and pathologies. Approaches for therapeutic correction of prolactin signaling impairments are discussed.

Endocytosis of GM-CSF receptor β is essential for signal transduction regulating mesothelial-macrophage transition

During Freund's adjuvant induced inflammation rat mesenteric mesothelial cells transdifferentiate into mesenchymal cell. They express macrophage markers, inflammatory cytokines (TGF-β, TNFα, IL-6), and specific receptors. When primary mesenteric cultures were treated with GM-CSF and/or TGF-β (in vitro), similar phenotypic and biological changes were induced. It seemed likely that GM-CSF receptor-ligand complex should be internalized to initiate mesothelial-macrophage transition. To follow the intracellular route of GM-CSF receptor β, we co-localized this receptor with various endocytic markers (Cav-1, EEA1, Rab7, and Rab11a), and carried out detailed immunocytochemical, statistical and biochemical analyses. Since STAT5 is one of the downstream element of GM-CSF signaling, we followed the expression and phosphorylation level of this transcription factor. Our results showed that in mesenteric mesothelial cells GM-CSF receptor β is internalized by caveolae, delivered into early endosomes where the signaling events occur, STAT5A is phosphorylated by JAK2, and then translocated into the nucleus. When dynamin-dependent endocytosis of GM-CSFR β is inhibited by dynasore, phosphorylation of STAT5A is not occurred, confirming, that the internalization of receptor β is indispensable for signal transduction. At the early time of inflammation a significant receptor recycling can be found to the plasma membrane. Later (day 8) the receptor is delivered into late endosomes, indicating that its degradation has already started, and the regeneration of mesothelial cells can start. All of these data strongly support that the internalization of GM-CSF receptor β is required and essential for signal transduction.

STAT3beta, a distinct isoform from STAT3

STAT3β is an isoform of STAT3 (signal transducer and activator of transcription 3) that differs from the STAT3α isoform by the replacement of the C-terminal 55 amino acid residues with 7 specific residues. The constitutive activation of STAT3α plays a pivotal role in the activation of oncogenic pathways, such as cell proliferation, maturation and survival, while STAT3β is often referred to as a dominant-negative regulator of cancer. STAT3β reveals a "spongy cushion" effect through its cooperation with STAT3α or forms a ternary complex with other co-activators. Especially in tumour cells, relatively high levels of STAT3β lead to some favourable changes. However, there are still many mechanisms that have not been clearly explained in contrast to STAT3α, such as STAT3β nuclear retention, more stable heterodimers and the prolonged Y705 phosphorylation. In addition to its transcriptional activities, STAT3β may also function in the cytosol with respect to the mitochondria, cytoskeleton rearrangements and metastasis of cancer cells. In this review, we summarize the mechanisms that underlie the unique roles of STAT3β combined with total STAT3 to enlighten and draw the attention of researchers studying STAT3 and discuss some interesting questions that warrant answers.

Targeting STATs in neuroinflammation: The road less traveled!

JAK/STAT transduction pathway is a highly conserved pathway implicated in regulating cellular proliferation, differentiation, survival and apoptosis. Dysregulation of this pathway is involved in the onset of autoimmune, haematological, oncological, metabolic and neurological diseases. Over the last few years, the research of anti-neuroinflammatory agents has gained considerable attention. The ability to diminish the STAT-induced transcription of inflammatory genes is documented for both natural compounds (such as polyphenols) and chemical drugs. Among polyphenols, quercetin and curcumin directly inhibit STAT, while Berberis vulgaris L. and Sophora alopecuroides L extracts act indirectly. Also, the Food and Drug Administration has approved several JAK/STAT inhibitors (direct or indirect) for treating inflammatory diseases, indicating STAT can be considered as a therapeutic target for neuroinflammatory pathologies. Considering the encouraging data obtained so far, clinical trials are warranted to demonstrate the effectiveness and potential use in the clinical practice of STAT inhibitors to treat inflammation-associated neurodegenerative pathologies.

Implications of STAT3 and STAT5 signaling on gene regulation and chromatin remodeling in hematopoietic cancer

STAT3 and STAT5 proteins are oncogenic downstream mediators of the JAK–STAT pathway. Deregulated STAT3 and STAT5 signaling promotes cancer cell proliferation and survival in conjunction with other core cancer pathways. Nuclear phosphorylated STAT3 and STAT5 regulate cell-type-specific transcription profiles via binding to promoter elements and exert more complex functions involving interaction with various transcriptional coactivators or corepressors and chromatin remodeling proteins. The JAK–STAT pathway can rapidly reshape the chromatin landscape upon cytokine, hormone, or growth factor stimulation and unphosphorylated STAT proteins also appear to be functional with respect to regulating chromatin accessibility. Notably, cancer genome landscape studies have implicated mutations in various epigenetic modifiers as well as the JAK–STAT pathway as underlying causes of many cancers, particularly acute leukemia and lymphomas. However, it is incompletely understood how mutations within these pathways can interact and synergize to promote cancer. We summarize the current knowledge of oncogenic STAT3 and STAT5 functions downstream of cytokine signaling and provide details on prerequisites for DNA binding and gene transcription. We also discuss key interactions of STAT3 and STAT5 with chromatin remodeling factors such as DNA methyltransferases, histone modifiers, cofactors, corepressors, and other transcription factors.

STAT3 targeting by polyphenols: Novel therapeutic strategy for melanoma

Melanoma or malignant melanocytes appear with the low incidence rate, but very high mortality rate worldwide. Epidemiological studies suggest that polyphenolic compounds contribute for prevention or treatment of several cancers particularly melanoma. Such findings motivate to dig out novel therapeutic strategies against melanoma, including research toward the development of new chemotherapeutic and biologic agents that can target the tumor cells by different mechanisms. Recently, it has been found that signal transducer and activator of transcription 3 (STAT3) is activated in many cancer cases surprisingly. Different evidences supply the aspect that STAT3 activation plays a vital role in the metastasis, including proliferation of cells, survival, invasion, migration, and angiogenesis. This significant feature plays a vital role in various cellular processes, such as cell proliferation and survival. Here, we reviewed the mechanisms of the STAT3 pathway regulation and their role in promoting melanoma. Also, we have evaluated the emerging data on polyphenols (PPs) specifically their contribution in melanoma therapies with an emphasis on their regulatory/inhibitory actions in relation to STAT3 pathway and current progress in the development of phytochemical therapeutic techniques. An understanding of targeting STAT3 by PPs brings an opportunity to melanoma therapy. © 2016 BioFactors, 43(3):347-370, 2017.

STAT5 and CD4 + T Cell Immunity

STAT5 plays a critical role in the development and function of many cell types. Here, we review the role of STAT5 in the development of T lymphocytes in the thymus and its subsequent role in the differentiation of distinct CD4 + helper and regulatory T-cell subsets.

STAT3 Represses Nitric Oxide Synthesis in Human Macrophages upon Mycobacterium tuberculosis Infection

Mycobacterium tuberculosis is a successful intracellular pathogen. Numerous host innate immune responses signaling pathways are induced upon mycobacterium invasion, however their impact on M. tuberculosis replication is not fully understood. Here we reinvestigate the role of STAT3 specifically inside human macrophages shortly after M. tuberculosis uptake. We first show that STAT3 activation is mediated by IL-10 and occurs in M. tuberculosis infected cells as well as in bystander non-colonized cells. STAT3 activation results in the inhibition of IL-6, TNF-α, IFN-γ and MIP-1β. We further demonstrate that STAT3 represses iNOS expression and NO synthesis. Accordingly, the inhibition of STAT3 is detrimental for M. tuberculosis intracellular replication. Our study thus points out STAT3 as a key host factor for M. tuberculosis intracellular establishment in the early stages of macrophage infection.

The anti-proliferative effects of type I IFN involve STAT6-mediated regulation of SP1 and BCL6

Type I IFN-induced STAT6 has been shown to have anti-proliferative effects in Daudi and B cells. IFN-sensitive (DS) and IFN-resistant (DR) subclones of Daudi cells were used to study the role of STAT6 in the anti-proliferative activities. Type I IFN significantly increased STAT6 mRNA and protein expression in DS but not DR cells. STAT6 knockdown significantly reduced the sensitivity to IFN in both cell lines. The molecular targets and functional importance of IFN-activated STAT6 were performed by chromatin immunoprecipitation-on-chip (ChIP-on-chip) experiments in type I IFN-treated Daudi cells. Two target genes (Sp1 and BCL6) were selected from the ChIP-on-chip data. IFN-induced STAT6 activation led to Sp1 upregulation and BCL6 downregulation in DS cells, with only minimal effects in DR cells. siRNA inhibition of STAT6 expression resulted in decreased Sp1 and BCL6 mRNA and protein levels in both DS and DR cells. IFN treatment did not increase Sp1 and BCL6 expression in a STAT2-deficient RST2 cell line, and this effect was mitigated by plasmid overexpression of STAT2, indicating that STAT2 is important for STAT6 activation. These results suggest that STAT6 plays an important role in regulating Sp1 and BCL6 through STAT2 to exert the anti-proliferative effects of type I IFN.

An invertebrate signal transducer and activator of transcription 5 (STAT5) ortholog from the disk abalone, Haliotis discus discus: Genomic structure, early developmental expression, and immune responses to bacterial and viral stresses

Signal transducer and activator of transcription (STAT) family members are key signaling molecules that transduce cellular responses from the cell membrane to the nucleus upon Janus kinase (JAK) activation. Although seven STAT members have been reported in mammals, very limited information on STAT genes in molluscans is available. In this study, we identified and characterized a STAT paralog that is homologous to STAT5 from the disk abalone, Haliotis discus discus, and designated as AbSTAT5. Comparison of the deduced amino acid sequence for AbSTAT5 (790 amino acids) with other counterparts revealed conserved residues important for functions and typical domain regions, including the N-terminal domain, coiled-coil domain, DNA-binding domain, linker domain, and Src homology 2 (SH2) domains as mammalian counterparts. Analysis of STAT phylogeny revealed that AbSTAT5 was clustered with the molluscan subgroup in STAT5 clade with distinct evolution. According to the genomic structure of AbSTAT5, the coding sequence was distributed into 20 exons with 19 introns. Immunologically essential transcription factor-binding sites, such as GATA-1, HNF, SP1, C/EBP, Oct-1, AP1, c-Jun, and Sox-2, were predicted at the 5'-proximal region of AbSTAT5. Expression of AbSTAT5 mRNA was detected in different stages of embryonic development and observed at considerably higher levels in the morula and late veliger stages. Tissue-specific expressional studies revealed that the highest level of AbSTAT5 transcripts was detected in hemocytes, followed by gill tissues. Temporal expressions of AbSTAT5 were analyzed upon live bacterial (Vibrio parahemolyticus and Listeria monocytogenes), viral (viral hemorrhagic septicemia virus), and pathogen-associated molecular pattern (lipopolysaccharides and Poly I:C) stimulations, and significant elevations indicated immune modulation. These results suggest that AbSTAT5 may be involved in maintaining innate immune responses from developmental to adult stages in the disk abalone. Further, this study provides a basis for structural and functional exploration of STAT members in the invertebrate JAK/STAT signaling pathway.

STAT5 in Cancer and Immunity

Signal transducers and activators of transcription 5 (STAT5a and STAT5b) are highly homologous proteins that are encoded by 2 separate genes and are activated by Janus-activated kinases (JAK) downstream of cytokine receptors. STAT5 proteins are activated by a wide variety of hematopoietic and nonhematopoietic cytokines and growth factors, all of which use the JAK-STAT signalling pathway as their main mode of signal transduction. STAT5 proteins critically regulate vital cellular functions such as proliferation, differentiation, and survival. The physiological importance of STAT5 proteins is underscored by the plethora of primary human tumors that have aberrant constitutive activation of these proteins, which significantly contributes to tumor cell survival and malignant progression of disease. STAT5 plays an important role in the maintenance of normal immune function and homeostasis, both of which are regulated by specific members of IL-2 family of cytokines, which share a common gamma chain (γ(c)) in their receptor complex. STAT5 critically mediates the biological actions of members of the γ(c) family of cytokines in the immune system. Essentially, STAT5 plays a critical role in the function and development of Tregs, and consistently activated STAT5 is associated with a suppression in antitumor immunity and an increase in proliferation, invasion, and survival of tumor cells. Thus, therapeutic targeting of STAT5 is promising in cancer.

Cloning and gene expression of signal transducers and activators of transcription (STAT) homologue provide new insights into the immune response and nucleus graft of the pearl oyster Pinctada fucata

The signal transducers and activators of the transcription (STAT) family play an important role in regulatory and cellular functions by regulating the expression of a variety of genes, including cytokines and growth factors. In the present study, a Pinctada fucata STAT protein, termed PfSTAT, was described. The deduced amino acid sequence of PfSTAT contains the conserved STAT_bind domain and the SH2 domain, and the additional Bin/Amphiphysin/Rvs (BAR) domain, but does not have STAT_alpha and STAT_int domains. Multiple sequence alignments revealed that PfSTAT showed relatively low identity with vertebrate and other invertebrate STATs, and phylogenetic analysis indicated that the evolution of STAT may have been more complex and ancient. Gene expression analysis revealed that PfSTAT is involved in the immune response to polyinosinic-polycytidylic acid (poly I:C) stimulation and in the nucleus insertion operation. This study contributes to a better understanding of PfSTAT in protecting the pearl oyster from disease or injury caused by grafting.

The good and the bad faces of STAT1 in solid tumours

Signal transducer and activator of transcription (STAT) 1 is part of the Janus kinase (JAK)/STAT signalling cascade and is best known for its essential role in mediating responses to all types of interferons (IFN). STAT1 regulates a variety of cellular processes, such as antimicrobial activities, cell proliferation and cell death. It exerts important immune modulatory activities both in the innate and the adaptive arm of the immune system. Based on studies in mice and data from human patients, STAT1 is generally considered a tumour suppressor but there is growing evidence that it can also act as a tumour promoter. This review aims at contrasting the two faces of STAT1 in tumourigenesis and providing an overview on the current knowledge of the underlying mechanisms or pathways.

STATdb: a specialised resource for the STATome

Signal transducers and activators of transcription (STAT) proteins are key signalling molecules in metazoans, implicated in various cellular processes. Increased research in the field has resulted in the accumulation of STAT sequence and structure data, which are scattered across various public databases, missing extensive functional annotations, and prone to effort redundancy because of the dearth of community sharing. Therefore, there is a need to integrate the existing sequence, structure and functional data into a central repository, one that is enriched with annotations and provides a platform for community contributions. Herein, we present STATdb (publicly available at http://statdb.bic.nus.edu.sg/), the first integrated resource for STAT sequences comprising 1540 records representing the known STATome, enriched with existing structural and functional information from various databases and literature and including manual annotations. STATdb provides advanced features for data visualization, analysis and prediction, and community contributions. A key feature is a meta-predictor to characterise STAT sequences based on a novel classification that integrates STAT domain architecture, lineage and function. A curation policy workflow has been devised for regulated and structured community contributions, with an update policy for the seamless integration of new data and annotations.

Interferon-α acts on the S/G2/M phases to induce apoptosis in the G1 phase of an IFNAR2-expressing hepatocellular carcinoma cell line

Interferon-α (IFN-α) is used clinically to treat hepatocellular carcinoma (HCC), although the detailed therapeutic mechanisms remain elusive. In particular, IFN-α has long been implicated in control of the cell cycle, but its actual point of action has not been clarified. Here, using time lapse imaging analyses of the human HCC cell line HuH7 carrying a fluorescence ubiquitination-based cell cycle indicator (Fucci), we found that IFN-α induced cell cycle arrest in the G0/G1 phases, leading to apoptosis through an IFN-α type-2 receptor (IFNAR2)-dependent signaling pathway. Detailed analyses by time lapse imaging and biochemical assays demonstrated that the IFN-α/IFNAR2 axis sensitizes cells to apoptosis in the S/G2/M phases in preparation for cell death in the G0/G1 phases. In summary, this study is the first to demonstrate the detailed mechanism of IFN-α as an anticancer drug, using Fucci-based time lapse imaging, which will be informative for treating HCC with IFN-α in clinical practice.

Comparative evolutionary genomics of the STAT family of transcription factors

The STAT signaling pathway is one of the seven common pathways that govern cell fate decisions during animal development. Comparative genomics revealed multiple incidences of stat gene duplications throughout metazoan evolutionary history. While pseudogenization is a frequent fate of duplicated genes, many of these STAT duplications evolved into novel genes through rapid sequence diversification and neofunctionalization. Additionally, the core of STAT gene regulatory networks, comprising stat1 through 4, stat5 and stat6, arose early in vertebrate evolution, probably through the two whole genome duplication events that occurred after the split of Cephalochordates but before the rise of Chondrichthyes. While another complete genome duplication event took place during the evolution of bony fish after their separation from the tetrapods about 450 million years ago (Mya), modern fish have only one set of these core stats, suggesting the rapid loss of most duplicated stat genes. The two stat5 genes in mammals likely arose from a duplication event in early Eutherian evolution, a period from about 310 Mya at the avian-mammal divergence to the separation of marsupials from other mammals about 130 Mya. These analyses indicate that whole genome duplications and gene duplications by unequal chromosomal crossing over were likely the major mechanisms underlying the evolution of STATs.

Targeting the STAT3 signaling pathway in cancer: role of synthetic and natural inhibitors

Signal transducers and activators of transcription (STATs) comprise a family of cytoplasmic transcription factors that mediate intracellular signaling that is usually generated at cell surface receptors and thereby transmit it to the nucleus. Numerous studies have demonstrated constitutive activation of STAT3 in a wide variety of human tumors, including hematological malignancies (leukemias, lymphomas, and multiple myeloma) as well as diverse solid tumors (such as head and neck, breast, lung, gastric, hepatocellular, colorectal and prostate cancers). There is strong evidence to suggest that aberrant STAT3 signaling promotes initiation and progression of human cancers by either inhibiting apoptosis or inducing cell proliferation, angiogenesis, invasion, and metastasis. Suppression of STAT3 activation results in the induction of apoptosis in tumor cells, and accordingly its pharmacological modulation by tyrosine kinase inhibitors, antisense oligonucleotides, decoy nucleotides, dominant negative proteins, RNA interference and chemopreventive agents have been employed to suppress the proliferation of various human cancer cells in culture and tumorigenicity in vivo. However, the identification and development of novel drugs that can target deregulated STAT3 activation effectively remains an important scientific and clinical challenge. This review presents the evidence for critical roles of STAT3 in oncogenesis and discusses the potential for development of novel cancer therapies based on mechanistic understanding of STAT3 signaling cascade.

Role of STAT3 in cancer metastasis and translational advances

Signal transducer and activator of transcription 3 (STAT3) is a latent cytoplasmic transcription factor, originally discovered as a transducer of signal from cell surface receptors to the nucleus. It is activated by tyrosine phosphorylation at position 705 leading to its dimerization, nuclear translocation, DNA binding, and activation of gene transcription. Under normal physiological conditions, STAT3 activation is tightly regulated. However, compelling evidence suggests that STAT3 is constitutively activated in many cancers and plays a pivotal role in tumor growth and metastasis. It regulates cellular proliferation, invasion, migration, and angiogenesis that are critical for cancer metastasis. In this paper, we first describe the mechanism of STAT3 regulation followed by how STAT3 is involved in cancer metastasis, then we summarize the various small molecule inhibitors that inhibit STAT3 signaling.

Constitutively active STAT5 constructs

The transcription factor Signal Tranducer and Activator of Transcription 5 (STAT5) plays an important role in many biological processes. To study STAT5 biology, several different constructs have been designed that render STAT5 constitutively active. These constructs have now been used to generate animal models that allow for targeted expression of constitutively active STAT5 including a model where STAT5 is expressed in developing B and T cells. Herein we briefly describe the design of constitutively active STAT5 constructs and recent advances in their use.

Prolactin signalling in the mouse hypothalamus is primarily mediated by signal transducer and activator of transcription factor 5b but not 5a

Prolactin acts at multiple targets throughout the body, including the mammary gland, heart, liver, muscle and brain. Upon binding to its receptors, prolactin signals through the phosphorylation and thus activation of signal transducer and activator of transcription 5 (STAT5). There are two very similar STAT5 isoforms, termed STAT5a and STAT5b, which are selectively activated by prolactin in specific tissues. Various brain regions, including the hypothalamus, are prolactin responsive, although the STAT5 isoform involved in these actions is unknown. Immunohistochemical and western blot analysis were used to determine the expression and activation of STAT5a and STAT5b throughout the hypothalamus in adult wild-type and STAT5b-deficient mice. Both groups were pretreated with bromocriptine to suppress endogenous prolactin levels followed by the administration of ovine prolactin (10 mg/kg) for 45 min. STAT5a and STAT5b were expressed throughout the hypothalamus of wild-type mice. As expected, only STAT5a was detected in STAT5b-deficient mice, although, unexpectedly, there was a marked reduction in its expression compared to wild-type mice. When stimulated with prolactin, phosphorylated STAT5 was observed in the hypothalamus of wild-type but not STAT5b-deficient mice. By contrast, phosphorylated STAT5 was detected in mammary gland epithelial cells and adipocytes of STAT5b-deficient animals. Thus, although STAT5a was still expressed in the STAT5b-deficient mice, it was not phosphorylated in the hypothalamus in response to prolactin. These observations indicate that STAT5b but not STAT5a is the primary mediator of the action of prolactin in the hypothalamus. Despite the similarity between the two STAT5 isoforms, STAT5a was unable to compensate for the absence of STAT5b, suggesting that each isoform exhibits a unique biological activity.

Potential role of signal transducer and activator of transcription (STAT)3 signaling pathway in inflammation, survival, proliferation and invasion of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is one of the most lethal malignancies, and is also the fourth most common cancer worldwide with around 700,000 new cases each year. Currently, first line chemotherapeutic drugs used for HCC include fluorouracil, cisplatin, doxorubicin, paclitaxel and mitomycin, but most of these are non-selective cytotoxic molecules with significant side effects. Sorafenib is the only approved targeted therapy by the U.S. Food and Drug Administration for HCC treatment, but patients suffer from various kinds of adverse effects, including hypertension. The signal-transducer-and-activator-of-transcription 3 (STAT3) protein, one of the members of STATs transcription factor family, has been implicated in signal transduction by different cytokines, growth factors and oncogenes. In normal cells, STAT3 activation is tightly controlled to prevent dysregulated gene transcription, whereas constitutively activated STAT3 plays an important role in tumorigenesis through the upregulation of genes involved in anti-apoptosis, proliferation and angiogenesis. Thus, pharmacologically safe and effective agents that can block STAT3 activation have the potential both for the prevention and treatment of HCC. In the present review, we discuss the possible role of STAT3 signaling cascade and its interacting partners in the initiation of HCC and also analyze the role of various STAT3 regulated genes in HCC progression, inflammation, survival, invasion and angiogenesis.

The SOCS and STAT from JAK/STAT signaling pathway of kuruma shrimp Marsupenaeus japonicus: molecular cloning, characterization and expression analysis

Signal transducer and activators of transcription (STAT) gene, suppressors of cytokine signaling (SOCS) has been isolated from kuruma shrimp, Marsupenaeus japonicus and characterized. The kuruma shrimp STAT (MjSTAT) cDNA was composed of 2901 bp consisting of 801 amino acid residues which includes a protein interaction domain, all alpha domain, DNA binding domain and SH2 domain. Homology analysis of MjSTAT showed 94.1% and 34.0% identities with Penaeus monodon STAT (PmSTAT) and Drosophila melanogaster STAT92E (DmSTAT), respectively. The kuruma shrimp SOCS (MjSOCS) cDNA was composed of 1675 bp consisting of 342 amino acid residues including a SH2 domain and C-terminal SOCS domain. Homology analysis of MjSOCS showed 52.6% and 21.3% identities with Chinese mitten crab (Eriocheir sinensis) SOCS2 and fruit fly (D. melanogaster) SOCS44A, respectively. The MjSTAT and MjSOCS genes are constitutively expressed in the muscle, stomach, brain and gill of kuruma shrimp. In lymphoid organ cells, an enhanced expression of both MjSTAT and MjSOCS genes are observed following stimulation with peptidoglycan and polycytidylic acid. These observations suggest that MjSTAT and MjSOCS might play a major role in the innate immune defense of kuruma shrimp. The discovery of JAK/STAT signaling pathway in shrimp will allow a complete and concrete understanding of shrimp cytokine signaling.