Prolactin induces SHP-2 association with Stat5, nuclear translocation, and binding to the beta-casein gene promoter in mammary cells

Setting sail: Maneuvering SHP2 activity and its effects in cancer

Since the discovery of tyrosine phosphorylation being a critical modulator of cancer signaling, proteins regulating phosphotyrosine levels in cells have fast become targets of therapeutic intervention. The nonreceptor protein tyrosine phosphatase (PTP) coded by the PTPN11 gene "SHP2" integrates phosphotyrosine signaling from growth factor receptors into the RAS/RAF/ERK pathway and is centrally positioned in processes regulating cell development and oncogenic transformation. Dysregulation of SHP2 expression or activity is linked to tumorigenesis and developmental defects. Even as a compelling anti-cancer target, SHP2 was considered "undruggable" for a long time owing to its conserved catalytic PTP domain that evaded drug development. Recently, SHP2 has risen from the "undruggable curse" with the discovery of small molecules that manipulate its intrinsic allostery for effective inhibition. SHP2's unique domain arrangement and conformation(s) allow for a truly novel paradigm of inhibitor development relying on skillful targeting of noncatalytic sites on proteins. In this review we summarize the biological functions, signaling properties, structural attributes, allostery and inhibitors of SHP2.

Comparative evolutionary and molecular genetics based study of Buffalo lysozyme gene family to elucidate their antibacterial function

Lysozyme is used as a food preservative, biological medicine, and infant food additive as a natural anti-infective chemical having bactericidal activity and abundantly secreted in mammals' milk, saliva, etc. We systematically analyzed the 16 coding LYZ genes (C and G-type) in buffalo and cattle to elucidate their evolutionary perspective thoroughly by evaluating an evolutionary relationship, motif patterning, physicochemical attributes, gene, and protein structure, as well as the functional role of the mammary gland-specific expressed buffalo and cattle LYZ genes precisely while considering expression levels difference and the interaction sites variation with bacteria envisaged the potential ability of buffalo LYZ protein with enhanced antibacterial effect. Thus, we speculated that the buffalo mammary glands expressed lysozyme has good antibacterial activity. This study on the buffalo lysozyme gene family not only provides comprehensive insights into the genetic architecture and their antibacterial effect but also offers a theoretical basis for the development of new veterinary drugs and animal health care for mastitis, as well as a new molecular genetic basis to study food or medical lysozyme.

A comprehensive review of SHP2 and its role in cancer

Src homology 2-containing protein tyrosine phosphatase 2 (SHP2) is a non-receptor protein tyrosine phosphatase ubiquitously expressed mainly in the cytoplasm of several tissues. SHP2 modulates diverse cell signaling events that control metabolism, cell growth, differentiation, cell migration, transcription and oncogenic transformation. It interacts with diverse molecules in the cell, and regulates key signaling events including RAS/ERK, PI3K/AKT, JAK/STAT and PD-1 pathways downstream of several receptor tyrosine kinases (RTKs) upon stimulation by growth factors and cytokines. SHP2 acts as both a phosphatase and a scaffold, and plays prominently oncogenic functions but can be tumor suppressor in a context-dependent manner. It typically acts as a positive regulator of RTKs signaling with some inhibitory functions reported as well. SHP2 expression and activity is regulated by such factors as allosteric autoinhibition, microRNAs, ubiquitination and SUMOylation. Dysregulation of SHP2 expression or activity causes many developmental diseases, and hematological and solid tumors. Moreover, upregulated SHP2 expression or activity also decreases sensitivity of cancer cells to anticancer drugs. SHP2 is now considered as a compelling anticancer drug target and several classes of SHP2 inhibitors with different mode of action are developed with some already in clinical trial phases. Moreover, novel SHP2 substrates and functions are rapidly growing both in cell and cancer. In view of this, we comprehensively and thoroughly reviewed literatures about SHP2 regulatory mechanisms, substrates and binding partners, biological functions, roles in human cancers, and different classes of small molecule inhibitors target this oncoprotein in cancer.

The Tyrosine Phosphatase SHP2: A New Target for Insulin Resistance?

The SH2 containing protein tyrosine phosphatase 2(SHP2) plays essential roles in fundamental signaling pathways, conferring on it versatile physiological functions during development and in homeostasis maintenance, and leading to major pathological outcomes when dysregulated. Many studies have documented that SHP2 modulation disrupted glucose homeostasis, pointing out a relationship between its dysfunction and insulin resistance, and the therapeutic potential of its targeting. While studies from cellular or tissue-specific models concluded on both pros-and-cons effects of SHP2 on insulin resistance, recent data from integrated systems argued for an insulin resistance promoting role for SHP2, and therefore a therapeutic benefit of its inhibition. In this review, we will summarize the general knowledge of SHP2’s molecular, cellular, and physiological functions, explaining the pathophysiological impact of its dysfunctions, then discuss its protective or promoting roles in insulin resistance as well as the potency and limitations of its pharmacological modulation.

Molecular evolutionary insights from PRLR in mammals

Prolactin (PRL) is a pleiotropic neurohormone secreted by the mammalian pituitary gland into the blood, thus reaching many tissues and organs beyond the brain. PRL binds to its receptor, PRLR, eliciting a molecular signaling cascade. This system modulates essential mammalian behaviors and promotes notable modifications in the reproductive female tissues and organs. Here, we explore how the intracellular domain of PRLR (PRLR-ICD) modulates the expression of the PRLR gene. Despite differences in the reproductive strategies between eutherian and metatherian mammals, there is no clear distinction between PRLR-ICD functional motifs. However, we found selection signatures that showed differences between groups, with many conserved functional elements strongly maintained through purifying selection across the class Mammalia. We observed a few residues under relaxed selection, the levels of which were more pronounced in Eutheria and particularly striking in primates (Simiiformes), which could represent a pre-adaptive genetic element protected from purifying selection. Alternative, new motifs, such as YLDP (318-321) and others with residues Y283 and Y290, may already be functional. These motifs would have been co-opted in primates as part of a complex genetic repertoire related to some derived adaptive phenotypes, but these changes would have no impact on the primordial functions that characterize the mammals as a whole and that are related to the PRL-PRLR system.

Comparative Genomics, Evolutionary and Gene Regulatory Regions Analysis of Casein Gene Family in Bubalus bubalis

Buffalo is a luxurious genetic resource with multiple utilities (as a dairy, draft, and meat animal) and economic significance in the tropical and subtropical regions of the globe. The excellent potential to survive and perform on marginal resources makes buffalo an important source for nutritious products, particularly milk and meat. This study was aimed to investigate the evolutionary relationship, physiochemical properties, and comparative genomic analysis of the casein gene family (CSN1S1, CSN2, CSN1S2, and CSN3) in river and swamp buffalo. Phylogenetic, gene structure, motif, and conserved domain analysis revealed the evolutionarily conserved nature of the casein genes in buffalo and other closely related species. Results indicated that casein proteins were unstable, hydrophilic, and thermostable, although αs1-CN, β-CN, and κ-CN exhibited acidic properties except for αs2-CN, which behaved slightly basic. Comparative analysis of amino acid sequences revealed greater variation in the river buffalo breeds than the swamp buffalo indicating the possible role of these variations in the regulation of milk traits in buffalo. Furthermore, we identified lower transcription activators STATs and higher repressor site YY1 distribution in swamp buffalo, revealing its association with lower expression of casein genes that might subsequently affect milk production. The role of the main motifs in controlling the expression of casein genes necessitates the need for functional studies to evaluate the effect of these elements on the regulation of casein gene function in buffalo.

The Attenuated Secretion of Hyaluronan by UVA-Exposed Human Fibroblasts Is Associated with Up- and Downregulation of HYBID and HAS2 Expression via Activated and Inactivated Signaling of the p38/ATF2 and JAK2/STAT3 Cascades

Little is known about the effects on hyaluronan (HA) metabolism of UVA radiation. This study demonstrates that the secretion of HA by human dermal fibroblasts (HDFs) is downregulated by UVA, accompanied by the down- and upregulation of mRNA and protein levels of the HA-synthesizing enzyme (HAS2) and the HA-degrading protein, HYaluronan Binding protein Involved in HA Depolymerization(HYBID), respectively. Signaling analysis revealed that the exposure distinctly elicits activation of the p38/MSK1/CREB/c-Fos/AP-1 axis, the JNK/c-Jun axis, and the p38/ATF-2 axis, but downregulates the phosphorylation of NF-kB and JAK/STAT3. A signal inhibition study demonstrated that the inhibition of p38 significantly abrogates the UVA-accentuated mRNA level of HYBID. Furthermore, the inhibition of STAT3 significantly downregulates the level of HAS2 mRNA in non-UVA exposed HDFs. Analysis using siRNAs demonstrated that transfection of ATF-2 siRNA but not c-Fos siRNA abrogates the increased protein level of HYBID in UVA-exposed HDFs. An inhibitor of protein tyrosine phosphatase but not of protein serine/threonine phosphatase restored the diminished phosphorylation level of STAT3 at Tyr 705, accompanied by a significant abolishing effect on the decreased mRNA expression level of HAS2. Silencing with a protein tyrosine phosphatase PTP-Meg2 siRNA revealed that it abrogates the decreased phosphorylation of STAT3 at Tyr 705 in UVA-exposed HDFs. These findings suggest that the UVA-induced decrease in HA secretion by HDFs is attributable to the down- and upregulation of HAS2 and HYBID expression, respectively, changes that are mainly ascribed to the inactivated signaling of the STAT3 axis due to the activated tyrosine protein phosphatase PTP-Meg2 and the activated signaling of the p38/ATF2 axis, respectively.

SHP2 Nuclear/Cytoplasmic Trafficking in Granulosa Cells Is Essential for Oocyte Meiotic Resumption and Maturation

Src-homology-2-containing phosphotyrosine phosphatase (SHP2), a classic cytoplasmic protein and a major regulator of receptor tyrosine kinases and G protein-coupled receptors, plays a significant role in preimplantation embryo development. In this study, we deciphered the role of SHP2 in the somatic compartment of oocytes during meiotic maturation. SHP2 showed nuclear/cytoplasmic localization in bovine cumulus and human granulosa (COV434) cells. Follicle-stimulating hormone (FSH) treatment significantly enhanced cytoplasmic SHP2 localization, in contrast to the E₂ treatment, which augmented nuclear localization. Enhanced cytoplasmic SHP2 was found to negatively regulate the expression of the ERα-transcribed NPPC and NPR2 mRNAs, which are vital for oocyte meiotic arrest. The co-immunoprecipitation results revealed the presence of the SHP2/ERα complex in the germinal vesicle-stage cumulus-oocyte complexes, and this complex significantly decreased with the progression of meiotic maturation. The complex formation between ERα and SHP2 was also confirmed by using a series of computational modeling methods. To verify the correlation between SHP2 and NPPC/NPR2, SHP2 was knocked down via RNA interference, and NPPC and NPR2 mRNAs were analyzed in the control, E₂, and FSH-stimulated COV434 cells. Furthermore, phenyl hydrazonopyrazolone sulfonate 1, a site-directed inhibitor of active SHP2, showed no significant effect on the ERα-transcribed NPPC and NPR2 mRNAs. Taken together, these findings support a novel nuclear/cytoplasmic role of SHP2 in oocyte meiotic resumption and maturation.

Growth Factors, and Cytokines; Understanding the Role of Tyrosine Phosphatase SHP2 in Gametogenesis and Early Embryo Development

Growth factors and cytokines have vital roles in germ cell development, gamete maturation, and early embryo development. Cell surface receptors are present for growth factors and cytokines to integrate with and trigger protein signaling in the germ and embryo intracellular milieu. Src-homology-2-containing phosphotyrosine phosphatase (SHP2) is a ubiquitously expressed, multifunctional protein that plays a central role in the signaling pathways involved in growth factor receptors, cytokine receptors, integrins, and G protein-coupled receptors. Over recent decades, researchers have recapitulated the protein signaling networks that influence gamete progenitor specification as well as gamete differentiation and maturation. SHP2 plays an indispensable role in cellular growth, survival, proliferation, differentiation, and migration, as well as the basic events in gametogenesis and early embryo development. SHP2, a classic cytosolic protein and a key regulator of signal transduction, displays unconventional nuclear expression in the genital organs. Several observations provided shreds of evidence that this behavior is essential for fertility. The growth factor and cytokine-dependent roles of SHP2 and its nuclear/cytoplasmic presence during gamete maturation, early embryonic development and embryo implantation are fascinating and complex subjects. This review is intended to summarize the previous and recent knowledge about the SHP2 functions in gametogenesis and early embryo development.

Therapeutic potential of targeting SHP2 in human developmental disorders and cancers

Src homology 2 (SH2)-containing protein tyrosine phosphatase 2 (SHP2), encoded by PTPN11, regulates cell proliferation, differentiation, apoptosis and survival via releasing intramolecular autoinhibition and modulating various signaling pathways, such as mitogen-activated protein kinase (MAPK) pathway. Mutations and aberrant expression of SHP2 are implicated in human developmental disorders, leukemias and several solid tumors. As an oncoprotein in some cancers, SHP2 represents a rational target for inhibitors to interfere. Nevertheless, its tumor suppressive effect has also been uncovered, indicating the context-specificity. Even so, two types of SHP2 inhibitors including targeting catalytic pocket and allosteric sites have been developed associated with resolved cocrystal complexes. Herein, we describe its structure, biological function, deregulation in human diseases and summarize recent advance in development of SHP2 inhibitors, trying to give an insight into the therapeutic potential in future.

Tyrosine phosphatase SHP2 negatively regulates NLRP3 inflammasome activation via ANT1-dependent mitochondrial homeostasis

Aberrant activation of NLRP3 inflammasome has an important function in the pathogenesis of various inflammatory diseases. Although many components and mediators of inflammasome activation have been identified, how NLRP3 inflammasome is regulated to prevent excessive inflammation is unclear. Here we show NLRP3 inflammasome stimulators trigger Src homology-2 domain containing protein tyrosine phosphatase-2 (SHP2) translocation to the mitochondria, to interact with and dephosphorylate adenine nucleotide translocase 1 (ANT1), a central molecule controlling mitochondrial permeability transition. This mechanism prevents collapse of mitochondrial membrane potential and the subsequent release of mitochondrial DNA and reactive oxygen species, thus preventing hyperactivation of NLRP3 inflammasome. Ablation or inhibition of SHP2 in macrophages causes intensified NLRP3 activation, overproduction of proinflammatory cytokines IL-1β and IL-18, and increased sensitivity to peritonitis. Collectively, our data highlight that, by inhibiting ANT1 and mitochondrial dysfunction, SHP2 orchestrates an intrinsic regulatory loop to limit excessive NLRP3 inflammasome activation.

STAT3 activation in infection and infection-associated cancer

The Janus kinase/signal transducers and activators for transcription (JAK/STAT) pathway plays crucial roles in regulating apoptosis, proliferation, differentiation, and the inflammatory response. The JAK/STAT families are composed of four JAK family members and seven STAT family members. STAT3 plays a key role in inducing and maintaining a pro-carcinogenic inflammatory microenvironment. Recent evidence suggests that STAT3 regulates diverse biological functions in pathogenesis of diseases, such as infection and cancer. In the current review, we will summarize the research progress of STAT3 activation in infection and cancers. We highlight our recent study on the novel role of STAT3 in Salmonella infection-associated colon cancer. Infection with bacterial AvrA-expressing Salmonella activates the STAT3 pathway, which induces the β-catenin signals and enhances colonic tumorigenesis. STAT3 may be a promising target in developing prevention and treatment for infectious diseases and infection-associated cancers.

Nuclear Shp2 directs normal embryo implantation via facilitating the ERα tyrosine phosphorylation by the Src kinase

Estrogen and progesterone coupled with locally produced signaling molecules are essential for embryo implantation. However, the hierarchical landscape of the molecular pathways that governs this process remains largely unexplored. Here we show that the protein tyrosine phosphatase Shp2, a positive transducer of RTK signaling, is predominately localized in the nuclei in the periimplantation mouse uterus. Uterine-specific deletion of Shp2 exhibits reduced progesterone receptor (PR) expression and progesterone resistance, which derails normal uterine receptivity, leading to complete implantation failure in mice. Notably, the PR expression defects are attributed to the limited estrogen receptor α (ERα) activation in uterine stroma. Further analysis reveals that nuclear Shp2, rather than cytosolic Shp2, promotes the ERα transcription activity. This function is achieved by enhancing the Src kinase-mediated ERα tyrosine phosphorylation, which facilitates ERα binding to Pgr promoter in an ERK-independent manner in periimplantation uteri. Besides uncovering a regulatory mechanism, this study could be clinically relevant to dysfunctional ERα-caused endometrial disorders in women.

STAT5 in Cancer and Immunity

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

Role of protein tyrosine phosphatases in the modulation of insulin signaling and their implication in the pathogenesis of obesity-linked insulin resistance

Insulin resistance is a major disorder that links obesity to type 2 diabetes mellitus (T2D). It involves defects in the insulin actions owing to a reduced ability of insulin to trigger key signaling pathways in major metabolic tissues. The pathogenesis of insulin resistance involves several inhibitory molecules that interfere with the tyrosine phosphorylation of the insulin receptor and its downstream effectors. Among those, growing interest has been developed toward the protein tyrosine phosphatases (PTPs), a large family of enzymes that can inactivate crucial signaling effectors in the insulin signaling cascade by dephosphorylating their tyrosine residues. Herein we briefly review the role of several PTPs that have been shown to be implicated in the regulation of insulin action, and then focus on the Src homology 2 (SH2) domain-containing SHP1 and SHP2 enzymes, since recent reports have indicated major roles for these PTPs in the control of insulin action and glucose metabolism. Finally, the therapeutic potential of targeting PTPs for combating insulin resistance and alleviating T2D will be discussed.

Distinct roles of STAT3 and STAT5 in the pathogenesis and targeted therapy of breast cancer

The transcription factors STAT3 and STAT5 play important roles in the regulation of mammary gland function during pregnancy, lactation, and involution. Given that STAT3 and STAT5 regulate genes involved in proliferation and survival, it is not surprising that inappropriate activation of STAT3 and STAT5 occurs commonly in breast cancer. Although these proteins are structurally similar, they have divergent and opposing effects on gene expression and cellular phenotype. Notably, when STAT5 and STAT3 are activated simultaneously, STAT5 has a dominant effect, and leads to decreased proliferation and increased sensitivity to cell death. Similarly, in breast cancer, activation of both STAT5 and STAT3 is associated with longer patient survival than activation of STAT3 alone. Pharmacological inhibitors of STAT3 and STAT5 are being developed for cancer therapy, though understanding the activation state and functional interaction of STAT3 and STAT5 in a patient's tumor may be critical for the optimal use of this strategy.

Buffalo alpha S1-casein gene 5'-flanking region and its interspecies comparison

The expression of milk protein genes is tightly regulated in a spatio-temporal manner through the combinatorial interaction of lactogenic hormones and a set of transcription factors mediating developmental and tissue-specific gene expression. The recruitment of a unique set of transcription factors is determined by the cis-regulatory motifs present in the gene promoter region. Here, we report the isolation, sequencing, structural analysis and interspecies comparison of the 5'cis-regulatory region of the buffalo alpha S1 (αS1)-casein gene. The proximal promoter region of the buffalo αS1-casein gene harbored the insertion of a 72-bp fragment of long interspersed nuclear element of the L1_BT retrotransposon family. Among the core and vertebrate-specific promoter elements, the motifs for the binding of Brn POU domain factors (BRNF), Lim homeodomain factors (LHXF), NK6 homeobox transcription factors (NKX6), nuclear factor kappa B/c-rel (NFKB), AT-rich interactive domain factor (ARID), Brn POU domain factor 5 (BRN5), pancreatic and intestinal homeodomain transcription factor (PDX1), Distal-less homeodomain transcription factors (DLXF), T-cell factor/lymphoid enhancer-binding factor-1 (LEFF) and GHF-1 pituitary-specific POU domain transcription factor (PIT1) were over-represented in the αS1-casein gene regulatory region (Z score >4.0). The Multiple EM for Motif elicitation predicted three motifs which consisted of the sequences known to bind mammary gland factor/signal transducer and activator of transcription 5 (MGF/STAT5), estrogen receptor-related alpha (ERα), steroidogenic factor 1 (SF1) and glucocorticoid receptor (GR), indicating their potential role in the mammary gland-specific gene expression. The interspecies comparison of the proximal promoter region revealed conserved sequences for TATA boxes and MGF/STAT5 in all species, whereas activator protein 1 (AP1), pregnancy-specific mammary nuclear factor (PMF), CCAAT/enhancer binding protein (C/EBP), double-stranded and single-stranded DNA-binding protein 1 (DS1 and SS), ying and yang factor 1 (YY1), and GR half-sites were among ruminants. The functional significance of the L1_BT retrotransposon insertion on the buffalo αS1-casein gene expression needs to be experimentally validated.

Activating mutations in protein tyrosine phosphatase Ptpn11 (Shp2) enhance reactive oxygen species production that contributes to myeloproliferative disorder

Gain of function (GOF) mutations in protein tyrosine phosphatase Ptpn11 have been identified in childhood leukemias, and these mutations are sufficient to drive the development of myeloproliferative disorder and malignant leukemias in mice. However, the molecular mechanisms by which Ptpn11 mutations induce these malignancies are not completely understood. Here we report that Ptpn11 GOF mutations cause cytokine hypersensitivity in hematopoietic cells partly by enhancing the production of reactive oxygen species (ROS). GOF mutations D61G or E76K in Ptpn11 increased ROS levels in myeloid progenitors but not in hematopoietic stem cells. Increased ROS enhanced cellular responses to cytokines by promoting cytokine signaling. Treatment with an antioxidant partially corrected cytokine hypersensitivity in Ptpn11 mutant progenitors. Further analyses demonstrated that Ptpn11 mutations increased mitochondrial aerobic metabolism by interacting with a novel substrate in the mitochondria. This study provides new insights into the pathogenic effects of GOF mutations of Ptpn11 and implies that antioxidants may have a therapeutic benefit for the leukemic patients with these mutations.

Protein tyrosine phosphatase SHP2/PTPN11 mistargeting as a consequence of SH2-domain point mutations associated with Noonan Syndrome and leukemia

SHP2/PTPN11 is a key regulator of cytokine, growth factor and integrin signaling. SHP2 influences cell survival, proliferation and differentiation by regulating major signaling pathways. Mutations in PTPN11 cause severe diseases like Noonan, LEOPARD syndrome or leukemia. Whereas several of these mutations result in altered enzymatic activity due to impaired auto-inhibition, not all disease patterns can be explained by this mechanism. In this study we analyzed altered binding properties of disease-related SHP2-mutants bearing point mutations within the SH2-domain (T42A, E139D, and R138Q). Mutants were chosen according to SPR assays, which revealed different binding properties of mutated SH2 towards phosphorylated receptor peptides. To analyze global changes in mutant binding properties we applied quantitative mass spectrometry (SILAC). Using an in vitro approach we identified overall more than 1000 protein candidates, which specifically bind to the SH2-domain of SHP2. We discovered that mutations in the SH2-domain selectively affected protein enrichment by altering the binding capacity of the SH2-domain. Mutation-dependent, enhanced or reduced exposure of SHP2 to its binding partners could have an impact on the dynamics of signaling networks. Thus, disease-associated mutants of SHP2 should not only be discussed in the context of deregulated auto-inhibition but also with respect to deregulated protein targeting of the SHP2 mutants.

BIOLOGICAL SIGNIFICANCE

Using quantitative mass spectrometry based proteomics we provided evidence that disease related mutations in SHP2 domains of SHP2 are able to influence SHP2 recruitment to its targets in mutation dependent manner. We discovered that mutations in the SH2-domain selectively affected protein enrichment ratios suggesting altered binding properties of the SH2-domain. We demonstrated that mutations within SHP2, which had been attributed to affect the enzymatic activity (i.e. affect the open/close status of SHP2), also differ in respect to binding properties. Our study indicates that SHP2 mutations need to be discussed not only in terms of deregulated auto-inhibition but also with respect to deregulated protein targeting properties of the SHP2 mutants. Discovery of the new binding partners for disease-related SHP2 mutants might provide a fruitful foundation for developing strategies targeting Noonan-associated leukemia.

The tyrosine phosphatase SHP2 regulates Sertoli cell junction complexes

The blood-testis barrier (BTB) is a large junctional complex composed of tight junctions, adherens junctions, and gap junctions between adjacent Sertoli cells in the seminiferous tubules of the testis. Maintenance of the BTB as well as the controlled disruption and reformation of the barrier is essential for spermatogenesis and male fertility. Tyrosine phosphorylation of BTB proteins is known to regulate the integrity of adherens and tight junctions found at the BTB. SHP2 is a nonreceptor protein tyrosine phosphatase (PTP) and a key regulator of growth factor-mediated tyrosine kinase signaling pathways. We found that SHP2 is localized to Sertoli-Sertoli cell junctions in rat testis. The overexpression of a constitutive active SHP2 mutant, SHP2 Q79R, up-regulated the BTB disruptor ERK1/2 via Src kinase in primary rat Sertoli cells in culture. Furthermore, focal adhesion kinase (FAK), which also supports BTB integrity, was found to interact with SHP2 and constitutive activation of SHP2 decreased FAK tyrosine phosphorylation. Expression of the SHP2 Q79R mutant in primary cultured Sertoli cells also resulted in the loss of tight junction and adherens junction integrity that corresponded with the disruption of the actin cytoskeleton and mislocalization of adherens junction and tight junction proteins N-cadherin, β-catenin, and ZO-1 away from the plasma membrane. These results suggest that SHP2 is a key regulator of BTB integrity and Sertoli cell support of spermatogenesis and fertility.

The Dual Role of TGFβ in Human Cancer: From Tumor Suppression to Cancer Metastasis

The transforming growth factor-beta (TGFβ) superfamily encompasses widespread and evolutionarily conserved polypeptide growth factors that regulate and orchestrate growth and differentiation in all cell types and tissues. While they regulate asymmetric cell division and cell fate determination during early development and embryogenesis, TGFβ family members play a major regulatory role in hormonal and immune responses, cell growth, cell death and cell immortalization, bone formation, tissue remodeling and repair, and erythropoiesis throughout adult life. The biological and physiological functions of TGFβ, the founding member of this family, and its receptors are of central importance to human diseases, particularly cancer. By regulating cell growth, death, and immortalization, TGFβ signaling pathways exert tumor suppressor effects in normal cells and early carcinomas. Thus, it is not surprising that a high number of human tumors arise due to mutations or deletions in the genes coding for the various TGFβ signaling components. As tumors develop and progress, these protective and cytostatic effects of TGFβ are often lost. TGFβ signaling then switches to promote cancer progression, invasion, and tumor metastasis. The molecular mechanisms underlying this dual role of TGFβ in human cancer will be discussed in depth in this paper, and it will highlight the challenge and importance of developing novel therapeutic strategies specifically aimed at blocking the prometastatic arm of the TGFβ signaling pathway without affecting its tumor suppressive effects.

The protein tyrosine phosphatase, Shp2, positively contributes to FLT3-ITD-induced hematopoietic progenitor hyperproliferation and malignant disease in vivo

Internal tandem duplications (ITDs) in the fms-like tyrosine kinase receptor (FLT3-ITDs) confer a poor prognosis in acute myeloid leukemia (AML). We hypothesized that increased recruitment of the protein tyrosine phosphatase, Shp2, to FLT3-ITDs contributes to FLT3 ligand (FL)-independent hyperproliferation and STAT5 activation. Co-immunoprecipitation demonstrated constitutive association of Shp2 with the FLT3-ITD, N51-FLT3, as well as with STAT5. Knockdown of Shp2 in Baf3/N51-FLT3 cells significantly reduced proliferation while having little effect on WT-FLT3-expressing cells. Consistently, mutation of N51-FLT3 tyrosine 599 to phenylalanine or genetic disruption of Shp2 in N51-FLT3-expressing bone marrow low-density mononuclear cells reduced proliferation and STAT5 activation. In transplants, genetic disruption of Shp2 in vivo yielded increased latency to and reduced severity of FLT3-ITD-induced malignancy. Mechanistically, Shp2 co-localizes with nuclear phospho-STAT5, is present at functional interferon-γ activation sites (GAS) within the BCL2L1 promoter, and positively activates the human BCL2L1 promoter, suggesting that Shp2 works with STAT5 to promote pro-leukemogenic gene expression. Further, using a small molecule Shp2 inhibitor, the proliferation of N51-FLT3-expressing bone marrow progenitors and primary AML samples was reduced in a dose-dependent manner. These findings demonstrate that Shp2 positively contributes to FLT3-ITD-induced leukemia and suggest that Shp2 inhibition may provide a novel therapeutic approach to AML.

Protein tyrosine phosphatase Shp2 (Ptpn11) plays an important role in maintenance of chromosome stability

Both activating and inactivating mutations in protein tyrosine phosphatase Ptpn11 (encoding Shp2) are associated with tumorigenesis. However, the underlying mechanisms remain unclear. Here, we show that Shp2 plays an important role in mitosis, dysregulation of which results in chromosome instability and cancer predisposition. Depletion of Shp2 compromised the mitotic checkpoint. Shp2-depleted cells exhibited a delay in mitotic entry and an earlier mitotic exit. Moreover, Shp2 deficiency caused defective kinetochore-microtubule attachment, chromosome misalignment, chromosomal congression defects, lagging chromosomes, and chromosome missegregation. Reintroduction of wild-type Shp2, but not a catalytically deficient mutant, restored the checkpoint function and chromosome alignment at metaphase in Shp2-deficient cells, establishing a requirement for the catalytic activity of Shp2 during mitosis. Further analyses revealed that Shp2 was required for the optimal activation of the mitotic kinases PLK1 and Aurora B and thereby the proper kinetochore localization and phosphorylation of BubR1, a core mitotic checkpoint protein that is also critical for chromosome alignment. Together, our findings show a previously unrecognized role for Shp2 in the maintenance of chromosome stability and suggest a new mechanism by which dysregulation of Shp2 signaling contributes to malignancy development.

Protein tyrosine phosphatase SHP2 mediates chronic insulin-induced endothelial inflammation

OBJECTIVE

Insulin promotes adhesion of leukocytes to the endothelium through increased expression of surface adhesion molecules. We determined whether src-homology domain-2-containing protein tyrosine phosphatase 2 (SHP2), a downstream effecter of insulin signaling, is involved in insulin-induced endothelial inflammation.

METHODS AND RESULTS

In human umbilical vein-derived endothelial cells, treatment with insulin (100 nmol/L) increased Tyr(542) phosphorylation, activity, and subsequently expression of SHP2. Increase in SHP2 accompanied a parallel decrease in the availability of the anti-inflammatory molecule, NO. This consequently enhanced the expression of cell adhesion molecules. Decrease in NO index was caused by endothelial NO synthase (eNOS) uncoupling and increased arginase activity. Among the 2 isoforms, insulin treatment induced the expression of arginase II. Inactivation of endogenous SHP2 via NSC87877 [8-hydroxy-7-(6-sulfonapthalen-2-yl)-diazenyl-quinoline-5-sulfonic acid] and its knockdown by small interfering RNA decreased arginase activity by blocking arginase II expression; however, it failed to restore eNOS coupling. Inactivation of SHP2 also abrogated insulin-mediated leukocyte adhesion by blocking the expression of adhesion molecules. Finally, downregulation of endogenous arginase II blocked insulin-mediated endothelial inflammation.

CONCLUSIONS

SHP2 mediates chronic insulin-induced endothelial inflammation by limiting the production of NO in an eNOS-independent and arginase-II-dependent manner.

Protein tyrosine phosphatase Meg2 dephosphorylates signal transducer and activator of transcription 3 and suppresses tumor growth in breast cancer

Introduction

Signal transducer and activator of transcription 3 (STAT3) is over-activated or phosphorylated in breast cancers. The hyper-phosphorylation of STAT3 was attributed to either up-regulated phosphorylation by several tyrosine-kinases or down-regulated activity of phosphatases. Although several factors have been identified to phosphorylate STAT3, it remains unclear how STAT3 is dephosphorylated by PTPMeg2. The aim of this study was to determine the role of PTPMeg2 as a phosphatase in regulation of the activity of STAT3 in breast cancers.

Methods

Immunoprecipitation assays were used to study the interaction of STAT3 with PTPMeg2. A series of biochemistry experiments were performed to evaluate the role of PTPMeg2 in the dephosphorylation of STAT3. Two breast cancer cell lines MCF7 (PTPMeg2 was depleted as it was endogenously high) and MDA-MB-231 (PTPMeg2 was overexpressed as it was endogenously low) were used to compare the level of phosphorylated STAT3 and the tumor growth ability in vitro and in vivo. Samples from breast carcinoma (n = 73) were subjected to a pair-wise Pearson correlation analysis for the correlation of levels of PTPMeg2 and phosphorylated STAT3.

Results

PTPMeg2 directly interacts with STAT3 and mediates its dephosphorylation in the cytoplasm. Over-expression of PTPMeg2 decreased tyrosine phosphorylation of STAT3 while depletion of PTPMeg2 increased its phosphorylation. The decreased tyrosine phosphorylation of STAT3 is coupled with suppression of STAT3 transcriptional activity and reduced tumor growth in vitro and in vivo. Levels of PTPMeg2 and phosphorylated STAT3 were inversely correlated in breast cancer tissues (P = 0.004).

Conclusions

PTPMeg2 is an important phosphatase for the dephosphorylation of STAT3 and plays a critical role in breast cancer development.

Signal transducer and activator of transcription-5 mediates neuronal apoptosis induced by inhibition of Rac GTPase activity

In several neuronal cell types, the small GTPase Rac is essential for survival. We have shown previously that the Rho family GTPase inhibitor Clostridium difficile toxin B (ToxB) induces apoptosis in primary rat cerebellar granule neurons (CGNs) principally via inhibition of Rac GTPase function. In the present study, incubation with ToxB activated a proapoptotic Janus kinase (JAK)/signal transducer and activator of transcription (STAT) pathway, and a pan-JAK inhibitor protected CGNs from Rac inhibition. STAT1 expression was induced by ToxB; however, CGNs from STAT1 knock-out mice succumbed to ToxB-induced apoptosis as readily as wild-type CGNs. STAT3 displayed enhanced tyrosine phosphorylation following treatment with ToxB, and a reputed inhibitor of STAT3, cucurbitacin (JSI-124), reduced CGN apoptosis. Unexpectedly, JSI-124 failed to block STAT3 phosphorylation, and CGNs were not protected from ToxB by other known STAT3 inhibitors. In contrast, STAT5A tyrosine phosphorylation induced by ToxB was suppressed by JSI-124. In addition, roscovitine similarly inhibited STAT5A phosphorylation and protected CGNs from ToxB-induced apoptosis. Consistent with these results, adenoviral infection with a dominant negative STAT5 mutant, but not wild-type STAT5, significantly decreased ToxB-induced apoptosis of CGNs. Finally, chromatin immunoprecipitation with a STAT5 antibody revealed increased STAT5 binding to the promoter region of prosurvival Bcl-xL. STAT5 was recruited to the Bcl-xL promoter region in a ToxB-dependent manner, and this DNA binding preceded Bcl-xL down-regulation, suggesting transcriptional repression. These data indicate that a novel JAK/STAT5 proapoptotic pathway significantly contributes to neuronal apoptosis induced by the inhibition of Rac GTPase.

Prolactin-stimulated activation of ERK1/2 mitogen-activated protein kinases is controlled by PI3-kinase/Rac/PAK signaling pathway in breast cancer cells

There is strong evidence that deregulation of prolactin (PRL) signaling contributes to pathogenesis and chemoresistance of breast cancer. Therefore, understanding cross-talk between distinct signal transduction pathways triggered by activation of the prolactin receptor (PRL-R), is essential for elucidating the pathogenesis of metastatic breast cancer. In this study, we applied a sequential inhibitory analysis of various signaling intermediates to examine the hierarchy of protein interactions within the PRL signaling network and to evaluate the relative contributions of multiple signaling branches downstream of PRL-R to the activation of the extracellular signal-regulated kinases ERK1 and ERK2 in T47D and MCF-7 human breast cancer cells. Quantitative measurements of the phosphorylation/activation patterns of proteins showed that PRL simultaneously activated Src family kinases (SFKs) and the JAK/STAT, phosphoinositide-3 (PI3)-kinase/Akt and MAPK signaling pathways. The specific blockade or siRNA-mediated suppression of SFK/FAK, JAK2/STAT5, PI3-kinase/PDK1/Akt, Rac/PAK or Ras regulatory circuits revealed that (1) the PI3-kinase/Akt pathway is required for activation of the MAPK/ERK signaling cascade upon PRL stimulation; (2) PI3-kinase-mediated activation of the c-Raf-MEK1/2-ERK1/2 cascade occurs independent of signaling dowstream of STATs, Akt and PKC, but requires JAK2, SFKs and FAK activities; (3) activated PRL-R mainly utilizes the PI3-kinase-dependent Rac/PAK pathway rather than the canonical Shc/Grb2/SOS/Ras route to initiate and sustain ERK1/2 signaling. By interconnecting diverse signaling pathways PLR may enhance proliferation, survival, migration and invasiveness of breast cancer cells.

Protein Tyrosine Phosphatase SHP-2 (PTPN11) in Hematopoiesis and Leukemogenesis

SHP-2 (PTPN11), a ubiquitously expressed protein tyrosine phosphatase, is critical for hematopoietic cell development and function owing to its essential role in growth factor/cytokine signaling. More importantly, germline and somatic mutations in this phosphatase are associated with Noonan syndrome, Leopard syndrome, and childhood hematologic malignancies. The molecular mechanisms by which SHP-2 mutations induce these diseases are not fully understood, as the biochemical bases of SHP-2 functions still remain elusive. Further understanding SHP-2 signaling activities and identification of its interacting proteins/substrates will shed light on the pathogenesis of PTPN11-associated hematologic malignancies, which, in turn, may lead to novel therapeutics for these diseases.

Synergy in ERK activation by cytokine receptors and tyrosine kinase growth factor receptors

Epidermal growth factor (EGF) and platelet-derived growth factor (PDGF) signal through EGF and PDGF receptors, which are important receptor tyrosine kinases (RTKs). Growth hormone (GH) and prolactin (PRL) are four helical bundle peptide hormones that signal via GHR and PRLR, members of the cytokine receptor superfamily. In this study, we examine crosstalk between signaling pathways emanating from these disparate receptor groups (RTKs and cytokine receptors). We find that GH and EGF specifically synergize for activation of ERK in murine preadipocytes. The locus of this synergy resides at the level of MEK activation, but not above this level (i.e., not at the level of EGFR, SHC, or Raf activation). Furthermore, dephosphorylation of the scaffold protein, KSR, at a critical serine residue is also synergistically promoted by GH and EGF, suggesting that GH sensitizes these cells to EGF-induced ERK activation by augmenting the actions of KSR in facilitating MEK-ERK activation. Similarly specific synergy in ERK activation is also detected in human T47D breast cancer cells by cotreatment with PRL and PDGF. This synergy also resides at the level of MEK activation. Consistent with this synergy, PRL and PDGF also synergized for c-fos-dependent transactivation of a luciferase reporter gene in T47D cells, indicating that events downstream of ERK activation reflect this signaling synergy. Important conceptual and physiological implications of these findings are discussed.

PTP1B suppresses prolactin activation of Stat5 in breast cancer cells

Basal levels of nuclear localized, tyrosine phosphorylated Stat5 are present in healthy human breast epithelia. In contrast, Stat5 phosphorylation is frequently lost during breast cancer progression, a finding that correlates with loss of histological differentiation and poor patient prognosis. Identifying the mechanisms underlying loss of Stat5 phosphorylation could provide novel targets for breast cancer therapy. Pervanadate, a general tyrosine phosphatase inhibitor, revealed marked phosphatase regulation of Stat5 activity in breast cancer cells. Lentiviral-mediated shRNA allowed specific examination of the regulatory role of five tyrosine phosphatases (PTP1B, TC-PTP, SHP1, SHP2, and VHR), previously implicated in Stat5 regulation in various systems. Enhanced and sustained prolactin-induced Stat5 tyrosine phosphorylation was observed in T47D and MCF7 breast cancer cells selectively in response to PTP1B depletion. Conversely, PTP1B overexpression suppressed prolactin-induced Stat5 tyrosine phosphorylation. Furthermore, PTP1B knockdown increased Stat5 reporter gene activity. Mechanistically, PTP1B suppression of Stat5 phosphorylation was mediated, at least in part, through inhibitory dephosphorylation of the Stat5 tyrosine kinase, Jak2. PTP1B knockdown enhanced sensitivity of T47D cells to prolactin phosphorylation of Stat5 by reducing the EC(50) from 7.2 nmol/L to 2.5 nmol/L. Immunohistochemical analyses of two independent clinical breast cancer materials revealed significant negative correlations between levels of active Stat5 and PTP1B, but not TC-PTP. Collectively, our data implicate PTP1B as an important negative regulator of Stat5 phosphorylation in invasive breast cancer.

Well-known signaling proteins exert new functions in the nucleus and mitochondria

One distinguishing feature of eukaryotic cells is their compartmentalization into organelles, which all have a unique structural and functional identity. Some proteins are exclusively localized in a single organelle, whereas others are found in more than one. A few proteins, whose function was thought to be completely understood, were only recently found to be present in the mitochondria. Although these proteins come from diverse functional classes, their common new denominator is the regulation of respiratory chain activity. Therefore, this review focuses on new functions of the Signal Transducer and Activator of Transcription 3, originally described as a transcription factor, the most prominent Src kinase family members, Src, Fyn, and Yes, which were so far known as plasma membrane-associated molecular effectors of a variety of extracellular stimuli, the tyrosine phosphatase Shp-2 previously characterized as a modulator of cytosolic signal transduction involved in cell growth, development, inflammation, and chemotaxis, and Telomerase Reverse Transcriptase, the key enzyme preventing telomere erosion in the nucleus. Their unexpected localization in other organelles and regulation of mitochondrial and/or nuclear functions by them adds a new layer of regulatory complexity. This extends the flexibility to cope with changing environmental demands using a limited number of genes and proteins.

The tyrosine phosphatase Shp2 in development and cancer

Deregulation of signaling pathways, through mutation or other molecular changes, can ultimately result in disease. The tyrosine phosphatase Shp2 has emerged as a major regulator of receptor tyrosine kinase (RTK) and cytokine receptor signaling. In the last decade, germline mutations in the human PTPN11 gene, encoding Shp2, were linked to Noonan (NS) and LEOPARD syndromes, two multisymptomatic developmental disorders that are characterized by short stature, craniofacial defects, cardiac defects, and mental retardation. Somatic Shp2 mutations are also associated with several types of human malignancies, such as the most common juvenile leukemia, juvenile myelomonocytic leukemia (JMML). Whereas NS and JMML are caused by gain-of-function (GOF) mutations of Shp2, loss-of-function (LOF) mutations are thought to be associated with LEOPARD syndrome. Animal models that carry conditional LOF and GOF mutations have allowed a better understanding of the mechanism of Shp2 function in disease, and shed light on the role of Shp2 in signaling pathways that control decisive events during embryonic development or during cellular transformation/tumorigenesis.

Nuclear redox signaling

Reactive oxygen species have been described to modulate proteins within the cell, a process called redox regulation. However, the importance of compartment-specific redox regulation has been neglected for a long time. In the early 1980s and 1990s, many in vitro studies introduced the possibility that nuclear redox signaling exists. However, the functional relevance for that has been greatly disregarded. Recently, it has become evident that nuclear redox signaling is indeed one important signaling mechanism regulating a variety of cellular functions. Transcription factors, and even kinases and phosphatases, have been described to be redox regulated in the nucleus. This review describes several of these proteins in closer detail and explains their functions resulting from nuclear localization and redox regulation. Moreover, the redox state of the nucleus and several important nuclear redox regulators [Thioredoxin-1 (Trx-1), Glutaredoxins (Grxs), Peroxiredoxins (Prxs), and APEX nuclease (multifunctional DNA-repair enzyme) 1 (APEX1)] are introduced more precisely, and their necessity for regulation of transcription factors is emphasized.

GH modulates hepatic epidermal growth factor signaling in the mouse

Epidermal growth factor (EGF) is a key regulator of cell survival and proliferation involved in the pathogenesis and progression of different types of cancer. The EGF receptor (EGFR) is activated by binding of the specific ligand but also by transactivation triggered by different growth factors including GH. Chronically, elevated GH levels have been associated with the progression of hepatocellular carcinoma. Considering EGF and GH involvement in cell proliferation and their signaling crosstalk, the objective of the present study was to analyze GH modulatory effects on EGF signaling in liver. For this purpose, GH receptor-knockout (GHR-KO) and GH-overexpressing transgenic mice were used. EGFR content was significantly decreased in GHR-KO mice. Consequently, EGF-induced phosphorylation of EGFR, AKT, ERK1/2, STAT3, and STAT5 was significantly decreased in these mice. In contrast, EGFR content as well as its basal tyrosine phosphorylation was increased in transgenic mice overexpressing GH. However, EGF stimulation caused similar levels of EGFR, AKT, and ERK1/2 phosphorylation in normal and transgenic mice, while EGF induction of STAT3 and STAT5 phosphorylation was inhibited in the transgenic mice. Desensitization of the STATs was related to decreased association of these proteins to the EGFR and increased association between STAT5 and the tyrosine phosphatase SH2-containing phosphatase-2. While GHR knockout is associated with diminished expression of the EGFR and a concomitant decrease in EGF signaling, GH overexpression results in EGFR overexpression with different effects depending on the signaling pathway analyzed: AKT and ERK1/2 pathways are induced by EGF, while STAT3 and STAT5 activation is heterologously desensitized.

Transcription factor Stat5a/b as a therapeutic target protein for prostate cancer

Prostate cancer is the most common non-cutaneous cancer in Western males. The majority of prostate cancer fatalities are caused by development of castration-resistant growth and metastatic spread of the primary tumor. The average duration of the response of primary prostate cancer to hormonal ablation is less than 3 years, and 75% of prostate cancers in the United States progress to castration-resistant disease. The existing pharmacological therapies for metastatic and/or castration-resistant prostate cancer do not provide significant survival benefit. This review summarizes the importance of transcription factor Stat5 signaling in the pathogenesis of prostate cancer and discusses the molecular basis of Stat5a/b inhibition as a therapeutic strategy for prostate cancer.

Intramolecular disulfide bonds of the prolactin receptor short form are required for its inhibitory action on the function of the long form of the receptor

The short form (S1b) of the prolactin receptor (PRLR) silences prolactin-induced activation of gene transcription by the PRLR long form (LF). The functional and structural contributions of two intramolecular disulfide (S-S) bonds within the extracellular subdomain 1 (D1) of S1b to its inhibitory function on the LF were investigated. Mutagenesis of the paired cysteines eliminated the inhibitory action of S1b. The expression of the mutated S1b (S1bx) on the cell surface was not affected, indicating native-like folding of the receptor. The constitutive JAK2 phosphorylation observed in S1b was not present in cells expressing S1bx, and JAK2 association was disrupted. BRET(50) (BRET(50) represents the relative affinity as acceptor/donor ratio required to reach half-maximal BRET [bioluminescence resonance energy transfer] values) showed decreased LF/S1bx heterodimeric-association and increased affinity in S1bx homodimerization, thus favoring LF homodimerization and prolactin-induced signaling. Computer modeling based on the PRLR crystal structure showed that minor changes in the tertiary structure of D1 upon S-S bond disruption propagated to the quaternary structure of the homodimer, affecting the dimerization interface. These changes explain the higher homodimerization affinity of S1bx and provide a structural basis for its lack of inhibitory function. The PRLR conformation as stabilized by S-S bonds is required for the inhibitory action of S1b on prolactin-induced LF-mediated function and JAK2 association.

SHD1 is a novel cytokine-inducible, negative feedback regulator of STAT5-dependent transcription

STAT5 is a critical mediator of a variety of cytokine signaling whose transcriptional activity is regulated by associating with various proteins. During a search for STAT5-interacting proteins, we identified SHD1, a mammalian homologue of yeast gene Sac3, as a potential interacter. SHD1 was localized in the nucleus, and induced by cytokines that activate STAT5, such as erythropoietin, interleukin-2 (IL-2), or IL-3. SHD1 interacted specifically with STAT5A and STAT5B, and interestingly, it specifically repressed STAT5-dependent transcription in vitro without affecting the stability or phosphorylation of STAT5 protein. Gene disruption study revealed that T, B, or bone marrow cells from mice lacking SHD1 were hyperresponsive to T-cell-receptor engagement, or stimulation with various STAT5-activating cytokines. These results suggest that SHD1 is a novel cytokine-inducible negative feedback regulator of STAT5.

Nuclear protein tyrosine phosphatase Shp-2 is one important negative regulator of nuclear export of telomerase reverse transcriptase

Aging is one major risk factor for numerous diseases. The enzyme telomerase reverse transcriptase (TERT) plays an important role for aging and apoptosis. Previously, we demonstrated that inhibition of oxidative stress-induced Src kinase family-dependent nuclear export of TERT results in delayed replicative senescence and reduced apoptosis sensitivity. Therefore, the aim of this study was to investigate mechanisms inhibiting nuclear export of TERT. First, we demonstrated that H2O2-induced nuclear export of TERT was abolished in Src, Fyn, and Yes-deficient embryonic fibroblasts. Next, we wanted to identify one potential negative regulator of this export process. One candidate is the protein tyrosine phosphatase Shp-2 (Shp-2), which can counteract activities of the Src kinase family. Indeed, Shp-2 was evenly distributed between the nucleus and cytosol. Nuclear Shp-2 associates with TERT in endothelial cells and dissociates from TERT prior to its nuclear export. Overexpression of Shp-2 wt inhibited H2O2-induced export of TERT. Overexpression of the catalytically inactive, dominant negative Shp-2 mutant (Shp-2(C459S)) reduced endogenous as well as overexpressed nuclear TERT protein and telomerase activity, whereas it had no influence on TERT(Y707F). Binding of TERT(Y707F) to Shp-2 is reduced compared with TERTwt. Ablation of Shp-2 expression led only to an increased tyrosine phosphorylation of TERTwt, but not of TERT(Y707F). Moreover, reduced Shp-2 expression decreased nuclear telomerase activity, whereas nuclear telomerase activity was increased in Shp-2-overexpressing endothelial cells. In conclusion, Shp-2 retains TERT in the nucleus by regulating tyrosine 707 phosphorylation.

Cloning and characterization of 5'-untranslated region of porcine beta casein gene (CSN2)

beta-Casein (CSN2) is a major milk protein in most mammals. The CSN2 gene is generally induced by lactogenic hormones bound to its promoter. The expression of this gene can be enhanced by signal transducers and activators of transcription (STAT) and glucocorticoid receptor (GR). Here, we analyzed the promoter and intron 1 regions of the porcine CSN2 gene. The porcine CSN2 promoter and intron 1 regions (-3098bp to +2446bp) were cloned into the pGL3-Basic vector containing the luciferase reporter gene (pCSN2-PEI). Lactogenic signals induced the transcription of porcine CSN2. By using AG490, a Janus kinase (JAK) inhibitor, we demonstrated that STAT5 positively regulates the transcription of porcine CSN2. Further, seven STAT mutants were generated by site-directed mutagenesis. By performing electrophoretic mobility shift assays (EMSAs), we located a critical element for pCSN2-PEI transcription bound to STAT5 in the -102bp to -84bp region. The construct containing only the promoter region (pCSN2-P), however, did not exert any promotive effects on transcription in two cell types-a mouse mammary epithelial cell line (HC11) and porcine mammary gland epithelial cells (PMECs). Thus, the construct containing intron 1 of porcine CSN2 exerts an elevating effect on transcription. We suggest that the transcription of porcine CSN2 is regulated by lactogenic signals via the STAT5 site (-102bp to -84bp) and intron 1.

Image-based evaluation of the molecular events underlying HC11 mammary epithelial cell differentiation

We have developed an image-based technique for signal pathway analysis, target validation, and compound screening related to mammary epithelial cell differentiation. This technique used the advantages of optical imaging and the HC11-Lux model system. The HC11-Lux cell line is a subclone of HC11 mammary epithelial cells transfected stably with a luciferase construct of the beta-casein gene promoter (p-344/-1betac-Lux). The promoter activity was imaged optically in real time following lactogenic induction. The imaging signal intensity was closely correlated with that measured using a luminometer following protein extraction (R=0.99, P<0.0001) and consistent with the messenger RNA (mRNA) level of the endogenous beta -casein gene. Using this technique, we examined the roles of JAK2/Stat5A, Raf-1/MEK/MAKP, and PI3K/Akt signal pathways with respect to differentiation. The imaging studies showed that treatment of the cells with epidermal growth factor (EGF), AG490 (JAK2-specific inhibitor), and LY294002 (PI3K-specific inhibitor) blocked lactogenic differentiation in a dose-dependent manner. PD98059 (MEK-specific inhibitor) could reverse EGF-mediated differentiation arrest. These results indicate that these pathways are essential in cell differentiation. This simple, sensitive, and reproducible technique permits visualization and real-time evaluation of the molecular events related to milk protein production. It can be adopted for high-throughput screening of small molecules for their effects on mammary epithelial cell growth, differentiation, and carcinogenesis.

Signal transducer and activator of transcription 5A/B in prostate and breast cancers

Protein kinase signaling pathways, such as Janus kinase 2-Signal transducer and activator of transcription 5A/B (JAK2-STAT5A/B), are of significant interest in the search for new therapeutic strategies in both breast and prostate cancers. In prostate cancer, the components of the JAK2-STAT5A/B signaling pathway provide molecular targets for small-molecule inhibition of survival and growth signals of the cells. At the same time, new evidence suggests that the STAT5A/B signaling pathway is involved in the transition of organ-confined prostate cancer to hormone-refractory disease. This implies that the active JAK2-STAT5A/B signaling pathway potentially provides the means for pharmacological intervention of clinical prostate cancer progression. In addition, active STAT5A/B may serve as a prognostic marker for identification of those primary prostate cancers that are likely to progress to aggressive disease. In breast cancer, the role of STAT5A/B is more complex. STAT5A/B may have a dual role in the regulation of malignant mammary epithelium. Data accumulated from mouse models of breast cancer suggest that in early stages of breast cancer STAT5A/B may promote malignant transformation and enhance growth of the tumor. This is in contrast to established breast cancer, where STAT5A/B may mediate the critical cues for maintaining the differentiation of mammary epithelium. In addition, present data suggest that activation of STAT5A/B in breast cancer predicts favorable clinical outcome. The dual nature of STAT5A/B action in breast cancer makes the therapeutic use of STAT5 A/B more complex.

Complex systems biology approach to understanding coordination of JAK-STAT signaling

In this work, we search for coordination as an organizing principle in a complex signaling system using a multilevel hierarchical paradigm. The objective is to explain the underlying mechanism of Interferon (IFN(gamma)) induced JAK-STAT (specifically JAK1/JAK2-STAT1) pathway behavior. Starting with a mathematical model of the pathway from the literature, we modularize the system using biological knowledge via principles of biochemical cohesion, biological significance, and functionality. The modularized system is then used as a basis for in silico inhibition, knockdown/deletion and perturbation experiments to discover a coordination mechanism. Our analysis shows that a module representing the SOCS1 complex can be identified as the coordinator. Analysis of the coordinator can then be used for the selection of biological experiments for the discovery of 'soft' molecular drug targets, that could lead to the development of improved therapeutics. The coordinator identified is also being investigated to determine its relationship to pathological conditions.

Regulation of Signal Transducer and Activator of Transcription Signaling by the Tyrosine Phosphatase PTP-BL

Signal Transducer and Activator of Transcription (STAT) proteins are a family of latent cytoplasmic transcription factors that are activated by tyrosine phosphorylation after cytokine stimulation. One mechanism by which STAT signaling is regulated is by dephosphorylation through the action of protein tyrosine phosphatases (PTP). We have identified PTP-Basophil like (PTP-BL) as a STAT PTP. PTP-BL dephosphorylates STAT proteins in vitro and in vivo, resulting in attenuation of STAT-mediated gene activation. In CD4(+) T cells, PTP-BL deficiency leads to increased and prolonged activation of STAT4 and STAT6, and consequently enhanced T helper 1 (Th1) and Th2 cell differentiation. Taken together, our findings demonstrate that PTP-BL is a physiologically important negative regulator of the STAT signaling pathway.

Prolactin modulates phosphorylation, signaling and trafficking of epidermal growth factor receptor in human T47D breast cancer cells

Prolactin (PRL) is a polypeptide hormone produced by the anterior pituitary gland and other sites that acts both systemically and locally to cause lactation and other biological effects by interacting with the PRL receptor, a Janus kinase (JAK)2-coupled cytokine receptor family member, and activating downstream signal pathways. Recent evidence suggests PRL is a player in the pathogenesis and progression of breast cancer. Epidermal growth factor (EGF) also has effects on breast tissue, working through its receptors, epidermal growth factor receptor (EGFR) and ErbB-2 (c-neu, HER2), both intrinsic tyrosine kinase growth factor receptors. EGFR promotes pubertal breast ductal morphogenesis in mice, and both EGFR and ErbB-2 are relevant in pathogenesis and behavior of breast and other human cancers. Previous studies showed that PRL and EGF synergize to enhance motility in the human breast cancer cell line, T47D. In this study, we explored crosstalk between the PRL and EGF signaling pathways in T47D cells, with an ultimate aim of understanding how these two important factors might work together in vivo to affect breast cancer behavior. Both PRL and EGF caused robust signaling in T47D cells; PRL acutely activated JAK2, signal transducer and activator of transcription-5 (STAT5), and extracellular signal-regulated kinase-1 and -2 (ERK1 and ERK2), whereas EGF caused EGFR activation and consequent src homology collagen (SHC) activation and ERK activation. Notably, PRL also caused phosphorylation of the EGFR and ErbB-2 at sites detected by PTP101, an antibody that recognizes threonine phosphorylation at consensus motifs for ERK-induced phosphorylation. PRL-induced PTP101-reactive phosphorylation was prevented by pretreatment with PD98059, an ERK pathway inhibitor. Furthermore, PRL synergized with EGF in activating SHC and ERK and transactivating a luciferase reporter driven by c-fos gene enhancer elements, suggesting that PRL allowed markedly enhanced EGF signaling. This was accompanied by substantial inhibition of EGF-induced EGFR downregulation when PRL and EGF cotreatment was compared to EGF treatment alone. This effect of PRL was abrogated by ERK pathway inhibitor pretreatment. Our data suggest that PRL synergistically augments EGF signaling in T47D breast cancer cells at least in part by lessening EGF-induced EGFR downregulation and that this effect requires PRL-induced ERK activity and threonine phosphorylation of EGFR.

Leukemia-associated, constitutively active mutants of SHP2 protein tyrosine phosphatase inhibit NF1 transcriptional activation by the interferon consensus sequence binding protein

Deficiency in either the interferon consensus sequence binding protein (ICSBP) or neurofibromin 1 (Nf1) increases the proliferative response of myeloid progenitor cell to hematopoietic cytokines. Consistent with this, we previously demonstrated that ICSBP activates transcription of the gene encoding Nf1 (the NF1 gene). In the studies presented here, we determine that ICSBP tyrosine phosphorylation is necessary for the activation of NF1 transcription. Since ICSBP is tyrosine phosphorylated in response to hematopoietic cytokines, these studies identify a novel pathway by which cytokine-induced posttranslational modification of ICSBP results in NF1 transcription. Nf1 subsequently inactivates cytokine-activated Ras, thereby creating a negative feedback mechanism for cytokine-induced proliferation. In these studies, we also determine that ICSBP is a substrate for SHP2 protein tyrosine phosphatase (SHP2-PTP). We find that wild-type SHP2-PTP dephosphorylates ICSBP only in undifferentiated myeloid cells. In contrast, a leukemia-associated, constitutively activated mutant form of SHP2-PTP dephosphorylates ICSBP in both myeloid progenitors and differentiating myeloid cells. Activated SHP2-PTP mutants thereby inhibit ICSBP-dependent NF1 transcription, impairing this negative feedback mechanism on cytokine-activated Ras. Therefore, these studies suggest that leukemia-associated ICSBP deficiency cooperates with leukemia-associated activating mutants of SHP2-PTP to contribute to the proliferative phenotype in myeloid malignancies.

Conditional deletion of Shp2 in the mammary gland leads to impaired lobulo-alveolar outgrowth and attenuated Stat5 activation

Stat5 and Stat3, two members of the Stat (signal transducer and activator of transcription) family, are known to play critical roles in mammopoiesis/lactogenesis and involution, respectively, in the mammary gland. Phosphotyrosine phosphatase Shp2 has been shown to dephosphorylate and thus inactivate both Stat5 and Stat3 in vitro. Paradoxically, cell culture studies also suggest a positive role of Shp2 in promoting prolactin-stimulated Stat5 activation. We have shown here that selective deletion of Shp2 in mouse mammary glands suppresses Stat5 activity during pregnancy and lactation, resulting in significant impairment of lobulo-alveolar outgrowth and lactation. In contrast, Stat3 activity was slightly up-regulated shortly before/at involution, leading to normal epithelial cell apoptosis/involution in Shp2-deficient mammary gland. Thus, Shp2 acts to promote Stat5 activation by the JAK2.prolactin receptor complex, while negatively modulating Stat3 activity before the onset of involution. This is the first demonstration that Shp2 manipulates Stat5 and Stat3 activities reciprocally in mammary epithelial cells, providing novel insight into the complex mechanisms for regulation of various Stat family members by a cytoplasmic tyrosine phosphatase.