The role of SHIP1 in T-lymphocyte life and death

SHIP1 [SH2 (Src homology 2)-containing inositol phosphatase-1], an inositol 5-phosphatase expressed in haemopoietic cells, acts by hydrolysing the 5-phosphates from PtdIns(3,4,5)P(3) and Ins(1,3,4,5)P(4), thereby negatively regulating the PI3K (phosphoinositide 3-kinase) pathway. SHIP1 plays a major role in inhibiting proliferation of myeloid cells. As a result, SHIP1(-/-) mice have an increased number of neutrophils and monocytes/macrophages due to enhanced survival and proliferation of their progenitors. Although SHIP1 contributes to PtdIns(3,4,5)P(3) metabolism in T-lymphocytes, its exact role in this cell type is much less explored. Jurkat cells have recently emerged as an interesting tool to study SHIP1 function in T-cells because they do not express SHIP1 at the protein level, thereby allowing reintroduction experiments in a relatively easy-to-use system. Data obtained from SHIP1 reintroduction have revealed that SHIP1 not only acts as a negative player in T-cell lines proliferation, but also regulates critical pathways, such as NF-kappaB (nuclear factor kappaB) activation, and also appears to remarkably inhibit T-cell apoptosis. On the other hand, experiments using primary T-cells from SHIP1(-/-) mice have highlighted a new role for SHIP1 in regulatory T-cell development, but also emphasize that this protein is not required for T-cell proliferation. In support of these results, SHIP1(-/-) mice are lymphopenic, suggesting that SHIP1 function in T-cells differs from its role in the myeloid lineage.

The inositol 5'-phosphatase SHIP-2 negatively regulates IgE-induced mast cell degranulation and cytokine production

Aggregation of the high-affinity IgE receptor (FcepsilonRI) on mast cells initiates signaling pathways leading to degranulation and cytokine release. It has been reported that SHIP-1 negatively regulates FcepsilonRI-triggered pathways but it is unknown whether its homologous protein SHIP-2 has the same function. We have used a lentiviral-based RNA interference technique to obtain SHIP-2 knockdown bone marrow-derived mast cells (BMMCs) and have found that elimination of SHIP-2 results in both increased mast cell degranulation and cytokine (IL-4 and IL-13) gene expression upon FcepsilonRI stimulation. Elimination of SHIP-2 from BMMCs has no effect on FcepsilonRI-triggered calcium flux, tyrosine phosphorylation of MAPKs or in actin depolymerization following activation. Rather, we observe that absence of SHIP-2 results in increased activation of the small GTPase Rac-1 and in enhanced microtubule polymerization upon FcepsilonRI engagement. Coimmunoprecipitation experiments in rat basophilic leukemia (RBL 2H3) cells show that SHIP-2 interacts with the FcepsilonRI beta-chain, Gab2 and Lyn and that unlike SHIP-1, it does not associate with SHC in mast cells. Our results report a negative regulatory role of SHIP-2 on mast cell activation that is calcium independent and distinct from the regulation by SHIP-1.

T cell-specific deletion of the inositol phosphatase SHIP reveals its role in regulating Th1/Th2 and cytotoxic responses

The 5'-phosphoinositol phosphatase SHIP negatively regulates signaling pathways triggered by antigen, cytokine and Fc receptors in both lymphocytes and myeloid cells. Mice with germ-line (null) deletion of SHIP develop a myeloproliferative-like syndrome that causes early lethality. Lymphocyte anomalies have been observed in SHIP-null mice, but it is unclear whether they are due to an intrinsic requirement of SHIP in these cells or a consequence of the severe myeloid pathology. To precisely address the function of SHIP in T cells, we have generated mice with T cell-specific deletion of SHIP. In the absence of SHIP, we found no differences in thymic selection or in the activation state and numbers of regulatory T cells in the periphery. In contrast, SHIP-deficient T cells do not skew efficiently to Th2 in vitro. Mice with T cell-specific deletion of SHIP show poor antibody responses on Alum/NP-CGG immunization and diminished Th2 cytokine production when challenged with Schistosoma mansoni eggs. The failure to skew to Th2 responses may be the consequence of increased basal levels of the Th1-associated transcriptional factor T-bet, resulting from enhanced sensitivity to cytokine-mediated T-bet induction. SHIP-deficient CD8(+) cells show enhanced cytotoxic responses, consistent with elevated T-bet levels in these cells. Overall our experiments indicate that in T cells SHIP negatively regulates cytokine-mediated activation in a way that allows effective Th2 responses and limits T cell cytotoxicity.

Multiple pathways involved in the biosynthesis of anandamide

Endocannabinoids, including anandamide (arachidonoyl ethanolamide) have been implicated in the regulation of a growing number of physiological and pathological processes. Anandamide can be generated from its membrane phospholipid precursor N-arachidonoyl phosphatidylethanolamine (NAPE) through hydrolysis by a phospholipase D (NAPE-PLD). Recent evidence indicates, however, the existence of two additional, parallel pathways. One involves the sequential deacylation of NAPE by alpha,beta-hydrolase 4 (Abhd4) and the subsequent cleavage of glycerophosphate to yield anandamide, and the other one proceeds through phospholipase C-mediated hydrolysis of NAPE to yield phosphoanandamide, which is then dephosphorylated by phosphatases, including the tyrosine phosphatase PTPN22 and the inositol 5' phosphatase SHIP1. Conversion of synthetic NAPE to AEA by brain homogenates from wild-type and NAPE-PLD(-/-) mice can proceed through both the PLC/phosphatase and Abdh4 pathways, with the former being dominant at shorter (<10 min) and the latter at longer (60 min) incubations. In macrophages, the endotoxin-induced synthesis of anandamide proceeds uniquely through the phospholipase C/phosphatase pathway.

Induced SHIP deficiency expands myeloid regulatory cells and abrogates graft-versus-host disease

Graft-vs-host disease (GVHD) is the leading cause of treatment-related death in allogeneic bone marrow (BM) transplantation. Immunosuppressive strategies to control GVHD are only partially effective and often lead to life-threatening infections. We previously showed that engraftment of MHC-mismatched BM is enhanced and GVHD abrogated in recipients homozygous for a germline SHIP mutation. In this study, we report the development of a genetic model in which SHIP deficiency can be induced in adult mice. Using this model, we show that the induction of SHIP deficiency in adult mice leads to a rapid and significant expansion of myeloid suppressor cells in peripheral lymphoid tissues. Consistent with expansion of myeloid suppressor cells, splenocytes and lymph node cells from adult mice with induced SHIP deficiency are significantly compromised in their ability to prime allogeneic T cell responses. These results demonstrate that SHIP regulates homeostatic signals for these immunoregulatory cells in adult physiology. Consistent with these findings, induction of SHIP deficiency before receiving a T cell-replete BM graft abrogates acute GVHD. These findings indicate strategies that target SHIP could increase the efficacy and utility of allogeneic BM transplantation, and thereby provide a curative therapy for a wide spectrum of human diseases.

Deficiency of Src homology 2 domain-containing inositol 5-phosphatase 1 affects platelet responses and thrombus growth

Platelets are critical for normal hemostasis. Their deregulation can lead to bleeding or to arterial thrombosis, a primary cause of heart attack and ischemic stroke. Src homology 2 domain-containing inositol 5-phosphatase 1 (SHIP1) is a 5-phosphatase capable of dephosphorylating the phosphatidylinositol 3,4,5-trisphosphate second messenger into phosphatidylinositol 3,4-bisphosphate. SHIP1 plays a critical role in regulating the level of these 2 lipids in platelets. Using SHIP1-deficient mice, we found that its loss affects platelet aggregation in response to several agonists with minor effects on fibrinogen binding and beta(3) integrin tyrosine phosphorylation. Accordingly, SHIP1-null mice showed defects in arterial thrombus formation in response to a localized laser-induced injury. Moreover, these mice had a prolonged tail bleeding time. Upon stimulation, SHIP1-deficient platelets showed large membrane extensions, abnormalities in the open canalicular system, and a dramatic decrease in close cell-cell contacts. Interestingly, SHIP1 appeared to be required for platelet contractility, thrombus organization, and fibrin clot retraction. These data indicate that SHIP1 is an important element of the platelet signaling machinery to support normal hemostasis. To our knowledge, this is the first report unraveling an important function of SHIP1 in the activation of hematopoietic cells, in contrast to its well-documented role in the negative regulation of lymphocytes.

s-SHIP associates with receptor complexes essential for pluripotent stem cell growth and survival

Embryonic stem (ES) cells are pluripotent cells that have the ability to either self-renew or differentiate into any cell type found in the mammalian body. The signaling pathways required for self-renewal of these cells are yet to be defined. Previously we identified a stem cell-specific isoform of the protein SH2 domain-containing 5'-inositol phosphatase (SHIP) that we call s-SHIP, which is expressed in both pluripotent ES cells and adult tissue-specific multipotent cells, such as hematopoietic stem cells (HSCs). s-SHIP lacks an SH2 domain but contains a 5'-inositol phosphatase domain and several protein-protein interaction domains that potentially enable its participation in many different signaling pathways. Here we show that s-SHIP associates with gp130, which forms a heterodimeric complex with the leukemia inhibitory factor receptor (LIFR). Signaling through LIFR and other receptors that heterodimerize with gp130 is critical for growth and survival of ES cells and HSCs. Our findings provide biochemical evidence that s-SHIP participates in signaling pathways important for the maintenance of pluripotent stem cell populations.

SHIP1 negatively regulates proliferation of osteoclast precursors via Akt-dependent alterations in D-type cyclins and p27

Osteoclasts arise from macrophage progenitors in bone marrow (BMMs) as a consequence of signaling events elicited by M-CSF and receptor activator of NF-kappaB ligand, acting on their unique receptors, via c-Fms and receptor activator of NF-kappaB. Both receptors activate the PI3K and MAPK pathways, which promote cell proliferation and survival. SHIP1 is essential for normal bone homeostasis, as mice lacking the protein exhibit osteoporosis resulting from increased numbers of hyper-resorptive osteoclasts. In this study, we show that BMMs from SHIP1 null mice respond to M-CSF, but not receptor activator of NF-kappaB ligand, by increasing Akt activation. In consequence, there are up-regulation of D-type cyclins, down-regulation of the cyclin-dependent kinase inhibitor p27, and, therefore, increased phosphorylation of the retinoblastoma protein and cell proliferation. Surprisingly, cell survival of wild-type and knockout BMMs is unaltered. Finally, osteoclastogenesis and periarticular bone erosions are markedly increased in SHIP1(-/-) mice with inflammatory arthritis, a condition characterized by increased M-CSF expression. The SHIP1/Akt pathway therefore suppresses bone loss in pathological states associated with an excess of the cytokine.

Src homology 2 domain-containing inositol 5-phosphatase 1 deficiency leads to a spontaneous allergic inflammation in the murine lung

BACKGROUND

Src homology 2 domain-containing inositol 5-phosphatase 1 (SHIP-1) controls the intracellular level of the phosphoinositide 3-kinase product phosphotidylinositol-3,4,5-trisphosphate and functions as a negative regulator of cytokine and immune receptor signaling. Emerging evidence suggests that the phosphoinositide 3-kinase pathway might be involved in allergic inflammation in the lung. However, the functional relevance of SHIP-1 in the T(H)2 activation pathway has not been established. SHIP-1(-/-) mice have spontaneous myeloproliferative inflammation in the lung, the nature of which has not been elucidated. We hypothesized that SHIP-1 plays an important role as a regulator in pulmonary allergic inflammation and in maintaining lung homeostasis.

OBJECTIVE

To test our hypothesis, we characterized the pulmonary phenotype of SHIP-1(-/-) mice.

RESULTS

Analyses of lung histopathology and bronchoalveolar lavage cellularity revealed that the majority of SHIP-1(-/-) mice had progressive and severe pulmonary inflammation of macrophages, lymphocytes, neutrophils, and eosinophils; mucous hyperplasia; airway epithelial hypertrophy; and subepithelial fibrosis. These pathologic changes were accompanied by exaggerated production of T(H)2 cytokines and chemokines, including IL-4, IL-13, eotaxin, and monocyte chemoattractant protein 1, in the lung. Furthermore, the number of mast cells significantly increased, and many of these cells were undergoing degranulation, which was correlated with increased content and spontaneous release of histamine in the lung tissue of SHIP-1(-/-) mice.

CONCLUSION

These findings provide strong evidence that mice lacking SHIP-1 have an allergic inflammation in the lung, suggesting that SHIP-1 plays an important role in regulating the T(H)2 signaling pathway and in maintaining lung homeostasis.

CLINICAL IMPLICATIONS

SHIP-1 as a regulator might be a potential therapeutic target for controlling allergic inflammation in diseases such as asthma.

Cutting edge: dominance by an MHC-independent inhibitory receptor compromises NK killing of complex targets

Inhibitory receptors that recognize MHC class I molecules regulate NK cell responses and self-tolerance. Recent evidence indicates that self-ligands not present in the MHC locus also can modulate NK function. In this study, we show that an inhibitory receptor that recognizes an MHC-independent ligand is over expressed in SHIP(-/-) mice at all stages of NK development and differentiation. Overexpression of this receptor compromises key cytolytic NK functions, including killing of allogeneic, tumor, and viral targets. These results further demonstrate the critical role that SHIP plays in regulation of the NK receptor repertoire and show that regulation of MHC-independent inhibitory receptors is crucial for NK recognition and cytolysis of complex targets.

Branchio-oto-renal syndrome associated mutations in Eyes Absent 1 result in loss of phosphatase activity

The Eyes Absent (Eya) proteins are tyrosine phosphatases and transcriptional activators involved in cell-fate determination and organ development. Mutations in the gene encoding Eya homologue 1 have been implicated in the multi-organ developmental disorder branchio-oto-renal syndrome (BOR) and in ocular defects. Here we report that BOR-associated mutations lead to a loss of phosphatase activity in Eya1 proteins, while mutations associated with ocular defects yield Eya1 proteins with near normal levels of phosphatase activity. Furthermore we demonstrate that the N-terminal domain attenuates the catalytic activity of Eya suggesting a mechanism of regulation.

MTH1, an oxidized purine nucleoside triphosphatase, suppresses the accumulation of oxidative damage of nucleic acids in the hippocampal microglia during kainate-induced excitotoxicity

Enhanced oxidative stress has been implicated in the excitotoxicity of the CNS, and 8-oxo-7,8-dihydro-guanine (8-oxoG), a major type of oxidative damage in nucleic acids, was reported to be accumulated in the rat hippocampus after kainate administration. We herein showed that the 8-oxoG levels in mitochondrial DNA and cellular RNA increased significantly in the CA3 subregion of the mouse hippocampus 6-12 h after kainate administration but returned to basal levels within a few days. Laser-scanning confocal microscopy revealed the 8-oxoG accumulation in mitochondrial DNA to be remarkable in CA3 microglia, whereas that in nuclear DNA or cellular RNA was also detected in the CA3 pyramidal cells and astrocytes. 8-oxoG accumulation in cellular DNA or RNA should be suppressed by MutT homolog 1 (MTH1) with 8-oxo-dGTPase (8-oxo-7,8-dihydro-2'-deoxyguanosine triphosphatase) activity and 8-oxoG-DNA glycosylase 1 (OGG1) with 8-oxoG DNA glycosylase activity. We thus examined the expression level of MTH1 and OGG1 in the mouse hippocampus after kainate administration. The Mth1 mRNA level decreased soon after kainate administration and then quickly recovered beyond the basal level, and a continuously increased MTH1 protein level was observed, whereas the Ogg1 mRNA level remained constant. MTH1-null and wild-type mice exhibited a similar degree of CA3 neuron loss after kainate administration; however, the 8-oxoG levels that accumulated in mitochondrial DNA and cellular RNA in the CA3 microglia significantly increased in the MTH1-null mice in comparison with wild-type mice, thus demonstrating that MTH1 efficiently suppresses the accumulation of 8-oxoG in both cellular DNA and RNA in the hippocampus, especially in microglia, caused by excitotoxicity.

MTH1, an oxidized purine nucleoside triphosphatase, prevents the cytotoxicity and neurotoxicity of oxidized purine nucleotides

In human and rodent cells, MTH1, an oxidized purine nucleoside triphosphatase, efficiently hydrolyzes oxidized dGTP, GTP, dATP and ATP such as 2'-deoxy-8-oxoguanosine triphosphate (8-oxo-dGTP) and 2'-deoxy-2-hydroxyadenosine triphosphate (2-OH-dATP) in nucleotide pools, thus avoiding their incorporation into DNA or RNA. MTH1 is expressed in postmitotic neurons as well as in proliferative tissues, and it is localized both in the mitochondria and nucleus, thus suggesting that MTH1 plays an important role in the prevention of the mutagenicity and cytotoxicity of such oxidized purines as 8-oxoG which are known to accumulate in the cellular genome. Our recent studies with MTH1-deficient mice or cells revealed that MTH1 efficiently minimizes accumulation of 8-oxoG in both nuclear and mitochondrial DNA in the mouse brain as well as in cultured cells, thus contributing to the protection of the brain from oxidative stress.

Treatment with amino acids in serine deficiency disorders

Serine deficiency disorders are rare defects in the biosynthesis of the amino acid L-serine. At present two disorders have been reported: 3-phosphoglycerate dehydrogenase deficiency and 3-phosphoserine phosphatase deficiency. These enzyme defects lead to severe neurological symptoms such as congenital microcephaly and severe psychomotor retardation and in addition in patients with 3-phosphoglycerate dehydrogenase deficiency to intractable seizures. These symptoms respond to a variable degree to treatment with L-serine, sometimes combined with glycine. In this paper the current practice of amino acid treatment with L-serine and glycine in serine deficiency is reviewed.

Downstream of Tyrosine Kinases-1 and Src Homology 2-Containing Inositol 5′-Phosphatase Are Required for Regulation of CD4+CD25+ T Cell Development

The adaptor protein, downstream of tyrosine kinases-1 (Dok-1), and the phosphatase SHIP are both tyrosine phosphorylated in response to T cell stimulation. However, a function for these molecules in T cell development has not been defined. To clarify the role of Dok-1 and SHIP in T cell development in vivo, we compared the T cell phenotype of wild-type, Dok-1 knockout (KO), SHIP KO, and Dok-1/SHIP double-knockout (DKO) mice. Dok-1/SHIP DKO mice were runted and had a shorter life span compared with either Dok-1 KO or SHIP KO mice. Thymocyte numbers from Dok-1/SHIP DKO mice were reduced by 90%. Surface expression of both CD25 and CD69 was elevated on freshly isolated splenic CD4(+) T cells from SHIP KO and Dok-1/SHIP DKO, suggesting these cells were constitutively activated. However, these T cells did not proliferate or produce IL-2 after stimulation. Interestingly, the CD4(+) T cells from SHIP KO and Dok-1/SHIP DKO mice produced higher levels of TGF-beta, expressed Foxp3, and inhibited IL-2 production by CD3-stimulated CD4(+)CD25(-) T cells in vitro. These findings suggest Dok-1 and SHIP function in pathways that influence regulatory T cell development.

SHIP deficiency enhances HSC proliferation and survival but compromises homing and repopulation

The SH2 domain-containing inositol 5'-phosphatase-1 (SHIP) has the potential to modulate multiple signaling pathways downstream of receptors that impact hematopoietic stem cell (HSC) biology. Therefore, we postulated that SHIP might play an important role in HSC homeostasis and function. Consistent with this hypothesis, HSC proliferation and numbers are increased in SHIP(-/-) mice. Despite expansion of the compartment, SHIP(-/-) HSCs exhibit reduced capacity for long-term repopulation. Interestingly, we observe that SHIP(-/-) stem/progenitor cells home inefficiently to bone marrow (BM), and consistent with this finding, have reduced surface levels of both CXCR4 and vascular cell adhesion marker-1 (VCAM-1). These studies demonstrate that SHIP is critical for normal HSC function, homeostasis, and homing.

At5PTase13 modulates cotyledon vein development through regulating auxin homeostasis

Phosphatidylinositol signaling pathway and the relevant metabolites are known to be critical to the modulation of different aspects of plant growth, development, and stress responses. Inositol polyphosphate 5-phosphatase is a key enzyme involved in phosphatidylinositol metabolism and is encoded by an At5PTase gene family in Arabidopsis thaliana. A previous study shows that At5PTase11 mediates cotyledon vascular development probably through the regulation of intracellular calcium levels. In this study, we provide evidence that At5PTase13 modulates the development of cotyledon veins through its regulation of auxin homeostasis. A T-DNA insertional knockout mutant, At5pt13-1, showed a defect in development of the cotyledon vein, which was rescued completely by exogenous auxin and in part by brassinolide, a steroid hormone. Furthermore, the mutant had reduced auxin content and altered auxin accumulation in seedlings revealed by the DR5:beta-glucuronidase fusion construct in seedlings. In addition, microarray analysis shows that the transcription of key genes responsible for auxin biosynthesis and transport was altered in At5pt13-1. The At5pt13-1 mutant was also less sensitive to auxin inhibition of root elongation. These results suggest that At5PTase13 regulates the homeostasis of auxin, a key hormone controlling vascular development in plants.

MTH1, an oxidized purine nucleoside triphosphatase, protects the dopamine neurons from oxidative damage in nucleic acids caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine

We previously reported that 8-oxoguanine (8-oxoG) accumulates in the cytoplasm of dopamine neurons in the substantia nigra of patients with Parkinson's disease and the expression of MTH1 carrying an oxidized purine nucleoside triphosphatase activity increases in these neurons, thus suggesting that oxidative damage in nucleic acids is involved in dopamine neuron loss. In the present study, we found that levels of 8-oxoG in cellular DNA and RNA increased in the mouse nigrostriatal system during the tyrosine hydroxylase (TH)-positive dopamine neuron loss induced by the administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MTH1-null mice exhibited a greater accumulation of 8-oxoG in mitochondrial DNA accompanied by a more significant decrease in TH and dopamine transporter immunoreactivities in the striatum after MPTP administration, than in wild-type mice. We thus demonstrated that MTH1 protects the dopamine neurons from oxidative damage in the nucleic acids, especially in the mitochondrial DNA of striatal nerve terminals of dopamine neurons.

Negative regulation of CXCR4-mediated chemotaxis by the lipid phosphatase activity of tumor suppressor PTEN

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN), a multifunctional tumor suppressor, has been shown to play a regulatory role in cell migration. Dictyostelium discoideum cells lacking PTEN exhibited impaired migration toward chemoattractant gradients. In the present study, we investigated the involvement of PTEN in chemotaxis of mammalian cells by examining PTEN-null Jurkat T cells. We observed that, in contrast to observations made in D discoideum, PTEN-null Jurkat T cells exhibited potent chemotactic responses to the chemokine stromal cell-derived factor 1alpha (SDF-1alpha), indicating that PTEN was not requisite for CXC chemokine receptor 4 (CXCR4)-mediated chemotaxis of Jurkat cells. Conversely, reconstitution of PTEN in Jurkat cells by using a tetracycline (Tet-on)-inducible expression system down-regulated CXCR4-mediated chemotaxis. Furthermore, we established the lipid phosphatase activity of PTEN as essential for its inhibitory effect on chemotaxis. In addition, using PTEN-expressing T-cell lines and primary T cells, we demonstrated that down-regulation of PTEN expression with vector-based small interfering RNAs (siRNAs) enhanced CXCR4-mediated chemotaxis. Based on these results, we conclude that PTEN expression negatively regulates chemotaxis of lymphoid mammalian cells via its lipid phosphatase activity. Our findings may account for the reported increase in metastatic activity of PTEN-null tumor cells.

Involvement of SHIP in TLR2-induced neutrophil activation and acute lung injury

The SHIP converts phosphatidylinositol 3,4,5 triphosphate to phosphatidyl 3,4 biphosphate. SHIP has negative regulatory functions on PI3K-dependent signaling pathways, which occupy important roles in modulating neutrophil functions. We used neutrophils from transgenic SHIP(-/-) and SHIP(+/+) mice that were stimulated with peptidoglycan (PGN) to examine the role of SHIP in TLR2-induced neutrophil activation. SHIP(-/-) neutrophils demonstrated significantly increased activation of the PI3K-dependent kinase Akt after exposure to PGN. Release of cytokines and chemokines, including TNF-alpha, IL-1beta, IL-6, IL-10, and MIP-2, was also increased in SHIP(-/-) compared with SHIP(+/+) neutrophils. There was no difference in the nuclear translocation of the transcriptional factor NF-kappaB between PGN-stimulated SHIP(-/-) and SHIP(+/+) neutrophils. However, phosphorylation of the p65 subunit of NF-kappaB, an event essential for optimal transcriptional activity of NF-kappaB, was increased in TLR2-activated SHIP(-/-) neutrophils. SHIP(-/-) neutrophils demonstrated greater activation of ERK1/2 and p38 MAPKs than did SHIP(+/+) neutrophils after exposure to PGN. The severity of acute lung injury induced by PGN was greater in SHIP(-/-) as compared with SHIP(+/+) mice. These results demonstrate that SHIP has a negative regulatory role in TLR2-induced neutrophil activation and in the development of related in vivo neutrophil-dependent inflammatory processes, such as acute lung injury.

Crucial role of p53-dependent cellular senescence in suppression of Pten-deficient tumorigenesis

Cellular senescence has been theorized to oppose neoplastic transformation triggered by activation of oncogenic pathways in vitro, but the relevance of senescence in vivo has not been established. The PTEN and p53 tumour suppressors are among the most commonly inactivated or mutated genes in human cancer including prostate cancer. Although they are functionally distinct, reciprocal cooperation has been proposed, as PTEN is thought to regulate p53 stability, and p53 to enhance PTEN transcription. Here we show that conditional inactivation of Trp53 in the mouse prostate fails to produce a tumour phenotype, whereas complete Pten inactivation in the prostate triggers non-lethal invasive prostate cancer after long latency. Strikingly, combined inactivation of Pten and Trp53 elicits invasive prostate cancer as early as 2 weeks after puberty and is invariably lethal by 7 months of age. Importantly, acute Pten inactivation induces growth arrest through the p53-dependent cellular senescence pathway both in vitro and in vivo, which can be fully rescued by combined loss of Trp53. Furthermore, we detected evidence of cellular senescence in specimens from early-stage human prostate cancer. Our results demonstrate the relevance of cellular senescence in restricting tumorigenesis in vivo and support a model for cooperative tumour suppression in which p53 is an essential failsafe protein of Pten-deficient tumours.

T/B lineage choice occurs prior to intrathymic Notch signaling

Commitment of hemopoietic progenitors to the T-cell lineage is a crucial requirement for T-cell development, yet the timing and developmental cues regulating this process remain controversial. Here we have devised a technique to analyze the T-cell/B-cell lineage potential of precursors that have been recruited to the fetal mouse thymus but which have yet to contact the thymic epithelial microenvironment. We show that lymphoid progenitors arriving at the thymus are not bipotent T/B precursors, and provide evidence that intrathymic Notch signaling is not the mechanism determining T/B lineage choice in migrant precursors. Rather, we provide evidence that Notch signaling influences T/B lineage choice in lymphoid precursors through interactions with defined stromal components within the fetal liver. Collectively, our data redefine our understanding of the role and timing of Notch signaling in relation to lineage choices in lymphoid precursors.

[Tumor suppressor gene PTEN and non-alcoholic steatohepatitis (NASH)]

Although hepatic steatosis had been considered to be a benign condition that does not deteriorate to either liver cirrhosis or hepatocellular carcinoma (HCC). Non-alcoholic steatohepatitis (NASH) is notable disease that has similar pathological features to alcoholic liver injury and progresses to liver cirrhosis and HCC. But the molecular mechanism for the onset of NASH, and for the transformation from steatosis to carcinogenesis are still unclear. Hepatocyte-specific PTEN deficient mice, we generated, have similar histological features to the patients of human NASH. These hepatocytes showed enhanced lipid accumulation, inflammatory change, and hyperoxidation. Moreover, they developed into HCC. Thus, impairment of PI3K/PTEN signaling may possibly be involved in a part of NASH/HCC cases in human.