Modifications of the GH Axis Reveal Unique Sexually Dimorphic Liver Signatures for Lcn13, Asns, Hamp2, Hao2, and Pgc1a

Growth hormone (GH) modifies liver gene transcription in a sexually dimorphic manner to meet liver metabolic demands related to sex; thus, GH dysregulation leads to sex-biased hepatic disease. We dissected the steps of the GH regulatory cascade modifying GH-dependent genes involved in metabolism, focusing on the male-predominant genes Lcn13, Asns, and Cyp7b1, and the female-predominant genes Hao2, Pgc1a, Hamp2, Cyp2a4, and Cyp2b9. We explored mRNA expression in 2 settings: (i) intact liver GH receptor (GHR) but altered GH and insulin-like growth factor 1 (IGF1) levels (NeuroDrd2KO, HiGH, aHepIGF1kd, and STAT5bCA mouse lines); and (ii) liver loss of GHR, with or without STAT5b reconstitution (aHepGHRkd, and aHepGHRkd + STAT5bCA). Lcn13 was downregulated in males in most models, while Asns and Cyp7b1 were decreased in males by low GH levels or action, or constant GH levels, but unexpectedly upregulated in both sexes by the loss of liver Igf1 or constitutive Stat5b expression. Hao, Cyp2a4, and Cyp2b9 were generally decreased in female mice with low GH levels or action (NeuroDrd2KO and/or aHepGHRkd mice) and increased in HiGH females, while in contrast, Pgc1a was increased in female NeuroDrd2KO but decreased in STAT5bCA and aHepIGF1kd females. Bioinformatic analysis of RNAseq from aHepGHRkd livers stressed the greater impact of GHR loss on wide gene expression in males and highlighted that GH modifies almost completely different gene signatures in each sex. Concordantly, we show that altering different steps of the GH cascade in the liver modified liver expression of Lcn13, Asns, Cyp7b1, Hao2, Hamp2, Pgc1a, Cyp2a4, and Cyp2b9 in a sex- and gene-specific manner.

Direct and systemic actions of growth hormone receptor (GHR)-signaling on hepatic glycolysis, de novo lipogenesis and insulin sensitivity, associated with steatosis

BACKGROUND

Evidence is accumulating that growth hormone (GH) protects against the development of steatosis and progression of non-alcoholic fatty liver disease (NAFLD). GH may control steatosis indirectly by altering systemic insulin sensitivity and substrate delivery to the liver and/or by the direct actions of GH on hepatocyte function.

APPROACH

To better define the hepatocyte-specific role of GH receptor (GHR) signaling on regulating steatosis, we used a mouse model with adult-onset, hepatocyte-specific GHR knockdown (aHepGHRkd). To prevent the reduction in circulating insulin-like growth factor 1 (IGF1) and the subsequent increase in GH observed after aHepGHRkd, subsets of aHepGHRkd mice were treated with adeno-associated viral vectors (AAV) driving hepatocyte-specific expression of IGF1 or a constitutively active form of STAT5b (STAT5bCA). The impact of hepatocyte-specific modulation of GHR, IGF1 and STAT5b on carbohydrate and lipid metabolism was studied across multiple nutritional states and in the context of hyperinsulinemic:euglycemic clamps.

RESULTS

Chow-fed male aHepGHRkd mice developed steatosis associated with an increase in hepatic glucokinase (GCK) and ketohexokinase (KHK) expression and de novo lipogenesis (DNL) rate, in the post-absorptive state and in response to refeeding after an overnight fast. The aHepGHRkd-associated increase in hepatic KHK, but not GCK and steatosis, was dependent on hepatocyte expression of carbohydrate response element binding protein (ChREBP), in re-fed mice. Interestingly, under clamp conditions, aHepGHRkd also increased the rate of DNL and expression of GCK and KHK, but impaired insulin-mediated suppression of hepatic glucose production, without altering plasma NEFA levels. These effects were normalized with AAV-mediated hepatocyte expression of IGF1 or STAT5bCA. Comparison of the impact of AAV-mediated hepatocyte IGF1 versus STAT5bCA in aHepGHRkd mice across multiple nutritional states, indicated the restorative actions of IGF1 are indirect, by improving systemic insulin sensitivity, independent of changes in the liver transcriptome. In contrast, the actions of STAT5b are due to the combined effects of raising IGF1 and direct alterations in the hepatocyte gene program that may involve suppression of BCL6 and FOXO1 activity. However, the direct and IGF1-dependent actions of STAT5b cannot fully account for enhanced GCK activity and lipogenic gene expression observed after aHepGHRkd, suggesting other GHR-mediated signals are involved.

CONCLUSION

These studies demonstrate hepatocyte GHR-signaling controls hepatic glycolysis, DNL, steatosis and hepatic insulin sensitivity indirectly (via IGF1) and directly (via STAT5b). The relative contribution of these indirect and direct actions of GH on hepatocytes is modified by insulin and nutrient availability. These results improve our understanding of the physiologic actions of GH on regulating adult metabolism to protect against NAFLD progression.

STAT5b: A master regulator of key biological pathways

The Signal Transducer and Activator of Transcription (STAT)-5 proteins are required in immune regulation and homeostasis and play a crucial role in the development and function of several hematopoietic cells. STAT5b activation is involved in the expression of genes that participate in cell development, proliferation, and survival. STAT5a and STAT5b are paralogs and only human mutations in STAT5B have been identified leading to immune dysregulation and hematopoietic malignant transformation. The inactivating STAT5B mutations cause impaired post-natal growth, recurrent infections and immune dysregulation, whereas gain of function somatic mutations cause dysregulated allergic inflammation. These mutations are rare, and they are associated with a wide spectrum of clinical manifestations which provide a disease model elucidating the biological mechanism of STAT5 by studying the consequences of perturbations in STAT5 activity. Further, the use of Jak inhibitors as therapy for a variety of autoimmune and malignant disorders has increased substantially heading relevant lessons for the consequences of Jak/STAT immunomodulation from the human model. This review summarizes the biology of the STAT5 proteins, human disease associate with molecular defects in STAT5b, and the connection between aberrant activation of STAT5b and the development of certain cancers.

[A particular presentation of a T cell large granular lymphocytic leukaemia]

T cell prolymphocytic leukemia (T-PLL) is a rare, aggressive neoplasm derived from post-thymic T cells. Patients are typically middle-aged with a slight male predominance who present with a high white blood cell count, hepatosplenomegaly, lymphadenopathy, and other symptoms typically associated with leukemia. Although cutaneous involvement has been reported in up to 30% of cases of T-PLL, to our knowledge, none have presented with a presentation resembling livedoid vasculopathy. In the correct clinical context, an underlying hematolymphoid neoplasm should be included in the differential diagnosis of a patient presenting with livedoid vasculopathy.

Dissecting Selectivity Determinants of Small-Molecule Inhibitors of SH2 Domains Via Fluorescence Polarization Assays

Fluorescence polarization (FP) assays can be used to identify small-molecule inhibitors that bind to SH2 domain-containing proteins. We have developed FP assays by which to identify inhibitors of the SH2 domains of the two closely-related transcription factors STAT5a and STAT5b. Point mutation of selected amino acids in the putative binding site of the protein is a valuable tool by which to gain insight into the molecular mechanism of binding. In this chapter, we describe the cloning and application of point mutant proteins in order to transfer the binding preference of selected SH2 domain-binding STAT5b inhibitors to STAT5a, with results that highlight the importance of considering a role for residues outside the SH2 domain in contributing to the binding interactions of SH2 domain inhibitors.

STAT5b is a marker of poor prognosis, rather than a therapeutic target in glioblastomas

The copy number and mRNA expression of STAT5b were assessed in samples from the TCGA repository of glioblastomas (GBM). The activation of this transcription factor was analyzed on tissue microarrays comprising 392 WHO 2016 GBM samples from our clinical practice. These data were correlated with patient survival using multivariable Cox analysis and, for a subset of 167 tumors, with signs of tumor invasiveness on the MRI. The effects of STAT5b knockdown by siRNA were assessed on the growth, therapeutic resistance, invasion and migration of GBM cell lines U87, U87-EGFRVIII and LN18 and primary cultures GM2 and GM3. The activation, but not the copy number or the mRNA expression of nuclear transcription factor STAT5b expression correlated inversely with patient survival independently of IDH1R132H status, age, Karnofsky Performance Score, treatment and tumor volume. STAT5b inhibition neither altered the cell proliferation nor reduced the clonogenic proliferative potency of GBM cells, and did not sensitize them to the cytotoxic effect of ionizing radiation and temozolomide in vitro. STAT5b inhibition significantly increased GBM cell migration, but decreased the invasion of some GBM cells in vitro. There was no correlation between the activation of STAT5b in clinical tumors and the extent of invasion on MRI OF patients. In conclusion, STAT5b is frequently activated in GBM and correlates inversely with patient survival. It does not contribute to the growth and resistance of these tumors, and is thus rather a potential prognostic marker than a therapeutic target in these tumors.

miR-146a enhances regulatory T-cell differentiation and function in allergic rhinitis by targeting STAT5b

BACKGROUND

MicroRNA (miR)-146a, as an important immune regulatory factor with an anti-inflammatory effect, plays a crucial role in regulatory T-cell (Tregs) differentiation and function in allergic rhinitis (AR). The present study aimed to investigate the regulatory mechanism employed by miR-146a to control Treg differentiation and function in AR.

METHODS

Expression of miR-146a and STAT5b in peripheral blood mononuclear cells (PBMCs) and nasal mucosa from patients with AR was detected by qPCR and Western blotting. Tregs were quantified by flow cytometry in miR-146a knockdown or STAT5b knockdown PBMCs. FOXP3, IL-10, and TGF-β levels were detected by Western blotting or ELISA in miR-146a knockdown or STAT5b overexpressing PBMCs, as well as in STAT5b knockdown PBMCs overexpressing miR-146a. The effect of miR-146a on STAT5b was observed by luciferase assay and knockdown experiments.

RESULTS

Levels of miR146a and STAT5b in the nasal mucosa or PBMCs were significantly lower in the AR group than in the control group. There were significantly fewer Tregs in miR-146a knockdown or STAT5b knockdown PBMCs compared to control PBMCs. Expression of FOXP3, IL-10, and TGF-β was decreased in the miR-146a knockdown group but increased in the STAT5b overexpression group. In contrast, miR-146a overexpression increased the levels of these factors, but knockdown of STAT5b significantly inhibited this effect. Luciferase assay and knockdown experiments showed that miR-146a bound directly to STAT5b.

CONCLUSIONS

miR-146a enhances Treg differentiation and function in AR by positively targeting STAT5b.

Analysis of a single-institution cohort of patients with Felty's syndrome and T-cell large granular lymphocytic leukemia in the setting of rheumatoid arthritis

T-cell large granular lymphocytic leukemia (T-LGLL) is a lymphoproliferative disorder characterized by a persistent increase in the number of large granular lymphocytes (LGLs), neutropenia, and splenomegaly. Clinical manifestations of T-LGLL in the setting of rheumatoid arthritis (RA) are often identical to those in which one would suspect Felty's syndrome (FS). These disorders are distinguished by the presence of T-cell clonality, which is present in T-LGLL but not in FS. Mutations in the signal transducer and activator of transcription 3 (STAT3) and 5b (STAT5b) genes can be used as molecular markers of T-LGLL, but their prevalence in FS is unknown.Eighty-one patients with RA and unexplained neutropenia or/and an increase in the number of LGLs above 2 × 10⁹/L were stratified into RA-associated T-LGLL (N = 56) or FS (N = 25) groups based on the presence or absence of T-cell clonality. STAT3 and STAT5b gene mutations were assessed in each group by means of allele-specific polymerase chain reaction assays. Clinical, immunological, laboratory data and the results of immunophenotyping of blood and bone marrow lymphocytes were also evaluated.Mutations of the STAT3 gene and an increase in the number of LGLs above 2 × 10⁹/L were detected in RA-associated T-LGLL, but not in FS (39% vs 0% and 21% vs 0%, respectively). Mutations in the STAT5b gene were not observed in either group. Expression of CD57, CD16, and CD5^-/dim on CD3⁺CD8⁺ T-lymphocytes was observed in both RA-associated T-LGLL and FS.STAT3 gene mutations or LGL counts over 2 × 10⁹/L in RA patients are indicative of T-LGLL.

MKL-1 is a coactivator for STAT5b, the regulator of Treg cell development and function

Background

Foxp3⁺CD4⁺ regulatory T cells (Treg) constitutes a key event in autoimmune diseases. STAT5b is the critical link between the IL-2/15 and FOXP3, the master regulator of Treg cells.

Methods

The CD3⁺T cell and Foxp3⁺CD4⁺ regulatory T cells were overexpressioned or knockdown MKL-1 and STAT5a and tested for Treg cell development and function. Direct interaction of MKL-1 and STAT5a were analyzed by coimmunoprecipitation assays, Luciferase assay, Immunofluoresence Staining and Yeast two-hybrid screening. The effect of MKL-1 and STAT5a on the Treg genes expression was analyzed by qPCR and western blotting and Flow cytometry.

Results

However, the molecular mechanisms mediating STAT5b-dependent Treg genes expression and Treg cell phenotype and function in autoimmune diseases are not well defined. Here, we report that the MKL-1 is a coactivator for the major Treg genes transcription factor STAT5b, which is required for human Treg cell phenotype and function. The N terminus of STAT5b, which contains a basic coiled-coil protein–protein interaction domain, binds the C-terminal activation domain of MKL-1 and enhances MKL-1 mediated transcriptional activation of Treg-specific, CArG containing promoters, including the Treg-specific genes Foxp3. Suppression of endogenous STAT5b expression by specific small interfering RNA attenuates MKL-1 transcriptional activation in cultured human cells. The STAT5b–MKL-1 interaction identifies a role of Treg-specific gene regulation and regulated mouse Treg cell development and function and suggests a possible mechanism for the protective effects of autoimmune disease Idiopathic Thrombocytopenic Purpura (ITP).

Conclusions

Our studies demonstrate for the first time that MKL-1 is a coactivator for STAT5b, the regulator of Treg cell development and function.

The Role of MiR-5094 as a Proliferation Suppressor during Cellular Radiation Response via Downregulating STAT5b

MicroRNAs (miRNAs) play important roles in the regulation of cellular stress responses. We previously uncovered 10 novel human miRNAs which are induced by X-ray irradiation in HeLa cells using Solexa deep sequencing. The most highly expressed new miRNA, miR-5094, was predicted to target STAT5b. This study wonders whether miR-5094 participates in cellular radiation response via STAT5b. Firstly, direct interaction between miRNA-5094 and the STAT5b 3'-UTR was confirmed by luciferase reporter assay. Then, the radiation responsive expression of miR-5094 and STAT5b were measured in HeLa and Jurkat cells, and the expressions of down-stream genes of STAT5b after ionizing radiation (IR) were detected in HeLa cells. At last, the effects of miR-5094 on survival fraction, cell proliferation, cell cycle arrest and apoptosis induced by IR were investigated in HeLa cells, Jurkat cells and human peripheral blood T cells. It was found that up-regulation of miR-5094 by radiation induction or miRNA mimic transfection suppressed expression of STAT5b, and consequently decreased the transcription of down-stream Igf-1 and Bcl-2. Additionally, over expression of miR-5094 resulted in proliferation suppression and knockdown of miR-5094 by miRNA inhibitor after irradiation partially reversed the proliferation suppression induced by miR-5094 in HeLa cells, Jurkat cells and CD4⁺ T cells. Collectively, our findings demonstrate that up-regulation of miR-5094 down-regulated the expression of STAT5b, thereby suppressing cell proliferation after X-ray irradiation.

Insights Into Genetic Landscape of Large Granular Lymphocyte Leukemia

Large granular lymphocyte leukemia (LGLL) is a chronic proliferation of clonal cytotoxic lymphocytes, usually presenting with cytopenias and yet lacking a specific therapy. The disease is heterogeneous, including different subsets of patients distinguished by LGL immunophenotype (CD8+ Tαβ, CD4+ Tαβ, Tγδ, NK) and the clinical course of the disease (indolent/symptomatic/aggressive). Even if the etiology of LGLL remains elusive, evidence is accumulating on the genetic landscape driving and/or sustaining chronic LGL proliferations. The most common gain-of-function mutations identified in LGLL patients are on STAT3 and STAT5b genes, which have been recently recognized as clonal markers and were included in the 2017 WHO classification of the disease. A significant correlation between STAT3 mutations and symptomatic disease has been highlighted. At variance, STAT5b mutations could have a different clinical impact based on the immunophenotype of the mutated clone. In fact, they are regarded as the signature of an aggressive clinical course with a poor prognosis in CD8+ T-LGLL and aggressive NK cell leukemia, while they are devoid of negative prognostic significance in CD4+ T-LGLL and Tγδ LGLL. Knowing the specific distribution of STAT mutations helps identify the discrete mechanisms sustaining LGL proliferations in the corresponding disease subsets. Some patients equipped with wild type STAT genes are characterized by less frequent mutations in different genes, suggesting that other pathogenetic mechanisms are likely to be involved. In this review, we discuss how the LGLL mutational pattern allows a more precise and detailed tumor stratification, suggesting new parameters for better management of the disease and hopefully paving the way for a targeted clinical approach.

Human signal transducer and activator of transcription 5b (STAT5b) mutation causes dysregulated human natural killer cell maturation and impaired lytic function

BACKGROUND

Patients with signal transducer and activator of transcription 5b (STAT5b) deficiency have impairment in T-cell homeostasis and natural killer (NK) cells which leads to autoimmunity, recurrent infections, and combined immune deficiency.

OBJECTIVE

In this study we characterized the NK cell defect in STAT5b-deficient human NK cells, as well as Stat5b^-/- mice.

METHODS

We used multiparametric flow cytometry, functional NK cell assays, microscopy, and a Stat5b^-/- mouse model to elucidate the effect of impaired and/or absent STAT5b on NK cell development and function.

RESULTS

This alteration generated a nonfunctional CD56^bright NK cell subset characterized by low cytokine production. The CD56^dim NK cell subset had decreased expression of perforin and CD16 and a greater frequency of cells expressing markers of immature NK cells. We observed low NK cell numbers and impaired NK cell maturation, suggesting that STAT5b is involved in terminal NK cell maturation in Stat5b^-/- mice. Furthermore, human STAT5b-deficient NK cells had low cytolytic capacity, and fixed-cell microscopy showed poor convergence of lytic granules. This was accompanied by decreased expression of costimulatory and activating receptors. Interestingly, granule convergence and cytolytic function were restored after IL-2 stimulation.

CONCLUSIONS

Our results show that in addition to the impaired terminal maturation of NK cells, human STAT5b mutation leads to impairments in early activation events in NK cell lytic synapse formation. Our data provide further insight into NK cell defects caused by STAT5b deficiency.

Epilepsy Associates with Decreased HIF-1α/STAT5b Signaling in Glioblastoma

Epilepsy at presentation is an independent favorable prognostic factor in glioblastoma (GBM). In this study, we analyze the oncologic signaling pathways that associate with epilepsy in human GBMs, and that can underlie this prognostic effect. Following ethical approval and patient consent, fresh frozen GBM tissue was obtained from 76 patient surgeries. Hospital records were screened for the presence of seizures at presentation of the disease. mRNA and miRNA expression-based and gene set enrichment analyses were performed on these tissues, to uncover candidate oncologic pathways that associate with epilepsy. We performed qPCR experiments and immunohistochemistry on tissue microarrays containing 286 GBMs to further explore the association of these candidate pathways and of markers of mesenchymal transformation (NF-κB, CEBP-β, STAT3, STAT5b, VEGFA, SRF) with epilepsy. Gene sets involved in hypoxia/HIF-1α, STAT5, CEBP-β and epithelial-mesenchymal transformation signaling were significantly downregulated in epileptogenic GBMs. On confirmatory protein expression analyses, epileptogenic tumors were characterized by a significant downregulation of phospho-STAT5b, a target of HIF-1α. Epilepsy status did not associate with molecular subclassification or miRNA expression patterns of the tumors. Epileptogenic GBMs correlate with decreased hypoxia/ HIF-1α/STAT5b signaling compared to glioblastomas that do not present with epilepsy.

From the Cover: Genomic Effects of Androstenedione and Sex-Specific Liver Cancer Susceptibility in Mice

Current strategies for predicting carcinogenic mode of action for nongenotoxic chemicals are based on identification of early key events in toxicity pathways. The goal of this study was to evaluate short-term key event indicators resulting from exposure to androstenedione (A4), an androgen receptor agonist and known liver carcinogen in mice. Liver cancer is more prevalent in men compared with women, but androgen-related pathways underlying this sex difference have not been clearly identified. Short-term hepatic effects of A4 were compared with reference agonists of the estrogen receptor (ethinyl estradiol, EE) and glucocorticoid receptor (prednisone, PRED). Male B6C3F1 mice were exposed for 7 or 28 days to A4, EE, or PRED. EE increased and PRED suppressed hepatocyte proliferation, while A4 had no detectable effects. In a microarray analysis, EE and PRED altered >3000 and >670 genes, respectively, in a dose-dependent manner, whereas A4 did not significantly alter any genes. Gene expression was subsequently examined in archival liver samples from male and female B6C3F1 mice exposed to A4 for 90 days. A4 altered more genes in females than males and did not alter expression of genes linked to activation of the mitogenic xenobiotic receptors AhR, CAR, and PPARα in either sex. A gene expression biomarker was used to show that in female mice, the high dose of A4 activated the growth hormone-regulated transcription factor STAT5b, which controls sexually dimorphic gene expression in the liver. These findings suggest that A4 induces subtle age-related effects on STAT5b signaling that may contribute to the higher risk of liver cancer in males compared with females.

Primary Immunodeficiencies Unravel the Role of IL-2/CD25/STAT5b in Human Natural Killer Cell Maturation

Natural killer (NK) cells play a pivotal role during immunity against viruses and circumstantial evidence also indicates that they can protect the host against developing tumors. Peripheral blood NK cells comprise CD56^brightCD16^lo/− cells that constitutively express CD25 (IL-2Rα) and CD56^dimCD16^hi cells that express CD25 upon activation. Using NK cells from two patients, one with a primary immunodeficiency characterized by a homozygous mutation in CD25 (born in year 2007 and studied since she was 3 years old) and one with a homozygous mutation in STAT5b (born in year 1992 and studied since she was 10 years old), we observed that the absence of IL-2 signaling through CD25 promotes the accumulation of CD56^brightCD16^high NK cells, and that CD56^brightCD16^lo, CD56^brightCD16^high, and CD56^dimCD16^high NK cells of this patient exhibited higher content of perforin and granzyme B, and proliferation capacity, compared to healthy donors. Also, CD56^bright and CD56^dim NK cells of this patient exhibited a reduced IFN-γ production in response to cytokine stimulation and increased degranulation against K562 cells. Also, the CD25-deficient patient presented a lower frequency of terminally differentiated NK cells in the CD56^dimCD16^hi NK subpopulation compared to the HD (assessed by CD57 and CD94 expression). Remarkably, CD56^dimCD16^high NK cells from both patients exhibited notoriously higher expression of CD62L compared to HD, suggesting that in the absence of IL-2 signaling through CD25 and STAT5b, NK cells fail to properly downregulate CD62L during their transition from CD56^brightCD16^lo/− to CD56^dimCD16^hi cells. Thus, we provide the first demonstration about the in vivo requirement of the integrity of the IL-2/CD25/STAT5b axis for proper human NK cell maturation.

MicroRNA fingerprints in juvenile myelomonocytic leukemia (JMML) identified miR-150-5p as a tumor suppressor and potential target for treatment

Juvenile myelomonocytic leukemia (JMML) is an aggressive leukemia of early childhood characterized by aberrant proliferation of myelomonocytic cells and hypersensitivity to GM-CSF stimulation. Mutually exclusive mutations in the RAS/ERK pathway genes such as PTPN11, NRAS, KRAS, CBL, or NF1 are found in ~90% of the cases. These mutations give rise to disease at least in part by activating STAT5 through phosphorylation and by promoting cell growth. MicroRNAs (miRs) are small non-coding RNAs that regulate gene expression, which are often deregulated in leukemia. However, little is known about their role in JMML. Here, we report distinctive miR expression signatures associated with the molecular subgroups of JMML. Among the downregulated miRs in JMML, miR-150-5p was found to target STAT5b, a gene which is often over-activated in JMML, and contributes to the characteristic aberrant signaling of this disorder. Moreover, loss of miR-150-5p and upregulation of STAT5b expression were also identified in a murine model of JMML. Ectopic overexpression of miR-150-5p in mononuclear cells from three JMML patients significantly decreased cell proliferation. Altogether, our data indicate that miR expression is deregulated in JMML and may play a role in the pathogenesis of this disorder by modulating key effectors of cytokine receptor pathways.

Expression and Purification of Soluble STAT5b/STAT3 Proteins for SH2 Domain Binding Assay

When a large hydrophobic full-length protein is expressed in bacteria, it is often challenging to obtain recombinant proteins in the soluble fraction. One way to overcome this challenge is expression of deletion mutants that have improved solubility while maintaining biological activity. In this chapter, we describe a protocol for expression of truncated forms of STAT5b and STAT3 proteins that are soluble and retain SH2-mediated activity for phospho-Tyr peptide recognition.

Alpha-Based Multiplexed Assay for Identifying SH2 Domain Antagonists

Constitutive activation of STAT3/5b frequently occurs in various human malignancies. STAT3/5b activation involves dimerization via intermolecular pTyr-SH2 binding; therefore, antagonizing this interaction is a feasible approach to inhibit STAT3/5b activation for cancer therapy. We have developed a multiplexed assay to assess STAT3- and STAT5b-SH2 binding in a single well by combining AlphaLISA and AlphaScreen beads. In this chapter, we describe application of the method for the purpose of identifying new STAT3 and STAT5b antagonists.

Role of EGF/ERBB1 in the transcriptional regulation of the prolactin receptor independent of estrogen and prolactin in breast cancer cells

Prolactin receptor (PRLR) and epidermal growth factor receptor (EGFR/ERBB1) have important roles in the physiology of the human breast and in the etiology and progression of breast cancer. Our present studies in MCF-7 cells revealed that EGF induces up-regulation of PRLR via activation of EGFR signalling pathways leading to activation of estrogen receptor α (ERα). EGF treatment of MCF-7 cells cultured in absence of estradiol induced expression of PRLR that was consistent with the activation of PRLR generic promoter (hPIII). These were abolished by ERα antagonist and siRNA, indicating involvement of ERα in EGF-induced hPIII promoter activity. MEK/MAPK and PI3K/AKT pathways participate in the phosphorylation of ERα induced by EGF/EGFR. PI3K and MEK inhibitors abolished EGF-induced PRLR promoter activity. Increased recruitment of non-DNA bound unliganded ERα to Sp1 and C/EBPβ bound to their sites at hPIII induced by EGF was abrogated by ERα siRNA demonstrating the requisite role of phospho-ERα in PRLR upregulation. EGF/EGFR, independent of endogenous prolactin induced phosphorylation of STAT5b with participation of c-SRC and recruitment of STAT5b:STAT5b to a GAS site at hPIII. STAT5b interaction with ERα was essential for stable phospho-ERα recruitment to the SP1/CEBPβ complex. These studies indicate a role for paracrine EGF via EGFR independent of estrogen and prolactin in the transcriptional activation of PRLR gene expression and its contribution to high levels of PRLRs in breast cancer. These by maximizing the actions of endogenous prolactin could have a role in cancer progression and resistance to endocrine therapy.

Impaired phosphorylation of JAK2-STAT5b signaling in fibroblasts from uremic children

BACKGROUND

Chronic kidney disease (CKD) in children is characterized by severe growth failure. The growth hormone/insulin-like growth factor-1 (GH/IGF-1) axis in uremic animals shows a post-receptor impaired phosphorylation of Janus kinase 2/signal transducer and activator of transcription (JAK-STAT) proteins. The objective of our study was to characterize the intracellular phosphorylation of JAK-STAT signaling in fibroblasts from children with CKD on chronic peritoneal dialysis (PD).

METHODS

Serum GH-binding protein (GHBP), IGF-1 and IGFBP3 were measured in 15 prepubertal CKD stage-5 children on PD. Cytoplasmic JAK2, cytoplasmic/nuclear STAT5b and nuclear IGFBP3, acid-labile subunit (ALS) and IGF-1 mRNA expression were quantified in fibroblasts obtained from skin biopsies before and after stimulation with 200 ng/ml recombinant human growth hormone (rhGH). Phosphorylation activity at both the cytoplasmic and nuclear level was expressed as the ratio phosphorylated (p)/total (t) abundance of the product (p/t) at 30 and 60 min. Fifteen healthy children were recruited as the control group. Values were expressed in arbitrary units (AU) and normalized for comparison. Significance was defined as p < 0.05.

RESULTS

Thirty minutes after rhGH stimulus, the cytoplasmic (p/t) JAK2 ratio was significantly lower in patients than in controls [median and interquartile range (IQR): 7.4 (4.56) vs. 20.5 (50.06) AU]. At 60 min after rhGH stimulation, median JAK2 phosphorylation activity was still significantly lower in the patients [7.14 (IQR 3.8) vs. 10.2 (IQR 29.8) AU; p < 0.05]. The increase in the cytoplasmic (p/t) STAT5b/β-actin ratio was lower at both measurement points in the patients compared to the controls, without reaching statistical significance between groups. Median IGFBP3 mRNA abundance was significantly decreased in fibroblasts from uremic patients 24 h after rhGH stimulation compared to the healthy controls [1.27 (IQR 0.83) vs. 2.37 (IQR 0.80) AU]. Median ALS and IGF-1 mRNA expression changed in response to rhGH stimuli at 24 and 48 h.

CONCLUSION

In this study, children with CKD undergoing PD therapy showed an impaired phosphorylation of JAK2/STAT5b signaling in fibroblasts after GH stimulation, as well as impaired IGFBP3 mRNA abundance. Both impairments may be partially responsible for the observed resistance to the growth-promoting actions of GH in chronic kidney failure.

RNAi-mediated gene silencing of ST6GalNAc I suppresses the metastatic potential in gastric cancer cells

BACKGROUND

ST6GalNAc I is a sialyltransferase controlling the expression of sialyl-Tn antigen (STn), which is overexpressed in several epithelial cancers, including gastric cancer, and is highly correlated with cancer metastasis. However, the functional contribution of ST6GalNAc I to development or progression of gastric cancer remains unclear. In this study, we investigated the effects of suppression of ST6GalNAc I on gastric cancer in vitro and in vivo.

METHODS

Gastric cancer cell lines were transfected with ST6GalNAc I siRNA and were examined by cell proliferation, migration, and invasion assays. We also evaluated the effect of ST6GalNAc I siRNA treatment in a peritoneal dissemination mouse model. The differences in mRNA levels of selected signaling molecules were analyzed by polymerase chain reaction (PCR) arrays associated with tumor metastasis in MKN45 cells. The signal transducer and activator of transcription 5b (STAT5b) signaling pathways that reportedly regulate the insulin-like growth factor-1 (IGF-1) were analyzed by Western blot.

RESULTS

ST6GalNAc I siRNA inhibited gastric cancer cell growth, migration, and invasion in vitro. Furthermore, intraperitoneal administration of ST6GalNAc I siRNA- liposome significantly inhibited peritoneal dissemination and prolonged the survival of xenograft model mice with peritoneal dissemination of gastric cancer. PCR array confirmed that suppression of ST6GalNAc I caused a significant reduction in expression of IGF-1 mRNA. Decreased IGF-1 expression in MKN45 cells treated with ST6GalNAc I siRNA was accompanied by reduced phosphorylation of STAT5b.

CONCLUSION

ST6GalNAc I may regulate the gene expression of IGF-1 through STAT5b activation in gastric cancer cells and may be a potential target for treatment of metastasizing gastric cancer.

Permanent uncoupling of male-specific CYP2C11 transcription/translation by perinatal glutamate

Perinatal exposure of rats and mice to the typically reported 4mg/g bd wt dose of monosodium glutamate (MSG) results in a complete block in GH secretion as well as obesity, growth retardation and a profound suppression of several cytochrome P450s, including CYP2C11, the predominant male-specific isoform--all irreversible effects. In contrast, we have found that a lower dose of the food additive, 2mg/g bd wt on alternate days for the first 9days of life results in a transient neonatal depletion of plasma GH, a subsequent permanent overexpression of CYP2C11 as well as subnormal (mini) GH pulse amplitudes in an otherwise normal adult masculine episodic GH profile. The overexpressed CYP2C11 was characterized by a 250% increase in mRNA, but only a 40 to 50% increase in CYP2C11 protein and its catalytic activity. Using freshly isolated hepatocytes as well as primary cultures exposed to the masculine-like episodic GH profile, we observed normal induction, activation, nuclear translocation and binding to the CYP2C11 promoter of the GH-dependent signal transducers required for CYP2C11 transcription. The disproportionately lower expression levels of CYP2C11 protein were associated with dramatically high expression levels of an aberrant, presumably nontranslated CYP2C11 mRNA, a 200% increase in CYP2C11 ubiquitination and a 70-80% decline in miRNAs associated, at normal levels, with a suppression of CYP2C expression. Whereas the GH-responsiveness of CYP2C7 and CYP2C6 as well as albumin was normal in the MSG-derived hepatocytes, the abnormal expression of CYP2C11 was permanent and irreversible.

STAT3 and STAT5b polymorphism contributes to breast cancer risk and clinical outcomes

We conducted a case-control study in a Chinese population, and investigated the role of STAT3 rs4796793 and STAT5b rs6503691 polymorphisms in the risk and clinical outcome of breast cancer. STAT5b rs6503691 polymorphisms and STAT3 rs4796793 polymorphisms were genotyped by TaqMan SNP Genotyping Assays on the ABI 7500 fast real-time PCR platform. Unconditional logistic regression analyses showed that subjects carrying the GG genotype of STAT3 rs4796793 had a significantly increased risk of breast cancer, with an adjusted OR (95% CI) of 0.35 (0.12-0.95). In the Cox proportional hazards model, we observed that individuals carrying CG+GG genotype of STAT3 rs4796793 was associated with reduced risk of death from breast cancer when compared with CC genotype (HR = 0.43, 95% CI = 0.20-0.93). Our study found that STAT3 rs4796793 polymorphism plays an important role in influence the development and overall survival of breast cancer patients.

Signal transducer and activator of transcription 5b drives malignant progression in a PDGFB-dependent proneural glioma model by suppressing apoptosis

Signal transducer and activator of transcription 5b (STAT5b) is likely the relevant STAT5 isoform with respect to the process of malignant progression in gliomas. STAT5b is a latent cytoplasmic protein involved in cell signaling through the modulation of growth factors, apoptosis, and angiogenesis. Previous in vitro studies have shown increased STAT5b expression in glioblastomas relative to low-grade tumors and normal brain. We recently demonstrated that phosphorylated STAT5b associates with delta epidermal growth factor receptor in the nucleus and subsequently binds the promoters of downstream effector molecules, including aurora kinase A. Analysis of TCGA dataset reveals that STAT5b is predominantly expressed in proneural (PN) gliomas relative to mesenchymal and neural gliomas. Here, we modeled ectopic expression of STAT5b in vivo using a platelet-derived growth factor subunit B (PDGFB)-dependent mouse model of PN glioma to determine its effect on tumor formation and progression. We showed that coexpression of STAT5b and PDGFB in mice yielded a significantly higher rate of high-grade gliomas than PDGFB expression alone. We also observed shorter survival in the combined expression set. High-grade tumors from the STAT5b + PDGFB expression set were found to have a lower rate of apoptosis than those from PDGFB alone. Furthermore, we showed that increased expression of STAT5b + PDGFB led to increased expression of downstream STAT5b targets, including Bcl-xL, cyclin D1 and aurora kinase A in high-grade tumors when compared to tumors derived from PDGFB alone. Our findings show that STAT5b promotes the malignant transformation of gliomas, particularly the PN subtype, and is a potential therapeutic target.

Irreversible perinatal imprinting of adult expression of the principal sex-dependent drug-metabolizing enzyme CYP2C11

We proposed to determine whether, like other sexual dimorphisms, drug metabolism is permanently imprinted by perinatal hormones, resulting in its irreversible sex-dependent expression. We treated newborn male rats with monosodium glutamate (MSG), a total growth hormone (GH) blocker, and, using cultured hepatocytes, examined expression of adult CYP2C11, the predominant cytochrome-P450 expressed only in males, as well as the signal transduction pathway by which episodic GH solely regulates the isoform's expression. In addition, adolescent hypophysectomized (hypox) male rats served as controls in which GH was eliminated after the critical imprinting period. Whereas renaturalization of the masculine episodic GH profile restored normal male-like levels of CYP2C11, as well as CYP2C12, in hepatocytes from hypox rats, the cells derived from the MSG-treated rats were completely unresponsive. Moreover, GH exposure of hepatocytes from hypox rats resulted in normal induction, activation, nuclear translocation, and binding to the CYP2C11 promoter of the signal transducers mediating GH regulation of CYP2C11 expression, which dramatically contrasted with the complete unresponsiveness of the MSG-derived hepatocytes, also associated with hypermethylation of GH-response elements in the CYP2C11 promoter. Lastly, neonatal MSG treatment had no adverse effect on postnatal and adult testosterone levels. The results demonstrate that the sexually dimorphic expression of CYP2C11 is irreversibly imprinted shortly after birth by a hormone other than the customary testosterone, but likely by GH.

The STAT5b Pathway Defect and Autoimmunity

The signal transducer and activator of transcription (STAT) 5b is a universal transcription factor that plays key biological roles in allergic diseases, immunodeficiencies, autoimmunities, cancers, hematological diseases, growth disorders, and lung diseases. The identification of distinct pathological manifestations of STAT5b deficiency in humans has highlighted the critical role of the STAT5b pathway. Proper gene transcription at IL-2R α, FOXP3, Bcl-2, and growth hormone (GH) associated loci are thought to be associated with normal STAT5b transcriptional activity. These genes are thought to play important roles in allergy/autoimmunity, immunodeficiency, cancer/anemia, and growth, respectively. The STAT5A and STAT5B genes are collocated on 17q11. Although these two monomeric proteins exhibit peptide sequence similarities of >90%, it is known through observations of STAT5b deficient subjects that STAT5a and STAT5b are not fully redundant in humans. Patients with STAT5b deficiency have decreased numbers of regulatory CD4⁺CD25^high T cell (Treg) despite their STAT5a levels being normal. Prior studies on STAT5b deficient subjects have revealed immunological aberrations associated with the following disease phenotype: modest lymphopenia and decreased populations of Treg, γ−δ T cells, and natural killer (NK) cells. Most subjects with STAT5b deficiency show severe eczema, and autoimmune disease (juvenile idiopathic arthritis, autoimmune thyroiditis, idiopathic thrombocytic purpura) which are thought to be associated with Treg dysfunction. We will review the likely pathophysiological mechanisms associated with STAT5b deficiency.