Direct association with and dephosphorylation of Jak2 kinase by the SH2-domain-containing protein tyrosine phosphatase SHP-1

Agonists of galanin subtype 2 receptor may prevent pancreatic cancer and agonists of angiotensin II type 2 receptor may prevent colorectal cancer

Pancreatic ductal adenocarcinoma (PDAC) remains a dreadful disease with poor prognosis. While the prognosis of colorectal carcinoma (CRC) is better than that of PDAC, it still is the second-leading cause of cancer deaths worldwide. Recently, a (methyl)lanthionine-stabilized, highly receptor-specific agonist of galanin subtype 2 (GAL2) receptor inhibited the growth of GAL2 receptor-expressing patient-derived xenografts (PDX) of pancreatic cancer. Furthermore, a lanthionine-constrained agonist of angiotensin II type 2 (AT2) receptor inhibited PDX of colorectal cancer in mice. Stimulation of GAL2 receptor may modulate immune surveillance and inhibits PDAC via cell cycle inhibition and apoptosis. Consistent with GAL2 receptor-mediated tumor inhibition, for PDAC, survival is much higher for patients with high GAL2 receptor expression. Importantly, a (methyl)lanthionine-stabilized GAL2 receptor-specific agonist enhances expression of GAL2 receptor, not only in PDAC-PDX but also in healthy tissue indicating therapeutic and preventive potentials for GAL2 receptor agonists. AT2 receptor is interacting with four tumor suppressor proteins, Src homology phosphatase 1, Src homology phosphatase 2, Promyelocytic Leukemia Zinc Finger protein and Microtuble-Associated Scaffold Protein1, the latter also known as Angiotensin-II type 2 receptor-Interacting Protein. Pathways linked to these tumor suppressor proteins may enhance immune surveillance, prevent carcinogenesis, counter proliferation and stimulate apoptosis. Taken together, current data are prompting the hypothesis of a prophylactic treatment option with stable, specific and safe agonists of GAL2 receptor and AT2 receptor to prevent the emergence of pancreatic and colorectal cancer in individuals at risk.

Leonurine ameliorates the STAT3 pathway through the upregulation of SHP-1 to retard the growth of hepatocellular carcinoma cells

Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that directs the transcription of genes involved in the promotion of cell survival and proliferation, inflammation, angiogenesis, invasion, and migration. Overactivation of STAT3 is often witnessed in human cancers, thereby making it a good target in oncology. Herein the efficacy of Leonurine (Leo), a bioactive alkaloid present in Herba leonuri, was investigated for its STAT3-inhibitory potential in hepatocellular carcinoma (HCC) cells. Leo downregulated the persistent as well as IL-6-driven activation of STAT3. Leo abrogated the nuclear localization and DNA interacting ability of STAT3. Leo was also found to impart STAT3 inhibition by mitigating the activation of upstream kinases such as JAK1, JAK2, and Src both in constitutive and IL-6 inducible systems. Leo curbed the STAT3-driven luciferase gene expression and the depletion of STAT3 resulted in the reduced responsiveness of HCC cells to Leo. Pervanadate exposure counteracted Leo-induced STAT3 inhibition suggesting the involvement of a protein tyrosine phosphatase. SHP-1 was significantly elevated upon Leo exposure whereas the depletion of SHP-1 was found to revert the effect of Leo on STAT3. Leo induced apoptosis and also significantly potentiated the cytotoxic effect of paclitaxel, doxorubicin, and sorafenib. Leo was found to be non-toxic up to the dose of 10 mg/kg in NCr nude mice. In conclusion, Leo was demonstrated to induce cytotoxicity in HCC cells by mitigating the persistent of activation of STAT3 pathway.

Consideration of SHP-1 as a Molecular Target for Tumor Therapy

Abnormal activation of receptor tyrosine kinases (RTKs) contributes to tumorigenesis, while protein tyrosine phosphatases (PTPs) contribute to tumor control. One of the most representative PTPs is Src homology region 2 (SH2) domain-containing phosphatase 1 (SHP-1), which is associated with either an increased or decreased survival rate depending on the cancer type. Hypermethylation in the promoter region of PTPN6, the gene for the SHP-1 protein, is a representative epigenetic regulation mechanism that suppresses the expression of SHP-1 in tumor cells. SHP-1 comprises two SH2 domains (N-SH2 and C-SH2) and a catalytic PTP domain. Intramolecular interactions between the N-SH2 and PTP domains inhibit SHP-1 activity. Opening of the PTP domain by a conformational change in SHP-1 increases enzymatic activity and contributes to a tumor control phenotype by inhibiting the activation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT3) pathway. Although various compounds that increase SHP-1 activation or expression have been proposed as tumor therapeutics, except sorafenib and its derivatives, few candidates have demonstrated clinical significance. In some cancers, SHP-1 expression and activation contribute to a tumorigenic phenotype by inducing a tumor-friendly microenvironment. Therefore, developing anticancer drugs targeting SHP-1 must consider the effect of SHP-1 on both cell biological mechanisms of SHP-1 in tumor cells and the tumor microenvironment according to the target cancer type. Furthermore, the use of combination therapies should be considered.

Interfering B cell receptor signaling via SHP-1/p-Lyn axis shows therapeutic potential in diffuse large B-cell lymphoma

Background

Diffuse large B cell lymphoma (DLBCL) is an aggressive and molecularly heterogeneous non-Hodgkin’s lymphoma. The B cell receptor (BCR) signaling pathway in DLBCL emerges as a new drug target. Protein phosphatase SHP-1 negatively regulates several oncogenic tyrosine kinases and plays a tumor suppressive role.

Methods

The direct SHP-1 agonists were used to evaluate the potential therapeutic implication of SHP-1 in DLBCL. Immunohistochemical staining for SHP-1 was quantified by H-score. The SHP-1 phosphatase activity was determined using tyrosine phosphatase assay. In vitro studies, including MTT, western blot analysis and cell apoptosis, were utilized to examined biological functions of SHP-1.

Results

Oral administration of SHP-1 agonist showed the potent anti-tumor effects compared to a selective Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib in mice bearing U2932 xenografts. SHP-1 agonist increased SHP-1 activity as well as downregulated p-Lyn in vivo. Here, we demonstrated that immunohistochemical staining for SHP-1 expression was positive in 76% of DLBCL samples. SHP-1 agonist exerted anti-proliferative and apoptotic effects compared with ibrutinib in DLBCL cells. Mechanistically, SHP-1 agonist decreased BCR signaling, especially p-Lyn, and led to apoptosis.

Conclusions

These data suggest that SHP-1 negatively regulates phosphorylation of Lyn, and targeting SHP-1/p-Lyn using SHP-1 agonist has therapeutic potential for treatment of DLBCL.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10020-022-00518-0.

Targeting DNMT1 by demethylating agent OR-2100 increases tyrosine kinase inhibitors-sensitivity and depletes leukemic stem cells in chronic myeloid leukemia

ABL1 tyrosine kinase inhibitors (TKIs) dramatically improve the prognosis of chronic myeloid leukemia (CML), but 10-20% of patients achieve suboptimal responses with low TKIs sensitivity. Furthermore, residual leukemic stem cells (LSCs) are involved in the molecular relapse after TKIs discontinuation. Aberrant DNA hypermethylation contributes to low TKIs sensitivity and the persistence of LSCs in CML. DNMT1 is a key regulator of hematopoietic stem cells, suggesting that aberrant DNA hypermethylation targeting DNMT1 represents a potential therapeutic target for CML. We investigated the efficacy of OR-2100 (OR21), the first orally available single-compound prodrug of decitabine. OR21 exhibited anti-tumor effects as a monotherapy, and in combination therapy it increased TKI-induced apoptosis and induction of tumor suppressor genes including PTPN6 encoding SHP-1 in CML cells. OR21 in combination with imatinib significantly suppressed tumor growth in a xenotransplant model. OR21 and combination therapy decreased the abundance of LSCs and inhibited engraftment in a BCR-ABL1-transduced mouse model. These results demonstrate that targeting DNMT1 using OR21 exerts anti-tumor effects and impairs LSCs in CML. Therefore, combination treatment of TKIs and OR21 represents a promising treatment strategy in CML.

Minecoside promotes apoptotic progression through STAT3 inactivation in breast cancer cells

Breast cancer is one of the most common malignant tumors in women worldwide, and is a major cause of mortality and morbidity in cancer patients. Constitutive activation of STAT3 has been found in a variety of malignant tumors, including breast cancer. Since STAT3 activation is capable of regulating various important features of tumor cells, identification of a novel STAT3 inhibitor is considered a potential strategy for treating breast cancer. The aim of the present study was to examine whether minecoside (MIN), an active compound extracted from Veronica peregrina L., exerts an antitumor effect by inhibiting STAT3 signaling pathway in MDA-MB-231 cells. The results revealed that MIN inhibited the constitutive STAT3 activation in a dose- and time-dependent manner. MIN also blocked the nuclear translocation of STAT3 and suppressed STAT3-DNA binding. In addition, MIN downregulated the STAT3-mediated expression of proteins such as Bcl-xL, Bcl-2, CXCR4, VEGF, and cyclin D1. Subsequently, MIN promoted the caspase-dependent apoptosis in MDA-MB-231 cells. Overall, results of the present study provide evidence that MIN exerted anticancer activity via inhibition of the STAT3 signaling pathway. Further studies using animal models are required to determine the potential of this molecule as an anticancer drug.

Hepatitis C Virus Core Protein Down-Regulates Expression of Src-Homology 2 Domain Containing Protein Tyrosine Phosphatase by Modulating Promoter DNA Methylation

Hepatitis C virus (HCV) is the major causative pathogen associated with liver cirrhosis and hepatocellular carcinoma. The main virion component, the core (C) protein, has been implicated in several aspects of HCV pathology including oncogenesis and immune subversion. Here we show that expression of the C protein induced specific tyrosine phosphorylation of the TCR-related signaling proteins ZAP-70, LAT and PLC-γ in the T cells. Stable expression of the C protein specifically reduced Src homology domain 2-containing protein tyrosine phosphatase 1 (SHP-1) mRNA and protein accumulation. Quantitative CpG methylation analysis revealed a distinct CpG methylation pattern at the SHP-1 gene promoter in the C protein expressing cells that included specific hypermethylation of the binding site for Sp1 transcription factor. Collectively, our results suggest that HCV may suppress immune responses and facilitate its own persistence by deregulating phosphotyrosine signaling via repressive epigenetic CpG modification at the SHP-1 promoter in the T cells.

An inhibitory immunoreceptor, Allergin-1, suppresses FITC-induced type 2 contact hypersensitivity

Although allergic contact dermatitis (ACD) is the most common T cell-mediated inflammatory responses against an allergen in the skin, the pathogenesis of ACD remains incompletely understood. In the sensitization phase in ACD, hapten-bearing dermal dendritic cells (DCs) play a pivotal role in the transport of an antigen to the lymph nodes (LNs), where they present the antigen to naïve T cells. Here we report that Allergin-1, an inhibitory immunoreceptor containing immunoreceptor tyrosine-based inhibitory motif (ITIM) in the cytoplasmic region, is highly expressed on dermal DCs. Mice deficient in Allergin-1 exhibited exacerbated fluorescein isothiocyanate (FITC)-induced type 2 contact hypersensitivity (CHS) such as ear swelling and skin eosinophilia. Allergin-1-deficient mice also showed larger numbers of CD4⁺ T cells and FITC-bearing DCs and greater expressions of type 2 cytokines, including IL-5, IL-10 and IL-13, in the draining LNs than did wild type mice. In sharp contrast, Allergin-1-deficient mice showed comparable level of type 1 CHS induced by 2,4-dinitrofluorobenzene (DNFB). These results suggest that Allergin-1 on dermal DC inhibits type 2, but not type 1, immune responses in the sensitization phase of CHS.

The JAK2 mutation

Myeloproliferative neoplasms (MPNs) are clonal hematopoietic stem cell (HSC) disorders with overproduction of mature myeloid blood cells, including essential thrombocythemia (ET), polycythemia vera (PV), and primary myelofibrosis (PMF). In 2005, several groups identified a single gain-of-function point mutation JAK2V617F in the majority of MPN patients. The JAK2V617F mutation confers cytokine independent proliferation to hematopoietic progenitor cells by constitutively activating canonical and non-canonical downstream pathways. In this chapter, we focus on (1) the regulation of JAK2, (2) the molecular mechanisms used by JAK2V617F to induce MPNs, (3) the factors that are involved in the phenotypic diversity in MPNs, and (4) the effects of JAK2V617F on hematopoietic stem cells (HSCs). The discovery of the JAK2V617F mutation led to a comprehensive understanding of MPN; however, the question still remains about how one mutation can give rise to three distinct disease entities. Various mechanisms have been proposed, including JAK2V617F allele burden, differential STAT signaling, and host genetic modifiers. In vivo modeling of JAK2V617F has dramatically enhanced the understanding of the pathophysiology of the disease and provided the pre-clinical platform. Interestingly, most of these models do not show an increased hematopoietic stem cell self-renewal and function compared to wildtype controls, raising the question of whether JAK2V617F alone is sufficient to give a clonal advantage in MPN patients. In addition, the advent of modern sequencing technologies has led to a broader understanding of the mutational landscape and detailed JAK2V617F clonal architecture in MPN patients.

A possible way to prevent the progression of bone lesions in multiple myeloma via Src-homology-region-2-domain-containing-phosphatase-1 activation

On the basis of our recent findings, in which multiple receptor-mediated mast cell functions are regulated via a common signaling cascade, we posit that the formation and functioning of osteoclasts are also controlled by a similar common mechanism. These cells are derived from the same granulocyte/monocyte progenitors and share multiple receptors except those that are cell-specific. In both types of cells, all known receptors reside in lipid rafts, form multiprotein complexes with recruited signaling molecules, and are internalized upon receptor engagement. Signal transduction proceeds in a chain of protein phosphorylations, where adaptor protein LAT (linker-for-activation-of-T-cells) plays a central role. The key kinase that associates LAT phosphorylation and lipid raft internalization is Syk (spleen-tyrosine-kinase) and/or an Src-family-kinase, most probably Lck (lymphocyte-specific-protein-tyrosine-kinase). Dephosphorylation of phosphorylated Syk and Lck by activated SHP-1 (Src-homology-region-2-domain-containing-phosphatase-1) terminates the signal transduction and endocytosis of receptors, resulting in inhibition of osteoclast differentiation and other functions. In malignant plasma cells (MM cells) too, SHP-1 plays a similar indispensable role in controlling signal transduction required for survival and proliferation, though BLNK (B-cell-linker-protein), a functional equivalent of LAT and SLP-76 (SH2-domain-containing-leukocyte-protein-of-76-kDa) in B cells, is used instead of LAT. In both osteoclasts and MM cells, therefore, activated SHP-1 acts negatively in receptor-mediated cellular functions. In osteoblasts, however, activated SHP-1 promotes differentiation, osteocalcin generation, and mineralization by preventing both downregulation of transcription factors, such as Ostrix and Runx2, and degradation of β-catenin required for activation of the transcription factors. SHP-1 is activated by tyrosine phosphorylation and micromolar doses (M-dose) of CCRI-ligand-induced SHP-1 activation. Small molecular compounds, such as A770041, Sorafenib, Nitedanib, and Dovitinib, relieve the autoinhibitory conformation. Activation of SHP-1 by M-dose CCRI ligands or the compounds described may prevent the progression of bone lesions in MM.

Inhibitor Binding Sites in the Protein Tyrosine Phosphatase SHP-2

Protein tyrosine phosphatase 2 (SHP-2) has long been proposed as a cancer drug target. Several small-molecule compounds with different mechanisms of SHP-2 inhibition have been reported, but none are commercially available. Pool selectivity over protein tyrosine phosphatase 1 (SHP-1) and a lack of cellular activity have hindered the development of selective SHP-2 inhibitors. In this review, we describe the binding modes of existing inhibitors and SHP-2 binding sites, summarize the characteristics of the sites involved in selectivity, and identify the suitable groups for interaction with the binding sites.

Erythropoietin regulation of red blood cell production: from bench to bedside and back

More than 50 years of efforts to identify the major cytokine responsible for red blood cell (RBC) production (erythropoiesis) led to the identification of erythropoietin (EPO) in 1977 and its receptor (EPOR) in 1989, followed by three decades of rich scientific discovery. We now know that an elaborate oxygen-sensing mechanism regulates the production of EPO, which in turn promotes the maturation and survival of erythroid progenitors. Engagement of the EPOR by EPO activates three interconnected signaling pathways that drive RBC production via diverse downstream effectors and simultaneously trigger negative feedback loops to suppress signaling activity. Together, the finely tuned mechanisms that drive endogenous EPO production and facilitate its downstream activities have evolved to maintain RBC levels in a narrow physiological range and to respond rapidly to erythropoietic stresses such as hypoxia or blood loss. Examination of these pathways has elucidated the genetics of numerous inherited and acquired disorders associated with deficient or excessive RBC production and generated valuable drugs to treat anemia, including recombinant human EPO and more recently the prolyl hydroxylase inhibitors, which act partly by stimulating endogenous EPO synthesis. Ongoing structure-function studies of the EPOR and its essential partner, tyrosine kinase JAK2, suggest that it may be possible to generate new "designer" drugs that control selected subsets of cytokine receptor activities for therapeutic manipulation of hematopoiesis and treatment of blood cancers.

Shp1 in Solid Cancers and Their Therapy

Shp1 is a cytosolic tyrosine phosphatase that regulates a broad range of cellular functions and targets, modulating the flow of information from the cell membrane to the nucleus. While initially studied in the hematopoietic system, research conducted over the past years has expanded our understanding of the biological role of Shp1 to other tissues, proposing it as a novel tumor suppressor gene functionally involved in different hallmarks of cancer. The main mechanism by which Shp1 curbs cancer development and progression is the ability to attenuate and/or terminate signaling pathways controlling cell proliferation, survival, migration, and invasion. Thus, alterations in Shp1 function or expression can contribute to several human diseases, particularly cancer. In cancer cells, Shp1 activity can indeed be affected by mutations or epigenetic silencing that cause failure of Shp1-mediated homeostatic maintenance. This review will discuss the current knowledge of the cellular functions controlled by Shp1 in non-hematopoietic tissues and solid tumors, the mechanisms that regulate Shp1 expression, the role of its mutation/expression status in cancer and its value as potential target for cancer treatment. In addition, we report information gathered from the public available data from The Cancer Genome Atlas (TCGA) database on Shp1 genomic alterations and correlation with survival in solid cancers patients.

Sanguinarine Induces Apoptosis Pathway in Multiple Myeloma Cell Lines via Inhibition of the JaK2/STAT3 Signaling

Sanguinarine (SNG), a benzophenanthridine alkaloid, has displayed various anticancer abilities in several vivo and in vitro studies. However, the anticancer potential of SNG is yet to be established in multiple myeloma (MM), a mostly incurable malignancy of plasma cells. In this study, we aimed to investigate the potential anti-proliferative and pro-apoptotic activities of SNG in a panel of MM cell lines (U266, IM9, MM1S, and RPMI-8226). SNG treatment of MM cells resulted in a dose-dependent decrease in cell viability through mitochondrial membrane potential loss and activation of caspase 3, 9, and cleavage of PARP. Pre-treatment of MM cells with a universal caspase inhibitor, Z-VAD-FMK, prevented SNG mediated loss of cell viability, apoptosis, and caspase activation, confirming that SNG-mediated apoptosis is caspase-dependent. The SNG-mediated apoptosis appears to be resulted from suppression of the constitutively active STAT3 with a concomitant increase in expression of protein tyrosine phosphatase (SHP-1). SNG treatment of MM cells leads to down-regulation of the anti-apoptotic proteins including cyclin D, Bcl-2, Bclxl, and XIAP. In addition, it also upregulates pro-apoptotic protein, Bax. SNG mediated cellular DNA damage in MM cell lines by induction of oxidative stress through the generation of reactive oxygen species and depletion of glutathione. Finally, the subtoxic concentration of SNG enhanced the cytotoxic effects of anticancer drugs bortezomib (BTZ) by suppressing the viability of MM cells via induction of caspase-mediated apoptosis. Altogether our findings demonstrate that SNG induces mitochondrial and caspase-dependent apoptosis, generates oxidative stress, and suppresses MM cell lines proliferation. In addition, co-treatment of MM cell lines with sub-toxic doses of SNG and BTZ potentiated the cytotoxic activity. These results would suggest that SNG could be developed into therapeutic agent either alone or in combination with other anticancer drugs in MM.

Targeting STAT3 signaling in kidney disease

The Janus kinase/signal transducer and activator of transcription (JAK/STAT) signaling pathway is a multifaceted transduction system that regulates cellular responses to incoming signaling ligands. STAT3 is a central member of the JAK/STAT signaling cascade and has long been recognized for its increased transcriptional activity in cancers and autoimmune disorders but has only recently been in the spotlight for its role in the progression of kidney disease. Although genetic knockout and manipulation studies have demonstrated the salutary benefits of inhibiting STAT3 activity in several kidney disease models, pharmacological inhibition has yet to make it to the clinical forefront. In recent years, significant effort has been aimed at suppressing STAT3 activation for treatment of cancers, which has led to the development of a wide variety of STAT3 inhibitors, but only a handful have been tested in kidney disease models. Here, we review the detrimental role of dysregulated STAT3 activation in a variety of kidney diseases and the current progress in the treatment of kidney diseases with pharmacological inhibition of STAT3 activity.

The Protein Phosphatase Shp1 Regulates Invariant NKT Cell Effector Differentiation Independently of TCR and Slam Signaling

Invariant NKT (iNKT) cells are innate lipid-reactive T cells that develop and differentiate in the thymus into iNKT1/2/17 subsets, akin to T_H1/2/17 conventional CD4 T cell subsets. The factors driving the central priming of iNKT cells remain obscure, although strong/prolonged TCR signals appear to favor iNKT2 cell development. The Src homology 2 domain-containing phosphatase 1 (Shp1) is a protein tyrosine phosphatase that has been identified as a negative regulator of TCR signaling. In this study, we found that mice with a T cell-specific deletion of Shp1 had normal iNKT cell numbers and peripheral distribution. However, iNKT cell differentiation was biased toward the iNKT2/17 subsets in the thymus but not in peripheral tissues. Shp1-deficient iNKT cells were also functionally biased toward the production of T_H2 cytokines, such as IL-4 and IL-13. Surprisingly, we found no evidence that Shp1 regulates the TCR and Slamf6 signaling cascades, which have been suggested to promote iNKT2 differentiation. Rather, Shp1 dampened iNKT cell proliferation in response to IL-2, IL-7, and IL-15 but not following TCR engagement. Our findings suggest that Shp1 controls iNKT cell effector differentiation independently of positive selection through the modulation of cytokine responsiveness.

Protein Tyrosine Phosphatases: Regulators of CD4 T Cells in Inflammatory Bowel Disease

Protein tyrosine phosphatases (PTPs) play a critical role in co-ordinating the signaling networks that maintain lymphocyte homeostasis and direct lymphocyte activation. By dephosphorylating tyrosine residues, PTPs have been shown to modulate enzyme activity and both mediate and disrupt protein-protein interactions. Through these molecular mechanisms, PTPs ultimately impact lymphocyte responses to environmental cues such as inflammatory cytokines and chemokines, as well as antigenic stimulation. Mouse models of acute and chronic intestinal inflammation have been shown to be exacerbated in the absence of PTPs such as PTPN2 and PTPN22. This increase in disease severity is due in part to hyper-activation of lymphocytes in the absence of PTP activity. In accordance, human PTPs have been linked to intestinal inflammation. Genome wide association studies (GWAS) identified several PTPs within risk loci for inflammatory bowel disease (IBD). Therapeutically targeting PTP substrates and their associated signaling pathways, such as those implicated in CD4⁺ T cell responses, has demonstrated clinical efficacy. The current review focuses on the role of PTPs in controlling CD4⁺ T cell activity in the intestinal mucosa and how disruption of PTP activity in CD4⁺ T cells can contribute to intestinal inflammation.

Two novel SHP-1 agonists, SC-43 and SC-78, are more potent than regorafenib in suppressing the in vitro stemness of human colorectal cancer cells

Signal transducer and activator of transcription 3 (STAT3) has been shown to play a critical role in the maintenance of cancer stem cells (CSCs). Hence, the inhibition of STAT3 signaling has been suggested to be a viable therapeutic approach for cancers. Moreover, the efficacy of combinations of chemotherapeutic drugs and napabucasin, a small-molecule STAT3 inhibitor, have been assessed in various clinical trials, including those involving patients with metastatic colorectal cancer (CRC).

Two recently developed small-molecule STAT3 inhibitors, SC-43 and SC-78, which can stimulate SHP-1 to inactivate STAT3, were found to have anti-tumor activity. In this study, the inhibitory effects of SC-43, SC-78, and regorafenib (a reference drug) on cell viability, STAT3 phosphorylation, and various stemness properties [e.g., sphere-forming and soft agar colony-forming abilities, CD133⁺/CD44⁺ (stem cell-like) subpopulations, and the expression of several CSC markers] were examined for both HCT-116 and HT-29 human CRC cells. We found that SC-43 and SC-78 but not regorafenib inhibited constitutive and IL-6-induced STAT3 phosphorylation in HCT-116 and HT-29 cells, respectively. Moreover, SC-43 and SC-78 were more potent than regorafenib in suppressing the stemness properties (except stem cell-like subpopulations) of these cells. As expected, SHP-1 knockdown almost completely abolished the suppressive effects of SC-43 and SC-78 on the sphere formation in both cell lines. Furthermore, SC-43 and SC-78 showed synergistic inhibitory effects with oxaliplatin and/or irinotecan on sphere formation. Overall, our results suggest that SC-43 and SC-78 are potent STAT3 inhibitors that may potentially be used in combination therapy for CRC.

Deletion of MBD2 inhibits proliferation of chronic myeloid leukaemia blast phase cells

Aberrant methylation of tumour suppressor genes is associated with the progression to a blast crisis in chronic myeloid leukaemia (CML). Methyl-CpG-binding domain protein 2 (MBD2) has been studied as a "reader" of DNA methylation in many cancers, but its role in CML is unclear. We constructed cell models of a homozygous deletion mutation of MBD2 using gene-editing technology in K562 cells and BV173 cells. Here, we demonstrated that the deletion of MBD2 inhibited cell proliferation capacity in vitro. MBD2 deletion also significantly inhibited K562 cell proliferation in a xenograft tumour model in vivo. Additionally, the JAK2/STAT3 signalling pathway, which is abnormally active in CML, was inhibited by MBD2 deletion, and MBD2 deletion could up-regulate the expression of SHP1. In conclusion, our findings suggest that MBD2 is a candidate therapeutic strategy for the CML blast phase.

New pathogenic mechanisms induced by germline erythropoietin receptor mutations in primary erythrocytosis

Primary familial and congenital polycythemia is characterized by erythropoietin hypersensitivity of erythroid progenitors due to germline nonsense or frameshift mutations in the erythropoietin receptor gene. All mutations so far described lead to the truncation of the C-terminal receptor sequence that contains negative regulatory domains. Their removal is presented as sufficient to cause the erythropoietin hypersensitivity phenotype. Here we provide evidence for a new mechanism whereby the presence of novel sequences generated by frameshift mutations is required for the phenotype rather than just extensive truncation resulting from nonsense mutations. We show that the erythropoietin hypersensitivity induced by a new erythropoietin receptor mutant, p.Gln434Profs*11, could not be explained by the loss of negative signaling and of the internalization domains, but rather by the appearance of a new C-terminal tail. The latter, by increasing erythropoietin receptor dimerization, stability and cell-surface localization, causes pre-activation of erythropoietin receptor and JAK2, constitutive signaling and hypersensitivity to erythropoietin. Similar results were obtained with another mutant, p.Pro438Metfs*6, which shares the same last five amino acid residues (MDTVP) with erythropoietin receptor p.Gln434Profs*11, confirming the involvement of the new peptide sequence in the erythropoietin hypersensitivity phenotype. These results suggest a new mechanism that might be common to erythropoietin receptor frameshift mutations. In summary, we show that primary familial and congenital polycythemia is more complex than expected since distinct mechanisms are involved in the erythropoietin hypersensitivity phenotype, according to the type of erythropoietin receptor mutation.

Regulation of T-Cell Signaling by Post-Translational Modifications in Autoimmune Disease

The adaptive immune system involves antigen-specific host defense mechanisms mediated by T and B cells. In particular, CD4⁺ T cells play a central role in the elimination of pathogens. Immunological tolerance in the thymus regulates T lymphocytes to avoid self-components, including induction of cell death in immature T cells expressing the self-reactive T-cell receptor repertoire. In the periphery, mature T cells are also regulated by tolerance, e.g., via induction of anergy or regulatory T cells. Thus, T cells strictly control intrinsic signal transduction to prevent excessive responses or self-reactions. If the inhibitory effects of T cells on these mechanisms are disrupted, T cells may incorrectly attack self-components, which can lead to autoimmune disease. The functions of T cells are supported by post-translational modifications, particularly phosphorylation, of signaling molecules, the proper regulation of which is controlled by endogenous mechanisms within the T cells themselves. In recent years, molecular targeted agents against kinases have been developed for treatment of autoimmune diseases. In this review, we discuss T-cell signal transduction in autoimmune disease and provide an overview of acetylation-mediated regulation of T-cell signaling pathways.

Identification of human age-associated gene co-expressions in functional modules using liquid association

Aging is a major risk factor for age-related diseases such as certain cancers. In this study, we developed Age Associated Gene Co-expression Identifier (AAGCI), a liquid association based method to infer age-associated gene co-expressions at thousands of biological processes and pathways across 9 human tissues. Several hundred to thousands of gene pairs were inferred to be age co-expressed across different tissues, the genes involved in which are significantly enriched in functions like immunity, ATP binding, DNA damage, and many cancer pathways. The age co-expressed genes are significantly overlapped with aging genes curated in the GenAge database across all 9 tissues, suggesting a tissue-wide correlation between age-associated genes and co-expressions. Interestingly, age-associated gene co-expressions are significantly different from gene co-expressions identified through correlation analysis, indicating that aging might only contribute to a small portion of gene co-expressions. Moreover, the key driver analysis identified biologically meaningful genes in important function modules. For example, IGF1, ERBB2, TP53 and STAT5A were inferred to be key genes driving age co-expressed genes in the network module associated with function “T cell proliferation”. Finally, we prioritized a few anti-aging drugs such as metformin based on an enrichment analysis between age co-expressed genes and drug signatures from a recent study. The predicted drugs were partially validated by literature mining and can be readily used to generate hypothesis for further experimental validations.

Lycorine inhibits the growth and metastasis of breast cancer through the blockage of STAT3 signaling pathway

Signal transducer and activator of transcription 3 (STAT3) is involved in the growth and metastasis of breast cancer, and represents a potential target for developing new anti-tumor drugs. The purpose of this study is to investigate whether Lycorine, a pyrrolo[de]phenanthridine ring-type alkaloid extracted from Amaryllidaceae genera, could inhibit breast cancer by targeting STAT3 signaling pathway. The human breast cancer cell lines were incubated with various concentrations of Lycorine, and cell proliferation, colony formation, cell cycle distribution, apoptosis, migration and invasion were assayed by several in vitro approaches. Results showed that Lycorine significantly suppressed cell proliferation, colony formation, migration and invasion, as well as induced cell apoptosis, but showed no apparent impact on cell cycle. In addition, the effect of Lycorine on tumor growth and metastasis in nude mouse models was investigated, and results showed that Lycorine significantly inhibited tumor growth and metastasis in vivo. Mechanistically, Lycorine significantly inhibited STAT3 phosphorylation and transcriptional activity through upregulating SHP-1 expression. Lycorine also downregulated the expressions of STAT3 target genes, including Mcl-1, Bcl-xL, MMP-2, MMP-9, which are involved in apoptosis and invasion of breast cancer. Taken together, these findings suggest that Lycorine may be a promising candidate for the prevention and treatment of human breast cancer.

Cucurmin, anticancer, & antitumor perspectives: A comprehensive review

Cucurmin, a naturally yellow component isolated from turmeric, ability to prevent various life-style related disorders. The current review article mainly emphasizes on different anticancer perspectives of cucurmin, i.e., colon, cervical, uterine, ovarian, prostate head and neck, breast, pulmonary, stomach and gastric, pancreatic, bladder oral, oesophageal, and bone cancer. It holds a mixture of strong bioactive molecule known as cucurminoids that has ability to reduce cancer/tumor at initial, promotion and progression stages of tumor development. In particular, these compounds block several enzymes required for the growth of tumors and may therefore involve in tumor treatments. Moreover, it modulates an array of cellular progressions, i.e., nitric oxide synthetase activity, protein kinase C activity, epidermal growth factor (EGF) receptor intrinsic kinase activity, nuclear factor kappa (NF-kB) activity, inhibiting lipid peroxidation and production of reactive oxygen species. However, current manuscript summarizes most of the recent investigations of cucurmin but still further research should be conducted to explore the role of curcumin to mitigate various cancers.

The tyrosine kinase inhibitor nintedanib activates SHP-1 and induces apoptosis in triple-negative breast cancer cells

Triple-negative breast cancer (TNBC) remains difficult to treat and urgently needs new therapeutic options. Nintedanib, a multikinase inhibitor, has exhibited efficacy in early clinical trials for HER2-negative breast cancer. In this study, we examined a new molecular mechanism of nintedanib in TNBC. The results demonstrated that nintedanib enhanced TNBC cell apoptosis, which was accompanied by a reduction of p-STAT3 and its downstream proteins. STAT3 overexpression suppressed nintedanib-mediated apoptosis and further increased the activity of purified SHP-1 protein. Moreover, treatment with either a specific inhibitor of SHP-1 or SHP-1-targeted siRNA reduced the apoptotic effects of nintedanib, which validates the role of SHP-1 in nintedanib-mediated apoptosis. Furthermore, nintedanib-induced apoptosis was attenuated in TNBC cells expressing SHP-1 mutants with constantly open conformations, suggesting that the autoinhibitory mechanism of SHP-1 attenuated the effects of nintedanib. Importantly, nintedanib significantly inhibited tumor growth via the SHP-1/p-STAT3 pathway. Clinically, SHP-1 levels were downregulated, whereas p-STAT3 was upregulated in tumor tissues, and SHP-1 transcripts were associated with improved disease-free survival in TNBC patients. Our findings revealed that nintedanib induces TNBC apoptosis by acting as a SHP-1 agonist, suggesting that targeting STAT3 by enhancing SHP-1 expression could be a viable therapeutic strategy against TNBC.

Alteration of SHP-1/p-STAT3 Signaling: A Potential Target for Anticancer Therapy

The Src homology 2 (SH2) domain-containing protein tyrosine phosphatase 1 (SHP-1), a non-receptor protein tyrosine phosphatase, has been reported as a negative regulator of phosphorylated signal transducer and activator of transcription 3 (STAT3) and linked to tumor development. In this present review, we will discuss the importance and function of SHP-1/p-STAT3 signaling in nonmalignant conditions as well as malignancies, its cross-talk with other pathways, the current clinical development and the potential role of inhibitors of this pathway in anticancer therapy and clinical relevance of SHP-1/p-STAT3 in cancers. Lastly, we will summarize and highlight work involving novel drugs/compounds targeting SHP-1/p-STAT3 signaling and combined strategies that were/are discovered in our and our colleagues’ laboratories.

Loss of function mutations in PTPN6 promote STAT3 deregulation via JAK3 kinase in diffuse large B-cell lymphoma

PTPN6 (SHP1) is a tyrosine phosphatase that negatively controls the activity of multiple signaling pathways including STAT signaling, however role of mutated PTPN6 is not much known. Here we investigated whether PTPN6 might also be a potential target for diffuse large B cell lymphoma (DLBCL) and performed Sanger sequencing of the PTPN6 gene. We have identified missense mutations within PTPN6 (N225K and A550V) in 5% (2/38) of DLBCL tumors. Site directed mutagenesis was performed to mutate wild type (WT) PTPN6 and stable cell lines were generated by lentiviral transduction of PTPN6(WT), PTPN6(N225K) and PTPN6(A550V) constructs, and effects of WT or mutated PTPN6 on STAT3 signaling were analyzed. WT PTPN6 dephosphorylated STAT3, but had no effect on STAT1, STAT5 or STAT6 phosphorylation. Both PTPN6 mutants were unable to inhibit constitutive, as well as cytokines induced STAT3 activation. Both PTPN6 mutants also demonstrated reduced tyrosine phosphatase activity and exhibited enhanced STAT3 transactivation activity. Intriguingly, a lack of direct binding between STAT3 and WT or mutated PTPN6 was observed. However, compared to WT PTPN6, cells expressing PTPN6 mutants exhibited increased binding between JAK3 and PTPN6 suggesting a more dynamic interaction of PTPN6 with upstream regulators of STAT3. Consistent with this notion, both the mutants demonstrated increased resistance to JAK3 inhibitor, WHIP-154 relative to WT PTPN6. Overall, this is the first study, which demonstrates that N225K and A550V PTPN6 mutations cause loss-of-function leading to JAK3 mediated deregulation of STAT3 pathway and uncovers a mechanism that tumor cells can use to control PTPN6 substrate specificity.

SHP-1 is directly activated by the aryl hydrocarbon receptor and regulates BCL-6 in the presence of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

The environmental contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), which is a strong AHR agonist, causes significant suppression of human B cell activation and differentiation. The current studies describe the identification of Src homology phosphatase 1 (SHP-1) encoded by the gene PTPN6 as a putative regulator of TCDD-mediated suppression of B cell activation. Shp-1 was initially identified through a genome-wide analysis of AHR binding in mouse B cells in the presence of TCDD. The binding of AHR to the PTPN6 promoter was further confirmed using electrophoretic mobility shift assays in which, specific binding of AHR was detected at four putative DRE sites within PTPN6 promoter. Time-course measurements performed in human B cells highlighted a significant increase in SHP-1 mRNA and protein levels in the presence of TCDD. The changes in the protein levels of SHP-1 were also observed in a TCDD concentration-dependent manner. The increase in SHP-1 levels was also seen to occur due to a change in early signaling events in the presence of TCDD. We have shown that BCL-6 regulates B cell activation by repressing activation marker CD80 in the presence of TCDD. TCDD-treatment led to a significant increase in the double positive (SHP-1^hi BCL-6^hi) population. Interestingly, treatment of naïve human B cells with SHP-1 inhibitor decreased BCL-6 protein levels suggesting possible regulation of BCL-6 by SHP-1 for the first time. Collectively, these results suggest that SHP-1 is regulated by AHR in the presence of TCDD and may, in part through BCL-6, regulate TCDD-mediated suppression of human B cell activation.

Csk-binding protein controls red blood cell development via regulation of Lyn tyrosine kinase activity

Erythropoiesis is controlled principally through erythropoietin (Epo) receptor signaling, which involves Janus kinase 2 (JAK2) and Lyn tyrosine kinase, both of which are important for regulating red blood cell (RBC) development. Negative regulation of Lyn involves C-Src kinase (Csk)-mediated phosphorylation of its C-terminal tyrosine, which is facilitated by the transmembrane adaptor Csk-binding protein (Cbp). Although Cbp has significant functions in controlling Lyn levels and activity in erythroid cells in vitro, its importance to primary erythroid cell development and signaling has remained unclear. To address this, we assessed the consequence of loss of Cbp on the erythroid compartment in vivo and whether Epo-responsive cells isolated from Cbp-knockout mice exhibited altered signaling. Our data show that male Cbp^-/- mice display a modest but significant alteration to late erythroid development in bone marrow with evidence of increased erythrocytes in the spleen, whereas female Cbp^-/- mice exhibit a moderate elevation in early erythroid progenitors (not seen in male mice) that does not influence the later steps in RBC development. In isolated primary erythroid cells and cell lines generated from Cbp^-/- mice, survival signaling through Lyn/Akt/FoxO3 was elevated, resulting in sustained viability during differentiation. The high Akt activity disrupted GAB2/SHP-2 feedback inhibition of Lyn; however, the elevated Lyn activity also increased inhibitory signaling via SHP-1 to restrict the Erk1/2 pathway. Interestingly, whereas loss of Cbp led to mild changes to late RBC development in male mice, this was not apparent in female Cbp^-/- mice, possibly due to their elevated estrogen, which is known to facilitate early progenitor self-renewal.

Leishmania exosomes and other virulence factors: Impact on innate immune response and macrophage functions

Leishmania parasites are the causative agents of the leishmaniases, a collection of vector-borne diseases that range from simple cutaneous to fatal visceral forms. Employing potent immune modulation mechanisms, Leishmania is able to render the host macrophage inactive and persist inside its phagolysosome. In the last few years, the role of exosomes in Leishmania-host interactions has been increasingly investigated. For instance, it was reported that Leishmania exosome release is augmented following temperature shift, a condition mimicking parasite's entry into its mammalian host. Leishmania exosomes were found to strongly affect macrophage cell signaling and functions, similarly to whole parasites. Importantly, these vesicles were shown to be pro-inflammatory, capable to recruit neutrophils at their inoculation site exacerbating the pathology. In this review, we provide the most recent insights on the role of exosomes and other virulence factors, especially the surface protease GP63, in Leishmania-host interactions, deepening our knowledge on leishmaniasis and paving the way for the development of new therapeutics.

Host SHP1 phosphatase antagonizes Helicobacter pylori CagA and can be downregulated by Epstein-Barr virus

Most if not all gastric cancers are associated with chronic infection of the stomach mucosa with Helicobacter pylori cagA-positive strains(1-4). Approximately 10% of gastric cancers also harbour Epstein-Barr virus (EBV) in the cancer cells(5,6). Following delivery into gastric epithelial cells via type IV secretion(7,8), the cagA-encoded CagA protein undergoes tyrosine phosphorylation on the Glu-Pro-Ile-Tyr-Ala (EPIYA) motifs initially by Src family kinases (SFKs) and then by c-Abl(9,10). Tyrosine-phosphorylated CagA binds to the pro-oncogenic protein tyrosine phosphatase SHP2 and thereby deregulates the phosphatase activity(11,12), which has been considered to play an important role in gastric carcinogenesis(13). Here we show that the SHP2 homologue SHP1 interacts with CagA independently of the EPIYA motif. The interaction potentiates the phosphatase activity of SHP1 that dampens the oncogenic action of CagA by dephosphorylating the CagA EPIYA motifs. In vitro infection of gastric epithelial cells with EBV induces SHP1 promoter hypermethylation, which strengthens phosphorylation-dependent CagA action via epigenetic downregulation of SHP1 expression. Clinical specimens of EBV-positive gastric cancers also exhibit SHP1 hypermethylation with reduced SHP1 expression. The results reveal that SHP1 is the long-sought phosphatase that can antagonize CagA. Augmented H. pylori CagA activity, via SHP1 inhibition, might also contribute to the development of EBV-positive gastric cancer.

Heme oxygenase-1 induction attenuates imiquimod-induced psoriasiform inflammation by negative regulation of Stat3 signaling

Heme oxygenase-1 (HO-1), a stress-inducible protein with a potential anti-inflammatory effect, plays an important role in skin injury and wound healing. However, the function of HO-1 in cutaneous inflammatory diseases, such as psoriasis, remains unknown. The abnormal activation of Stat3, a known transcription factor that induces inflammation and regulates cell differentiation, is directly involved in the pathogenesis and development of psoriasis. Hence, targeting Stat3 is potentially beneficial in the treatment of psoriasis. In this study, HO-1 activation significantly alleviated the disease-related pathogenesis abnormality. To determine the mechanism by which HO-1 exerts immune protection on Th17-related cytokines, IL6/IL22-induced Stat3 activation was significantly suppressed, accompanied by decreased cell proliferation and reversed abnormal cell proliferation. Importantly, HO-1-induced Stat3 suppression was mediated through the activation of protein tyrosine phosphatase SHP-1. Overall, our study provides direct evidence indicating that HO-1 might be a useful therapeutic target for psoriasis. SHP-1-mediated suppression of Stat3 activation after HO-1 activation is a unique molecular mechanism for the regulation of Stat3 activation.

Enhancing SHP-1 expression with 5-azacytidine may inhibit STAT3 activation and confer sensitivity in lestaurtinib (CEP-701)-resistant FLT3-ITD positive acute myeloid leukemia

Background

Tumor-suppressor genes are inactivated by methylation in several cancers including acute myeloid leukemia (AML). Src homology-2 (SH2)-containing protein-tyrosine phosphatase 1 (SHP-1) is a negative regulator of the JAK/STAT pathway. Transcriptional silencing of SHP-1 plays a critical role in the development and progression of cancers through STAT3 activation. 5-Azacytidine (5-Aza) is a DNA methyltransferase inhibitor that causes DNA demethylation resulting in re-expression of silenced SHP-1. Lestaurtinib (CEP-701) is a multi-targeted tyrosine kinase inhibitor that potently inhibits FLT3 tyrosine kinase and induces hematological remission in AML patients harboring the internal tandem duplication of the FLT3 gene (FLT3-ITD). However, the majority of patients in clinical trials developed resistance to CEP-701. Therefore, the aim of this study, was to assess the effect of re-expression of SHP-1 on sensitivity to CEP-701 in resistant AML cells.

Methods

Resistant cells harboring the FLT3-ITD were developed by overexposure of MV4-11 to CEP-701, and the effects of 5-Aza treatment were investigated. Apoptosis and cytotoxicity of CEP-701 were determined using Annexin V and MTS assays, respectively. Gene expression was performed by quantitative real-time PCR. STATs activity was examined by western blotting and the methylation profile of SHP-1 was studied using MS-PCR and pyrosequencing analysis. Repeated-measures ANOVA and Kruskal–Wallis tests were used for statistical analysis.

Results

The cytotoxic dose of CEP-701 on resistant cells was significantly higher in comparison with parental and MV4-11R-cep + 5-Aza cells (p = 0.004). The resistant cells showed a significant higher viability and lower apoptosis compared with other cells (p < 0.001). Expression of SHP-1 was 7-fold higher in MV4-11R-cep + 5-Aza cells compared to parental and resistant cells (p = 0.011). STAT3 was activated in resistant cells. Methylation of SHP-1 was significantly decreased in MV4-11R-cep + 5-Aza cells (p = 0.002).

Conclusions

The restoration of SHP-1 expression induces sensitivity towards CEP-701 and could serve as a target in the treatment of AML. Our findings support the hypothesis that, the tumor-suppressor effect of SHP-1 is lost due to epigenetic silencing and its re-expression might play an important role in re-inducing sensitivity to TKIs. Thus, SHP-1 is a plausible candidate for a role in the development of CEP-701 resistance in FLT3-ITD+ AML patients.

Sorafenib and its derivative SC-1 exhibit antifibrotic effects through signal transducer and activator of transcription 3 inhibition

Signal transducer and activator of transcription 3 (STAT3) had been involved in liver fibrogenesis. We aimed to explore the antifibrotic activities of sorafenib and its derivative SC-1 (devoid of Raf kinase inhibition activity) both in vivo and in vitro with special focus on the STAT3 pathway in hepatic stellate cells (HSCs). The clinical role of STAT3 in chronic hepatitis B (CHB) was also investigated. Experimental fibrosis mouse models were established by thioacetamide injection and bile duct ligation in Balb/C mice and treated with sorafenib and SC-1. Rat and human HSCs were used for mechanistic investigations. Forty CHB patients were enrolled to quantify the hepatic phospho-STAT3 (p-STAT3) levels and correlated with liver fibrosis. Both sorafenib and SC-1 ameliorated liver fibrosis in vivo and promoted HSC apoptosis in vitro. p-STAT3 and downstream signals were down-regulated after sorafenib and SC-1 treatment in HSC. STAT3 overexpression in HSC enhanced cell proliferation and undermined the apoptotic effects of sorafenib and SC-1, whereas STAT3-specific inhibition promoted HSC apoptosis. Sorafenib and SC-1 activated Src-homology protein tyrosine phosphatase-1 (SHP-1) and STAT3 inhibition followed. Of particular interest, in CHB patients with advanced liver fibrosis, p-STAT3 in HSC was significantly overexpressed and positively correlated with the severity of liver fibrosis and plasma IL-6 levels. In conclusion, sorafenib and SC-1 ameliorate liver fibrosis through STAT3 inhibition in HSC and STAT3 may potentially serve as a promising fibrotic biomarker and target in liver fibrosis. SHP-1 phosphatase-directed STAT3 inhibition may represent a previously unidentified strategy for antifibrotic drug discovery.

A derivative of epigallocatechin-3-gallate induces apoptosis via SHP-1-mediated suppression of BCR-ABL and STAT3 signalling in chronic myelogenous leukaemia

BACKGROUND AND PURPOSE

Epigallocatechin-3-gallate (EGCG) is a component of green tea known to have chemo-preventative effects on several cancers. However, EGCG has limited clinical application, which necessitates the development of a more effective EGCG prodrug as an anticancer agent.

EXPERIMENTAL APPROACH

Derivatives of EGCG were evaluated for their stability and anti-tumour activity in human chronic myeloid leukaemia (CML) K562 and KBM5 cells.

KEY RESULTS

EGCG-mono-palmitate (EGCG-MP) showed most prolonged stability compared with other EGCG derivatives. EGCG-MP exerted greater cytotoxicity and apoptosis in K562 and KBM5 cells than the other EGCG derivatives. EGCG-MP induced Src-homology 2 domain-containing tyrosine phosphatase 1 (SHP-1) leading decreased oncogenic protein BCR-ABL and STAT3 phosphorylation in CML cells, compared with treatment with EGCG. Furthermore, EGCG-MP reduced phosphorylation of STAT3 and survival genes in K562 cells, compared with EGCG. Conversely, depletion of SHP-1 or application of the tyrosine phosphatase inhibitor pervanadate blocked the ability of EGCG-MP to suppress phosphorylation of BCR-ABL and STAT3, and the expression of survival genes downstream of STAT3. In addition, EGCG-MP treatment more effectively suppressed tumour growth in BALB/c athymic nude mice compared with untreated controls or EGCG treatment. Immunohistochemistry revealed increased caspase 3 and SHP-1 activity and decreased phosphorylation of BCR-ABL in the EGCG-MP-treated group relative to that in the EGCG-treated group.

CONCLUSIONS AND IMPLICATIONS

EGCG-MP induced SHP-1-mediated inhibition of BCR-ABL and STAT3 signalling in vitro and in vivo more effectively than EGCG. This derivative may be a potent chemotherapeutic agent for CML treatment.

Novel sorafenib analogues induce apoptosis through SHP-1 dependent STAT3 inactivation in human breast cancer cells

Introduction

Signal transducers and activators of transcription 3 (STAT3) signaling is constitutively activated in various cancers including breast cancer and has emerged as a novel potential anti-cancer target. STAT3 has been demonstrated to be a target of sorafenib, and a protein tyrosine phosphatase Src homology 2-domain containing tyrosine phosphatase 1 (SHP-1) has been demonstrated to downregulate p-STAT3 via its phosphatase activity. Here, we tested the efficacy of two sorafenib analogues, SC-1 and SC-43, in breast cancer cells and examined the drug mechanism.

Methods

Breast cancer cell lines were used for in vitro studies. Cell viability was examined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Apoptosis was examined by flow cytometry and western blot. Signal transduction pathways in cells were assessed by western blot. In vivo efficacy of sorafenib, SC-1 and SC-43 was tested in xenografted nude mice.

Results

SC-1 and SC-43 induced more potent apoptosis than sorafenib, in association with downregulation of p-STAT3 and its downstream proteins cyclin D1 and survivin in a dose-dependent manner in breast cancer cell lines (HCC-1937, MDA-MB-468, MDA-MB-231, MDA-MB-453, SK-BR3, MCF-7). Overexpression of STAT3 in MDA-MB-468 cells protected the cells from apoptosis induced by sorafenib, SC-1 and SC-43. Moreover, SC-1 and SC-43 upregulated SHP-1 activity to a greater extent than sorafenib as measured by in vitro phosphatase assays. Knockdown of SHP-1 by siRNA reduced apoptosis induced by SC-1 and SC-43. Importantly, SC-1 and SC-43 showed more efficacious antitumor activity and p-STAT3 downregulation than sorafenib in MDA-MB-468 xenograft tumors.

Conclusions

Novel sorafenib analogues SC-1 and SC-43 induce apoptosis through SHP-1 dependent STAT3 inactivation and demonstrate greater potency than sorafenib in human breast cancer cells.

JAK2 tyrosine kinase phosphorylates and is negatively regulated by centrosomal protein Ninein

JAK2 is a cytoplasmic tyrosine kinase critical for cytokine signaling. In this study, we have identified a novel centrosome-associated complex containing ninein and JAK2. We have found that active JAK2 localizes around the mother centrioles, where it partly colocalizes with ninein, a protein involved in microtubule (MT) nucleation and anchoring. We demonstrated that JAK2 is an important regulator of centrosome function. Depletion of JAK2 or use of JAK2-null cells causes defects in MT anchoring and increased numbers of cells with mitotic defects; however, MT nucleation is unaffected. We showed that JAK2 directly phosphorylates the N terminus of ninein while the C terminus of ninein inhibits JAK2 kinase activity in vitro. Overexpressed wild-type (WT) or C-terminal (amino acids 1179 to 1931) ninein inhibits JAK2. This ninein-dependent inhibition of JAK2 significantly decreases prolactin- and interferon gamma (IFN-γ)-induced tyrosyl phosphorylation of STAT1 and STAT5. Downregulation of ninein enhances JAK2 activation. These results indicate that JAK2 is a novel member of centrosome-associated complex and that this localization regulates both centrosomal function and JAK2 kinase activity, thus controlling cytokine-activated molecular pathways.

Small molecule 1'-acetoxychavicol acetate suppresses breast tumor metastasis by regulating the SHP-1/STAT3/MMPs signaling pathway

Signal transducer and activator of transcription 3 (STAT3) is implicated breast cancer metastasis and represents a potential target for developing new anti-tumor metastasis drugs. The purpose of this study is to investigate whether the natural agent 1'-acetoxychavicol acetate (ACA), derived from the rhizomes and seeds of Languas galanga, could suppress breast cancer metastasis by targeting STAT3 signaling pathway. ACA was examined for its effects on breast cancer migration/invasion and metastasis using Transwell assays in vitro and breast cancer skeletal metastasis mouse model in vivo (n = 10 mice per group). The inhibitory effect of ACA on cellular STAT3 signaling pathway was investigated by series of biochemistry analysis. The chavicol preferentially suppressed cancer cell migration and invasion, and this activity was superior to its cytotoxic effects. ACA suppressed both constitutive and interleukin-6-inducible STAT3 activation and diminished the accumulation of STAT3 in the nucleus and its DNA-binding activity. More importantly, ACA treatment led to significant up-regulation of Src homology region 2 domain-containing phosphatase 1 (SHP-1), and the ACA-induced depression of cancer cell migration and STAT3 signaling could be apparently reversed by blockade of SHP-1. Matrix metalloproteinase (MMP)-2 and -9, gene products of STAT3 that regulate cell invasion, were specifically suppressed by ACA. In tumor metastasis model, ACA potently inhibited the human breast cancer cell-induced osteolysis, and had little apparent in vivo toxicity at the test concentrations. ACA is a novel drug candidate for the inhibition of tumor metastasis through interference with the SHP-1/STAT3/MMPs signaling pathway.

The molecular regulation of Janus kinase (JAK) activation

The JAK (Janus kinase) family members serve essential roles as the intracellular signalling effectors of cytokine receptors. This family, comprising JAK1, JAK2, JAK3 and TYK2 (tyrosine kinase 2), was first described more than 20 years ago, but the complexities underlying their activation, regulation and pleiotropic signalling functions are still being explored. Here, we review the current knowledge of their physiological functions and the causative role of activating and inactivating JAK mutations in human diseases, including haemopoietic malignancies, immunodeficiency and inflammatory diseases. At the molecular level, recent studies have greatly advanced our knowledge of the structures and organization of the component FERM (4.1/ezrin/radixin/moesin)-SH2 (Src homology 2), pseudokinase and kinase domains within the JAKs, the mechanism of JAK activation and, in particular, the role of the pseudokinase domain as a suppressor of the adjacent tyrosine kinase domain's catalytic activity. We also review recent advances in our understanding of the mechanisms of negative regulation exerted by the SH2 domain-containing proteins, SOCS (suppressors of cytokine signalling) proteins and LNK. These recent studies highlight the diversity of regulatory mechanisms utilized by the JAK family to maintain signalling fidelity, and suggest alternative therapeutic strategies to complement existing ATP-competitive kinase inhibitors.

Taenia crassiceps infection and its excreted/secreted products inhibit STAT1 activation in response to IFN-γ

It is well understood that helminth infections modulate the immune responses of their hosts but the mechanisms involved in this modulation are not fully known. Macrophages and dendritic cells appear to be consistently affected during this type of infection and are common target cells for helminth-derived molecules. In this report, we show that macrophages obtained from chronically Taenia crassiceps-infected mice displayed an impaired response to recombinant murine IFN-γ, but not to recombinant murine IL-4, as measured based on the phosphorylation of STAT1 and STAT6, respectively. These macrophages expressed high levels of SOCS3. However, the inhibition of phosphatase activity by orthovanadate restored the IFN-γ response of these macrophages by increasing STAT1 phosphorylation without affecting SOCS3 expression. Therefore, we aimed to identify the phosphatases associated with IFN-γ signaling inhibition and found that macrophages from T. crassiceps-infected mice displayed enhanced SHP-1 expression. Interestingly, the exposure of naïve macrophages to T. crassiceps excreted/secreted products similarly interfered with IFN-γ-induced STAT1 phosphorylation. Moreover, macrophages exposed to T. crassiceps excreted/secreted products expressed high levels of SOCS3 as well as SHP-1. Strikingly, human peripheral blood mononuclear cells that were exposed to T. crassiceps excreted/secreted products in vitro also displayed impaired STAT1 phosphorylation in response to IFN-γ; again, phosphatase inhibition abrogated the T. crassiceps excreted/secreted product-altered IFN-γ signaling. These data demonstrate a new mechanism by which helminth infection and the products derived during this infection target intracellular pathways to block the response to inflammatory cytokines such as IFN-γ in both murine and human cells.

Lyn kinase plays important roles in erythroid expansion, maturation and erythropoietin receptor signalling by regulating inhibitory signalling pathways that control survival

In erythroid cells both positive viability signals and feedback inhibitory signalling require the Src family kinase Lyn, influencing cell survival and their ability to differentiate. This illustrates that Lyn is critical for normal erythropoiesis and erythroid cell development.

Protein tyrosine phosphatases as wardens of STAT signaling

Signaling by signal transducers and activators of transcription (STATs) is controlled at many levels of the signaling cascade. Protein tyrosine phosphatases (PTPs) regulate STAT activation at several layers, including direct pSTAT dephosphorylation in both cytoplasm and nucleus. Despite the importance of this regulation mode, many aspects are still incompletely understood, e.g., the identity of PTPs acting on certain members of the STAT family. After a brief introduction into the STAT and PTP families, we discuss here the current knowledge on PTP mediated regulation of STAT activity, focusing on the interaction of individual STATs with specific PTPs. Finally, we highlight open questions and propose important tasks of future research.

Shp1 regulates T cell homeostasis by limiting IL-4 signals

Absence of the phosphatase Shp1 in T cells does not affect the TCR signaling threshold but results in IL-4 sensitivity and memory phenotype cells.

The protein-tyrosine phosphatase Shp1 is expressed ubiquitously in hematopoietic cells and is generally viewed as a negative regulatory molecule. Mutations in Ptpn6, which encodes Shp1, result in widespread inflammation and premature death, known as the motheaten (me) phenotype. Previous studies identified Shp1 as a negative regulator of TCR signaling, but the severe systemic inflammation in me mice may have confounded our understanding of Shp1 function in T cell biology. To define the T cell–intrinsic role of Shp1, we characterized mice with a T cell–specific Shp1 deletion (Shp1^fl/fl CD4-cre). Surprisingly, thymocyte selection and peripheral TCR sensitivity were unaltered in the absence of Shp1. Instead, Shp1^fl/fl CD4-cre mice had increased frequencies of memory phenotype T cells that expressed elevated levels of CD44. Activation of Shp1-deficient CD4⁺ T cells also resulted in skewing to the Th2 lineage and increased IL-4 production. After IL-4 stimulation of Shp1-deficient T cells, Stat 6 activation was sustained, leading to enhanced Th2 skewing. Accordingly, we observed elevated serum IgE in the steady state. Blocking or genetic deletion of IL-4 in the absence of Shp1 resulted in a marked reduction of the CD44^hi population. Therefore, Shp1 is an essential negative regulator of IL-4 signaling in T lymphocytes.

Epigenetic mechanisms of protein tyrosine phosphatase 6 suppression in diffuse large B-cell lymphoma: implications for epigenetic therapy

Protein tyrosine phosphatases such as PTPN6 can be downregulated in various neoplasms. PTPN6 expression by immunohistochemistry in 40 diffuse large B-cell lymphoma (DLBCL) tumors was lost or suppressed in 53% (21/40). To elucidate the molecular mechanisms of PTPN6 suppression, we performed a comprehensive epigenetic analysis of PTPN6 promoter 2 (P2). None of the DLBCL primary tumors (0/37) had PTPN6 hypermethylation on the CpG1 island using methylation-specific PCR, pyrosequencing, and high-resolution melting assays. However, hypermethylation in 57% (21/37) of cases was found in a novel CpG island (CpG2) in P2. PTPN6 gene suppression was reversed by 5-aza-deoxycytidine (5-Aza), a DNA methyltransferase inhibitor, and the histone deacetylase inhibitor (HDACi) LBH589. LBH589 and 5-Aza in combination inhibited DLBCL survival and PTPN6 hypermethylation at CpG2. The role of histone modifications was investigated with a chromatin-immunoprecipitation assay demonstrating that PTPN6 P2 is associated with silencing histone marks H3K27me3 and H3K9me3 in DLBCL cells but not normal B cells. 3-Deazaneplanocin A, a histone methyltransferase inhibitor, decreased the H3K27me3 mark, whereas HDACi LBH589 increased the H3K9Ac mark within P2 resulting in re-expression of PTPN6. These studies have uncovered novel epigenetic mechanisms of PTPN6 suppression and suggest that PTPN6 may be a potential target of epigenetic therapy in DLBCL.

Pharmacological activation of AMPK suppresses inflammatory response evoked by IL-6 signalling in mouse liver and in human hepatocytes

Interleukin-6 (IL-6) induces inflammatory signalling in liver, leading to impaired insulin action in hepatocytes. In this study, we demonstrate that pharmacological activation of AMP-activated protein kinase (AMPK) represses IL-6-stimulated expression of proinflammatory markers serum amyloid A (Saa) as well as suppressor of cytokine signalling 3 (Socs3) in mouse liver. Further studies using the human hepatocellular carcinoma cell line HepG2 suggest that AMPK inhibits IL-6 signalling by repressing IL-6-stimulated phosphorylation of several downstream components of the pathway such as Janus kinase 1 (JAK1), SH2-domain containing protein tyrosine phosphatase 2 (SHP2) and signal transducer and activator of transcription 3 (STAT3). In summary, inhibition of IL-6 signalling cascade in liver by the metabolic master switch of the body, AMPK, supports the role of this kinase as a crucial point of convergence of metabolic and inflammatory pathways in hepatocytes.

Tyrosyl phosphorylated PAK1 regulates breast cancer cell motility in response to prolactin through filamin A

The p21-activated serine-threonine kinase (PAK1) is activated by small GTPase-dependent and -independent mechanisms and regulates cell motility. Both PAK1 and the hormone prolactin (PRL) have been implicated in breast cancer by numerous studies. We have previously shown that the PRL-activated tyrosine kinase JAK2 (Janus tyrosine kinase 2) phosphorylates PAK1 in vivo and identified tyrosines (Tyr) 153, 201, and 285 in the PAK1 molecule as sites of JAK2 tyrosyl phosphorylation. Here, we have used human breast cancer T47D cells stably overexpressing PAK1 wild type or PAK1 Y3F mutant in which Tyr(s) 153, 201, and 285 were mutated to phenylalanines to demonstrate that phosphorylation of these three tyrosines are required for maximal PRL-dependent ruffling. In addition, phosphorylation of these three tyrosines is required for increased migration of T47D cells in response to PRL as assessed by two independent motility assays. Finally, we show that PAK1 phosphorylates serine (Ser) 2152 of the actin-binding protein filamin A to a greater extent when PAK1 is tyrosyl phosphorylated by JAK2. Down-regulation of PAK1 or filamin A abolishes the effect of PRL on cell migration. Thus, our data presented here bring some insight into the mechanism of PRL-stimulated motility of breast cancer cells.