The role of SHIP in growth factor induced signalling

SHIP1 Controls Internal Platelet Contraction and αIIbβ3 Integrin Dynamics in Early Platelet Activation

The Src homology 2 domain-containing inositol 5-phosphatase 1 (SHIP1) is known to dephosphorylate PtdIns(3,4,5)P₃ into PtdIns(3,4)P₂ and to interact with several signaling proteins though its docking functions. It has been shown to negatively regulate platelet adhesion and spreading on a fibrinogen surface and to positively regulate thrombus growth. In the present study, we have investigated its role during the early phase of platelet activation. Using confocal-based morphometric analysis, we found that SHIP1 is involved in the regulation of cytoskeletal organization and internal contractile activity in thrombin-activated platelets. The absence of SHIP1 has no significant impact on thrombin-induced Akt or Erk1/2 activation, but it selectively affects the RhoA/Rho-kinase pathway and myosin IIA relocalization to the cytoskeleton. SHIP1 interacts with the spectrin-based membrane skeleton, and its absence induces a loss of sustained association of integrins to this network together with a decrease in α_IIbβ₃ integrin clustering following thrombin stimulation. This α_IIbβ₃ integrin dynamics requires the contractile cytoskeleton under the control of SHIP1. RhoA activation, internal platelet contraction, and membrane skeleton integrin association were insensitive to the inhibition of PtdIns(3,4,5)P₃ synthesis or SHIP1 phosphatase activity, indicating a role for the docking properties of SHIP1 in these processes. Altogether, our data reveal a lipid-independent function for SHIP1 in the regulation of the contractile cytoskeleton and integrin dynamics in platelets.

AKT in Bone Metastasis of Solid Tumors: A Comprehensive Review

Simple Summary

Bone metastasis is a frequent complication of solid tumors and leads to a reduced overall survival. Although much progress has been made in the field of tumor therapy in the last years, bone metastasis depicts a stage of the disease with a lack of appropriate therapeutical options. Hence, this review aims to present the role of AKT in bone metastasis of solid tumors to place the spotlight on AKT as a possible therapeutical approach for patients with bone metastases. Furthermore, we intended to discuss postulated underlying molecular mechanisms of the bone metastasis-promoting effect of AKT, especially in highly bone-metastatic breast, prostate, and lung cancer. To conclude, this review identified the AKT kinase as a potential therapeutical target in bone metastasis and revealed remaining questions, which need to be addressed in further research projects.

Abstract

Solid tumors, such as breast cancer and prostate cancer, often form bone metastases in the course of the disease. Patients with bone metastases frequently develop complications, such as pathological fractures or hypercalcemia and exhibit a reduced life expectancy. Thus, it is of vital importance to improve the treatment of bone metastases. A possible approach is to target signaling pathways, such as the PI3K/AKT pathway, which is frequently dysregulated in solid tumors. Therefore, we sought to review the role of the serine/threonine kinase AKT in bone metastasis. In general, activation of AKT signaling was shown to be associated with the formation of bone metastases from solid tumors. More precisely, AKT gets activated in tumor cells by a plethora of bone-derived growth factors and cytokines. Subsequently, AKT promotes the bone-metastatic capacities of tumor cells through distinct signaling pathways and secretion of bone cell-stimulating factors. Within the crosstalk between tumor and bone cells, also known as the vicious cycle, the stimulation of osteoblasts and osteoclasts also causes activation of AKT in these cells. As a consequence, bone metastasis is reduced after experimental inhibition of AKT. In summary, AKT signaling could be a promising therapeutical approach for patients with bone metastases of solid tumors.

Influence of ARHGAP29 on the Invasion of Mesenchymal-Transformed Breast Cancer Cells

Aggressive and mesenchymal-transformed breast cancer cells show high expression levels of Rho GTPase activating protein 29 (ARHGAP29), a negative regulator of RhoA. ARHGAP29 was the only one of 32 GTPase-activating enzymes whose expression significantly increased after the induction of mesenchymal transformation in breast cancer cells. Therefore, we investigated the influence of ARHGAP29 on the invasiveness of aggressive and mesenchymal-transformed breast cancer cells. After knock-down of ARHGAP29 using siRNA, invasion of HCC1806, MCF-7-EMT, and T-47D-EMT breast cancer cells was significantly reduced. This could be explained by reduced inhibition of RhoA and a consequent increase in stress fiber formation. Proliferation of the breast cancer cell line T-47D-EMT was slightly increased by reduced expression of ARHGAP29, whereas that of HCC1806 and MCF-7-EMT significantly increased. Using interaction analyses we found that AKT1 is a possible interaction partner of ARHGAP29. Therefore, the expression of AKT1 after siRNA knock-down of ARHGAP29 was tested. Reduced ARHGAP29 expression was accompanied by significantly reduced AKT1 expression. However, the ratio of active pAKT1 to total AKT1 remained unchanged or was significantly increased after ARHGAP29 knock-down. Our results show that ARHGAP29 could be an important factor in the invasion of aggressive and mesenchymal-transformed breast cancer cells. Further research is required to fully understand the underlying mechanisms.

Interleukin-10 and Small Molecule SHIP1 Allosteric Regulators Trigger Anti-inflammatory Effects through SHIP1/STAT3 Complexes

The anti-inflammatory actions of interleukin-10 (IL10) are thought to be mediated primarily by the STAT3 transcription factor, but pro-inflammatory cytokines such as interleukin-6 (IL6) also act through STAT3. We now report that IL10, but not IL6 signaling, induces formation of a complex between STAT3 and the inositol polyphosphate-5-phosphatase SHIP1 in macrophages. Both SHIP1 and STAT3 translocate to the nucleus in macrophages. Remarkably, sesquiterpenes of the Pelorol family, which we previously described as allosteric activators of SHIP1 phosphatase activity, could induce SHIP1/STAT3 complex formation in cells and mimic the anti-inflammatory action of IL10 in a mouse model of colitis. Using crystallography and docking studies we identified a drug-binding pocket in SHIP1. Our studies reveal new mechanisms of action for both STAT3 and SHIP1 and provide a rationale for use of allosteric SHIP1-activating compounds, which mimic the beneficial anti-inflammatory actions of IL10.

Video Abstract

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Loss of normal interleukin-10 (IL10) function results in inflammatory diseases

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IL10 or SHIP1 agonists induce formation of SHIP1/STAT3 complexes

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SHIP1 Y190 phosphorylation is required for SHIP1/STAT3 complex formation

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SHIP1 agonists mimic IL10 anti-inflammatory action in a mouse model of colitis

Distinct functions of AKT isoforms in breast cancer: a comprehensive review

BACKGROUND

AKT, also known as protein kinase B, is a key element of the PI3K/AKT signaling pathway. Moreover, AKT regulates the hallmarks of cancer, e.g. tumor growth, survival and invasiveness of tumor cells. After AKT was discovered in the early 1990s, further studies revealed that there are three different AKT isoforms, namely AKT1, AKT2 and AKT3. Despite their high similarity of 80%, the distinct AKT isoforms exert non-redundant, partly even opposing effects under physiological and pathological conditions. Breast cancer as the most common cancer entity in women, frequently shows alterations of the PI3K/AKT signaling.

MAIN CONTENT

A plethora of studies addressed the impact of AKT isoforms on tumor growth, metastasis and angiogenesis of breast cancer as well as on therapy response and overall survival in patients. Therefore, this review aimed to give a comprehensive overview about the isoform-specific effects of AKT in breast cancer and to summarize known downstream and upstream mechanisms. Taking account of conflicting findings among the studies, the majority of the studies reported a tumor initiating role of AKT1, whereas AKT2 is mainly responsible for tumor progression and metastasis. In detail, AKT1 increases cell proliferation through cell cycle proteins like p21, p27 and cyclin D1 and impairs apoptosis e.g. via p53. On the downside AKT1 decreases migration of breast cancer cells, for instance by regulating TSC2, palladin and EMT-proteins. However, AKT2 promotes migration and invasion most notably through regulation of β-integrins, EMT-proteins and F-actin. Whilst AKT3 is associated with a negative ER-status, findings about the role of AKT3 in regulation of the key properties of breast cancer are sparse. Accordingly, AKT1 is mutated and AKT2 is amplified in some cases of breast cancer and AKT isoforms are associated with overall survival and therapy response in an isoform-specific manner.

CONCLUSIONS

Although there are several discussed hypotheses how isoform specificity is achieved, the mechanisms behind the isoform-specific effects remain mostly unrevealed. As a consequence, further effort is necessary to achieve deeper insights into an isoform-specific AKT signaling in breast cancer and the mechanism behind it.

Targeting the Akt, GSK-3, Bcl-2 axis in acute myeloid leukemia

Over the last few decades, there has been significant progress in the understanding of the pathogenetic mechanisms of the Acute Myeloid Leukemia (AML). However, despite important advances in elucidating molecular mechanisms, the treatment of AML has not improved significantly, remaining anchored at the standard chemotherapy regimen "3 + 7", with the prognosis of patients remaining severe, especially for the elderly and for those not eligible for transplant procedures. The biological and clinical heterogeneity of AML represents the major obstacle that hinders the improvement of prognosis and the identification of new effective therapeutic approaches. To date, abundant information has been collected on the genetic and molecular alterations of AML carrying prognostic significance. However, not enough is known on how AML progenitors regulate proliferation and survival by redundant and cross-talking signal transduction pathways (STP). Furthermore, it remains unclear how such complicated network affects prognosis and therapeutic treatment options, although many of these molecular determinants are potentially attractive for their druggable characteristics. In this review, some of the key STP frequently deregulated in AML, such as PI3k/Akt/mTOR pathway, GSK3 and components of Bcl-2 family of proteins, are summarized, highlighting in addition their interplay. Based on this information, we reviewed new targeted therapeutic approaches, focusing on the aberrant networks that sustain the AML blast proliferation, survival and drug resistance, aiming to improve disease treatment. Finally, we reported the approaches aimed at disrupting key signaling cross-talk overcoming resistances based on the combination of different targeting therapeutic strategies.

Inflammation in Alzheimer's Disease and Molecular Genetics: Recent Update

Alzheimer's disease (AD) is a complex age-related neurodegenerative disorder of the central nervous system. Since the first description of AD in 1907, many hypotheses have been established to explain its causes. The inflammation theory is one of them. Pathological and biochemical studies of brains from AD individuals have provided solid evidence of the activation of inflammatory pathways. Furthermore, people with long-term medication of anti-inflammatory drugs have shown a reduced risk to develop the disease. After three decades of genetic study in AD, dozens of loci harboring genetic variants influencing inflammatory pathways in AD patients has been identified through genome-wide association studies (GWAS). The most well-known GWAS risk factor that is responsible for immune response and inflammation in AD development should be APOE ε4 allele. However, a growing number of other GWAS risk AD candidate genes in inflammation have recently been discovered. In the present study, we try to review the inflammation in AD and immunity-associated GWAS risk genes like HLA-DRB5/DRB1, INPP5D, MEF2C, CR1, CLU and TREM2.

Akt/PKB: one kinase, many modifications

Akt/PKB, a serine/threonine kinase member of the AGC family of proteins, is involved in the regulation of a plethora of cellular processes triggered by a wide diversity of extracellular signals and is thus considered a key signalling molecule in higher eukaryotes. Deregulation of Akt signalling is associated with a variety of human diseases, revealing Akt-dependent pathways as an attractive target for therapeutic intervention. Since its discovery in the early 1990s, a large body of work has focused on Akt phosphorylation of two residues, Thr308 and Ser473, and modification of these two sites has been established as being equivalent to Akt activation. More recently, Akt has been identified as a substrate for many different post-translational modifications, including not only phosphorylation of other residues, but also acetylation, glycosylation, oxidation, ubiquitination and SUMOylation. These modifications could provide additional regulatory steps for fine-tuning Akt function, Akt trafficking within the cell and/or for determining the substrate specificity of this signalling molecule. In the present review, we provide an overview of these different post-translational modifications identified for Akt, focusing on their consequences for this kinase activity.

PTEN-inhibition by zinc ions augments interleukin-2-mediated Akt phosphorylation

Free zinc ions (Zn(2+)) participate in several signaling pathways. The aim of the present study was to investigate a potential involvement of Zn(2+) in the PI3K/Akt pathway of interleukin (IL)-2 signaling in T-cells. The IL-2 receptor triggers three major pathways, ERK1/2, JAK/STAT5, and PI3K/Akt. We have previously shown that an IL-2-mediated release of lysosomal Zn(2+) into the cytoplasm activates ERK1/2, but not STAT5. In the present study, Akt phosphorylation in response to IL-2 was abrogated by the Zn(2+) chelator N,N,N',N'-tetrakis-2(pyridyl-methyl)ethylenediamine, and was induced by treatment with Zn(2+) and the ionophore pyrithione. The latter were ineffective in cells that were treated with siRNA against the phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a phosphatase that degrades the lipid second messenger PI(3,4,5)P3, which is produced by PI3K and leads to activation of Akt. Inhibition of recombinant PTEN by Zn(2+)in vitro yielded an IC50 of 0.59 nM. Considering a resting free cytoplasmic Zn(2+) level of 0.2 nM in the T-cell line CTLL-2, this seems ideally suited for dynamic regulation by cellular Zn(2+). Oxidation with H2O2 and supplementation with Zn(2+) led to similar changes in the CD spectrum of PTEN. Moreover, Zn(2+) partially prevented the oxidation of cysteines 71 and 124. Hence, we hypothesize that zinc signals affect the IL-2-dependent PI3K/Akt pathway by inhibiting the negative regulator PTEN through binding with a sub-nanomolar affinity to cysteine residues that are essential for its catalytic activity.

Microfilaments make mast cells migrate (rather than degranulate)

Expression of the high-affinity receptor for IgE (FcεRI) provides mast cells with the ability to react in a proinflammatory manner to antigens (Ags). In particular, the immediate secretion of preformed mediators from secretory lysosomes (degranulation) is typical for FcεRI-mediated mast cell activation. In addition to the FcεRI, the stem cell factor receptor, KIT, is expressed at high levels on the surface of mast cells. KIT activation controls mast cell differentiation and survival in vivo and potently stimulates the chemotaxis of these cells. Although FcεRI and KIT initiate many of the same early signaling events in mast cells, FcεRI activation results in potent degranulation and a poor chemotactic response while KIT activation triggers very little degranulation and a strong chemotactic response. Novel data published in this issue of the European Journal of Immunology [Smrž et al. Eur. J. Immunol. 2013. 43: 1873-1882] demonstrate that actin de- and repolymerization, involved in both degranulation and chemotaxis, make all the difference: Pharmacological suppression of F-actin formation converts activated KIT into a strong degranulator. The possible implications for mast cell physiology and pathophysiology are discussed in this Commentary.

Semi-supervised prediction of SH2-peptide interactions from imbalanced high-throughput data

Src homology 2 (SH2) domains are the largest family of the peptide-recognition modules (PRMs) that bind to phosphotyrosine containing peptides. Knowledge about binding partners of SH2-domains is key for a deeper understanding of different cellular processes. Given the high binding specificity of SH2, in-silico ligand peptide prediction is of great interest. Currently however, only a few approaches have been published for the prediction of SH2-peptide interactions. Their main shortcomings range from limited coverage, to restrictive modeling assumptions (they are mainly based on position specific scoring matrices and do not take into consideration complex amino acids inter-dependencies) and high computational complexity. We propose a simple yet effective machine learning approach for a large set of known human SH2 domains. We used comprehensive data from micro-array and peptide-array experiments on 51 human SH2 domains. In order to deal with the high data imbalance problem and the high signal-to-noise ration, we casted the problem in a semi-supervised setting. We report competitive predictive performance w.r.t. state-of-the-art. Specifically we obtain 0.83 AUC ROC and 0.93 AUC PR in comparison to 0.71 AUC ROC and 0.87 AUC PR previously achieved by the position specific scoring matrices (PSSMs) based SMALI approach. Our work provides three main contributions. First, we showed that better models can be obtained when the information on the non-interacting peptides (negative examples) is also used. Second, we improve performance when considering high order correlations between the ligand positions employing regularization techniques to effectively avoid overfitting issues. Third, we developed an approach to tackle the data imbalance problem using a semi-supervised strategy. Finally, we performed a genome-wide prediction of human SH2-peptide binding, uncovering several findings of biological relevance. We make our models and genome-wide predictions, for all the 51 SH2-domains, freely available to the scientific community under the following URLs: http://www.bioinf.uni-freiburg.de/Software/SH2PepInt/SH2PepInt.tar.gz and http://www.bioinf.uni-freiburg.de/Software/SH2PepInt/Genome-wide-predictions.tar.gz, respectively.

TSLP signaling network revealed by SILAC-based phosphoproteomics

Thymic stromal lymphopoietin (TSLP) is a cytokine that plays diverse roles in the regulation of immune responses. TSLP requires a heterodimeric receptor complex consisting of IL-7 receptor α subunit and its unique TSLP receptor (gene symbol CRLF2) to transmit signals in cells. Abnormal TSLP signaling (e.g. overexpression of TSLP or its unique receptor TSLPR) contributes to the development of a number of diseases including asthma and leukemia. However, a detailed understanding of the signaling pathways activated by TSLP remains elusive. In this study, we performed a global quantitative phosphoproteomic analysis of the TSLP signaling network using stable isotope labeling by amino acids in cell culture. By employing titanium dioxide in addition to antiphosphotyrosine antibodies as enrichment methods, we identified 4164 phosphopeptides on 1670 phosphoproteins. Using stable isotope labeling by amino acids in cell culture-based quantitation, we determined that the phosphorylation status of 226 proteins was modulated by TSLP stimulation. Our analysis identified activation of several members of the Src and Tec families of kinases including Btk, Lyn, and Tec by TSLP for the first time. In addition, we report TSLP-induced phosphorylation of protein phosphatases such as Ptpn6 (SHP-1) and Ptpn11 (Shp2), which has also not been reported previously. Co-immunoprecipitation assays showed that Shp2 binds to the adapter protein Gab2 in a TSLP-dependent manner. This is the first demonstration of an inducible protein complex in TSLP signaling. A kinase inhibitor screen revealed that pharmacological inhibition of PI-3 kinase, Jak family kinases, Src family kinases or Btk suppressed TSLP-dependent cellular proliferation making them candidate therapeutic targets in diseases resulting from aberrant TSLP signaling. Our study is the first phosphoproteomic analysis of the TSLP signaling pathway that greatly expands our understanding of TSLP signaling and provides novel therapeutic targets for TSLP/TSLPR-associated diseases in humans.

SHIP2 multiple functions: a balance between a negative control of PtdIns(3,4,5)P₃ level, a positive control of PtdIns(3,4)P₂ production, and intrinsic docking properties

The SH2 domain containing inositol 5-phosphatase 2 (SHIP2) belongs to the family of the mammalian inositol polyphosphate 5-phosphatases. The two closely related isoenzymes SHIP1 (or SHIP) and SHIP2 contain a N-terminal SH2 domain, a catalytic domain, potential PTB domain-binding sites (NPXY), and C-terminal proline-rich regions with consensus sites for SH3 domain interactions. In addition, SHIP2 contains a unique sterile alpha motif (SAM) domain that could be involved in SAM-SAM domain interactions with other proteins or receptors. SHIP2 also shows the presence of an ubiquitin interacting motif at the C-terminal end. SHIP2 is essentially a PI(3,4,5)P(3) 5-phosphatase that negatively controls PI(3,4,5)P(3) levels in intact cells and produce PI(3,4)P(2) . Depending on the cells and stimuli, PI(3,4)P(2) could accumulate at important levels and be a "second messenger" by its own. It could interact with a very large number of target proteins such as PKB or TAPP1 and 2 that control insulin sensitivity. In addition to its catalytic activity, SHIP2 is also a docking protein for a large number of proteins: Cytoskeletal, focal adhesion proteins, scaffold proteins, adaptors, protein phosphatases, and tyrosine kinase associated receptors. These interactions could play a role in the control of cell adhesion, migration, or endocytosis of some receptors. SHIP2 could be acting independently of its phosphatase activity being part of a protein network of some receptors, e.g., the EGF receptor or BCR/ABL. These non-catalytic properties associated to a PI phosphatase have also been reported for other enzymes of the metabolism of myo-inositol such as Ins(1,4,5)P(3) 3-kinases, inositol phosphate multikinase (IPMK), or PTEN.

Murine pancreatic adenocarcinoma dampens SHIP-1 expression and alters MDSC homeostasis and function

Background

Pancreatic cancer is one of the most aggressive cancers, with tumor-induced myeloid-derived suppressor cells (MDSC) contributing to its pathogenesis and ineffective therapies. In response to cytokine/chemokine receptor activation, src homology 2 domain-containing inositol 5′-phosphatase-1 (SHIP-1) influences phosphatidylinositol-3-kinase (PI3K) signaling events, which regulate immunohomeostasis. We hypothesize that factors from murine pancreatic cancer cells cause the down-regulation of SHIP-1 expression, which may potentially contribute to MDSC expansion, and the suppression of CD8⁺ T cell immune responses. Therefore, we sought to determine the role of SHIP-1 in solid tumor progression, such as murine pancreatic cancer.

Methodology and Principal Findings

Immunocompetent C57BL/6 mice were inoculated with either murine Panc02 cells (tumor-bearing [TB] mice) or Phosphate Buffer Saline (PBS) (control mice). Cytometric Bead Array (CBA) analysis of supernatants of cultured Panc02 detected pro-inflammatory cytokines such as IL-6, IL-10 and MCP-1. TB mice showed a significant increase in serum levels of pro-inflammatory factors IL-6 and MCP-1 measured by CBA. qRT-PCR and Western blot analyses revealed the in vivo down-regulation of SHIP-1 expression in splenocytes from TB mice. Western blot analyses also detected reduced SHIP-1 activity, increased AKT-1 and BAD hyper-phosphorylation and up-regulation of BCL-2 expression in splenocytes from TB mice. In vitro, qRT-PCR and Western blot analyses detected reduced SHIP-1 mRNA and protein expression in control splenocytes co-cultured with Panc02 cells. Flow cytometry results showed significant expansion of MDSC in peripheral blood and splenocytes from TB mice. AutoMACS sorted TB MDSC exhibited hyper-phosphorylation of AKT-1 and over-expression of BCL-2 detected by western blot analysis. TB MDSC significantly suppressed antigen-specific CD8⁺ T cell immune responses in vitro.

Conclusion/Significance

SHIP-1 may regulate immune development that impacts MDSC expansion and function, contributing to pancreatic tumor progression. Thus, SHIP-1 can be a potential therapeutic target to help restore immunohomeostasis and improve therapeutic responses in patients with pancreatic cancer.

Inhibitor and activator: dual functions for SHIP in immunity and cancer

SHIP1 is at the nexus of intracellular signaling pathways in immune cells that mediate bone marrow (BM) graft rejection, production of inflammatory and immunosuppressive cytokines, immunoregulatory cell formation, the BM niche that supports development of the immune system, and immune cancers. This review summarizes how SHIP participates in normal immune physiology or the pathologies that result when SHIP is mutated. This review also proposes that SHIP can have either inhibitory or activating roles in cell signaling that are determined by whether signaling pathways distal to PI3K are promoted by SHIP's substrate (PI(3,4,5)P(3) ) or its product (PI(3,4)P(2) ). This review also proposes the "two PIP hypothesis" that postulates that both SHIP's product and its substrate are necessary for a cancer cell to achieve and sustain a malignant state. Finally, due to the recent discovery of small molecule antagonists and agonists for SHIP, this review discusses potential therapeutic settings where chemical modulation of SHIP might be of benefit.

Phosphoinositide phosphatases in cell biology and disease

Phosphoinositides are essential signaling molecules linked to a diverse array of cellular processes in eukaryotic cells. The metabolic interconversions of these phospholipids are subject to exquisite spatial and temporal regulation executed by arrays of phosphatidylinositol (PtdIns) and phosphoinositide-metabolizing enzymes. These include PtdIns- and phosphoinositide-kinases that drive phosphoinositide synthesis, and phospholipases and phosphatases that regulate phosphoinositide degradation. In the past decade, phosphoinositide phosphatases have emerged as topics of particular interest. This interest is driven by the recent appreciation that these enzymes represent primary mechanisms for phosphoinositide degradation, and because of their ever-increasing connections with human diseases. Herein, we review the biochemical properties of six major phosphoinositide phosphatases, the functional involvements of these enzymes in regulating phosphoinositide metabolism, the pathologies that arise from functional derangements of individual phosphatases, and recent ideas concerning the involvements of phosphoinositide phosphatases in membrane traffic control.

The Interleukin (IL)‐2 Family Cytokines: Survival and Proliferation Signaling Pathways in T Lymphocytes

Lymphocyte populations in the immune system are maintained by a well-organized balance between cellular proliferation, cellular survival and programmed cell death (apoptosis). One of the primary functions of many cytokines is to coordinate these processes. In particular, the interleukin (IL)-2 family of cytokines, which consists of six cytokines (IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21) that all share a common receptor subunit (gammac), plays a major role in promoting and maintaining T lymphocyte populations. The details of the molecular signaling pathways mediated by these cytokines have not been fully elucidated. However, the three major pathways clearly involved include the JAK/STAT, MAPK and phosphatidylinositol 3-kinase (P13K) pathways. The details of these pathways as they apply to the IL-2 family of cytokines is discussed, with a focus on their roles in proliferation and survival signaling.

Differential roles for the inositol phosphatase SHIP in the regulation of macrophages and lymphocytes

The SH2 domain-containing inositol 5'-phosphatase (SHIP) negatively regulates antigen, cytokine, and Fc receptor signaling pathways in immune cells. Our knowledge of the function of SHIP largely derives from in vitro studies that utilized SHIP-deficient cell lines and immune cells isolated from SHIP null mice. To avoid the pleiotropic effects observed in mice with germline deletion of SHIP, we have used the Cre-lox system to generate SHIP conditional knockout mice with deletion in specific immune cell populations. In this review we summarize our observations from mice with deletion of SHIP in lymphocyte and macrophage lineages and contrast them with earlier data gathered by the analysis of SHIP null mice.

Survival of monocytes and macrophages and their role in health and disease

Macrophages are versatile cells involved in health and disease. These cells act as scavengers to rid the body of apoptotic and senescent cells and debris through their phagocytic function. Although this is a primary function of these cells, macrophages play vital roles in inflammation and repair of damaged tissue. Macrophages secrete a large number of cytokines, chemokines and growth factors that recruit and activate a variety of cell types to inflamed tissue compartments. These cells are also critical in cell-mediated immunity and in the resolution of inflammation. Since macrophages, and their precursors, blood monocytes, are important in regulating and resolving inflammation, prolonged cellular survival in tissue compartments could be detrimental. Thus, factors that regulate the fate of monocyte and macrophage survival are important in cellular homeostasis. In this article, we will explore stimuli and the intracellular pathways important in regulating macrophage survival and implication in human disease.

PI(3,4,5)P3 and PI(3,4)P2 levels correlate with PKB/akt phosphorylation at Thr308 and Ser473, respectively; PI(3,4)P2 levels determine PKB activity

The PI3K-PKB pathway is an important and widely studied pathway in cell signaling. The enzyme activity of PI3K produces D-3 phosphoinositides, including the lipid second messengers PI(3,4,5)P3 and PI(3,4)P2. PI(3,4,5)P3 has been deemed to be the most important second messenger for triggering PKB phosphorylation. PKB has two regulatory phosphorylation sites, Thr308 and Ser473, both of which contribute to its full activity. The direct relationship between PI3K lipid products and PKB phosphorylation is still not entirely clear. Our previous study showed that PI(3,4)P2 has a specific role in contributing to PKB phosphorylation on Ser473 sites in mast cells. In this study, we used two strategies to further elucidate this question in a well-established B cell system. First, by SHIP overexpression, we examined PKB activation under conditions where PI(3,4,5)P3 accumulation is largely suppressed. Second, we used dose response of different forms of B-cell receptor ligands to manipulate the relative levels of PI(3,4,5)P3 and PI(3,4)P2. Our results demonstrate a close relationship between PI(3,4,5)P3 levels and Thr308 phosphorylation levels, and PI(3,4)P2 levels and Ser473 phosphorylation levels, respectively. Furthermore, overall PKB activity, primarily consisting of cytosolic enzyme, was dependent upon levels of PI(3,4)P2, while only membrane-associated PKB activity was dependent upon PI(3,4,5)P3 levels. We conclude that PI(3,4,5)P3 and PI(3,4)P2 have distinct roles in determining PKB phosphorylation and activity. Thus, when investigating PI3K-PKB pathways, the importance of both lipids must be considered.

Phosphoinositide phosphatases in a network of signalling reactions

Phosphoinositide phosphatases dephosphorylate the three positions (D-3, 4 and 5) of the inositol ring of the poly-phosphoinositides. They belong to different families of enzymes. The PtdIns(3,4)P(2) 4-phosphatase family, the tumour suppressor phosphatase and tensin homolog deleted on chromosome 10 (PTEN), SAC1 domain phosphatases and myotubularins belong to the tyrosine protein phosphatases superfamily. They share the presence of a conserved cysteine residue in the consensus CX(5)RT/S. Another family consists of the inositol polyphosphate 5-phosphatase isoenzymes. The importance of these phosphoinositide phosphatases in cell regulation is illustrated by multiple examples of their implications in human diseases such as Lowe syndrome, X-linked myotubular myopathy, cancer, diabetes or bacterial infection.

The role of SHIP in cytokine-induced signaling

The phosphatidylinositol (PI)-3 kinase (PI3K) pathway plays a central role in regulating many biological processes via the generation of the key second messenger PI-3,4,5-trisphosphate (PI-3,4,5-P3). This membrane-associated phospholipid, which is rapidly, albeit transiently, synthesized from PI-4,5-P2 by PI3K in response to a diverse array of extracellular stimuli, attracts pleckstrin homology (PH) domain-containing proteins to membranes to mediate its many effects. To ensure that the activation of this pathway is appropriately suppressed/terminated, the ubiquitously expressed tumor suppressor PTEN hydrolyzes PI-3,4,5-P3 back to PI-4,5-P2 while the 145-kDa hemopoietic-restricted SH2-containing inositol 5'- phosphatase, SHIP (also known as SHIP1), the 104-kDa stem cell-restricted SHIP (sSHIP) and the more widely expressed 150-kDa SHIP2 hydrolyze PI-3,4,5-P3 to PI-3,4-P2. In this review we will concentrate on the properties of the three SHIPs, with special emphasis being placed on the role that SHIP plays in cytokine-induced signaling.

SHIP, SHIP2, and PTEN activities are regulated in vivo by modulation of their protein levels: SHIP is up-regulated in macrophages and mast cells by lipopolysaccharide

The phosphatidylinositol-3 kinase (PI3K) pathway plays a central role in regulating numerous biologic processes, including survival, adhesion, migration, metabolic activity, proliferation, differentiation, and end cell activation through the generation of the potent second messenger PI-3,4,5-trisphosphate (PI-3,4,5-P(3)). To ensure that activation of this pathway is appropriately suppressed/terminated, the ubiquitously expressed 54-kDa tumor suppressor PTEN hydrolyzes PI-3,4,5-P(3) to PI-4,5-P(2), whereas the 145-kDa hematopoietic-restricted SH2-containing inositol 5'-phosphatase SHIP (also known as SHIP1), the 104-kDa stem cell-restricted SHIP sSHIP, and the more widely expressed 150-kDa SHIP2 break it down to PI-3,4-P(2). In this review, we focus on the properties of these phospholipid phosphatases and summarize recent data showing that the activities of these negative regulators often are modulated by simply altering their protein levels. We also highlight the critical role that SHIP plays in lipopolysaccharide-induced macrophage activation and in endotoxin tolerance.

SH2-containing inositol 5-phosphatases 1 and 2 in blood platelets: their interactions and roles in the control of phosphatidylinositol 3,4,5-trisphosphate levels

Src homology domain 2-containing inositol 5-phosphatases 1 and 2 (SHIP1 and SHIP2) are capable of dephosphorylating the second messenger PtdIns(3,4,5) P3 (phosphatidylinositol 3,4,5-trisphosphate) and interacting with several signalling proteins. SHIP1 is essentially expressed in haematopoietic cells, whereas SHIP2, a closely related enzyme, is ubiquitous. In the present study, we show that SHIP1 and SHIP2 are expressed as functional PtdIns(3,4,5) P3 5-phosphatases in human blood platelets and are capable of interacting when these two lipid phosphatases are co-expressed, either naturally (platelets and A20 B lymphoma cells) or artificially (COS-7 cells). Using COS-7 cells transfected with deletion mutants of SHIP2, we demonstrate that the Src homology domain 2 of SHIP2 is the minimal and sufficient protein motif responsible for the interaction between the two phosphatases. These results prompted us to investigate the relative importance of SHIP1 and SHIP2 in the control of PtdIns(3,4,5) P3 levels in platelets using homozygous or heterozygous SHIP1- or SHIP2-deficient mice. Our results strongly suggest that SHIP1, rather than SHIP2, plays a major role in controlling PtdIns(3,4,5) P3 levels in response to thrombin or collagen activation of mouse blood platelets.

Survival of acute myeloid leukemia cells requires PI3 kinase activation

The mechanisms that regulate the growth and survival of acute myeloid leukemia (AML) cells are largely unknown. We hypothesized that constitutive activation of phosphatidyl-inositide 3 kinase (PI3 kinase) could regulate survival in primary cells from patients with AML. Here we demonstrate that Akt, a critical substrate of PI3 kinase, is activated in AML blasts. In a short-term culture system, most AML patient samples showed a dose-dependent decrease in survival after incubation with the PI3 kinase inhibitor LY294002. This decrease in survival was partially due to the induction of apoptosis. Furthermore, we have shown that p70 S6 kinase and 4EBP-1, downstream mediators of Akt signaling, also are phosphorylated in AML blasts. Phosphorylation of these proteins is inhibited by the mTOR inhibitor RAD001. Incubation of AML blasts with RAD001 induces only a small decrease in survival of the cells; however, when combined with Ara-C, RAD001 enhances the toxicity of Ara-C. These results demonstrate that constitutive activation of the PI3 kinase pathway is necessary for the survival of AML blasts and that targeting of this pathway with pharmacologic inhibitors may be of clinical benefit in treatment of AML.

Association of the Src homology 2 domain-containing inositol 5' phosphatase (SHIP) to releasability in human basophils

During the study of the biology of the Human recombinant Histamine Releasing Factor (HrHRF), we uncovered a hyperreleasable phenotype of basophils from HrHRF-responder donors. Basophils from these donors released histamne to HrHRF, IL-3 and D(2)O. While there has been a significant amount of work elucidating signal transduction events in human basophils, the reason for this hyperreleasable phenotype remained illusive. A clue to the releasability of these highly allergic, asthmatic HrHRF-responder donor basophils was demonstrated in studies using SHIP knockout mice. Bone marrow-derived mast cells from the SHIP knockout mice demonstrated hyperreleasability to stimuli through the IgE receptor and alteration of subsequent signal transduction events. We have demonstrated a highly significant negative correlation between the amount of SHIP protein per cell equivalent and maximum histamine release to HrHRF. These results provide a clue to the hyperreleasable phenotype and implicate SHIP as an additional regulator of secretion in human basophils.

The role of SHIP in mast cell degranulation and IgE-induced mast cell survival

Atopic disorders are on the increase in the Western world and are due, at least in part, to an overactive mast cell response. A better understanding of the intracellular signalling pathways that regulate both mast cell degranulation and the secretion of arachidonic acid metabolites and inflammatory cytokines could help in the treatment of these disorders. The src homology 2-containing inositol-polyphosphate 5'-phosphatase, SHIP, has been shown to be a key 'gatekeeper' of mast cell degranulation. SHIP prevents degranulation from occuring when IgE alone binds to the high-affinity receptor for IgE (FcvarepsilonR1), SHIP restrains it when IgE-bound FcvarepsilonR1 are engaged by multivalent allergens, and SHIP inhibits it when an IgG against the same allergen co-clusters the inhibitory low-affinity receptor for IgG (FcgammaRIIB) with the IgE receptor. SHIP acts as a negative regulator of degranulation by hydrolyzing phosphatidylinositol-3,4,5-trisphosphate, a second messenger generated in activated cells by phosphatidylinositol 3-kinase. Our finding that binding of only IgE to the FcvarepsilonR1 of SHIP-deficient mast cells results in massive degranulation, led us to investigate the signalling pathways that are triggered in normal murine bone marrow-derived mast cells by monomeric IgE. We report here that monomeric IgE activates signalling pathways resulting in mast cell survival, without stimulating degranulation or proliferation. These studies demonstrate that mast cell sensitization by IgE is an active rather than a passive process.

Activation of SHIP by NADPH oxidase-stimulated Lyn leads to enhanced apoptosis in neutrophils

Neutrophils undergo rapid spontaneous apoptosis. Multiple antiapoptotic stimuli can inhibit this process via activation of the Akt pathway. However, despite no such effect singly, combined anti- and proapoptotic stimuli inhibit Akt activity, leaving the cells susceptible to accelerated apoptosis. The blockade of Akt activation depended on reduced phosphoinositide 3,4,5-trisphosphate levels but not decreased phosphatidylinositol 3-kinase activity, thus implicating the involvement of an inositol phosphatase. Evidence for SHIP involvement was provided by SHIP localization to membrane receptors and subsequent activation along with the observed inability of SHIP -/- neutrophils to exhibit enhanced apoptosis with the stimulus combination. Activation of SHIP was found to depend on Lyn activation, and this, in turn, required NADPH oxidase. Neutrophils from chronic granulomatous disease patients and Lyn -/- mice no longer responded to the combined stimuli. Thus, we propose a role for oxidants and Lyn in SHIP regulation and suggest a novel mechanism for regulating neutrophil apoptosis.

Embryonic and hematopoietic stem cells express a novel SH2-containing inositol 5'-phosphatase isoform that partners with the Grb2 adapter protein

SH2-containing inositol 5'-phosphatase (SHIP) modulates the activation of immune cells after recruitment to the membrane by Shc and the cytoplasmic tails of receptors. A novel SHIP isoform of approximately 104 kd expressed in primitive stem cell populations (s-SHIP) is described. It was found that s-SHIP is expressed in totipotent embryonic stem cells to the exclusion of the 145-kd SHIP isoform expressed in differentiated hematopoietic cells. s-SHIP is also expressed in primitive hematopoietic stem cells, but not in lineage-committed hematopoietic cells. In embryonic stem cells, s-SHIP partners with the adapter protein Grb2 without tyrosine phosphorylation and is present constitutively at the cell membrane. It is postulated that s-SHIP modulates the activation threshold of primitive stem cell populations.

Partially distinct molecular mechanisms mediate inhibitory FcgammaRIIB signaling in resting and activated B cells

FcgammaRIIB functions as an inhibitory receptor to dampen B cell Ag receptor signals and immune responses. Accumulating evidence indicates that ex vivo B cells require the inositol 5-phosphatase, Src homology domain 2-containing inositol 5-phosphatase (SHIP), for FcgammaRIIB-mediated inhibitory signaling. However, we report here that LPS-activated primary B cells do not require SHIP and thus differ from resting B cells. SHIP-deficient B cell blasts display efficient FcgammaRIIB-dependent inhibition of calcium mobilization as well as Akt and extracellular signal-related protein kinase phosphorylation. Surprisingly, FcgammaRIIB-dependent degradation of phosphatidylinositol 3,4,5-trisphosphate and conversion into phosphatidylinositol 3,4-bisphosphate occur in SHIP-deficient B cell blasts, demonstrating the function of an additional inositol 5-phosphatase. Further analysis reveals that while resting cells express only SHIP, B cell blasts also express the recently described inositol 5-phosphatase, SHIP-2. Finally, data suggest that both SHIP-2 and SHIP can mediate downstream biologic consequences of FcgammaRIIB signaling, including inhibition of the proliferative response.

Identification of a novel lipopolysaccharide-inducible gene with key features of both A kinase anchor proteins and chs1/beige proteins

Mutations in chs1/beige result in a deficiency in intracellular transport of vesicles that leads to a generalized immunodeficiency in mice and humans. The function of NK cells, CTL, and granulocytes is impaired by these mutations, indicating that polarized trafficking of vesicles is controlled by CHS1/beige proteins. However, a molecular explanation for this defect has not been identified. Here we describe a novel gene with orthologues in mice, humans, and flies that contains key features of both chs1/beige and A kinase anchor genes. We designate this novel gene lba for LPS-responsive, beige-like anchor gene. Expression of lba is induced after LPS stimulation of B cells and macrophages. In addition, lba is expressed in many other tissues in the body and has three distinct mRNA isoforms that are differentially expressed in various tissues. Strikingly, LBA-green-fluorescent protein (GFP) fusion proteins are localized to vesicles after LPS stimulation. Confocal microscopy indicates this protein is colocalized with the trans-Golgi complex and some lysosomes. Further analysis by immunoelectron microscopy demonstrates that LBA-GFP fusion protein can localize to endoplasmic reticulum, plasma membrane, and endocytosis vesicles in addition to the trans-Golgi complex and lysosomes. We hypothesize that LBA/CHS1/BG proteins function in polarized vesicle trafficking by guiding intracellular vesicles to activated receptor complexes and thus facilitate polarized secretion and/or membrane deposition of immune effector molecules.

SHIP's C-terminus is essential for its hydrolysis of PIP3 and inhibition of mast cell degranulation

The SH2-containing inositol-5'-phosphatase, SHIP, restrains bone marrow-derived mast cell (BMMC) degranulation, at least in part, by hydrolyzing phosphatidylinositol (PI)-3-kinase generated PI-3,4,5-P(3) (PIP3) to PI-3,4-P(2). To determine which domains within SHIP influence its ability to hydrolyze PIP3, bone marrow from SHIP(-/-) mice was retrovirally infected with various SHIP constructs. Introduction of wild-type SHIP into SHIP(-/-) BMMCs reverted the Steel factor (SF)-induced increases in PIP3, calcium entry, and degranulation to those observed in SHIP(+/+) BMMCs. A 5'-phosphatase dead SHIP, however, could not revert the SHIP(-/-) response, whereas a SHIP mutant in which the 2 NPXY motifs were converted to NPXFs (2NPXF) could partially revert the SHIP(-/-) response. SF stimulation of BMMCs expressing the 2NPXF, which could not bind Shc, led to the same level of mitogen-activated protein kinase (MAPK) phosphorylation as that seen in BMMCs expressing the other constructs. Surprisingly, C-terminally truncated forms of SHIP, lacking different amounts of the proline rich C-terminus, could not revert the SHIP(-/-) response at all. These results suggest that the C-terminus plays a critical role in enabling SHIP to hydrolyze PIP(3) and inhibit BMMC degranulation.

SH2-containing inositol 5'-phosphatase SHIP2 associates with the p130(Cas) adapter protein and regulates cellular adhesion and spreading

In a previous study, we found that the SHIP2 protein became tyrosine phosphorylated and associated with the Shc adapter protein in response to the treatment of cells with growth factors and insulin (T. Habib, J. A. Hejna, R. E. Moses, and S. J. Decker, J. Biol. Chem. 273:18605-18609, 1998). We describe here a novel interaction between SHIP2 and the p130(Cas) adapter protein, a mediator of actin cytoskeleton organization. SHIP2 and p130(Cas) association was detected in anti-SHIP2 immunoprecipitates from several cell types. Reattachment of trypsinized cells stimulated tyrosine phosphorylation of SHIP2 and increased the formation of a complex containing SHIP2 and a faster-migrating tyrosine-phosphorylated form of p130(Cas). The faster-migrating form of p130(Cas) was no longer recognized by antibodies to the amino terminus of p130(Cas) and appeared to be generated through proteolysis. Interaction of the SHIP2 protein with the various forms of p130(Cas) was mediated primarily through the SH2 domain of SHIP2. Immunofluorescence studies indicated that SHIP2 localized to focal contacts and to lamellipodia. Increased adhesion was observed in HeLa cells transiently expressing exogenous WT-SHIP2. These effects were not seen with SHIP2 possessing a mutation in the SH2 domain (R47G). Transfection of a catalytic domain deletion mutant of SHIP2 (DeltaRV) inhibited cell spreading. Taken together, our studies suggest an important role for SHIP2 in adhesion and spreading.

SHP2 and cbl participate in alpha-chemokine receptor CXCR4-mediated signaling pathways

Stromal cell-derived factor (SDF)-1alpha and its receptor, CXCR4, play an important role in cell migration, embryonic development, and human immunodeficiency virus infection. However, the cellular signaling pathways that mediate these processes are not fully elucidated. We and others have shown that the binding of SDF-1alpha to CXCR4 activates phosphatidylinositol-3 kinase (PI-3 kinase), p44/42 mitogen-associated protein kinase, and the transcription factor nuclear factor-kappaB, and it also enhances the tyrosine phosphorylation and association of proteins involved in the formation of focal adhesions. In this study, we examined the role of phosphatases in CXCR4-mediated signaling pathways. We observed significant inhibition of SDF-1alpha-induced migration by phosphatase inhibitors in CXCR4-transfected pre-B lymphoma L1.2 cells, Jurkat T cells, and peripheral blood lymphocytes. Further studies revealed that SDF-1alpha stimulation induced robust tyrosine phosphorylation in the SH2-containing phosphatase SHP2. SHP2 associated with the CXCR4 receptor and the signaling molecules SHIP, cbl, and fyn. Overexpression of wild-type SHP2 increased SDF-1alpha-induced chemotaxis. Enhanced activation of fyn and lyn kinases and the tyrosine phosphorylation of cbl were also observed. In addition, SDF-1alpha stimulation enhanced the association of cbl with PI-3 kinase, Crk-L, and 14-3-3beta proteins. Our results suggest that CXCR4-mediated signaling is regulated by SHP2 and cbl, which collectively participate in the formation of a multimeric signaling complex.

A regulatory role for Src homology 2 domain-containing inositol 5'-phosphatase (SHIP) in phagocytosis mediated by Fc gamma receptors and complement receptor 3 (alpha(M)beta(2); CD11b/CD18)

The Src homology 2 domain-containing inositol 5'-phosphatase (SHIP) is recruited to immunoreceptor tyrosine-based inhibition motif (ITIM)-containing proteins, thereby suppressing phosphatidylinositol 3-kinase (PI 3-kinase)-dependent pathways. The role of SHIP in phagocytosis, a PI 3-kinase-dependent pathway, is unknown. Overexpression of SHIP in macrophages led to an inhibition of phagocytosis mediated by receptors for the Fc portion of IgG (Fc gamma Rs). In contrast, macrophages expressing catalytically inactive SHIP or lacking SHIP expression demonstrated enhanced phagocytosis. To determine whether SHIP regulates phagocytosis mediated by receptors that are not known to recruit ITIMs, we determined the effect of SHIP expression on complement receptor 3 (CR3; CD11b/CD18; alpha(M)beta(2))-dependent phagocytosis. Macrophages overexpressing SHIP demonstrated impaired CR3-mediated phagocytosis, whereas macrophages expressing catalytically inactive SHIP demonstrated enhanced phagocytosis. CR3-mediated phagocytosis in macrophages derived from SHIP(-/-) mice was up to 2.5 times as efficient as that observed in macrophages derived from littermate controls. SHIP was localized to Fc gamma R- and CR3-containing phagocytic cups and was recruited to the cytoskeleton upon clustering of CR3. In a transfected COS cell model of activation-independent CR3-mediated phagocytosis, catalytically active but not inactive SHIP also inhibited phagocytosis. We conclude that PI 3-kinase(s) and SHIP regulate multiple forms of phagocytosis and that endogenous SHIP plays a role in modulating beta(2) integrin outside-in signaling.

Enzymatic activity of the Src homology 2 domain-containing inositol phosphatase is regulated by a plasma membrane location

The negative regulatory role of the Src homology 2 domain-containing inositol 5-phosphatase (SHIP) has been invoked in a variety of receptor-mediated signaling pathways. In B lymphocytes, co-clustering of antigen receptor surface immunoglobulin with FcgammaRIIb promotes the negative effects of SHIP, but how SHIP activity is regulated is unknown. To explore this issue, we investigated the effect of SHIP phosphorylation, receptor tyrosine engagement by its Src homology 2 domain, and membrane recruitment of SHIP on its enzymatic activity. We examined two SHIP phosphorylation kinase candidates, Lyn and Syk, and observed that the Src protein-tyrosine kinase, Lyn is far superior to Syk in its ability to phosphorylate SHIP both in vitro and in vivo. However, we found a minimal effect of phosphorylation or receptor tyrosine engagement of SHIP on its enzymatic activity, whereas membrane localization of SHIP significantly reduced cellular phosphatidylinositol 3,4, 5-triphosphate levels. Based on our results, we propose that a membrane localization of SHIP is the crucial event in the induction of its phosphatase effects.