T cell selective apoptosis by a novel immunosuppressant,FTY720, is closely regulated with Bcl-2

1. A novel immunosuppressant FTY720 caused a significant decrease in peripheral T lymphocytes, but not in B lymphocytes upon oral administration. This decrease was mainly a result of FTY720-induced apoptosis. In this study, we confirmed FTY720-induced T cell selective apoptosis using lymphoma cell lines in vitro. 2. Viability loss, DNA fragmentation, Annexin V binding, and caspases activation (caspase-3, -8, and -9) were observed in Jurkat cells (T lymphoma cells), but not significantly in BALL-1 cells (B lymphoma cells). These results indicated that FTY720 selectively induced apoptosis in T cell lymphoma to a greater extent than in B cell lymphoma, a finding that is similar to the result observed when FTY720 was treated with T lymphocytes and B lymphocytes in vitro. 3. FTY720 released cytochrome c from mitochondria in Jurkat intact cells as well as from isolated Jurkat mitochondria directly, but not from mitochondria in BALL-1 cells nor from isolated BALL-1 mitochondria. 4. BALL-1 cells and B cells had more abundant mitochondria-localized anti-apoptotic protein Bcl-2 than did Jurkat cells and T cells. 5. FTY720-induced apoptosis is inhibited by the overexpression of Bcl-2, suggesting that the cellular Bcl-2 level regulates the sensitivity to FTY720.     

Activation of caspases and mitochondria in FTY720-mediated apoptosis in human T cell line Jurkat

FTY720, a novel immunosuppressive drug originally derived from a metabolite from Isaria sinclairii, is known to induce apoptosis in lymphocytes. In this study, we investigated the involvement of caspases and mitochondria in FTY720-mediated apoptosis using Jurkat cells, a human T cell line. Our results indicated that FTY720-induced activation of caspases 2, 3, 6, 8, 9 and 10, whereas caspases 1 and 5 were not activated. We also observed in the FTY720-treated cells a loss of mitochondrial membrane potential, a release of cytochrome c into cytosol and an exposed phosphatidylserine (PS) at the outer surface of the cell membrane. Pretreatment with a peptide inhibitor, benzyloxycarbonyl-Asp-CH2COC-2, 6-dichlorobenzene (Z-Asp-CH2-DCB), prevented apoptosis and externalization of phosphatidylserine, whereas the inhibitor did not prevent the mitochondrial events. This suggests that caspases may play a role downstream of the mitochondrial pathway. Therefore, caspase cascade in FTY720-treated cells may be initiated by activation of mitochondria.     

萘酰亚胺-多胺缀合物NNINspm通过PI_3 K/Akt信号通路诱导肝癌细胞凋亡

目的探讨新型萘酰亚胺-多胺缀合物NNINspm对多胺转运体的识别及诱导肝癌HepG2细胞凋亡的机制。方法以MTT法检测细胞毒性;流式细胞仪检测细胞周期、凋亡率及线粒体膜电位的变化;高内涵活细胞成像系统检测NNINspm对多胺转运体识别及Akt易位的影响;Western blot检测NNINspm对cytochrome C、14-3-3、Bad、Bcl-xL、mTOR、p70S6K、Cdk4、p27kip1、Akt、Caspase-3、Caspase-9等蛋白表达的影响。结果NNINspm具有良好的多胺转运体识别能力及肿瘤细胞靶向性,其通过抑制Akt磷酸化从而引起一系列的信号分子发生改变,如14-3-3蛋白与Bad解离并与Bcl-xL结合,随后引起cytochromeC释放及caspase-9及caspase-3活化并最终诱导细胞凋亡;此外,NNINspm诱导mTOR和p70S6K脱磷酸化,Cdk4下调及p27kip1上调并最终诱导细胞周期阻滞于G0/G1期。结论NNINspm通过PI3K/Akt信号途径诱导肝癌HepG2细胞凋亡。     

Lithium inhibits ceramide- and etoposide-induced protein phosphatase 2A methylation, Bcl-2 dephosphorylation, caspase-2 activation, and apoptosis

Lithium confers cell protection against stress and toxic stimuli. Although lithium inhibits a number of enzymes, the antiapoptotic mechanisms of lithium remain unresolved. Here, we report a novel role of lithium on the blockage of ceramide- and etoposide-induced apoptosis via inhibition of protein phosphatase 2A (PP2A) activity. Overexpression of PP2A resulted in caspase-2 activation, mitochondrial damage, and cell apoptosis that were inhibited by okadaic acid (OA) and lithium. Lithium and OA abrogated ceramide- and etoposide-induced Bcl-2 dephosphorylation at serine 70. Furthermore, ceramide- and etoposide-induced PP2A activation involved methylation of PP2A C subunit, which lithium suppressed. Lithium caused dissociation of PP2A B subunit from the PP2A core enzyme, whereas ceramide caused recruitment of the B subunit. Taken together, lithium exhibited an antiapoptotic effect by inhibiting Bcl-2 dephosphorylation and caspase-2 activation, which involved, at least in part, a mechanism of down-regulating PP2A methylation and PP2A activity.     

Ceramide produces apoptosis through induction of p27(kip1) by protein phosphatase 2A-dependent Akt dephosphorylation in PC-3 prostate cancer cells

Ceramide induces cell cycle arrest and apoptotic cell death associated with increased levels of p27(kip1). The aim of this study was to examine the effects of ceramide on p27(kip1) protein levels as a measure of cell cycle arrest and apoptosis. Results showed that ceramide increased p27(kip1) protein levels through activation of protein phosphatase 2A (PP2A) in PC-3 prostate cancer cells. Treatment of cells with the PP2A inhibitor okadaic acid or with PP2A-Cα siRNA inhibited ceramide-induced enhanced p27(kip1) protein expression and Akt dephosphorylation, and prevented Skp2 downregulation. Overexpression of constitutively active Akt attenuated ceramide-induced Skp2 downregulation and p27(kip1) upregulation. In addition, ceramide stimulated binding of the PP2A catalytic subunit PP2A-Cαβ to Akt as assessed by immunoprecipitation experiments, indicating that PP2A is involved in the induction of p27(kip1) via inhibition of Akt pathway. Finally, whether PP2A can regulate p27(kip1) expression independently of Akt pathway was determined. Knockdown of PP2A-Cα with siRNA reduced p27(kip1) levels in the presence of Akt inhibitor. These data reveal that PP2A is a regulator of ceramide-induced p27(kip1) expression via Akt-dependent and Akt-independent pathways.     

Novel FTY720-Based Compounds Stimulate Neurotrophin Expression and Phosphatase Activity in Dopaminergic Cells

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Potential anti-tumor effects of FTY720 associated with PP2A activation: a brief review

FTY720 (Fingolimod, Gilenya^?) is an FDA-approved immunosuppressant currently used in the treatment of multiple sclerosis. However, a large number of studies over the last few years have shown that FTY720 shows potent antitumor properties that suggest its potential usefulness as a novel anticancer agent. Interestingly, the restoration of protein phosphatase 2A (PP2A) activity mediated by FTY720 could play a key role in its antitumor effects. Taking into account that PP2A inactivation is a common event that determines poor outcome in several tumor types, FTY720 could serve as an alternative therapeutic strategy for cancer patients with such alterations.     

Regulation of AMPA receptor dephosphorylation by glutamate receptor agonists

Phosphorylation of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subunit GluR1 at Ser(845) enhances AMPA channel activity. This study demonstrates that Ser(845) is rapidly dephosphorylated upon AMPA receptor activation in nucleus accumbens slices. AMPA-induced dephosphorylation at Ser(845) was blocked by CNQX, an AMPA receptor antagonist, by nifedipine, an L-type Ca(2+) channel antagonist, or by cyclosporin A, a calcineurin inhibitor. N-methyl-D-aspartate (NMDA) treatment also decreased phosphorylation of Ser(845), an effect that was blocked by MK-801, an NMDA receptor antagonist, but not by nifedipine. Accumbens neurons are enriched for dopamine- and cyclic AMP (cAMP)-regulated phosphoprotein, Mr 32,000 (DARPP-32), a potent inhibitor of protein phosphatase 1 (PP1) when phosphorylated by PKA (at Thr(34)). We tested the hypothesis that the AMPA/KA or NMDA-stimulated dephosphorylation of DARPP-32 via calcineurin, leading to increased PP1 activity and dephosphorylation of GluR1. AMPA or NMDA treatment decreased phospho-Thr(34)-DARPP-32 levels, effects that were blocked by receptor antagonists, or cyclosporin A. However, dephosphorylation of Ser(845) mediated by AMPA or NMDA receptors was unaffected in DARPP-32/inhibitor-1 knockout mice. These data suggest that AMPA- or NMDA-induced dephosphorylation of GluR1 at Ser(845) occurs by a mechanism that is independent of DARPP-32 and PP1, but involves activation of calcineurin. Thus, Ca(2+)-dependent dephosphorylation of GluR1 may serve as a negative feedback mechanism for the regulation of AMPA receptor activity in neurons.     

AMP-activated protein kinase (AMPK) activating agents cause dephosphorylation of Akt and glycogen synthase kinase-3

AMP-activated protein kinase (AMPK) is a key cellular sensor of reduced energy supply that is activated by increases in the cellular ratio of AMP/ATP. Phenformin and 5-aminoimidazole-4-carboxamide riboside (AICAR) are two drugs widely used to activate AMPK experimentally. In both differentiated hippocampal neurons and neuroblastoma SH-SY5Y cells we found that these two agents not only activated AMPK, but conversely greatly reduced the activating Ser/Thr phosphorylation of Akt. This blockade of Akt activity consequently lowered the inhibitory serine-phosphorylation of its substrates, glycogen synthase kinase-3alpha/beta (GSK3alpha/beta). An inhibitor of AMPK (Compound C) did not block dephosphorylation of Akt and GSK3. Thus, both drugs widely used to activate AMPK also caused dephosphorylation of Akt and of GSK3. The mechanism for Akt dephosphorylation caused by phenformin, but not AICAR, was due to inhibition of growth factor-induced signaling that leads to Akt phosphorylation. Stimulation of muscarinic receptors with carbachol in SH-SY5Y cells also activated AMPK and transiently caused dephosphorylation of Akt. These findings show that Akt dephosphorylation often occurs concomitantly with AMPK activation when cells are treated with phenformin or AICAR, indicating that these drugs do not only affect AMPK but also cause a coordinated inverse regulation of AMPK and Akt.     

Analysis of the mode of action of a novel immunosuppressant FTY720 in mice.

Accelerated lymphocyte homing and apoptosis have been suggested to contribute to potent immunosuppressive effects of FTY720, however, its main mechanism of action remains to be fully elucidated. Here, we examined the mode of action of FTY720 in mice. FTY720, when given at a single dose of 1 mg/kg, markedly decreased the number of peripheral blood lymphocytes (PBL) but moderately increased the lymphocyte numbers in lymph nodes (LN) and Peyer's patches (PP) in normal mice, as previously observed in rats. However, the sharp decrease in PBL numbers was also observed in aly/aly mice lacking LN and PP, indicating that this phenomenon is not explained by accelerated lymphocyte homing to LN and PP. In addition, the finding that a single administration of FTY720 did not suppress proliferative responses of T cells suggested that the PBL reduction could occur without inhibiting lymphocyte functions. However, when administered at the same dose for 2 weeks, FTY720 induced severe systemic lymphopenia, as well as marked suppression of lymphocyte proliferative responses in normal mice. The same treatment also prolonged skin allograft survival in aly/aly mice. Our results suggest that FTY720 suppresses in vivo immune functions mainly by inducing systemic lymphopenia and also by inhibiting T cell functions.     

Discovery of protein phosphatase 2C inhibitors by virtual screening

Protein phosphatase 2C (PP2C) is an archetype of the PPM Ser/Thr phosphatases, characterized by dependence on divalent magnesium or manganese cofactors, absence of known regulatory proteins, and resistance to all known Ser/Thr phosphatase inhibitors. We have used virtual ligand screening with the AutoDock method and the National Cancer Institute Diversity Set to identify small-molecule inhibitors of PP2Calpha activity at a protein substrate. These inhibitors are active in the micromolar range and represent the first non-phosphate-based molecules found to inhibit a type 2C phosphatase. The compounds docked to three recurrent binding sites near the PP2Calpha active site and displayed novel Ser/Thr phosphatase selectivity profiles. Common chemical features of these compounds may form the basis for development of a PP2C inhibitor pharmacophore and may facilitate investigation of PP2C control and cellular function.     

The Discodermia calyx Toxin Calyculin A Enhances Cyclin D1 Phosphorylation and Degradation, and Arrests Cell Cycle Progression in Human Breast Cancer Cells

Cyclin D1 is a key regulator of the cell cycle that is over expressed in more than half of breast cancer patients. The levels of cyclin D1 are controlled primarily through post-translational mechanisms and phosphorylation of cyclin D1 at T286 induces its proteasomal degradation. To date, no studies have explored the involvement of phosphatases in this process. Here we treated human breast cancer cells with the structurally distinct toxins calyculin A, okadaic acid, and cantharidin, which are known to inhibit Ser/Thr phosphatases of the PPP family. At low nanomolar concentrations calyculin A induced T286 phosphorylation and degradation of cyclin D1 via the proteosome in MDA-MB-468 and MDA-MB-231 cells. Cyclin D1 degradation also was dose-dependently induced by okadaic acid and catharidin, implicating a negative regulatory role for type-2A phosphatases. These effects occurred without increasing phosphorylation of p70S6K, cyclin D3, or myosin light chain that were used as endogenous reporters of cellular PP2A and PP1 activity. A reverse phase phosphoprotein array analysis revealed increased phosphorylation of only 6 out of 33 Ser/Thr phosphosites, indicating selective inhibition of phosphatases by calyculin A. Calyculin A treatment induced cell cycle arrest in MDA-MB-468 and MCF-7 breast cancer cells. These findings suggest that a specific pool of type-2A phosphatase is inhibited by calyculin A leading to the degradation of cyclin D1 in human breast cancer cells. The results highlight the utility of toxins as pharmacological probes and points to the T286 cyclin D1 phosphatase inhibited by calyculin A as a possible target for chemotherapy to treat triple negative breast cancer.     

Autophagy induced by FTY720 promotes apoptosis in U266 cells

Despite recent treatment advances, multiple myeloma (MM) remains incurable and patients develop a progressively relapsing disease with subsequent poor prognosis. Studies have shown FTY720 has activities against a number of hematological malignancies including MM, no reports about autophagy induced by FTY720 in MM. Therefore, we investigated the potential application of FTY720 on MM using U266 cell line. We observed that FTY720 could induce caspase-3 dependent apoptosis in a dose- and time-dependent manner in U266 cells. FTY720 caused apoptosis by down-regulating antiapoptotic proteins Mcl-1, bcl-2, survivin and cleavage of Bid. Interestingly, FTY720 induce autophagy which could promote the apoptosis in U266 cells. Furthermore, activation of reactive oxygen species (ROS) regulates FTY720 induced apoptosis and autophagy in U266 cells. The study implicated that FTY720 could be a good candidate for MM treatment.     

Novel regulatory roles for protein phosphatase-2A in the islet beta cell

Protein phosphorylation constitutes one of the key signaling steps in physiological insulin secretion. The phosphorylation status of a given protein represents the balance of the activities of protein kinases and phosphatases, which induce the addition and removal of phosphate from that protein, respectively. Although several extant studies were focused on the identification and characterization of protein kinases in islets, relatively little information is available on the localization and regulation of protein phosphatases in beta cells. Emerging evidence implicates protein phosphatase 2A (PP2A) in the phenomenon of insulin secretion. The three principal objectives of this commentary are to: (i) review the existing evidence, which suggests regulation, by glucose and other insulin secretagogues, of PP2A in the beta cell; (ii) discuss the experimental evidence, which implicates PP2A-like enzymes in the dephosphorylation and inactivation of key beta cell phosphoprotein substrates (e.g., Akt and Bcl-2), which may be necessary for beta cell proliferation and survival, culminating in the loss of the beta cell mass; and (iii) highlight potential avenues for future research, including the development of specific pharmacological and therapeutic interventional modalities for the inhibition of specific PP2A-like phosphatases for the prevention of loss of beta cell mass leading to the onset of diabetes.     

Stimulation of protein kinase B and p70 S6 kinase by the histamine H1 receptor in DDT1MF-2 smooth muscle cells

1. Previous studies have shown that the histamine H(1) receptor activates p42/p44 mitogen-activated protein kinases (MAPK) in DDT(1)MF-2 smooth muscle cells via a phosphatidylinositol 3-kinase (PI-3K)-dependent pathway. In this study the effect of histamine H(1) receptor stimulation on protein kinase B (PKB) and p70 S6 kinase, both of which are downstream targets of PI-3K, has been investigated. Increases in PKB and p70 S6 kinase activation were monitored by Western blotting using phospho-specific PKB (Ser(473)) and p70 S6 kinase (Thr(421)/Ser(424)) antibodies. 2. Histamine stimulated time and concentration-dependent increases in the phosphorylation of PKB and p70 S6 kinase in DDT(1)MF-2 cells. Both responses were completely inhibited by the histamine H(1) receptor antagonist mepyramine and following pre-treatment with pertussis toxin, to block G(i)/G(o) protein dependent pathways. 3. The PI-3K inhibitors wortmannin (IC(50) 5.9+/-0.5 nM) and LY 294002 (IC(50) 6.9+/-0.8 microM) attenuated the increase in PKB phosphorylation induced by histamine (100 microM) in a concentration-dependent manner. 4. Histamine-induced increases in p70 S6 kinase phosphorylation were partially sensitive to rapamycin (20 nM; 68% inhibition) but completely blocked by wortmannin (100 nM), LY 294002 (30 microM) and the MAPK kinase inhibitor PD 98059 (50 microM). 5. In summary, these data demonstrate that the histamine H(1) receptor stimulates PKB and p70 S6 kinase phosphorylation in DDT(1)MF-2 smooth muscle cells. However, functional studies revealed that histamine does not stimulate DDT(1)MF-2 cell proliferation or attenuate staurosporine-induced caspase-3 activity. The challenge for future research will be to link the stimulation of these kinase pathways with the physiological and pathophysiological roles of the histamine H(1) receptor.     

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) inhibition by 4-hydroxynonenal leads to increased Akt activation in hepatocytes

The production of reactive aldehydes such as 4-hydroxynonenal (4-HNE) is proposed to be an important factor in the etiology of alcoholic liver disease. To understand the effects of 4-HNE on homeostatic signaling pathways in hepatocytes, cellular models consisting of the human hepatocellular carcinoma cell line (HepG2) and primary rat hepatocytes were evaluated. Treatment of both HepG2 cells and primary hepatocytes with subcytotoxic concentrations of 4-HNE resulted in the activation of Akt within 30 min as demonstrated by increased phosphorylation of residues Ser473 and Thr308. Quantification and subsequent immunocytochemistry of phosphatidylinositol-3,4,5-trisphosphate [PtdIns(3,4,5)P(3)[rsqb] resulted in a 6-fold increase in total PtdIns(3,4,5)P(3) and increased immunostaining at the plasma membrane after 4-HNE treatment. Cotreatment of HepG2 cells with 4-HNE and the phosphatidylinositol 3-kinase (PI3K) inhibitor 2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one (Ly294002) or the protein phosphatase 2A (PP2A) inhibitor okadaic acid revealed that the mechanism of activation of Akt is PI3K-dependent and PP2A-independent. Using biotin hydrazide detection, it was established that the incubation of HepG2 cells with 4-HNE resulted in increased carbonylation of the lipid phosphatase known as "phosphatase and tensin homolog deleted on chromosome 10" (PTEN), a key regulator of Akt activation. Activity assays both in HepG2 cells and recombinant PTEN revealed a decrease in PTEN lipid phosphatase activity after 4-HNE application. Mass spectral analysis of 4-HNE-treated recombinant PTEN detected a single 4-HNE adduct. Subsequent analysis of Akt dependent physiological consequences of 4-HNE in HepG2 cells revealed significant increases in the accumulation of neutral lipids. These results provide a potential mechanism of Akt activation and cellular consequences of 4-HNE in hepatocytes.