The role of STAT5 in lymphocyte development and transformation

Hyperactive STAT5 hijacks T cell receptor signaling and drives immature T cell acute lymphoblastic leukemia

T cell acute lymphoblastic leukemia (T-ALL) is an aggressive immature T cell cancer. Mutations in IL7R have been analyzed genetically, but downstream effector functions such as STAT5A and STAT5B hyperactivation are poorly understood. Here, we studied the most frequent and clinically challenging STAT5BN642H driver in T cell development and immature T cell cancer onset and compared it with STAT5A hyperactive variants in transgenic mice. Enhanced STAT5 activity caused disrupted T cell development and promoted an early T cell progenitor-ALL phenotype, with upregulation of genes involved in T cell receptor (TCR) signaling, even in absence of surface TCR. Importantly, TCR pathway genes were overexpressed in human T-ALL and mature T cell cancers and activation of TCR pathway kinases was STAT5 dependent. We confirmed STAT5 binding to these genes using ChIP-Seq analysis in human T-ALL cells, which were sensitive to pharmacologic inhibition by dual STAT3/5 degraders or ZAP70 tyrosine kinase blockers in vitro and in vivo. We provide genetic and biochemical proof that STAT5A and STAT5B hyperactivation can initiate T-ALL through TCR pathway hijacking and suggest similar mechanisms for other T cell cancers. Thus, STAT5 or TCR component blockade are targeted therapy options, particularly in patients with chemoresistant clones carrying STAT5BN642H.

Microbial ligand-independent regulation of lymphopoiesis by NOD1

Aberrant differentiation of progenitor cells in the hematopoietic system is known to severely impact host immune responsiveness. Here we demonstrate that NOD1, a cytosolic innate sensor of bacterial peptidoglycan, also functions in murine hematopoietic cells as a major regulator of both the generation and differentiation of lymphoid progenitors as well as peripheral T lymphocyte homeostasis. We further show that NOD1 mediates these functions by facilitating STAT5 signaling downstream of hematopoietic cytokines. In steady-state, loss of NOD1 resulted in a modest but significant decrease in numbers of mature T, B and natural killer cells. During systemic protozoan infection this defect was markedly enhanced, leading to host mortality. Lack of functional NOD1 also impaired T cell-dependent anti-tumor immunity while preventing colitis. These findings reveal that, in addition to its classical role as a bacterial ligand receptor, NOD1 plays an important function in regulating adaptive immunity through interaction with a major host cytokine signaling pathway.

Immune cells and immune cell-targeted therapy in chronic pancreatitis

In recent years, studies have attempted to understand the immune cells and mechanisms underlying the pathogenesis of chronic pancreatitis (CP) by constructing a model of CP. Based on these studies, the innate immune response is a key factor in disease pathogenesis and inflammation severity. Novel mechanisms of crosstalk between immune and non-immune pancreatic cells, such as pancreatic stellate cells (PSC), have also been explored. Immune cells, immune responses, and signaling pathways in CP are important factors in the development and progression of pancreatitis. Based on these mechanisms, targeted therapy may provide a feasible scheme to stop or reverse the progression of the disease in the future and provide a new direction for the treatment of CP. This review summarizes the recent advances in research on immune mechanisms in CP and the new advances in treatment based on these mechanisms.

Cannabinoid Mixture Affects the Fate and Functions of B Cells through the Modulation of the Caspase and MAP Kinase Pathways

Cannabis use is continuously increasing in Canada, raising concerns about its potential impact on immunity. The current study assessed the impact of a cannabinoid mixture (CM) on B cells and the mechanisms by which the CM exerts its potential anti-inflammatory properties. Peripheral blood mononuclear cells (PBMCs) were treated with different concentrations of the CM to evaluate cytotoxicity. In addition, flow cytometry was used to evaluate oxidative stress, antioxidant levels, mitochondrial membrane potential, apoptosis, caspase activation, and the activation of key signaling pathways (ERK1/2, NF-κB, STAT5, and p38). The number of IgM- and IgG-expressing cells was assessed using FluoroSpot, and the cytokine production profile of the B cells was explored using a cytokine array. Our results reveal that the CM induced B-cell cytotoxicity in a dose-dependent manner, which was mediated by apoptosis. The levels of ROS and those of the activated caspases, mitochondrial membrane potential, and DNA damage increased following exposure to the CM (3 µg/mL). In addition, the activation of MAP Kinase, STATs, and the NF-κB pathway and the number of IgM- and IgG-expressing cells were reduced following exposure to the CM. Furthermore, the exposure to the CM significantly altered the cytokine profile of the B cells. Our results suggest that cannabinoids have a detrimental effect on B cells, inducing caspase-mediated apoptosis.

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.

Genomic distribution of signal transducer and activator of transcription (STAT) family in colorectal cancer

JAK/STAT pathway has been widely acknowledged in the development of human cancers. However, the role of different phosphorylated STAT proteins translocating into nucleus in transcription activation of target genes is not fully understood. In present research, ChIP-seq was carried on to investigate the genome-wide distribution of the activated STAT1, STAT2, STAT3, STAT5 and STAT6 in colorectal cancer HCT-116 cells. Our observations indicated that the homodimers rather than heterodimers of STAT protein predominantly occupied on genomic DNA. STAT3 accounted for the largest proportion among all STAT proteins HCT-116 cells. Furthermore, the biased binding motif targeted by different STAT homodimers suggested the distinct biological functions. Here, we noticed that NR5A2 was a specific co-activator of STAT3 by DNA motif analysis. Co-IP assay determined that NR5A2 indeed interacted with STAT3 homodimer rather than other homodimers or heterodimers. NR5A2 knockdown resulted in a reduced binding affinity of STAT3 homodimer in the original regions. Taken together, we characterize the genome-wide landscape of activated STAT proteins, and reveal the differences of binding patterns as well as the target genes and associated functions between homodimer and heterodimer of STAT proteins in HCT-116 cells. We also present some new findings and possible mechanisms regarding the role of NR5A2 on STAT3 in CRC. Our findings may provide new insights into the design of STAT inhibitors to treat CRC and other diseases.

The Ups and Downs of STAT Inhibition in Acute Myeloid Leukemia

Aberrant Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling is implicated in the pathogenesis of acute myeloid leukemia (AML), a highly heterogeneous hematopoietic malignancy. The management of AML is complex and despite impressive efforts into better understanding its underlying molecular mechanisms, survival rates in the elderly have not shown a substantial improvement over the past decades. This is particularly due to the heterogeneity of AML and the need for personalized approaches. Due to the crucial role of the deregulated JAK-STAT signaling in AML, selective targeting of the JAK-STAT pathway, particularly constitutively activated STAT3 and STAT5 and their associated upstream JAKs, is of great interest. This strategy has shown promising results in vitro and in vivo with several compounds having reached clinical trials. Here, we summarize recent FDA approvals and current potential clinically relevant inhibitors for AML patients targeting JAK and STAT proteins. This review underlines the need for detailed cytogenetic analysis and additional assessment of JAK-STAT pathway activation. It highlights the ongoing development of new JAK-STAT inhibitors with better disease specificity, which opens up new avenues for improved disease management.

STAT5 promotes chronic pancreatitis by enhancing GM-CSF-dependent neutrophil augmentation

Chronic pancreatitis (CP) is a continuing or relapsing inflammatory disease of the pancreas, characterized by fibrosis of the whole tissue. The regulatory mechanisms of the immune microenvironment in the pathogenesis of CP are still not clear. Immune cells, especially myeloid cells, play an important role in the pathogenesis of pancreatitis. Understanding the regulatory mechanisms of immune infiltration has a significant impact on CP intervention. Here, we demonstrated that transcription factor STAT5 was involved in and critical for the progression of CP. Inflammatory stress could significantly increase the expression and activation of STAT5 during CP. STAT5 deficiency or inhibition contributed to alleviating pancreatic inflammation and fibrosis in CP mice. The increased neutrophil infiltration, mediated by up-regulated GM-CSF, was responsible for the pancreatitis-promoting activity of STAT5. Our investigation highlighted the importance of STAT5 in regulating the immune microenvironment of CP. Targeting STAT5 may hold distinct promise for clinical treatment to alleviate CP.

Deregulation of enhancer structure, function, and dynamics in acute lymphoblastic leukemia

Enhancers control dynamic changes in gene expression and orchestrate the tightly controlled transcriptional circuitries that direct and coordinate cell growth, proliferation, survival, lineage commitment, and differentiation during lymphoid development. Enhancer hijacking and neoenhancer formation at oncogene loci, as well as aberrant activation of oncogene-associated enhancers, can induce constitutive activation of self-perpetuating oncogenic transcriptional circuitries, and contribute to the malignant transformation of immature lymphoid progenitors in acute lymphoblastic leukemia (ALL). In this review, we present recent discoveries of the role of enhancer dynamics in mouse and human lymphoid development, and discuss how genetic and epigenetic alterations of enhancer function can promote leukemogenesis, and potential strategies for targeting the enhancer machinery in the treatment of ALL.

STAT5: From Pathogenesis Mechanism to Therapeutic Approach in Acute Leukemia

BACKGROUND

Based on the results of multiple studies, multiple signaling pathways is a major cause of resistence to chemotherapy in leukemia cells. Signal transducer and activator of transcription 5 (STAT5) is among these factors; it plays an essential role in proliferation of leukemic cells.

METHODS

We obtained the materials used in our study via PubMed search from 1996 through 2019. The key search terms included "STAT5," "acute leukemia," "leukemogenesis," and "mutation."

RESULTS

On activation, STAT5 not only inhibits apoptosis of leukemic cells via activating the B-cell lymphoma 2 (BCL-2) gene but also inhibits resistance to chemotherapy by enhancing human telomerase reverse transcriptase (hTERT) expression and maintaining telomere length in cells. It has also been shown that a number of mutations in the STAT5 gene and in related genes alter the expression of STAT5.

CONCLUSION

The identification of STAT5 and the factors activated in its up- or downstream expression, affecting its function, contribute to better treatments such as targeted therapy rather than chemotherapy, improving the quality of life patients.

Cyba-deficient mice display an increase in hematopoietic stem cells and an overproduction of immunoglobulins

The regulation of protein function by reversible oxidation is increasingly recognized as a key mechanism for the control of cellular signaling, modulating crucial biological processes such as cell differentiation. In this scenario, NADPH oxidases must occupy a prominent position. Our results show that hematopoietic stem and progenitor cells express three p22^phox -dependent NADPH oxidase members (NOX1, NOX2 and NOX4). By deleting the p22^phox coding gene (Cyba), here we have analyzed the importance of this family of enzymes during in vivo hematopoiesis. Cyba^-/- mice show a myeloid bias, and an enrichment of hematopoietic stem cell populations. By means of hematopoietic transplant experiments we have also tried to dissect the specific role of the NADPH oxidases. While the absence of NOX1 or NOX2 provides a higher level of reconstitution, a lack of NOX4 rendered the opposite result, suggesting a functional specificity among the different NADPH oxidases. Cyba^-/- cells showed a hampered activation of AKT1 and a sharp decrease in STAT5 protein. This is in line with the diminished response to IL-7 shown by our results, which could explain the overproduction of immunoglobulins observed in Cyba^-/- mice.

Novel method for effectively amplifying human peripheral blood T cells in vitro

The use of chimeric antigen receptor-modified T cells (CAR T cells) is an effective therapy for advanced cancer, especially hematological malignancies, and this method has attracted widespread attention in the last several years. The type, number and vitality of the effector cells clearly play important roles in this approach. In this study, to expand the possibility of curing cancer through adoptive cell therapy (ACT), we developed a novel method for effectively obtaining abundant T cells in vitro. The fusion proteins of three cytokines, SA-hIL-2, SA-hIL-7 and SA-hIL-21, were anchored onto biotin magnetic beads to increase the number of cytokines on the surface of the magnetic beads, which increased the local concentration of cytokines and thus promoted the binding of cytokines to T cells. Next, we examined the effects of these modified magnetic beads on the proliferation rate of T cells and CD19 CAR T cells. In this study, we report the expression and purification of the active bifunctional fusion proteins SA-hIL-2, SA-hIL-7 and SA-hIL-21, which were bound to biotin magnetic beads to develop a platform that was employed to increase the local concentration of cytokines. When the cells had been cultured for 14 days, the proliferation rate of the CD3⁺ T cells in the group that received cytokine-coupled biotin magnetic beads (Beads-SA-CK) was higher than that of the cells in the groups that received soluble cytokines (Soluble-SA-CK) and that of the cells in the standard group (Standard-CK). We speculate that this difference may be the result of the increased expression of Bcl-2 and the increased phosphorylation of Stat5. Moreover, our results preliminarily indicate that compared with the other two treatments, Soluble-SA-CK and Standard-CK, adding cytokine-coupled biotin magnetic beads more effectively increases the proliferation rate of CD19 CAR-T cells. As expected, the CD19 CAR-T cells stimulated by Beads-SA-CK had a stronger anticancer effect than the cells stimulated by the other two treatments. An effective method of preparing abundant T cells in vitro was developed, and it may provide a novel strategy for ACT.

Transcriptome analysis reveals modulation of the STAT family in PEDV-infected IPEC-J2 cells

BACKGROUND

Porcine epidemic diarrhea virus (PEDV) is a causative agent of serious viral enteric disease in suckling pigs. Such diseases cause considerable economic losses in the global swine industry. Enhancing our knowledge of PEDV-induced transcriptomic responses in host cells is imperative to understanding the molecular mechanisms involved in the immune response. Here, we analyzed the transcriptomic profile of intestinal porcine epithelial cell line J2 (IPEC-J2) after infection with a classical strain of PEDV to explore the host response.

RESULTS

In total, 854 genes were significantly differentially expressed after PEDV infection, including 716 upregulated and 138 downregulated genes. Functional annotation analysis revealed that the differentially expressed genes were mainly enriched in the influenza A, TNF signaling, inflammatory response, cytokine receptor interaction, and other immune-related pathways. Next, the putative promoter regions of the 854 differentially expressed genes were examined for the presence of transcription factor binding sites using the MEME tool. As a result, 504 sequences (59.02%) were identified as possessing at least one binding site of signal transducer and activator of transcription (STAT), and five STAT transcription factors were significantly induced by PEDV infection. Furthermore, we revealed the regulatory network induced by STAT members in the process of PEDV infection.

CONCLUSION

Our transcriptomic analysis described the host genetic response to PEDV infection in detail in IPEC-J2 cells, and suggested that STAT transcription factors may serve as key regulators in the response to PEDV infection. These results further our understanding of the pathogenesis of PEDV.

Flow Cytometric Methods for the Detection of Intracellular Signaling Proteins and Transcription Factors Reveal Heterogeneity in Differentiating Human B Cell Subsets

The flow cytometric detection of intracellular (IC) signaling proteins and transcription factors (TFs) will help to elucidate the regulation of B cell survival, proliferation and differentiation. However, the simultaneous detection of signaling proteins or TFs with membrane markers (MMs) can be challenging, as the required fixation and permeabilization procedures can affect the functionality of conjugated antibodies. Here, a phosphoflow method is presented for the detection of activated NF-κB p65 and phosphorylated STAT1, STAT3, STAT5 and STAT6, together with the B cell differentiation MMs CD19, CD27 and CD38. Additionally, a TF-flow method is presented that allows the detection of the B cell TFs PAX5, c-MYC, BCL6 and AID and antibody-secreting cell (ASC) TFs BLIMP1 and XBP-1s, together with MMs. Applying these methods on in vitro-induced human B cell differentiation cultures showed significantly different steady-state levels, and responses to stimulation, of phosphorylated signaling proteins in CD27-expressing B cell and ASC populations. The TF-flow protocol and Uniform Manifold Approximation and Projection (UMAP) analysis revealed heterogeneity in TF expression within stimulated CD27- or CD38-expressing B cell subsets. The methods presented here allow for the sensitive analysis of STAT, NF-κB p65 signaling and TFs, together with B cell differentiation MMs, at single-cell resolution. This will aid the further investigation of B cell responses in both health and disease.

Inactivated STAT5 pathway underlies a novel inhibitory role of EBF1 in chronic lymphocytic leukemia

B-cell chronic lymphocytic leukemia (CLL) is a disease caused by gradual accumulation of functionally incompetent lymphocytes. The majority of CLL cases are accompanied by chemoresistance. Early B cell factor 1 (EBF1) is a crucial contributor to B-cell lymphopoiesis. This study is to explore the effect of EBF1 on CLL cell progression and its involvement in regulating the signal transducers and activators of transcription 5 (STAT5) pathway. We conducted a correlation analysis between EBF1 and the clinical characteristics of CLL patients. Subsequently, EBF1 was overexpressed by transfection with EBF1 overexpression plasmid and the STAT5 pathway was also blocked by treatment with SH-4-54 in isolated CD20⁺ B lymphocytes to investigate their roles in the regulation of cellular functions. STAT5, Janus kinase 2 (JAK2) expression and their phosphorylation levels were determined by quantitative PCR and Western blot analyses. The in vivo effects of EBF1 on tumor growth were evaluated using a xenotransplant model. Downregulation of EBF1 was observed in CD20⁺ B lymphocytes of CLL patients. EBF1 overexpression disrupted the activation of STAT5 pathway, as evidenced by decreased expression and phosphorylation levels of STAT5 and JAK2. Furthermore, overexpression of EBF1 repressed viability and cell cycle entry, and increased apoptosis of CD20⁺ B lymphocytes by inhibiting the STAT5 pathway. Finally, EBF1 exerted antitumor effects in nude mice. Overall, our study elucidates the inhibitory role of EBF1 in CLL through inactivation of the STAT5 pathway, which may provide new targets for CLL treatment.

High activation of STAT5A drives peripheral T-cell lymphoma and leukemia

Recurrent gain-of-function mutations in the transcription factors STAT5A and much more in STAT5B were found in hematopoietic malignancies with the highest proportion in mature T- and natural killer-cell neoplasms (peripheral T-cell lymphoma, PTCL). No targeted therapy exists for these heterogeneous and often aggressive diseases. Given the shortage of models for PTCL, we mimicked graded STAT5A or STAT5B activity by expressing hyperactive Stat5a or STAT5B variants at low or high levels in the hematopoietic system of transgenic mice. Only mice with high activity levels developed a lethal disease resembling human PTCL. Neoplasia displayed massive expansion of CD8⁺ T cells and destructive organ infiltration. T cells were cytokine-hypersensitive with activated memory CD8⁺ T-lymphocyte characteristics. Histopathology and mRNA expression profiles revealed close correlation with distinct subtypes of PTCL. Pronounced STAT5 expression and activity in samples from patients with different subsets underline the relevance of JAK/STAT as a therapeutic target. JAK inhibitors or a selective STAT5 SH₂ domain inhibitor induced cell death and ruxolitinib blocked T-cell neoplasia in vivo. We conclude that enhanced STAT5A or STAT5B action both drive PTCL development, defining both STAT5 molecules as targets for therapeutic intervention.

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

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

Balancing STAT Activity as a Therapeutic Strategy

Driven by dysregulated IL-6 family member cytokine signaling in the tumor microenvironment (TME), aberrant signal transducer and activator of transcription (STAT3) and (STAT5) activation have been identified as key contributors to tumorigenesis. Following transformation, persistent STAT3 activation drives the emergence of mesenchymal/cancer-stem cell (CSC) properties, important determinants of metastatic potential and therapy failure. Moreover, STAT3 signaling within tumor-associated macrophages and neutrophils drives secretion of factors that facilitate metastasis and suppress immune cell function. Persistent STAT5 activation is responsible for cancer cell maintenance through suppression of apoptosis and tumor suppressor signaling. Furthermore, STAT5-mediated CD4+/CD25+ regulatory T cells (T_regs) have been implicated in suppression of immunosurveillance. We discuss these roles for STAT3 and STAT5, and weigh the attractiveness of different modes of targeting each cancer therapy. Moreover, we discuss how anti-tumorigenic STATs, including STAT1 and STAT2, may be leveraged to suppress the pro-tumorigenic functions of STAT3/STAT5 signaling.

Transcriptional, Epigenetic and Pharmacological Control of JAK/STAT Pathway in NK Cells

Differentiation of Natural Killer (NK) cells is a stepwise process having its origin in the bone marrow and proceeding in the periphery, where these cells follow organ specific trajectories. Several soluble factors and cytokines regulate the distinct stages of NK cell differentiation, and ultimately, their functional properties. Cytokines activating the Janus kinases (JAKs) and members of the signal transducer and activator of transcription (STAT) pathway control distinct aspects of NK cell biology, ranging from development, terminal differentiation, activation, and generation of cells with adaptive properties. Here, we discuss how the recent advances of next generation sequencing (NGS) technology have led to unravel novel molecular aspects of gene regulation, with the aim to provide genomic views of how STATs regulate transcriptional and epigenetic features of NK cells during the different functional stages.

A survey of inter-individual variation in DNA methylation identifies environmentally responsive co-regulated networks of epigenetic variation in the human genome

While population studies have resulted in detailed maps of genetic variation in humans, to date there are few robust maps of epigenetic variation. We identified sites containing clusters of CpGs with high inter-individual epigenetic variation, termed Variably Methylated Regions (VMRs) in five purified cell types. We observed that VMRs occur preferentially at enhancers and 3' UTRs. While the majority of VMRs have high heritability, a subset of VMRs within the genome show highly correlated variation in trans, forming co-regulated networks that have low heritability, differ between cell types and are enriched for specific transcription factor binding sites and biological pathways of functional relevance to each tissue. For example, in T cells we defined a network of 95 co-regulated VMRs enriched for genes with roles in T-cell activation; in fibroblasts a network of 34 co-regulated VMRs comprising all four HOX gene clusters enriched for control of tissue growth; and in neurons a network of 18 VMRs enriched for roles in synaptic signaling. By culturing genetically-identical fibroblasts under varying environmental conditions, we experimentally demonstrated that some VMR networks are responsive to the environment, with methylation levels at these loci changing in a coordinated fashion in trans dependent on cellular growth. Intriguingly these environmentally-responsive VMRs showed a strong enrichment for imprinted loci (p<10-80), suggesting that these are particularly sensitive to environmental conditions. Our study provides a detailed map of common epigenetic variation in the human genome, showing that both genetic and environmental causes underlie this variation.

Recent Advances in the Role of SLC39A/ZIP Zinc Transporters In Vivo

Zinc (Zn), which is an essential trace element, is involved in numerous mammalian physiological events; therefore, either a deficiency or excess of Zn impairs cellular machineries and influences physiological events, such as systemic growth, bone homeostasis, skin formation, immune responses, endocrine function, and neuronal function. Zn transporters are thought to mainly contribute to Zn homeostasis within cells and in the whole body. Recent genetic, cellular, and molecular studies of Zn transporters highlight the dynamic role of Zn as a signaling mediator linking several cellular events and signaling pathways. Dysfunction in Zn transporters causes various diseases. This review aims to provide an update of Zn transporters and Zn signaling studies and discusses the remaining questions and future directions by focusing on recent progress in determining the roles of SLC39A/ZIP family members in vivo.

STAT5BN642H is a driver mutation for T cell neoplasia

STAT5B is often mutated in hematopoietic malignancies. The most frequent STAT5B mutation, Asp642His (N642H), has been found in over 90 leukemia and lymphoma patients. Here, we used the Vav1 promoter to generate transgenic mouse models that expressed either human STAT5B or STAT5B^N642H in the hematopoietic compartment. While STAT5B-expressing mice lacked a hematopoietic phenotype, the STAT5B^N642H-expressing mice rapidly developed T cell neoplasms. Neoplasia manifested as transplantable CD8⁺ lymphoma or leukemia, indicating that the STAT5B^N642H mutation drives cancer development. Persistent and enhanced levels of STAT5B^N642H tyrosine phosphorylation in transformed CD8⁺ T cells led to profound changes in gene expression that were accompanied by alterations in DNA methylation at potential histone methyltransferase EZH2-binding sites. Aurora kinase genes were enriched in STAT5B^N642H-expressing CD8⁺ T cells, which were exquisitely sensitive to JAK and Aurora kinase inhibitors. Together, our data suggest that JAK and Aurora kinase inhibitors should be further explored as potential therapeutics for lymphoma and leukemia patients with the STAT5B^N642H mutation who respond poorly to conventional chemotherapy.

DNA damage response is hijacked by human papillomaviruses to complete their life cycle

The DNA damage response (DDR) is activated when DNA is altered by intrinsic or extrinsic agents. This pathway is a complex signaling network and plays important roles in genome stability, tumor transformation, and cell cycle regulation. Human papillomaviruses (HPVs) are the main etiological agents of cervical cancer. Cervical cancer ranks as the fourth most common cancer among women and the second most frequent cause of cancer-related death worldwide. Over 200 types of HPVs have been identified and about one third of these infect the genital tract. The HPV life cycle is associated with epithelial differentiation. Recent studies have shown that HPVs deregulate the DDR to achieve a productive life cycle. In this review, I summarize current findings about how HPVs mediate the ataxia-telangiectasia mutated kinase (ATM) and the ATM-and RAD3-related kinase (ATR) DDRs, and focus on the roles that ATM and ATR signalings play in HPV viral replication. In addition, I demonstrate that the signal transducer and activator of transcription-5 (STAT)-5, an important immune regulator, can promote ATM and ATR activations through different mechanisms. These findings may provide novel opportunities for development of new therapeutic targets for HPV-related cancers.

Early B Cell Progenitors Deficient for GON4L Fail To Differentiate Due to a Block in Mitotic Cell Division

B cell development in Justy mutant mice is blocked due to a precursor mRNA splicing defect that depletes the protein GON4-like (GON4L) in B cell progenitors. Genetic and biochemical studies have suggested that GON4L is a transcriptional regulator that coordinates cell division with differentiation, but its role in B cell development is unknown. To understand the function of GON4L, we characterized B cell differentiation, cell cycle control, and mitotic gene expression in GON4L-deficient B cell progenitors from Justy mice. We found that these cells established key aspects of the transcription factor network that guides B cell development and proliferation and rearranged the IgH gene locus. However, despite intact IL-7 signaling, GON4L-deficient pro-B cell stage precursors failed to undergo a characteristic IL-7-dependent proliferative burst. These cells also failed to upregulate genes required for mitotic division, including those encoding the G₁/S cyclin D3 and E2F transcription factors and their targets. Additionally, GON4L-deficient B cell progenitors displayed defects in DNA synthesis and passage through the G₁/S transition, contained fragmented DNA, and underwent apoptosis. These phenotypes were not suppressed by transgenic expression of prosurvival factors. However, transgenic expression of cyclin D3 or other regulators of the G₁/S transition restored pro-B cell development from Justy progenitor cells, suggesting that GON4L acts at the beginning of the cell cycle. Together, our findings indicate that GON4L is essential for cell cycle progression and division during the early stages of B cell development.

Antagonism of B cell enhancer networks by STAT5 drives leukemia and poor patient survival

The transcription factor STAT5 has a critical role in B cell acute lymphoblastic leukemia (B-ALL). How STAT5 mediates this effect is unclear. Here we found that activation of STAT5 worked together with defects in signaling components of the precursor to the B cell antigen receptor (pre-BCR), including defects in BLNK, BTK, PKCβ, NF-κB1 and IKAROS, to initiate B-ALL. STAT5 antagonized the transcription factors NF-κB and IKAROS by opposing regulation of shared target genes. Super-enhancers showed enrichment for STAT5 binding and were associated with an opposing network of transcription factors, including PAX5, EBF1, PU.1, IRF4 and IKAROS. Patients with a high ratio of active STAT5 to NF-κB or IKAROS had more-aggressive disease. Our studies indicate that an imbalance of two opposing transcriptional programs drives B-ALL and suggest that restoring the balance of these pathways might inhibit B-ALL.

STAT5-Interacting Proteins: A Synopsis of Proteins that Regulate STAT5 Activity

Signal Transducers and Activators of Transcription (STATs) are key components of the JAK/STAT pathway. Of the seven STATs, STAT5A and STAT5B are of particular interest for their critical roles in cellular differentiation, adipogenesis, oncogenesis, and immune function. The interactions of STAT5A and STAT5B with cytokine/hormone receptors, nuclear receptors, transcriptional regulators, proto-oncogenes, kinases, and phosphatases all contribute to modulating STAT5 activity. Among these STAT5 interacting proteins, some serve as coactivators or corepressors to regulate STAT5 transcriptional activity and some proteins can interact with STAT5 to enhance or repress STAT5 signaling. In addition, a few STAT5 interacting proteins have been identified as positive regulators of STAT5 that alter serine and tyrosine phosphorylation of STAT5 while other proteins have been identified as negative regulators of STAT5 via dephosphorylation. This review article will discuss how STAT5 activity is modulated by proteins that physically interact with STAT5.

T Cell Receptor and Cytokine Signaling Can Function at Different Stages to Establish and Maintain Transcriptional Memory and Enable T Helper Cell Differentiation

Experienced T cells exhibit immunological memory via a rapid recall response, responding to restimulation much faster than naïve T cells. The formation of immunological memory starts during an initial slow response, when naïve T cells become transformed to proliferating T blast cells, and inducible immune response genes are reprogrammed as active chromatin domains. We demonstrated that these active domains are supported by thousands of priming elements which cooperate with inducible transcriptional enhancers to enable efficient responses to stimuli. At the conclusion of this response, a small proportion of these cells return to the quiescent state as long-term memory T cells. We proposed that priming elements can be established in a hit-and-run process dependent on the inducible factor AP-1, but then maintained by the constitutive factors RUNX1 and ETS-1. This priming mechanism may also function to render genes receptive to additional differentiation-inducing factors such as GATA3 and TBX21 that are encountered under polarizing conditions. The proliferation of recently activated T cells and the maintenance of immunological memory in quiescent memory T cells are also dependent on various cytokine signaling pathways upstream of AP-1. We suggest that immunological memory is established by T cell receptor signaling, but maintained by cytokine signaling.

Interleukins 7 and 15 Maintain Human T Cell Proliferative Capacity through STAT5 Signaling

T lymphocytes require signals from self-peptides and cytokines, most notably interleukins 7 and 15 (IL-7, IL-15), for survival. While mouse T cells die rapidly if IL-7 or IL-15 is withdrawn, human T cells can survive prolonged withdrawal of IL-7 and IL-15. Here we show that IL-7 and IL-15 are required to maintain human T cell proliferative capacity through the STAT5 signaling pathway. T cells from humanized mice proliferate better if stimulated in the presence of human IL-7 or IL-15 or if T cells are exposed to human IL-7 or IL-15 in mice. Freshly isolated T cells from human peripheral blood lose proliferative capacity if cultured for 24 hours in the absence of IL-7 or IL-15. We further show that phosphorylation of STAT5 correlates with proliferation and inhibition of STAT5 reduces proliferation. These results reveal a novel role of IL-7 and IL-15 in maintaining human T cell function, provide an explanation for T cell dysfunction in humanized mice, and have significant implications for in vitro studies with human T cells.

Manipulation of the innate immune response by human papillomaviruses

The innate immune response constitutes the first line of defense against infections by pathogens. Successful pathogens such as human papillomaviruses (HPVs) have evolved mechanisms that target several points in these pathways including sensing of viral genomes, blocking the synthesis of interferons and inhibiting the action of JAK/STAT transcription factors. Disruption of these inhibitory mechanisms contributes to the ability of HPVs to establish persistent infections, which is the major etiological factor in the development of anogenital cancers. Interestingly, HPVs also positively activate several members of these pathways such as STAT-5 that are important for their differentiation-dependent life cycle. STAT-5 activation induces the ATM and ATR DNA damage response pathways that play critical roles in HPV genome amplification. Targeting of these pathways by pharmaceuticals can provide novel opportunities to inhibit infections by these important human pathogens.

Roles of Zinc Signaling in the Immune System

Zinc (Zn) is an essential micronutrient for basic cell activities such as cell growth, differentiation, and survival. Zn deficiency depresses both innate and adaptive immune responses. However, the precise physiological mechanisms of the Zn-mediated regulation of the immune system have been largely unclear. Zn homeostasis is tightly controlled by the coordinated activity of Zn transporters and metallothioneins, which regulate the transport, distribution, and storage of Zn. There is growing evidence that Zn behaves like a signaling molecule, facilitating the transduction of a variety of signaling cascades in response to extracellular stimuli. In this review, we highlight the emerging functional roles of Zn and Zn transporters in immunity, focusing on how crosstalk between Zn and immune-related signaling guides the normal development and function of immune cells.

Intramolecular hydrophobic interactions are critical mediators of STAT5 dimerization

STAT5 is an essential transcription factor in hematopoiesis, which is activated through tyrosine phosphorylation in response to cytokine stimulation. Constitutive activation of STAT5 is a hallmark of myeloid and lymphoblastic leukemia. Using homology modeling and molecular dynamics simulations, a model of the STAT5 phosphotyrosine-SH2 domain interface was generated providing first structural information on the activated STAT5 dimer including a sequence, for which no structural information is available for any of the STAT proteins. We identified a novel intramolecular interaction mediated through F706, adjacent to the phosphotyrosine motif, and a unique hydrophobic interface on the surface of the SH2 domain. Analysis of corresponding STAT5 mutants revealed that this interaction is dispensable for Epo receptor-mediated phosphorylation of STAT5 but essential for dimer formation and subsequent nuclear accumulation. Moreover, the herein presented model clarifies molecular mechanisms of recently discovered leukemic STAT5 mutants and will help to guide future drug development.

GRAM domain-containing protein 1A (GRAMD1A) promotes the expansion of hepatocellular carcinoma stem cell and hepatocellular carcinoma growth through STAT5

Hepatocellular carcinoma (HCC) is the leading cause for cancer death worldwide, new prognostic factors and targets are critical for HCC treatment. Here, we found GRAMD1A was upregulated in HCC tissues, patients with high GRAMD1A levels had poor outcome, statistical analyses found GRAMD1A expression was positively correlated with pathologic differentiation and survival or mortality. It was an unfavorable prognostic factor for HCC patients. Functional analyses revealed GRAMD1A contributed to the self-renewal of HCC stem cells, resistance to chemotherapy and tumor growth of HCC determined by hepatosphere formation assay, side population (SP) analysis, TUNEL assay, soft agar growth ability assay and tumor growth model in vivo. Mechanism analyses found signal transducer and activator of transcription 5 (STAT5) was the target of GRAMD1A, GRAMD1A regulated the target genes of STAT5 and the transcriptional activity of STAT5. Inhibition of STAT5 in indicated HCC cells overexpressing GRAMD1A suppressed the effects of GRAMD1A on the self-renewal of HCC stem cell, resistance to chemotherapy and tumor growth, suggesting GRAMD1A promoted the self-renewal of HCC stem cells and the development of HCC by increasing STAT5 level. GRAMD1A might be a useful biomarker and target for HCC.

Jak3, STAT3, and STAT5 inhibit expression of miR-22, a novel tumor suppressor microRNA, in cutaneous T-Cell lymphoma

Aberrant activation of Janus kinase-3 (Jak3) and its key down-stream effectors, Signal Transducer and Activator of Transcription-3 (STAT3) and STAT5, is a key feature of malignant transformation in cutaneous T-cell lymphoma (CTCL). However, it remains only partially understood how Jak3/STAT activation promotes lymphomagenesis. Recently, non-coding microRNAs (miRNAs) have been implicated in the pathogenesis of this malignancy. Here, we show that (i) malignant T cells display a decreased expression of a tumor suppressor miRNA, miR-22, when compared to non-malignant T cells, (ii) STAT5 binds the promoter of the miR-22 host gene, and (iii) inhibition of Jak3, STAT3, and STAT5 triggers increased expression of pri-miR-22 and miR-22. Curcumin, a nutrient with anti-Jak3 activity and histone deacetylase inhibitors (HDACi) also trigger increased expression of pri-miR-22 and miR-22. Transfection of malignant T cells with recombinant miR-22 inhibits the expression of validated miR-22 targets including NCoA1, a transcriptional co-activator in others cancers, as well as HDAC6, MAX, MYCBP, PTEN, and CDK2, which have all been implicated in CTCL pathogenesis. In conclusion, we provide the first evidence that de-regulated Jak3/STAT3/STAT5 signalling in CTCL cells represses the expression of the gene encoding miR-22, a novel tumor suppressor miRNA.

Along the Axis between Type 1 and Type 2 Immunity; Principles Conserved in Evolution from Fish to Mammals

A phenomenon already discovered more than 25 years ago is the possibility of naïve helper T cells to polarize into TH1 or TH2 populations. In a simplified model, these polarizations occur at opposite ends of an "immune 1-2 axis" (i1-i2 axis) of possible conditions. Additional polarizations of helper/regulatory T cells were discovered later, such as for example TH17 and Treg phenotypes; although these polarizations are not selected by the axis-end conditions, they are affected by i1-i2 axis factors, and may retain more potential for change than the relatively stable TH1 and TH2 phenotypes. I1-i2 axis conditions are also relevant for polarizations of other types of leukocytes, such as for example macrophages. Tissue milieus with "type 1 immunity" ("i1") are biased towards cell-mediated cytotoxicity, while the term "type 2 immunity" ("i2") is used for a variety of conditions which have in common that they inhibit type 1 immunity. The immune milieus of some tissues, like the gills in fish and the uterus in pregnant mammals, probably are skewed towards type 2 immunity. An i2-skewed milieu is also created by many tumors, which allows them to escape eradication by type 1 immunity. In this review we compare a number of i1-i2 axis factors between fish and mammals, and conclude that several principles of the i1-i2 axis system seem to be ancient and shared between all classes of jawed vertebrates. Furthermore, the present study is the first to identify a canonical TH2 cytokine locus in a bony fish, namely spotted gar, in the sense that it includes RAD50 and bona fide genes of both IL-4/13 and IL-3/ IL-5/GM-CSF families.

BRAF and MEK inhibition variably affect GD2-specific chimeric antigen receptor (CAR) T-cell function in vitro

Cancer immunotherapy has long been used in the treatment of metastatic melanoma, and an anti-CTLA-4 monoclonal antibody treatment has recently been approved by the US Food and Drug Administration. Targeted therapies such as small molecule kinase inhibitors targeting deregulated mitogen-activated protein kinase (MAPK) signaling have markedly improved melanoma control in up to 50% of metastatic disease patients and have likewise been recently approved. Combination therapies for melanoma have been proposed as a way to exploit the high-level but short-term responses associated with kinase inhibitor therapies and the low-level but longer-term responses associated with immunotherapy. Cancer immunotherapy now includes adoptive transfer of autologous tumor-specific chimeric antigen receptor (CAR) T cells and this mode of therapy is a candidate for combination with small molecule drugs. This paper describes CART cells that target GD2-expressing melanoma cells and investigates the effects of approved MAPK pathway-targeted therapies for melanoma [vemurafenib (Vem), dabrafenib (Dab), and trametinib (Tram)] on the viability, activation, proliferation, and cytotoxic T lymphocyte activity of these CAR T cells, as well as on normal peripheral blood mononuclear cells. We report that, although all these drugs lead to inhibition of stimulated T cells at high concentrations in vitro, only Vem inhibited T cells at concentrations equivalent to reported plasma concentrations in treated patients. Although the combination of Dab and Tram also resulted in inhibition of T-cell effector functions at some therapeutic concentrations, Dab itself had little adverse effect on CAR T-cell function. These findings may have implications for novel therapeutic combinations of adoptive CAR T-cell immunotherapy and MAPK pathway inhibitors.

STAT-5 is activated constitutively in T cells, B cells and monocytes from patients with primary Sjögren's syndrome

The expression and phosphorylation of signal transducer and activator of transcription-1 (STAT-1) have been shown to be markedly increased in the salivary gland epithelial cells of patients with primary Sjögren's syndrome (pSS). The present aim was to investigate the activation status of different STAT proteins in peripheral blood (PB) lymphocytes and monocytes, and their correlations with clinical parameters in patients with pSS. To this end, PB samples were drawn from 16 patients with active pSS and 16 healthy blood donors, and the phosphorylation of STAT-1, -3, -4, -5 and -6 proteins was studied in T cells, B cells and monocytes using multi-colour flow cytometry. In addition, mRNA expression of STAT molecules in PB mononuclear cells (PBMC) was studied with quantitative reverse transcriptase-polymerase chain reaction (RT-PCR). Basal phosphorylation of STAT-5 was found to be significantly higher in PB T cells, B cells and monocytes in patients with pSS than in healthy controls. The expression of STAT-5 mRNA was not increased in PBMC. pSTAT-5 levels in B cells and monocytes showed a significant correlation with serum immunoglobulin (Ig)G levels and anti-SSB antibody titres. Constitutive STAT-5 activation in monocytes and CD4(+) T cells was associated with purpura. There were no major differences in the activation of other STATs between pSS patients and healthy controls. In conclusion, STAT-5 is activated constitutively in PB leucocytes in patients with pSS, and basal STAT-5 phosphorylation seems to associate with hypergammaglobulinaemia, anti-SSB antibody production and purpura.

Cross Talk between Proliferative, Angiogenic, and Cellular Mechanisms Orchestred by HIF-1α in Psoriasis

Psoriasis is a chronic inflammatory skin disease where the altered regulation in angiogenesis, inflammation, and proliferation of keratinocytes are the possible causes of the disease, and the transcription factor “hypoxia-inducible factor 1-alpha” (HIF-1α) is involved in the homeostasis of these three biological phenomena. In this review, the role of HIF-1α in the cross talk between the cytokines and cells of the immunological system involved in the pathogenesis of psoriasis is discussed.

Stat5 Exerts Distinct, Vital Functions in the Cytoplasm and Nucleus of Bcr-Abl+ K562 and Jak2(V617F)+ HEL Leukemia Cells

Signal transducers and activators of transcription (Stats) play central roles in the conversion of extracellular signals, e.g., cytokines, hormones and growth factors, into tissue and cell type specific gene expression patterns. In normal cells, their signaling potential is strictly limited in extent and duration. The persistent activation of Stat3 or Stat5 is found in many human tumor cells and contributes to their growth and survival. Stat5 activation plays a pivotal role in nearly all hematological malignancies and occurs downstream of oncogenic kinases, e.g., Bcr-Abl in chronic myeloid leukemias (CML) and Jak2(V617F) in other myeloproliferative diseases (MPD). We defined the mechanisms through which Stat5 affects growth and survival of K562 cells, representative of Bcr-Abl positive CML, and HEL cells, representative for Jak2(V617F) positive acute erythroid leukemia. In our experiments we suppressed the protein expression levels of Stat5a and Stat5b through shRNA mediated downregulation and demonstrated the dependence of cell survival on the presence of Stat5. Alternatively, we interfered with the functional capacities of the Stat5 protein through the interaction with a Stat5 specific peptide ligand. This ligand is a Stat5 specific peptide aptamer construct which comprises a 12mer peptide integrated into a modified thioredoxin scaffold, S5-DBD-PA. The peptide sequence specifically recognizes the DNA binding domain (DBD) of Stat5. Complex formation of S5-DBD-PA with Stat5 causes a strong reduction of P-Stat5 in the nuclear fraction of Bcr-Abl-transformed K562 cells and a suppression of Stat5 target genes. Distinct Stat5 mediated survival mechanisms were detected in K562 and Jak2(V617F)-transformed HEL cells. Stat5 is activated in the nuclear and cytosolic compartments of K562 cells and the S5-DBD-PA inhibitor most likely affects the viability of Bcr-Abl⁺ K562 cells through the inhibition of canonical Stat5 induced target gene transcription. In HEL cells, Stat5 is predominantly present in the cytoplasm and the survival of the Jak2(V617F)⁺ HEL cells is impeded through the inhibition of the cytoplasmic functions of Stat5.

Stat5 gene dosage in T cells modulates CD8+ T-cell homeostasis and attenuates contact hypersensitivity response in mice

BACKGROUND

Contact hypersensitivity assay (CHS) faithfully models human allergies. The Stat5 transcription factors are essential for both lymphocyte development and acute immune responses. Although consequences of Stat5 ablation and transgenic overexpression for the lymphocyte development and functions have been extensively studied, the role of Stat5 gene dosage in contact allergies has not been addressed.

OBJECTIVE

We investigated the effect of Stat5 gene dosage modulation in contact allergies using CHS in mice.

METHODS

Transgenic animals heterozygous for the germline Stat5 null allele were subjected to CHS. To dissect cell type sensitive to Stat5 gene dosage, animals with Stat5 haplo-insufficiency in T cells, where one Stat5 allele was removed by Lck-Cre-mediated deletion (Stat5(ΔT/+)), were tested by CHS. Frequency of T cells, B cells, and monocytes were analyzed in Stat5(ΔT/+) and wild-type animals by flow cytometry. Proliferation of Stat5(ΔT/+) CD8(+) T cells was studied in vitro by stimulation with IL-4 and IL-2 cytokines, and changes in the expression of Stat5 target genes were assayed by quantitative real-time PCR assay.

RESULT

Haplo-insufficiency of Stat5 in T cells leads to the reduction in CD8(+) T cells in all lymphoid organs and attenuates CHS response. Stat5(ΔT/+) CD8(+) T cells failed to fully activate Stat5-dependent expression of cell cycle/survival target genes, such as Bcl2 and Pim1, and to proliferate efficiently in response to IL-2 and IL-4 cytokine.

CONCLUSION

Our data identify Stat5 as a dose-dependent regulator of CD8(+) T-cell functions in contact allergies and suggest that modulation of Stat5 dosage could be used to target contact allergies in humans.

Reciprocal occupancy of BCL6 and STAT5 on Growth Hormone target genes: contrasting transcriptional outcomes and promoter-specific roles of p300 and HDAC3

Expression of the Growth Hormone (GH)-stimulated gene Socs2 (Suppressor of Cytokine Signaling 2) is mediated by the transcription activator STAT5 (Signal Transducer and Activator of Transcription 5) and the transcription repressor BCL6 (B-Cell Lymphoma 6). ChIP-Sequencing identified Cish (Cytokine-Inducible SH2-containing protein) and Bcl6 as having similar patterns of reciprocal occupancy by BCL6 and STAT5 in response to GH, though GH stimulates Cish and inhibits Bcl6 expression. The co-activator p300 occupied Socs2, Cish and Bcl6 promoters, and enhanced STAT5-mediated activation of Socs2 and Cish. In contrast, on Bcl6, p300 functioned as a repressor and inhibited in conjunction with STAT5 or BCL6. The co-repressor HDAC3 (Histone deacetylase 3) inhibited the Socs2, Cish and Bcl6 promoters in the presence of STAT5. Thus transcriptional outcomes on GH-regulated genes occupied by BCL6 and STAT5 are determined in a promoter-specific fashion by co-regulatory proteins which mediate the distinction between activating and repressive transcription factors.

Zinc transporter SLC39A10/ZIP10 facilitates antiapoptotic signaling during early B-cell development

The immune system is influenced by the vital zinc (Zn) status, and Zn deficiency triggers lymphopenia; however, the mechanisms underlying Zn-mediated lymphocyte maintenance remain elusive. Here we investigated ZIP10, a Zn transporter expressed in the early B-cell developmental process. Genetic ablation of Zip10 in early B-cell stages resulted in significant reductions in B-cell populations, and the inducible deletion of Zip10 in pro-B cells increased the caspase activity in parallel with a decrease in intracellular Zn levels. Similarly, the depletion of intracellular Zn by a chemical chelator resulted in spontaneous caspase activation leading to cell death. Collectively, these findings indicated that ZIP10-mediated Zn homeostasis is essential for early B-cell survival. Moreover, we found that ZIP10 expression was regulated by JAK-STAT pathways, and its expression was correlated with STAT activation in human B-cell lymphoma, indicating that the JAK-STAT-ZIP10-Zn signaling axis influences the B-cell homeostasis. Our results establish a role of ZIP10 in cell survival during early B-cell development, and underscore the importance of Zn homeostasis in immune system maintenance.

Platelet-derived growth factor alpha mediates the proliferation of peripheral T-cell lymphoma cells via an autocrine regulatory pathway

Peripheral T-cell lymphomas not otherwise specified (PTCL/NOS) are very aggressive tumors characterized by consistent aberrant expression of platelet-derived growth factor receptor alpha (PDGFRA). In this study, we aimed to identify the determinants of PDGFRA activity in PTCL/NOS and to elucidate the biological consequences of its activation. We observed overexpression of the PDGFRA gene by gene expression profiling in most of the tested PTCLs and confirmed the expression of PDGFRA and phospho-PDGFRA using immunohistochemistry. The integrity of the PDFGRA locus was demonstrated using several different approaches, including massive parallel sequencing and Sanger sequencing. PDGF-AA was found to be expressed and secreted by PTCL/NOS cells and to be necessary and sufficient for PDGFRA phosphorylation ex vivo by sustaining an autocrine stimulation. We documented consistently high PDGF-A expression in primary biopsies and patients' plasma and tracked PDGFRA signaling in primary tumors, achieving evidence of its activation. Indeed, we found that STAT1 and STAT5 are implicated in PDGFRA signaling transduction. Finally, we demonstrated that PDGFRA activation supported tumor cell proliferation and provided the first evidence of the anti-lymphoma activity of PDGRA inhibition in a PTCL/NOS patient. Altogether, our data demonstrated that PDGFRA activity fosters PTCL/NOS proliferation via an autocrine loop.

The role of the JAK-STAT pathway and related signal cascades in telomerase activation during the development of hematologic malignancies

Telomerase, comprising a reverse transcriptase protein (TERT) and an RNA template, plays a critical role during senescence and carcinogenesis; however, the mechanisms by which telomerase is regulated remain to be elucidated. Several signaling pathways are involved in the activation of TERT at multistep levels. The JAK-STAT pathway is indispensable for mediating signals through growth factor and cytokine receptors during the development of hematopoietic cells, and its activity is frequently upregulated in hematological malignancies. Here, we review the role of the JAK-STAT pathway and related signaling cascades in the regulation of telomerase in hematological malignancies.