c-Src activates both STAT1 and STAT3 in PDGF-stimulated NIH3T3 cells

The Role of Catestatin in Preeclampsia

Preeclampsia (PE) is a unique pregnancy disorder affecting women across the world. It is characterized by the new onset of hypertension with coexisting end-organ damage. Although the disease has been known for centuries, its exact pathophysiology and, most importantly, its prevention remain elusive. The basis of its associated molecular changes has been attributed to the placenta and the hormones regulating its function. One such hormone is chromogranin A (CgA). In the placenta, CgA is cleaved to form a variety of biologically active peptides, including catestatin (CST), known inter alia for its vasodilatory effects. Recent studies indicate that the CST protein level is diminished both in patients with hypertension and those with PE. Therefore, the aim of the present paper is to review the most recent and most relevant in vitro, in vivo, and clinical studies to provide an overview of the proposed impact of CST on the molecular processes of PE and to consider the possibilities for future experiments in this area.

Role of c-Src in Carcinogenesis and Drug Resistance

The aberrant transformation of normal cells into cancer cells, known as carcinogenesis, is a complex process involving numerous genetic and molecular alterations in response to innate and environmental stimuli. The Src family kinases (SFK) are key components of signaling pathways implicated in carcinogenesis, with c-Src and its oncogenic counterpart v-Src often playing a significant role. The discovery of c-Src represents a compelling narrative highlighting groundbreaking discoveries and valuable insights into the molecular mechanisms underlying carcinogenesis. Upon oncogenic activation, c-Src activates multiple downstream signaling pathways, including the PI3K-AKT pathway, the Ras-MAPK pathway, the JAK-STAT3 pathway, and the FAK/Paxillin pathway, which are important for cell proliferation, survival, migration, invasion, metastasis, and drug resistance. In this review, we delve into the discovery of c-Src and v-Src, the structure of c-Src, and the molecular mechanisms that activate c-Src. We also focus on the various signaling pathways that c-Src employs to promote oncogenesis and resistance to chemotherapy drugs as well as molecularly targeted agents.

JAK-STAT core cancer pathway: An integrative cancer interactome analysis

Through a comprehensive review and in silico analysis of reported data on STAT-linked diseases, we analysed the communication pathways and interactome of the seven STATs in major cancer categories and proposed rational targeting approaches for therapeutic intervention to disrupt critical pathways and addictions to hyperactive JAK/STAT in neoplastic states. Although all STATs follow a similar molecular activation pathway, STAT1, STAT2, STAT4 and STAT6 exert specific biological profiles associated with a more restricted pattern of activation by cytokines. STAT3 and STAT5A as well as STAT5B have pleiotropic roles in the body and can act as critical oncogenes that promote many processes involved in cancer development. STAT1, STAT3 and STAT5 also possess tumour suppressive action in certain mutational and cancer type context. Here, we demonstrated member-specific STAT activity in major cancer types. Through systems biology approaches, we found surprising roles for EGFR family members, sex steroid hormone receptor ESR1 interplay with oncogenic STAT function and proposed new drug targeting approaches of oncogenic STAT pathway addiction.

STAT3 pathway in cancers: Past, present, and future

Signal transducer and activator of transcription 3 (STAT3), a member of the STAT family, discovered in the cytoplasm of almost all types of mammalian cells, plays a significant role in biological functions. The duration of STAT3 activation in normal tissues is a transient event and is strictly regulated. However, in cancer tissues, STAT3 is activated in an aberrant manner and is induced by certain cytokines. The continuous activation of STAT3 regulates the expression of downstream proteins associated with the formation, progression, and metastasis of cancers. Thus, elucidating the mechanisms of STAT3 regulation and designing inhibitors targeting the STAT3 pathway are considered promising strategies for cancer treatment. This review aims to introduce the history, research advances, and prospects concerning the STAT3 pathway in cancer. We review the mechanisms of STAT3 pathway regulation and the consequent cancer hallmarks associated with tumor biology that are induced by the STAT3 pathway. Moreover, we summarize the emerging development of inhibitors that target the STAT3 pathway and novel drug delivery systems for delivering these inhibitors. The barriers against targeting the STAT3 pathway, the focus of future research on promising targets in the STAT3 pathway, and our perspective on the overall utility of STAT3 pathway inhibitors in cancer treatment are also discussed.

Inhibition of the Na+/K+-ATPase by cardiac glycosides suppresses expression of the IDO1 immune checkpoint in cancer cells by reducing STAT1 activation

Despite extensive basic and clinical research on immune checkpoint regulatory pathways, little is known about the effects of the ionic tumor microenvironment on immune checkpoint expression and function. Here we describe a mechanistic link between Na+/K+-ATPase (NKA) inhibition and activity of the immune checkpoint protein indoleamine-pyrrole 2',3'-dioxygenase 1 (IDO1). We found that IDO1 was necessary and sufficient for production of kynurenine, a downstream tryptophan metabolite, in cancer cells. We developed a spectrophotometric assay to screen a library of 31 model ion transport-targeting compounds for potential effects on IDO1 function in A549 lung and MDA-MB-231 breast cancer cells. This revealed that the cardiac glycosides ouabain and digoxin inhibited kynurenine production at concentrations that did not affect cell survival. NKA inhibition by ouabain and digoxin resulted in increased intracellular Na+ levels and downregulation of IDO1 mRNA and protein levels, which was consistent with the reduction in kynurenine levels. Knockdown of ATP1A1, the ɑ1 subunit of the NKA and target of cardiac glycosides, increased Na+ levels to a lesser extent than cardiac glycoside treatment and did not affect IDO1 expression. However, ATP1A1 knockdown significantly enhanced the effect of cardiac glycosides on IDO1 expression and kynurenine production. Mechanistically, we show that cardiac glycoside treatment resulted in curtailing the length of phosphorylation-mediated stabilization of STAT1, a transcriptional regulator of IDO1 expression, an effect enhanced by ATP1A1 knockdown. Our findings reveal cross talk between ionic modulation via cardiac glycosides and immune checkpoint protein expression in cancer cells with broad mechanistic and clinical implications.

STAT3 and its targeting inhibitors in osteosarcoma

Signal transducer and activator of transcription 3 (STAT3) is one of seven STAT family members involved with the regulation of cellular growth, differentiation and survival. STAT proteins are conserved among eukaryotes and are important for biological functions of embryogenesis, immunity, haematopoiesis and cell migration. STAT3 is widely expressed and located in the cytoplasm in an inactive form. STAT3 is rapidly and transiently activated by tyrosine phosphorylation by a range of signalling pathways, including cytokines from the IL‐6 family and growth factors, such as EGF and PDGF. STAT3 activation and subsequent dimer formation initiates nuclear translocation of STAT3 for the regulation of target gene transcription. Four STAT3 isoforms have been identified, which have distinct biological functions. STAT3 is considered a proto‐oncogene and constitutive activation of STAT3 is implicated in the development of various cancers, including multiple myeloma, leukaemia and lymphomas. In this review, we focus on recent progress on STAT3 and osteosarcoma (OS). Notably, STAT3 is overexpressed and associated with the poor prognosis of OS. Constitutive activation of STAT3 in OS appears to upregulate the expression of target oncogenes, leading to OS cell transformation, proliferation, tumour formation, invasion, metastasis, immune evasion and drug resistance. Taken together, STAT3 is a target for cancer therapy, and STAT3 inhibitors represent potential therapeutic candidates for the treatment of OS.

NOK associates with c-Src and promotes c-Src-induced STAT3 activation and cell proliferation

Signal transducers and activators of transcription 3 (STAT3) is reported to regulate cell proliferation, survival, and differentiation, and thus plays a central role in development and carcinogenesis. Accumulating evidence demonstrated the involvement of cellular Src (c-Src) tyrosine kinase in the activation of STAT3. Additionally, novel oncogene with kinase-domain (NOK), a receptor protein tyrosine kinase that involves in cell transformation and tumorigenesis, was found to activate STAT3 signaling by a JAK2-dependent mechanism. However, whether the existence of the interaction between c-Src/STAT3 and NOK/STAT3 signals is still unknown. In this study, we showed that NOK formed a complex with c-Src and facilitated the interaction between c-Src and STAT3. In the complex, NOK greatly elevated the c-Src-mediated STAT3 activation by increasing the phosphorylation level of STAT3 on Tyr705. Truncated and mutation experiments further demonstrated that the kinase activity was responsible for the synergistic effect of NOK and c-Src on STAT3 activation. In addition, NOK and c-Src synergistically promoted cell proliferation and tumor growth in nude mice. Taken together, our results indicate that NOK associates with c-Src and promotes c-Src-induced STAT3 activation in a kinase-dependent manner. We proposed that the axis that NOK promoted c-Src-induced STAT3 activation is critical in cell proliferation and tumorigenesis.

The loss of STAT3 in mature osteoclasts has detrimental effects on bone structure

Signal Transducer and Activator of Transcription 3 (STAT3) has recently been shown to be involved in bone development and has been implicated in bone diseases, such as Job’s Syndrome. Bone growth and changes have been known for many years to differ between sexes with male bones tending to have higher bone mass than female bones and older females tending to lose bone mass at faster rates than older males. Previous studies using conditional knock mice with Stat3 specifically deleted from the osteoblasts showed both sexes exhibited decreased bone mineral density (BMD) and strength. Using the Cre-Lox system with Cathepsin K promotor driving Cre to target the deletion of the Stat3 gene in mature osteoclasts (STAT3-cKO mice), we observed that 8-week old STAT3-cKO female femurs exhibited significantly lower BMD and bone mineral content (BMC) compared to littermate control (CN) females. There were no differences in BMD and BMC observed between male knock-out and male CN femurs. However, micro-computed tomography (μCT) analysis showed that both male and female STAT3-cKO mice had significant decreases in bone volume/tissue volume (BV/TV). Bone histomorphometry analysis of the distal femur, further revealed a decrease in bone formation rate and mineralizing surface/bone surface (MS/BS) with a significant decrease in osteoclast surface in female, but not male, STAT3-cKO mice. Profiling gene expression in an osteoclastic cell line with a knockdown of STAT3 showed an upregulation of a number of genes that are directly regulated by estrogen receptors. These data collectively suggest that regulation of STAT3 differs in male and female osteoclasts and that inactivation of STAT3 in osteoclasts affects bone turnover more in females than males, demonstrating the complicated nature of STAT3 signaling pathways in osteoclastogenesis. Drugs targeting the STAT3 pathway may be used for treatment of diseases such as Job’s Syndrome and osteoporosis.

Innate Priming of Neutrophils Potentiates Systemic Multiorgan Injury

Excessive inflammatory reactions mediated by first-responder cells such as neutrophils contribute to the severity of multiorgan failure associated with systemic injury and infection. Systemic subclinical endotoxemia due to mucosal leakage may aggravate neutrophil activation and tissue injury. However, mechanisms responsible for neutrophil inflammatory polarization are not well understood. In this study, we demonstrate that subclinical low-dose endotoxemia can potently polarize neutrophils into an inflammatory state in vivo and in vitro, as reflected in elevated expression of adhesion molecules such as ICAM-1 and CD29, and reduced expression of suppressor molecule CD244. When subjected to a controlled administration of gut-damaging chemical dextran sulfate sodium, mice conditioned with subclinical dose LPS exhibit significantly elevated infiltration of neutrophils into organs such as liver, colon, and spleen, associated with severe multiorgan damage as measured by biochemical as well as histological assays. Subclinical dose LPS is sufficient to induce potent activation of SRC kinase as well as downstream activation of STAT1/STAT5 in neutrophils, contributing to the inflammatory neutrophil polarization. We also demonstrate that the administration of 4-phenylbutyric acid, an agent known to relieve cell stress and enhance peroxisome function, can reduce the activation of SRC kinase and enhance the expression of suppressor molecule CD244 in neutrophils. We show that i.v. injection of 4-phenylbutyric acid conditioned neutrophils can effectively reduce the severity of multiorgan damage in mice challenged with dextran sulfate sodium. Collectively, our data, to our knowledge, reveal novel inflammatory polarization of neutrophils by subclinical endotoxemia conducive for aggravated multiorgan damage as well as potential therapeutic intervention.

Activation of STAT1 by the FRK tyrosine kinase is associated with human glioma growth

PURPOSE

Glioma is a highly aggressive and lethal brain tumor. Signal transducers and activators of transcription (STAT) pathway are widely implicated in glioma carcinogenesis. Our previous study found that the Fynrelated kinase (FRK) gene, plays as a tumor suppressor in the development and progression of glioma. This study aimed to investigate the role of FRK in the activation pathway of STATs and its effect on the growth of glioma.

METHODS

The U251 and U87 cells with stable FRK overexpression were generated by lentivirus technique. The effects of FRK on the related proteins of STAT signaling pathway were detected by western blotting. Coimmunoprecipitation was used to detect the association of FRK and STAT1. The effects of STAT1 on the proliferation of glioma cells were detected by CCK8 or Edu cell proliferation assays. The expressions and correlation of FRK and p-STAT1 in glioma tissues were detectd by western blotting or immunohistochemistry. The effect of FRK on the growth of glioma was investigated in vivo mouse model.

RESULTS

The level of p-JAK2 and p-STAT1 increased after FRK overexpression, while they decreased after FRK downregulation both in U251 and U87 cells. However, FRK had no effect on STAT3 phosphorylation. FRK-induced STAT1 activation was not dependent on JAK2. FRK associated with STAT1, induced STAT1 nuclear translocation and regulated the expressions of STAT1-related target genes. STAT1 overexpression suppressed the proliferation of glioma cells. In contrast, STAT1 knockdown by siRNA promoted glioma cell growth. Importantly, down-regulation of STAT1 partially attenuated FRK-induced growth suppression. The clinical sample-based study indicated that the expression of FRK was significantly correlated with the expression of p-STAT1. FRK significantly inhibited glioma tumor growth in vivo.

CONCLUSIONS

Our findings highlighted a critical role of FRK in tumor suppression ability through promoting STAT1 activation, and provided a potential therapeutic target for glioma.

Transfected poly(I:C) activates different dsRNA receptors, leading to apoptosis or immunoadjuvant response in androgen-independent prostate cancer cells

Despite the effectiveness of surgery or radiation therapy for the treatment of early-stage prostate cancer (PCa), there is currently no effective strategy for late-stage disease. New therapeutic targets are emerging; in particular, dsRNA receptors Toll-like receptor 3 (TLR3) and cytosolic helicases expressed by cancer cells, once activated, exert a pro-apoptotic effect in different tumors. We previously demonstrated that the synthetic analog of dsRNA poly(I:C) induces apoptosis in the androgen-dependent PCa cell line LNCaP in a TLR3-dependent fashion, whereas only a weak apoptotic effect is observed in the more aggressive and androgen-independent PCa cells PC3 and DU145. In this paper, we characterize the receptors and the signaling pathways involved in the remarkable apoptosis induced by poly(I:C) transfected by Lipofectamine (in-poly(I:C)) compared with the 12-fold higher free poly(I:C) concentration in PC3 and DU145 cells. By using genetic inhibition of different poly(I:C) receptors, we demonstrate the crucial role of TLR3 and Src in in-poly(I:C)-induced apoptosis. Therefore, we show that the increased in-poly(I:C) apoptotic efficacy is due to a higher binding of endosomal TLR3. On the other hand, we show that in-poly(I:C) binding to cytosolic receptors MDA5 and RIG-I triggers IRF3-mediated signaling, leading uniquely to the up-regulation of IFN-β, which likely in turn induces increased TLR3, MDA5, and RIG-I proteins. In summary, in-poly(I:C) activates two distinct antitumor pathways in PC3 and DU145 cells: one mediated by the TLR3/Src/STAT1 axis, leading to apoptosis, and the other one mediated by MDA5/RIG-I/IRF3, leading to immunoadjuvant IFN-β expression.

An endoplasmic reticulum stress-initiated sphingolipid metabolite, ceramide-1-phosphate, regulates epithelial innate immunity by stimulating β-defensin production

Antimicrobial peptides (AMP) are ubiquitous innate immune elements in epithelial tissues. We recently discovered that a signaling lipid, the ceramide metabolite sphingosine-1-phosphate (S1P), regulates production of a major AMP, cathelicidin antimicrobial peptide (CAMP), in response to a subtoxic level of endoplasmic reticulum (ER) stress that can be induced by external perturbants in keratinocytes. We hypothesized that an ER stress-initiated signal could also regulate production of another major class of AMPs: i.e., the human beta-defensins 2 (hBD2) and 3 (hBD3). Keratinocytes stimulated with a pharmacological ER stressor, thapsigargin (Tg), increased hBD2/hBD3 as well as CAMP mRNA expression. While inhibition of sphingosine-1-phosphate production did not alter hBD expression following ER stress, blockade of ceramide-1-phosphate (C1P) suppressed Tg-induced hBD2/hBD3 but not CAMP expression. Exogenous C1P also increased hBD2/hBD3 production, indicating that C1P stimulates hBD expression. We showed further that C1P-induced hBD2/hBD3 expression is regulated by a novel pathway in which C1P stimulates downstream hBD via a cPLA2a→15d-PGJ2→PPARα/PPARβ/δ→Src kinase→STAT1/STAT3 transcriptional mechanism. Finally, conditioned medium from C1P-stimulated keratinocytes showed antimicrobial activity against Staphylococcus aureus. In summary, our present and recent studies discovered two new regulatory mechanisms of key epidermal AMP, hBD2/hBD3 and CAMP. The C1P and S1P pathways both signal to enhance innate immunity in response to ER stress.

Phosphatase of regenerating liver 3 (PRL3) provokes a tyrosine phosphoproteome to drive prometastatic signal transduction

Phosphatase of regenerating liver 3 (PRL3) is suspected to be a causative factor toward cellular metastasis when in excess. To date, the molecular basis for PRL3 function remains an enigma, making efforts at distilling a concerted mechanism for PRL3-mediated metastatic dissemination very difficult. We previously discovered that PRL3 expressing cells exhibit a pronounced increase in protein tyrosine phosphorylation. Here we take an unbiased mass spectrometry-based approach toward identifying the phosphoproteins exhibiting enhanced levels of tyrosine phosphorylation with a goal to define the "PRL3-mediated signaling network." Phosphoproteomic data support intracellular activation of an extensive signaling network normally governed by extracellular ligand-activated transmembrane growth factor, cytokine, and integrin receptors in the PRL3 cells. Additionally, data implicate the Src tyrosine kinase as the major intracellular kinase responsible for "hijacking" this network and provide strong evidence that aberrant Src activation is a major consequence of PRL3 overexpression. Importantly, the data support a PDGF(α/β)-, Eph (A2/B3/B4)-, and Integrin (β1/β5)-receptor array as being the predominant network coordinator in the PRL3 cells, corroborating a PRL3-induced mesenchymal-state. Within this network, we find that tyrosine phosphorylation is increased on a multitude of signaling effectors responsible for Rho-family GTPase, PI3K-Akt, STAT, and ERK activation, linking observations made by the field as a whole under Src as a primary signal transducer. Our phosphoproteomic data paint the most comprehensive picture to date of how PRL3 drives prometastatic molecular events through Src activation.

Critical analysis of the potential for targeting STAT3 in human malignancy

The signal transducer and activator of transcription (STAT) family of proteins was originally discovered in the context of normal cell biology where they function to transduce intracellular and extracellular signals to the nucleus, ultimately leading to transcription of specific target genes and downstream phenotypic effects. It was quickly appreciated that the STATs, especially STAT3, play a fundamental role in human malignancy. In contrast to normal biology in which transient STAT3 signaling is strictly regulated by a tightly coordinated network of activators and deactivators, STAT3 is constitutively activated in human malignancies. Constitutive STAT3 signaling has been associated with many cancerous phenotypes across nearly all human cancers, including the upregulation of cell growth, proliferation, survival, and motility, among others. Studies involving candidate preclinical STAT3 inhibitors have further demonstrated that the reversal of these phenotypes results from pharmacologic or genetic inhibition of STAT3, suggesting that STAT3 may be a promising target for clinical interventions. Indeed, a Phase 0 clinical trial involving a STAT3 decoy oligonucleotide demonstrated that STAT3 is a drug-gable target in human tumors. Because of the ubiquity of overactive STAT3 in cancer, its role in promoting a wide variety of cancerous phenotypes, and the strong clinical and preclinical studies performed to date, STAT3 represents a promising target for the development of inhibitors for the treatment of human cancers.

Dynamin inhibitors impair endocytosis and mitogenic signaling of PDGF

Platelet-derived growth factor (PDGF) isoforms regulate cell proliferation, migration and differentiation both in embryonic development and adult tissue remodeling. At the cellular level, growth-factor signaling is often modulated by endocytosis. Despite important functions of PDGF, its endocytosis remains poorly studied, mainly for lack of tools to track internalized ligand by microscopy. Here, we developed such a tool and quantitatively analyzed internalization and endosomal trafficking of PDGF-BB in human fibroblasts. We further show that PDGF can be internalized in the presence of dynamin inhibitors, arguing that both dynamin-dependent and dynamin-independent pathways can mediate PDGF uptake. Although these routes operate with somewhat different kinetics, they both ultimately lead to lysosomal degradation of PDGF. Although acute inhibition of dynamin activity only moderately affects PDGF endocytosis, it specifically decreases downstream signaling of PDGF via signal transducer and activator of transcription 3 (STAT3). This correlates with reduced expression of MYC and impaired cell entry into S-phase, indicating that dynamin activity is required for PDGF-induced mitogenesis. Our data support a general view that the components governing endocytic trafficking may selectively regulate certain signaling effectors activated by a growth factor.

Hck is a key regulator of gene expression in alternatively activated human monocytes

IL-13 is a Th2 cytokine that promotes alternative activation (M2 polarization) in primary human monocytes. Our studies have characterized the functional IL-13 receptor complex and the downstream signaling events in response to IL-13 stimulation in alternatively activated monocytes/macrophages. In this report, we present evidence that IL-13 induces the activation of a Src family tyrosine kinase, which is required for IL-13 induction of M2 gene expression, including 15-lipoxygenase (15-LO). Our data show that Src kinase activity regulates IL-13-induced p38 MAPK tyrosine phosphorylation via the upstream kinases MKK3 or MKK6. Our findings also reveal that the IL-13 receptor-associated tyrosine kinase Jak2 is required for the activation of both Src kinase as well as p38 MAPK. Further, we found that Src tyrosine kinase-mediated activation of p38 MAPK is required for Stat1 and Stat3 serine 727 phosphorylation in alternatively activated monocytes/macrophages. Additional studies identify Hck as the specific Src family member, stimulated by IL-13 and involved in regulating both p38 MAPK activation and p38 MAPK-mediated 15-LO expression. Finally we show that the Hck regulates the expression of other alternative state (M2)-specific genes (Mannose receptor, MAO-A, and CD36) and therefore conclude that Hck acts as a key regulator controlling gene expression in alternatively activated monocytes/macrophages.

A Phosphotyrosine Proteomic Screen Identifies Multiple Tyrosine Kinase Signaling Pathways Aberrantly Activated in Malignant Mesothelioma

Malignant mesothelioma (MM) is a highly aggressive cancer that is refractory to all current chemotherapeutic regimens. Therefore, uncovering new rational therapeutic targets is imperative in the field. Tyrosine kinase signaling pathways are aberrantly activated in many human cancers and are currently being targeted for chemotherapeutic intervention. Thus, we sought to identify tyrosine kinases hyperactivated in MM. An unbiased phosphotyrosine proteomic screen was employed to identify tyrosine kinases activated in human MM cell lines. From this screen, we have identified novel signaling molecules, such as JAK1, STAT1, cortactin (CTTN), FER, p130Cas (BCAR1), SRC and FYN as tyrosine phosphorylated in human MM cell lines. Additionally, STAT1 and SRC family kinases (SFK) were confirmed to be active in primary MM specimens. We also confirmed that known signal transduction pathways previously implicated in MM, such as EGFR and MET signaling axes, are co-activated in the majority of human MM specimens and cell lines tested. EGFR, MET, and SFK appear to be co-activated in a significant proportion of MM cell lines, and dual inhibition of these kinases was demonstrated to be more efficacious for inhibiting MM cell viability and downstream effector signaling than inhibition of a single tyrosine kinase. Consequently, these data suggest that TKI mono-therapy may not represent an efficacious strategy for the treatment of MM, due to multiple tyrosine kinases potentially signaling redundantly to cellular pathways involved in tumor cell survival and proliferation.

A novel derivative of the natural agent deguelin for cancer chemoprevention and therapy

The natural compound deguelin has promising preventive and therapeutic activity against diverse cancers by directly binding to heat shock protein-90 and thus suppressing its function. Potential side effects of deguelin over a certain dose, however, could be a substantial obstacle to its clinical use. To develop a derivative(s) of deguelin with reduced potential side effects, we synthesized five deguelin analogues (SH-02, SH-03, SH-09, SH-14, and SH-15) and compared them with the parent compound and each other for structural and biochemical features; solubility; and antiproliferative effects on normal, premalignant, and malignant human bronchial epithelial (HBE) and non-small-cell lung cancer (NSCLC) cell lines. Four derivatives destabilized hypoxia-inducible factor-1alpha as potently as did deguelin. Reverse-phase protein array (RPPA) analysis in H460 NSCLC cells revealed that deguelin and the derivatives suppressed expression of a number of proteins including heat shock protein-90 clients and proteins involved in the phosphoinositide 3-kinase/Akt pathway. One derivative, SH-14, showed several features of potential superiority for clinical use: the highest apoptotic activity; no detectable influence on Src/signal transducer and activator of transcription signaling, which can promote cancer progression and is closely related to pathogenesis of Parkinson's disease (deguelin, SH-02 and SH-03 strongly activated this signaling); better aqueous solubility; and less cytotoxicity to immortalized HBE cells (versus deguelin) at a dose (1 micromol/L) that induced apoptotic activity in most premalignant and malignant HBE and NSCLC cell lines. These collective results suggest that the novel derivative SH-14 has strong potential for cancer chemoprevention and therapy, with equivalent efficacy and lesser toxicity (versus deguelin).

Platelet-derived growth factor-induced stabilization of cyclooxygenase 2 mRNA in rat smooth muscle cells requires the c-Src family of protein-tyrosine kinases

Cyclooxygenases (COXs) are crucial rate-limiting enzymes required for the biosynthesis of prostaglandins. COX-2 is an inducible isoform of this enzyme, which is believed to play important roles in the development of atherosclerotic vascular disease. We found that COX-2 expression rapidly increases in response to various signaling events, including activation of the platelet-derived growth factor (PDGF) pathway. Activation of PDGF receptor (PDGFR) in rat aortic vascular smooth muscle cells leads to c-Src-dependent stabilization of COX-2 mRNA requiring an AU-rich region within the 3'-untranslated region of this transcript. This regulation correlates with tyrosine phosphorylation of the RNA-associated protein, CUG-binding protein 2 (CUGBP2), which appears to enhance its interaction with COX-2 mRNA. Site-directed mutagenesis of putative tyrosine phosphorylation sites in CUGBP2 identified tyrosine 39 as a c-Src target, and a CUGBP2 with a mutated tyrosine 39 displayed an attenuated ability to bind COX-2 mRNA. We further show that silencing of CUGBP2 with specific small interference RNAs significantly reduces PDGF-dependent induction of COX-2 at both mRNA and protein levels. Furthermore, forced expression of CUGBP2 or constitutively active c-Src leads to stabilization of co-expressed COX-2 mRNA. Finally, in vitro RNA decay assay demonstrates that CUGBP2 is functionally required for the stabilization of COX-2 mRNA. Therefore, our data suggest that tyrosine phosphorylation of CUGBP2 is an important underlying mechanism for the ability of PDGFR/c-Src signaling to control the stability of COX-2 mRNA.

Engagement of the B-cell antigen receptor activates STAT through Lyn in a Jak-independent pathway

Engagement of the B-cell antigen receptor (BCR) initiated by the Src kinase Lyn triggers rapid signaling cascades, leading to proliferation, differentiation or growth arrest of B cells. The Janus kinase (JAK)-STAT (signal transducer and activator of transcription) pathway, activated through cytokine receptors, mediates similar responses. Hypothesizing that Src and JAK pathways engage in crosstalk in B-cell signaling, we studied wild-type and Lyn-null B-cell lines, which express BCR. We found that activated BCR results in tyrosine phosphorylation of JAK-STAT, which required Lyn. To confirm that STAT activation is not due to JAK, we cloned the chicken homologs of JAK1 and JAK2 and made their antisense constructs. In cells expressing antisense JAK1 and JAK2, tyrosine phosphorylation of STAT was not inhibited following BCR stimulation. Using activation loop-specific phosphotyrosine antibodies, we did not detect phospho-JAK1 and phospho-JAK2 after BCR stimulation. The JAK inhibitor AG490 did not inhibit the tyrosine phosphorylation of Lyn or STAT after BCR simulation. An in vitro phosphorylation assay showed that Lyn directly phosphorylates STAT3. In an electrophoretic mobility shift assay, BCR stimulation led to enhanced DNA binding of the STAT3 in DT40, but not in the Lyn-null cells. We conclude that BCR engagement activates the STAT pathway via Lyn, independent of JAK.

PI3-kinase/Akt-dependent antiapoptotic signaling by the PDGF alpha receptor is negatively regulated by Src family kinases

Regulation of growth factor dependent cell survival is crucial for development and disease progression. Here, we report a novel function of Src kinases as a negative regulator of platelet-derived growth factor (PDGF) dependent cell survival. We characterized a series of PDGF alpha receptor (PDGFRA) mutants, which lack the binding sites for Src, phosphatidylinositol 3'-kinase (PI3K), SHP-2 or phospholipase C-gamma. We found that PDGFRA-dependent cell survival was mainly mediated through activation of PI3K, and was negatively regulated by Src. Characterization of the downstream signaling events revealed that PI3K activates the protein kinase Akt, which in turn phosphorylates and thus inactivates proapoptotic Forkhead transcription factors. Src phosphorylates the ubiquitin-ligase c-Cbl, which is required for degradation of the activated receptor. Consequently, overexpression of c-Cbl prevented PDGFRA-mediated cell survival, whereas it did not affect this response, when Src was unable to associate with the receptor. This novel function of Src in antiapoptotic signaling introduces Src kinases as an interesting therapeutic target in apoptosis related diseases.

Activation of STAT3 by Gαs Distinctively Requires Protein Kinase A, JNK, and Phosphatidylinositol 3-Kinase

Signal transducer and activator of transcription 3 (STAT3) can be stimulated by several G(s)-coupled receptors, but the precise mechanism of action has not yet been elucidated. We therefore examined the ability of Galpha(s)Q226L (Galpha(s)QL), a constitutively active mutant of Galpha(s), to stimulate STAT3 Tyr705 and Ser727 phosphorylations in human embryonic kidney 293 cells. Apart from Galpha(s)QL, the stimulation of Galpha(s) by cholera toxin or beta2-adrenergic receptor and the activation of adenylyl cyclase by forskolin, (Sp)-cAMP, or dibutyryl-cAMP all promoted both STAT3 Tyr705 and Ser727 phosphorylations. Moreover, the removal of Galpha(s) by RNA interference significantly reduced the beta2-adrenergic receptor-mediated STAT3 phosphorylations, denoting its capacity to regulate STAT3 activation by a G protein-coupled receptor. The possible downstream signaling molecules involved were assessed by using specific inhibitors and dominant negative mutants. Induction of STAT3 Tyr705 and Ser727 phosphorylations by Galpha(s)QL was suppressed by inhibition of protein kinase A, Janus kinase 2/3, Rac1, c-Jun N-terminal kinase (JNK), or phosphatidylinositol 3-kinase, and a similar profile was observed in response to beta2-adrenergic receptor stimulation. In contrast to the Galpha16-mediated regulation of STAT3 in HEK 293 cells (Lo, R. K., Cheung, H., and Wong, Y. H. (2003) J. Biol. Chem. 278, 52154-52165), the Galpha(s)-mediated responses, including STAT3-driven luciferase activation, were resistant to inhibition of phospholipase Cbeta. Surprisingly, Galpha(s)-mediated phosphorylation at Tyr705, but not at Ser727, was resistant to inhibition of c-Src, Raf-1, and MEK1/2 as well as to the expression of dominant negative Ras. Therefore, as with other Galpha-mediated activations of STAT3, the stimulatory signal arising from Galpha(s) is transduced via multiple signaling pathways. However, unlike the mechanisms employed by Galpha(i) and Galpha(14/16), Galpha(s) distinctively requires protein kinase A, JNK, and phosphatidylinositol 3-kinase for STAT3 activation.

Neoplastic transformation by the gep oncogene, Galpha12, involves signaling by STAT3

Galpha(12), the alpha-subunit of G12, which has been referred to as the gep oncogene, stimulates mitogenic pathways in different cell types and readily induces neoplastic transformation of fibroblast cell lines. Recently, we have shown that the oncogenic pathway activated by Galpha(12) involves the receptor tyrosine kinase platelet derived growth factor receptor-alpha (PDGFRalpha) and JAK3. In the present study, we demonstrate that the GTPase-deficient activated mutant of Galpha(12) activates signal transducer and activator of transcription 3 (STAT3) via PDGFRalpha as well as JAK3. Here we show that Galpha(12) stimulates the phosphorylation of STAT3 at both Tyrosine-705 and Serine-727 residues. Studies to delineate the mechanism by which Galpha(12) stimulates STAT3 have indicated that the Tyrosine-705-phosphorylation of STAT3 involves the tyrosine kinases, Janus Kinase-3 as well as Src kinase, whereas the Serine-727 phosphorylation of STAT3 occurs via the receptor tyrosine kinase, PDGFRalpha and phosphatidylinositol 3-OH kinase pathway. Our results also indicate that the coexpression of the dominant negative, DNA binding mutant of STAT3 (STAT3DB) inhibits the foci formation as well as anchorage-independent growth of Galpha(12)QL-transfectants, thereby establishing the critical role of STAT3 in Galpha(12)QL-mediated neoplastic cell growth. The results presented here demonstrate, for the first time, the ability of Galpha(12) to recruit multiple receptor-, nonreceptor-, and Ser/Thr kinases to stimulate STAT3-signaling to promote neoplastic transformation.

Signaling pathways associated with colonic mucosa hyperproliferation in mice overexpressing gastrin precursors

MTI/G-Gly mice and hGAS mice, overexpressing glycine-extended gastrin (G-Gly) and progastrin, respectively, display colonic mucosa hyperplasia, hyperproliferation, and an increased susceptibility to intestinal neoplasia. Here, we have used these transgenic mice to analyze in vivo the modulation of intracellular signaling pathways that may be responsible for the proliferative effects of gastrin precursors. The expression, activation, and localization of signaling and cell-to-cell adhesion molecules were studied using immunofluorescence and Western blot techniques on colonic tissues derived from MTI/G-Gly, hGAS, or wild-type FVB/N mice. These analyses revealed an up-regulation of Src tyrosine kinase and related signaling pathways [phosphatidyl inositol 3'-kinase (PI3K)/Akt, Janus-activated kinase (JAK) 2, signal transducer and activator of transcription (STAT) 3, and extracellular-signal regulated kinases (ERK)] in both MTI/G-Gly and hGAS mice compared with the wild-type control animals as well as an overexpression of transforming growth factor-alpha (TGF-alpha). In contrast, overexpression of the gastrin precursors did not affect the activation status of STAT1 nor the expression and the distribution of adhesion proteins (focal adhesion kinase, cadherins, and catenins). We report for the first time that the transition from a normal colonic epithelium to a hyperproliferative epithelium in MTI/G-Gly and hGAS mice may be a consequence of the up-regulation of Src, PI3K/Akt, JAK2, STAT3, ERKs, and TGF-alpha. Deregulation of cell adhesion, a late event in tumor progression, does not occur in these transgenic models.

Stat3 is required for full neoplastic transformation by the Simian Virus 40 large tumor antigen

To investigate the role of Stat3 (signal transducer and activator of transcription-3) in neoplastic transformation by the Large Tumor antigen of Simian Virus 40 (TAg), murine fibroblasts were rendered deficient in Stat3 activity through expression of a Stat3-specific siRNA or a Cre-loxP recombination system. The results demonstrate that growth rate, formation of foci overgrowing a monolayer of normal cells and colony formation in soft agar were dramatically reduced in Stat3-deficient cells. In addition, TAg expression led to increased Stat3 tyrosine phosphorylation, DNA binding, and transcriptional activity, suggesting that Stat3 is required for TAg-mediated neoplasia. Stat3 activation was prevented by blocking the binding of TAg to pRb (retinoblastoma-susceptibility gene product), whereas genetic ablation of pRb increased Stat3 activity, suggesting that pRb inactivation by TAg might be responsible for the observed Stat3 activation. Stat3 activation by TAg was suppressed after inhibition of c-Src, JAKs or the insulin-like growth factor receptor. On the other hand, targeted disruption of the Fer kinase or pharmacological inhibition of Abl had no effect. Inhibition of Src activity led to Stat3 down-regulation as well as apoptosis of sparsely growing, TAg-transformed cells. However, Src inhibition was relatively ineffective in confluent cells, consistent with previous results indicating that cell to cell adhesion activates Stat3 by a Src-independent mechanism. Direct Stat3 inhibition on the other hand induced apoptosis very effectively in confluent cells, which could have significant therapeutic implications. Taken together, our results suggest that Stat3 is an important component of a pathway emanating from TAg and leading to neoplastic conversion.

IL-10-independent STAT3 activation by Toxoplasma gondii mediates suppression of IL-12 and TNF-alpha in host macrophages

Infection of mouse macrophages by Toxoplasma gondii renders the cells resistant to proinflammatory effects of LPS triggering. In this study, we show that cell invasion is accompanied by rapid and sustained activation of host STAT3. Activation of STAT3 did not occur with soluble T. gondii extracts or heat-killed tachyzoites, demonstrating a requirement for live parasites. Parasite-induced STAT3 phosphorylation and suppression of LPS-triggered TNF-alpha and IL-12 was intact in IL-10-deficient macrophages, ruling out a role for this anti-inflammatory cytokine in the suppressive effects of T. gondii. Most importantly, Toxoplasma could not effectively suppress LPS-triggered TNF-alpha and IL-12 synthesis in STAT3-deficient macrophages. These results demonstrate that T. gondii exploits host STAT3 to prevent LPS-triggered IL-12 and TNF-alpha production, revealing for the first time a molecular mechanism underlying the parasite's suppressive effect on macrophage proinflammatory cytokine production.

Systematic Evaluation of Anti-apoptotic Growth Factor Signaling in Vascular Smooth Muscle Cells

Peptide growth factors contribute to the pathogenesis of cardiovascular diseases by inducing a variety of cellular responses including anti-apoptotic effects. Several of the signaling molecules that are activated by growth factor receptors such as Src family kinases (Src), phosphatidylinositol 3'-kinase (PI3K), phospholipase Cgamma (PLCgamma), Ras, and SHP-2 were shown to mediate survival signals. We systematically investigated the relative contribution of each signaling molecule for growth factor-dependent cell survival in vascular smooth muscle cells (VSMC). Our approach was the use of mutated plateletderived growth factor (PDGF) beta-receptors (betaPDGFR) in which the tyrosine residues required for binding of each signaling molecule were individually mutated to phenylalanine. To bypass endogenous PDGFR in VSMC we used chimeric receptors (ChiRs), containing the extracellular domain of the macrophage colony-stimulating factor (M-CSF) receptor and the cytoplasmic domain of the wild type (WT) or mutated betaPDGFR. Selective activation of the ChiR-WT with M-CSF significantly reduced apoptosis to the same extent as PDGF-BB in non-transfected cells. Deletion of the binding site for PI3K, but not for Src, RasGAP, SHP-2, or PLCgamma, completely abolished the anti-apoptotic effect. Consistently, a ChiR mutant that only binds PI3K was fully able to mediate cell survival as efficiently as the ChiR-WT. Furthermore, the PDGF-dependent anti-apoptotic effect in non-transfected cells was completely abolished by the PI3K inhibitor wortmannin, whereas inhibitors of Src, PLCgamma, ERK, or p38 MAP kinase had no effect. The exploration of downstream signaling events revealed that PDGF-BB activates the anti-apoptotic Akt signaling pathway in a PI3K-dependent manner. Moreover, Akt phosphorylates and thus inactivates the pro-apoptotic proteins BAD and Forkhead transcription factors (FKHR, FKHRL1). We conclude that growth factor-dependent cell survival in VSMC is mediated only by activation of the PI3K/Akt pathway, whereas all other receptor-associated signaling molecules do not play a significant role.

Regulation of Signal Transducer and Activator of Transcription 1 (STAT1) and STAT1-Dependent Genes by RET/PTC (Rearranged in Transformation/Papillary Thyroid Carcinoma) Oncogenic Tyrosine Kinases

Chimeric RET/PTC (rearranged in transformation/papillary thyroid carcinoma) oncoproteins are constitutively active tyrosine kinases found in thyroid papillary carcinoma and nonneoplastic Hashimoto’s thyroiditis. Although several proteins have been identified to be substrates of RET/PTC kinases, the pathogenic roles played by RET/PTC in malignant and benign thyroid diseases and the molecular mechanisms that are involved are not fully understood. We found that RET/PTC expression phosphorylates the Y701 residue of STAT1, a type II interferon (IFN)-responsive protein. RET/PTC-mediated signal transducer and activator of transcription 1 (STAT1) phosphorylation requires RET/PTC kinase activity to be intact but other tyrosine kinases, such as Janus kinases or c-Src, are not involved. RET/PTC-induced STAT1 transcriptional activation was not inhibited by suppressor of cytokine signaling-1 or -3, or protein inhibitors of activated STAT3 [(protein inhibitor of activated STAT (PIAS3)], but PIAS1 strongly repressed the RET/PTC-induced transcriptional activity of STAT1. RET/PTC-induced STAT1 activation caused IFN regulatory factor-1 expression. We found that STAT1 and IFN regulatory factor-1 cooperated to significantly increase transcription from type IV IFN-γresponsive promoters of class II transactivator genes. Significantly, cells stably expressing RET/PTC expressed class II transactivator and showed enhanced de novo membrane expression of major histocompatibility complex (MHC) class II proteins. Furthermore, RET/PTC1-bearing papillary thyroid carcinoma cells strongly expressed MHC class II (human leukocyte-associated antigen-DRα) genes, whereas the surrounding normal tissues did not. Thus, RET/PTC is able to phosphorylate and activate STAT1. This may lead to enhanced MHC class II expression, which may explain why the tissues surrounding RET/PTC-positive cancers are infiltrated with lymphocytes. Such immune response-promoting activity of RET/PTC may also relate to the development of Hashimoto’s thyroiditis.

Cell-to-cell adhesion modulates Stat3 activity in normal and breast carcinoma cells

Stat3 (signal transducer and activator of transcription-3) activity is required for transformation by a number of oncogenes, while a constitutively active form of Stat3 alone is sufficient to induce neoplastic transformation. Although in most instances Stat3 is growth-promoting, the impact of cell density on Stat3 activation status and the biological importance of Stat3 during growth arrest have not been characterized. Previous results indicated that cell density alters tyrosine phosphorylation levels of cultured cells. Since signalling through Stat3 is determined by a key phosphorylation at tyr705, we examined the effects of cell density upon Stat3 activity in normal breast epithelial cells, breast carcinoma lines and normal mouse fibroblasts. Intriguingly, the results revealed a dramatic increase in Stat3, tyr705 phosphorylation and activity with cell density, which gradually declined at later stages. This activation was dependent upon cell-cell contact, since it was eliminated if cell adhesion was disrupted through calcium chelation, while it was reinstated through cell aggregation. Furthermore, this activation was suppressed following inhibition of JAKs (Janus kinases) but not inhibition of Fer, IGF1-R, or kinases of the c-Src family. On the other hand, constitutively active Stat3 in carcinoma lines, known to harbor activated Src, was blocked by pharmacological inhibitors of Src as well as JAKs. These results point to the existence of two distinct pathways of Stat3 activation in breast carcinomas, based on Src dependence. More importantly, our results suggest that Stat3 activity is upregulated during the confluence-mediated growth arrest by a signalling mechanism that requires JAKs.

Oxidized phospholipids increase interleukin 8 (IL-8) synthesis by activation of the c-src/signal transducers and activators of transcription (STAT)3 pathway

Oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (Ox-PAPC) and its component phospholipids 1-palmitoyl-2-epoxyisoprostane-sn-glycero-3-phosphorylcholine (PEIPC) and 1-palmitoyl-2-(5-oxovaleroyl)-sn-glycero-3-phosphorylcholine induce endothelial cells to synthesize chemotactic factors, such as interleukin 8 (IL-8). We have shown recently that Ox-PAPC-mediated induction of IL-8 transcription is independent of NF-kappaB activation, a major transcription factor utilized by cytokines and lipopolysaccharide for the induction of IL-8 transcription. In this study, we provide evidence for the role of c-src in Ox-PAPC and, specifically, PEIPC-mediated IL-8 induction. Ox-PAPC and its component phospholipids induced a rapid and transient phosphorylation of c-src Tyr418, a hallmark of c-src activation, in human aortic endothelial cells (HAEC). Ox-PAPC-mediated IL-8 protein synthesis in HAEC was inhibited by Src family kinase inhibitors, PP1 and PP2, but not by an inactive analog, PP3. Transient expression of plasmids containing C-terminal Src kinase or kinase-deficient dominant-negative c-src resulted in a 72 and 50% reduction in Ox-PAPC-induced IL-8 promoter activation in human microvascular endothelial cells, respectively. In contrast, overexpression of v-src kinase resulted in a 4-fold increase in IL-8 promoter activation, without inducing NF-kappaB promoter activation. Furthermore, treatment of HAEC with Ox-PAPC and its component PEIPC induced the activation of STAT3 by phosphorylating Tyr705, a feature of STAT3 activation. STAT3 is a known downstream effector of c-src. Ox-PAPC-induced activation of STAT3 resulted in the translocation of STAT3 from the cytoplasm of HAEC into their nuclear compartment. Transient expression of a dominant-negative STAT3beta construct in HMEC strongly inhibited IL-8 induction by Ox-PAPC. Taken together, these data demonstrate the role of the c-src kinase/STAT3 pathway in Ox-PAPC-mediated IL-8 expression in endothelial cells.

Differential role of Janus family kinases (JAKs) in interferon-gamma-induced lung epithelial ICAM-1 expression: involving protein interactions between JAKs, phospholipase Cgamma, c-Src, and STAT1

The signaling pathway for IFN-gamma-mediated induction of ICAM-1 expression was further studied in human NCI-H292 epithelial cells. The Tyr701 phosphorylation of signal transducer and activator of transcription 1 (STAT1) induced by interferon-gamma (IFN-gamma) and 12-O-tetradecanoylphorbol 13-acetate (TPA) was inhibited by the protein kinase C (PKC) inhibitor staurosporine, the tyrosine kinase inhibitor herbimycin, or the Src kinase inhibitor PP2. An association between c-Src and STAT1 was increased by IFN-gamma and TPA, indicating the direct phosphorylation of STAT1 by PKC-dependent c-Src activation. Tyrosine phosphorylation of Janus kinases (JAK) 1/2 was induced by IFN-gamma but not by TPA. In addition, ICAM-1 promoter activity induced by IFN-gamma, but not that induced by TPA, was inhibited by the dominant-negative JAK1 and JAK2 mutants. IFN-gamma-induced tyrosine phosphorylation of phospholipase C (PLC)-gamma was inhibited by AG 490 (a JAK inhibitor), and the association between JAK1/2 and PLC-gamma was increased after IFN-gamma treatment, indicating the activation of PLC-gamma via JAK1/2 phosphorylation. ICAM-1 promoter activities induced by the overexpression of wild-type JAK1- and PLC-gamma2 were blocked by the PLCgamma2 mutant or the dominant-negative PKCalpha (Lys-->Arg), c-Src (Lys-->Met), or STAT1 (Y701M) mutants, but not by dominant-negative STAT3 (DN) mutants. These results confirmed that IFN-gamma activated PLC-gamma via JAK1/2 phosphorylation to induce PKC, c-Src, STAT1 activation, and ICAM-1 expression. The association between JAK1/2 and STAT1 was increased by IFN-gamma but not by TPA. It was inhibited by AG 490 but not by U73122, indicating the possible involvement of the JAK1/2-STAT1 pathway. All the results show that IFN-gamma induces ICAM-1 expression by two different pathways in NCI-H292 epithelial cells. One is the JAK1/2-dependent PLC-gamma pathway inducing the activations of PKCalpha, c-Src, and STAT1, and the other is the direct activation of STAT1 by JAK1/2.

The use of c-src knockout mice for the identification of the main toxic signaling pathway of TCDD to Induce wasting syndrome

The effect of single intraperitoneal injection of 115 microg/kg of TCDD (i.e., approximately 1/2 of LD50) to male C57BL/6 mice on the liver mRNA expression changes of several growth factor related genes was assessed at 3 h, 24 h, 10 days, and 30 days posttreatment. The results revealed that the most consistently elevated mRNAs during the entire test period were those of c-Src, TGFalpha, and PDGFa. In contrast, those observed to be consistently suppressed were mRNAs for EGF receptor (EGFR), Ki-Ras, SAPKK, Sp-1, C/EBPbeta, and NFkB. Elevation of mRNAs for TGFbeta and STAT3 was observed only on day 10 and day 30. To assess the role of c-Src in the above action of TCDD, we conducted a parallel study with congenic C57BL/6 male c-src -/- mice. The results showed that in scr -/- mice the effect of TCDD was less in the case of mRNA expression of PDGF(AA), STAT3, C/EPBbeta, NMT-1, and AP-2gamma in addition to c-src as compared to scr +/+ mice. Those affected least by the absence of c-Src were SAPKK, and surprisingly, EGF receptor mRNAs, both of which were consistently downregulated in both strains. In most of the other cases, the extent of TCDD-induced changes were generally less pronounced in src -/- mice as compared to +/+ mice. These observations support the notion that c-Src is an important mediator of the effects of TCDD on TGFalpha, PDGF(AA), and C/EBPalpha, beta.

Constitutively active Galpha16 stimulates STAT3 via a c-Src/JAK- and ERK-dependent mechanism

The hematopoietic-specific Galpha16 protein has recently been shown to mediate receptor-induced activation of the signal transducer and activator of transcription 3 (STAT3). In the present study, we have delineated the mechanism by which Galpha16 stimulates STAT3 in human embryonic kidney 293 cells. A constitutively active Galpha16 mutant, Galpha16QL, stimulated STAT3-dependent luciferase activity as well as the phosphorylation of STAT3 at both Tyr705 and Ser727. Galpha16QL-induced STAT3 activation was enhanced by overexpression of extracellular signal-regulated kinase 1 (ERK1), but was inhibited by U0126, a Raf-1 inhibitor, and coexpression of the dominant negative mutants of Ras and Rac1. Inhibition of phospholipase Cbeta, protein kinase C, and calmodulin-dependent kinase II by their respective inhibitors also suppressed Galpha16QL-induced STAT3 activation. The involvement of tyrosine kinases such as c-Src and Janus kinase 2 and 3 (JAK2 and JAK3) in Galpha16QL-induced activation of STAT3 was illustrated by the combined use of selective inhibitors and dominant negative mutants. In contrast, c-Jun N-terminal kinase, p38 MAPK, RhoA, Cdc42, phosphatidylinositol 3-kinase, and the epidermal growth factor receptor did not appear to be required. Similar observations were obtained with human erythroleukemia cells, where STAT3 phosphorylation was stimulated by C5a in a PTX-insensitive manner. Collectively, these results highlight the important regulatory roles of the Ras/Raf/MEK/ERK and c-Src/JAK pathways on the stimulation of STAT3 by activated Galpha16. Demonstration of the involvement of different kinases in Galpha16QL-induced STAT3 activation supports the involvement of multiple signaling pathways in the regulation of transcription by G proteins.

Src family kinase-independent signal transduction and gene induction by leukemia inhibitory factor

Members of the interleukin-6 (IL-6) family of cytokines exert their biological effects via binding to their cognate ligand-binding receptor subunit on a target cell. The subsequent recruitment of the common signal transducer glycoprotein 130 and activation of the JAK/STAT and SHP-2/Ras/mitogen-activated protein kinase (MAPK) pathways are responsible for the majority of cellular responses elicited by IL-6 cytokines. Several types of experiments suggest that the Src family of kinases (SFK) also participates in IL-6 family cytokine-mediated signaling events. SYF cells, which lack expression of SFKs Src, Yes, and Fyn, were used to determine the role of SFKs in IL-6 family cytokine signaling and gene induction. SYF and wild type (WT) control fibroblasts displayed similar activation of signaling intermediates following stimulation with leukemia inhibitory factor (LIF). LIF-stimulated tyrosine phosphorylation of SHP-2 and subsequent activation of MAPK in SYF cells were identical to that seen in LIF-stimulated WT cells. Both LIF-stimulated tyrosine phosphorylation of STAT1 and STAT3, as well as LIF-stimulated DNA binding activity of STAT-containing nuclear complexes were indistinguishable when compared in SYF and WT cells. In addition, the phosphatidylinositol 3-kinase-sensitive Akt kinase and p38 MAPK were activated by LIF in both SYF and WT cells. Furthermore, LIF-stimulated expression of c-fos, egr-1, and suppressor of cytokine signaling-3 was retained in SYF cells. The IL-6 family cytokine oncostatin M was also capable of activating MAPK, STAT3, STAT1, Akt, and p38 in both WT and SYF cells. These results demonstrate that IL-6 family cytokines can activate a full repertoire of signaling pathways and induce gene expression independent of SFKs.

ErbB-2 activates Stat3 alpha in a Src- and JAK2-dependent manner

Stats (signal transducer and activator of transcription) are latent transcription factors that translocate from the cytoplasm to the nucleus. Constitutive activation of Stat3 alpha by upstream oncoproteins and receptor tyrosine kinases has been found in many human tumors and tumor-derived cell lines. Constitutively activated Stat3 alpha is often correlated with the activation of ErbB-2, a member of the EGFR family. To explore the involvement of ErbB-2 in the activation of Stat3 and the mechanism underlying this event, an ErbB-2 point mutant was used as a model of constitutively activated receptor. Phenylalanine mutations (Y-->F) were made in the autophosphorylation sites of the receptor, and their ability to activate Stat3 alpha was evaluated. Our results suggest that Stat3 alpha and JAK2 associates with ErbB-2 prior to phosphorylation of the receptor and that full activation of Stat3 alpha by ErbB-2 requires the participation of other non-receptor tyrosine kinases. Both Src and Jak2 kinases contribute to the activation of Stat3 alpha but Src binds to ErbB-2 only when the receptor is phosphorylated. Our results also suggest that tyrosine 1139 may be important for Src homology 2 domain association because a mutant lacking this tyrosine reduces the ability of the Src homology 2 domain to bind to ErbB-2 and significantly decreases its ability to activate Stat3 alpha.

Interferon-gamma-induced epithelial ICAM-1 expression and monocyte adhesion. Involvement of protein kinase C-dependent c-Src tyrosine kinase activation pathway

Interferon-gamma (IFN-gamma) induced intercellular adhesion molecule-1 (ICAM-1) expression in human NCI-H292 epithelial cells, as shown by enzyme-linked immunosorbent assay and immunofluorescence staining. The enhanced ICAM-1 expression resulted in increased adhesion of U937 cells to NCI-H292 cells. Tyrosine kinase inhibitors (genistein or herbimycin), Src family inhibitor (PP2), or a phosphatidylinositol-phospholipase C inhibitor (U73122) attenuated the IFN-gamma-induced ICAM-1 expression. Protein kinase C (PKC) inhibitors (staurosporine or Ro 31-8220) also inhibited IFN-gamma-induced response. 12-O-Tetradecanoylphorbol-13-acetate (TPA), a PKC activator, stimulated ICAM-1 expression; this effect was inhibited by tyrosine kinase or Src inhibitor. ICAM-1 promoter activity was enhanced by IFN-gamma and TPA in cells transfected with pIC339-Luc, containing the downstream NF-kappaB and gamma-activated site (GAS) sites, but not in cells transfected with GAS-deletion mutant, pIC135 (DeltaAP2). Electrophoretic gel mobility shift assay demonstrated that GAS-binding complexes in IFN-gamma-stimulated cells contained STAT1alpha. The IFN-gamma-induced ICAM-1 promoter activity was inhibited by tyrosine kinase inhibitors, a phosphatidylinositol-phospholipase C inhibitor, or PKC inhibitors, and the TPA-induced ICAM-1 promoter activity was also inhibited by tyrosine kinase inhibitors. Cotransfection with a PLC-gamma2 mutant inhibited IFN-gamma- but not TPA-induced ICAM-1 promoter activity. However, cotransfection with dominant negative mutants of PKCalpha or c-Src inhibited both IFN-gamma- and TPA-induced ICAM-1 promoter activity. The ICAM-1 promoter activity was stimulated by cotransfection with wild type PLC-gamma2, PKCalpha, c-Src, JAK1, or STAT1. An immunocomplex kinase assay showed that both IFN-gamma and TPA activated c-Src and Lyn activities and that these effects were inhibited by staurosporine and herbimycin. Thus, in NCI-H292 epithelial cells, IFN-gamma activates PLC-gamma2 via an upstream tyrosine kinase to induce activation of PKC-alpha and c-Src or Lyn, resulting in activation of STAT1alpha, and GAS in the ICAM-1 promoter, followed by initiation of ICAM-1 expression and monocyte adhesion.

Co-operative effect of c-Src tyrosine kinase and Stat3 in activation of hepatocyte growth factor expression in mammary carcinoma cells

We have previously shown coexpression of hepatocyte growth factor (HGF) and its receptor Met in the invasive tumor front of human breast carcinomas. We have also demonstrated secretion of HGF, constitutive activation of Met, and increased invasion in a murine breast carcinoma cell line, SP1. These observations suggest the presence of an HGF autocrine loop in some breast carcinoma cells, which confers increased survival, growth, and invasiveness during tumor progression and metastasis. c-Src tyrosine kinase, which is critical in regulating the expression of many genes, is activated in SP1 carcinoma cells, as well as in most human breast cancers. We therefore examined the role of c-Src kinase in HGF expression in breast carcinoma cells. Expression of activated c-Src in SP1 cells increased transcription from the HGF promoter and expression of HGF mRNA and protein, while dominant negative c-Src had the opposite effect. Using deletion analysis, we showed that the region between -254 and -70 base pairs was required for c-Src responsiveness of the HGF promoter. This region contains two putative consensus sequences (at -110 and -149 base pairs) for the Stat3 transcription factor, which bind protein complexes containing Stat3 (but not Stat1, -5A, or -5B). Coexpression of activated c-Src and Stat3 synergistically induced strong HGF promoter activity in SP1 cells, as well as in a nonmalignant epithelial cell line, HC11 (HGF negative). c-Src kinase activity correspondingly increased the tyrosine 705 phosphorylation and DNA binding affinity of Stat3 (but not Stat1, -5A, or -5B). Collectively, our data indicate a cooperative effect of c-Src kinase and Stat3 in the activation of HGF transcription and protein expression in breast carcinoma cells. This process may be important in overriding the strong repression of HGF expression in nonmalignant epithelium, and thereby promote tumorigenesis.

Expression of protein tyrosine kinases and stem cell factor in chicken blastodermal cells

Chicken blastodermal cells (CBC) from Stage X embryos, which were isolated from newly laid, fertile, unincubated eggs, are pluripotent cells and can produce somatic and germline chimeras when injected into recipient stage X embryos. The CBC retain their pluripotential ability for up to 7 d in vitro. The molecular mechanisms that control proliferation and differentiation of CBC are largely unknown, although protein tyrosine kinases (PTK) are known to play important roles in these processes in similar cells. To understand better the molecular mechanisms of proliferation and differentiation in CBC, expression profiles of PTK and stem cell factor (SCF) were analyzed by reverse transcription polymerase chain reaction (RT-PCR) using gene-specific and degenerate oligonucleotide primers. Seventeen distinct PTK, including 14 receptor-type and 3 nonreceptor-type PTK and SCF were identified by RT-PCR. Expression of all of the genes was confirmed by northern blot analysis. The northern blot analysis showed that all probes hybridized with one or more transcripts at various expression levels. The expression of the 17 PTK and SCF genes in CBC suggests that they might play a role in signal transduction pathways that control the proliferation or differentiation in CBC.

Lymphokine dependence of STAT3 activation produced by surface immunoglobulin cross-linking and by phorbol ester plus calcium ionophore treatment in B cells

Stimulation of B cells by surface immunoglobulin (sIg) triggering, or through the mitogenic combination of phorbol ester and calcium ionophore, is accompanied by activation of STAT transcription factors. The mechanism responsible for the delayed nuclear accumulation of phosphorylated STAT3 was examined in detail, focusing on the role of B cell-derived lymphokines. sIg-induced activation of STAT3 was partially inhibited in B cells obtained from IL-6- or IL-10-deficient mice, and was partially blocked by neutralizing antibodies directed against either of these lymphokines. sIg-induced STAT3 activation was completely inhibited by combining IL-6- and IL-10-specific neutralizing antibodies, or by adding individual neutralizing antibodies to B cells obtained from lymphokine-deficient animals. In contrast, IL-10 alone appeared to account for STAT3 activation resulting from B cell stimulation with phorbol ester and calcium ionophore. In keeping with these results, soluble IL-6 and IL-10 were found in supernatant fluid obtained from stimulated B cells. This work indicates that a lymphokine pathway is responsible for STAT3 activation that occurs late after B cell stimulation, and points out differences in B cell activation that result from stimulation through the antigen receptor and through pharmacological mimicry of signaling mediators.

Biochemical and cellular effects of c-Src kinase-selective pyrido[2, 3-d]pyrimidine tyrosine kinase inhibitors

Increased expression or activity of c-Src tyrosine kinase has been associated with the transformed phenotype in tumor cells and with progression of neoplastic disease. A number of pyrido[2, 3-d]pyrimidines have been characterized biochemically and in cells as part of an assessment of their potential as anti-tumor agents. The compounds were ATP-competitive inhibitors of c-Src kinase with IC(50) values < 10 nM and from 6 to >100-fold selectivity for c-Src tyrosine kinase relative to basic fibroblast growth factor receptor (bFGFr) tyrosine kinase, platelet-derived growth factor receptor (PDGFr) tyrosine kinase, and epidermal growth factor receptor (EGFr) tyrosine kinase. The compounds yielded IC(50) values < 5 nM against Lck. Human colon tumor cell growth in culture was inhibited, as was colony formation in soft agar at concentrations < 1 microM. Phosphorylation of the c-Src cellular substrates paxillin, p130(cas), and Stat3 was also inhibited at concentrations < 1 microM. Autophosphorylation of EGFr tyrosine kinase or PDGFr tyrosine kinase was not inhibited by c-Src inhibitors, thus showing the selective nature of the compounds in cells. In a mitogenesis assay measuring thymidine incorporation stimulated by specific mitogens, the c-Src tyrosine kinase inhibitors reduced incorporated thymidine in a manner consistent with previously reported roles of c-Src in mitogenic signaling. Progression through the cell cycle was inhibited at G(2)/M in human colon tumor cells treated with two of the c-Src-selective compounds, which is also consistent with earlier reports describing a requirement for active c-Src tyrosine kinase for G(2) to M phase progression. The compounds described here are selective inhibitors of c-Src tyrosine kinase and have antiproliferative effects in tumor cells consistent with inhibition of c-Src.

Activation of Stat3 in v-Src-transformed fibroblasts requires cooperation of Jak1 kinase activity

Signal transducers and activators of transcription (STATs) are latent cytoplasmic transcription factors that transduce signals from the cell membrane to the nucleus upon activation by tyrosine phosphorylation. Several protein-tyrosine kinases can induce phosphorylation of STATs in cells, including Janus kinase (JAK) and Src family kinases. One STAT family member, Stat3, is constitutively activated in Src-transformed NIH3T3 cells and is required for cell transformation. However, it is not entirely clear whether Src kinase can phosphorylate Stat3 directly or through another pathway, such as JAK family kinases. To address this question, we investigated the phosphorylation of STATs in baculovirus-infected Sf-9 insect cells in the presence of Src. Our results show that Src can tyrosine-phosphorylate Stat1 and Stat3 but not Stat5 in this system. The phosphorylated Stat1 and Stat3 proteins are functionally activated, as measured by their abilities to specifically bind DNA oligonucleotide probes. In addition, the JAK family member Jak1 efficiently phosphorylates Stat1 but not Stat3 in Sf-9 cells. By contrast, we observe that AG490, a JAK family-selective inhibitor, and dominant negative Jak1 protein can significantly inhibit Stat3-induced DNA binding activity as well as Stat3-mediated gene activation in NIH3T3 cells. Furthermore, wild-type or kinase-inactive platelet-derived growth factor receptor enhances Stat3 activation by v-Src, consistent with the receptor serving a scaffolding function for recruitment and activation of Stat3. Our results demonstrate that Src kinase is capable of activating STATs in Sf-9 insect cells without expression of JAK family members; however, Jak1 and platelet-derived growth factor receptor are required for maximal Stat3 activation by Src kinase in mammalian cells. Based on these findings, we propose a model in which Jak1 serves to recruit Stat3 to a receptor complex with Src kinase, which in turn directly phosphorylates and activates Stat3 in Src-transformed fibroblasts.

Activation of Stat3 preassembled with platelet-derived growth factor beta receptors requires Src kinase activity

Members of the STAT family of transcriptional regulators modulate the expression of a variety of gene products that promote cell proliferation, survival and transformation. Although initially identified as mediators of cytokine signaling, the STAT proteins are also activated by, and thus may contribute to the actions of, polypeptide growth factors. To define the mechanism by which these factors activate STATs, we examined the process of Stat3 activation in Balb/c-3T3 fibroblasts treated with platelet-derived growth factor (PDGF). As STATs are activated by tyrosine phosphorylation, and as PDGF receptors are ligand-activated tyrosine kinases, we considered the possibility that Stat3 interacts with and is phosphorylated by PDGF receptors. We find that Stat3 associates with PDGF beta receptors in both the presence and, surprisingly, the absence of PDGF. Moreover, Stat3 was phosphorylated on tyrosine in PDGF beta receptor immunoprecipitates of PDGF-treated but not untreated cells. Although required, receptor activation was insufficient for Stat3 activation. When added to cells in combination with a pharmacologic agent (PD180970) that specifically inhibits the activity of Src family tyrosine kinases, PDGF did not activate Stat3 as monitored by electrophoretic mobility shift assay. PD180970 did not affect MAPK activation by PDGF or the JAK-dependent activation of Stat3 by interleukin-6. The necessity of Src activity for Stat3 activation by PDGF was further evidenced by data showing the presence of Src in complexes containing both Stat3 and PDGF beta receptors in PDGF-treated cells. These results suggest a novel mechanism of STAT activation in which inactive Stat3 pre-assembles with inactive PDGF receptors, and in response to ligand binding and in a manner dependent on Src kinase activity, is rapidly phosphorylated and activated. Additional data demonstrate that Src kinase activity is also required for PDGF stimulation of DNA synthesis in density-arrested cells.

An EGF receptor/Ral-GTPase signaling cascade regulates c-Src activity and substrate specificity

c-Src is a membrane-associated tyrosine kinase that can be activated by many types of extracellular signals, and can regulate the function of a variety of cellular protein substrates. We demonstrate that epidermal growth factor (EGF) and beta-adrenergic receptors activate c-Src by different mechanisms leading to the phosphorylation of distinct sets of c-Src substrates. In particular, we found that EGF receptors, but not beta(2)-adrenergic receptors, activated c-Src by a Ral-GTPase-dependent mechanism. Also, c-Src activated by EGF treatment or expression of constitutively activated Ral-GTPase led to tyrosine phosphorylation of Stat3 and cortactin, but not Shc or subsequent Erk activation. In contrast, c-Src activated by isoproterenol led to tyrosine phosphorylation of Shc and subsequent Erk activation, but not tyrosine phosphorylation of cortactin or Stat3. These results identify a role for Ral-GTPases in the activation of c-Src by EGF receptors and the coupling of EGF to transcription through Stat3 and the actin cytoskeleton through cortactin. They also show that c-Src kinase activity can be used differently by individual extracellular stimuli, possibly contributing to their ability to generate unique cellular responses.

Early events in M-CSF receptor signaling

The M-CSF receptor (M-CSFR) is expressed in monocytes-macrophages and their progenitors, and drives growth and development of this blood cell lineage. The M-CSFR is a member of a small family of growth factor receptors exhibiting related structures but distinct tissue-specific functions. This review discusses the early molecular events in the M-CSF signaling mechanisms, positive signals, negative signals, the possible organization of individual signaling pathways, and the problem of achieving specificity in the signal transduction mechanism.

c-Src activates the DNA binding and transcriptional activity of Stat3 molecules: serine 727 is not required for transcriptional activation under certain circumstances

Stat3 proteins are constitutively activated in cells transformed by v-Src and the proteins have been shown to interact directly. Subsequent studies have shown that Stat3 is required for cellular transformation of NIH fibroblasts by v-Src, suggesting a potential role for Stat3 in aberrant cell growth. Stat3 is phosphorylated on a single tyrosine (tyrosine 705) which is required for effective dimer formation. An additional phosphorylation event (serine 727) is believed to be required for full transcriptional activity of Stat1 and Stat3 molecules. Here we report that c-Src activates the DNA binding activity of Stat3alpha, Stat3beta, and three Stat3 mutants, one in which serine 727 was replaced by alanine (Stat3alphaS727A) and C-terminal truncated molecules Delta48 and Delta55. Consistent with this finding is a general increase in the tyrosine 705-phosphorylated Stat3 in cells cotransfected with c-Src. Furthermore, transcription from an alpha-2 macroglobulin reporter gene is activated by Stat3alphaS727A to the same magnitude as compared to Stat3alpha and Stat3beta in the presence of c-Src. These results suggest that serine 727, contained in a consensus MAP kinase recognition site and shown to be the only serine in Stat3 phosphorylated in epidermal growth factor (EGF) treated cells, is not necessary for transcriptional activity comparable to wild-type Stat3alpha or Stat3beta when activated by c-Src in COS-7 cells.

Stat3 participates in the metabotropic glutamate signaling pathway in Bergmann glial cells

Purkinje cells establish a glutamatergic synapse with the parallel fibers in the cerebellum. Bergmann glial cells surround this synapse. The transcription factor Stat3, highly expressed in cerebellum, is present in cultures of chick Bergmann glia. Treatment of these cells with L-glutamate induces the tyrosine-phosphorylation of Stat3. The maximal phosphorylation was observed after 15 min and by 30 min returned to basal levels. This effect correlated with Stat3 translocation to nucleus and the appearance of a retarded band in gel mobility shift assays. The effects observed with L-glutamate were mediated through metabotropic glutamate receptors. These results further support the notion that glial cells respond to L-glutamate through changes in the existing proteins and also in gene expression regulation.

Expression of a Y559F mutant CSF-1 receptor in M1 myeloid cells: a role for Src kinases in CSF-1 receptor-mediated differentiation

We have established two M1 myeloid cell lines, M1/WT cells overexpressing the wild-type CSF-1 receptor and M1/Y559F cells expressing a specific tyrosine mutant. M1/WT cells differentiated in response to CSF-1, with a reduction in their proliferative capacity. CSF-1-mediated differentiation was partially abrogated in the M1/Y559F cells, with a less marked reduction in proliferative capacity. The Src tyrosine kinases c-Src, c-Yes, c-Fyn, and c-Hck were tyrosine phosphorylated in the M1/WT cells in response to CSF-1 and bound to the WT CSF-1R through their SH2 domains. Binding of the Src kinases to the CSF-1 receptor was greatly reduced in the M1/Y559F cells. CSF-1-mediated activation of STAT3 was also abrogated in the M1/Y559F cell line. Treatment of M1/WT cells with the Src family inhibitor PP2 resulted in an inhibition of CSF-1-mediated differentiation, equivalent to that observed in the M1/Y559F cells. These data suggest that the reduced Src binding observed in the M1/Y559F cells may contribute to their reduced ability to differentiate.