Sodium stibogluconate is a potent inhibitor of protein tyrosine phosphatases and augments cytokine responses in hemopoietic cell lines

Tyrosine phosphatase inhibitor-3 sensitizes melanoma and colon cancer to biotherapeutics and chemotherapeutics

Drug resistance is a major obstacle in cancer treatments and diminishes the clinical efficacy of biological, cytotoxic, or targeted therapeutics. Being an antiapoptotic mediator of chemoresistance in breast and lung cancer cells, MKP1 phosphatase might be targeted for overcoming chemoresistance and improving therapeutic efficacy. In this work, tyrosine phosphatase inhibitor-3 (TPI-3) was identified as a novel small molecule inhibitor of MKP1 and was capable of sensitizing tumors to bio- and chemotherapeutics in mice as a tolerated oral agent. Effective against recombinant MKP1, TPI-3 selectively increased MKP1 phosphosubstrates in Jurkat cells and induced cell death via apoptosis at nanomolar concentrations. TPI-3 also increased MKP1 phosphosubstrates in WM9 human melanoma cells and synergized with biotherapeutic IFN alpha 2b in the growth inhibition of melanoma cells in vitro (combination index, <1). WM9 xenografts unresponsive to individual agents were significantly inhibited (62%, P = 0.001) in mice by a tolerated combination of oral TPI-3 (10 mg/kg, 5 d/wk) and IFN alpha 2b. MKP1 expression was detected in human melanoma cell lines and tissue samples at levels up to six times higher than those in normal or nonmalignant melanocytes. TPI-3 also interacted positively with chemotherapeutics, 5-fluorouracil/leucovorin, against MC-26 colon cancer cells in vitro and in mice. Altogether, our data show the preclinical activities of TPI-3 in overcoming cancer resistance to bio- and chemotherapeutics, implicate MKP1 as a drug-resistant molecule in melanoma, and support the targeting of MKP1 for improving cancer therapeutic efficacy.

Leishmania donovani isolates with antimony-resistant but not -sensitive phenotype inhibit sodium antimony gluconate-induced dendritic cell activation

The inability of sodium antimony gluconate (SAG)-unresponsive kala-azar patients to clear Leishmania donovani (LD) infection despite SAG therapy is partly due to an ill-defined immune-dysfunction. Since dendritic cells (DCs) typically initiate anti-leishmanial immunity, a role for DCs in aberrant LD clearance was investigated. Accordingly, regulation of SAG-induced activation of murine DCs following infection with LD isolates exhibiting two distinct phenotypes such as antimony-resistant (Sb^RLD) and antimony-sensitive (Sb^SLD) was compared in vitro. Unlike Sb^SLD, infection of DCs with Sb^RLD induced more IL-10 production and inhibited SAG-induced secretion of proinflammatory cytokines, up-regulation of co-stimulatory molecules and leishmanicidal effects. Sb^RLD inhibited these effects of SAG by blocking activation of PI3K/AKT and NF-κB pathways. In contrast, Sb^SLD failed to block activation of SAG (20 µg/ml)-induced PI3K/AKT pathway; which continued to stimulate NF-κB signaling, induce leishmanicidal effects and promote DC activation. Notably, prolonged incubation of DCs with Sb^SLD also inhibited SAG (20 µg/ml)-induced activation of PI3K/AKT and NF-κB pathways and leishmanicidal effects, which was restored by increasing the dose of SAG to 40 µg/ml. In contrast, Sb^RLD inhibited these SAG-induced events regardless of duration of DC exposure to Sb^RLD or dose of SAG. Interestingly, the inhibitory effects of isogenic Sb^SLD expressing ATP-binding cassette (ABC) transporter MRPA on SAG-induced leishmanicidal effects mimicked that of Sb^RLD to some extent, although antimony resistance in clinical LD isolates is known to be multifactorial. Furthermore, NF-κB was found to transcriptionally regulate expression of murine γglutamylcysteine synthetase heavy-chain (mγGCS_hc) gene, presumably an important regulator of antimony resistance. Importantly, Sb^RLD but not Sb^SLD blocked SAG-induced mγGCS expression in DCs by preventing NF-κB binding to the mγGCS_hc promoter. Our findings demonstrate that Sb^RLD but not Sb^SLD prevents SAG-induced DC activation by suppressing a PI3K-dependent NF-κB pathway and provide the evidence for differential host-pathogen interaction mediated by Sb^RLD and Sb^SLD.

Kala-azar, a life-threatening parasitic disease caused by Leishmania donovani (LD), is widening its base in different parts of the world. Currently, there is no effective vaccine against kala-azar. The antimonial drugs like sodium antimony gluconate (SAG) have been the mainstay of therapy for this disease. Recently, due to the emergence of antimony-resistance in parasites, SAG often fails to cure kala-azar patients, which is compounding the disaster further. It is still unknown how infection with LD exhibiting antimony-resistant phenotype, in contrast to antimony-sensitive phenotype, is handled by the kala-azar patients upon SAG treatment. This demands an understanding of the nature of host immune responses against these two distinct categories of parasites. Accordingly, we compared the impact of infection with LD exhibiting antimony-resistant versus antimony-sensitive phenotype on dendritic cells (DCs). DCs upon activation/maturation initiate anti-leishmanial immunity. We showed that parasites with antimony-resistant but not antimony-sensitive phenotype prevented SAG-induced DC activation/maturation by blocking activation of NF-κB. The latter is a key signaling pathway regulating DC activation/maturation. Our studies for the first time provide both a cellular and molecular basis for differential response of host cells to parasite isolates with antimony-resistant and antimony-sensitive phenotype, which may influence the outcome of the disease.

Novel SHP-1 inhibitors tyrosine phosphatase inhibitor-1 and analogs with preclinical anti-tumor activities as tolerated oral agents

Src homology region 2 domain-containing phosphatase 1 (SHP-1) has been implicated as a potential cancer therapeutic target by its negative regulation of immune cell activation and the activity of the SHP-1 inhibitor sodium stibogluconate that induced IFN-gamma(+) cells for anti-tumor action. To develop more potent SHP-1-targeted anti-cancer agents, inhibitory leads were identified from a library of 34,000 drug-like compounds. Among the leads and active at low nM for recombinant SHP-1, tyrosine phosphatase inhibitor-1 (TPI-1) selectively increased SHP-1 phospho-substrates (pLck-pY394, pZap70, and pSlp76) in Jurkat T cells but had little effects on pERK1/2 or pLck-pY505 regulated by phosphatases SHP-2 or CD45, respectively. TPI-1 induced mouse splenic-IFN-gamma(+) cells in vitro, approximately 58-fold more effective than sodium stibogluconate, and increased mouse splenic-pLck-pY394 and -IFN-gamma(+) cells in vivo. TPI-1 also induced IFN-gamma(+) cells in human peripheral blood in vitro. Significantly, TPI-1 inhibited ( approximately 83%, p < 0.002) the growth of B16 melanoma tumors in mice at a tolerated oral dose in a T cell-dependent manner but had little effects on B16 cell growth in culture. TPI-1 also inhibited B16 tumor growth and prolonged tumor mice survival as a tolerated s.c. agent. TPI-1 analogs were identified with improved activities in IFN-gamma(+) cell induction and in anti-tumor actions. In particular, analog TPI-1a4 as a tolerated oral agent completely inhibited the growth of K1735 melanoma tumors and was more effective than the parental lead against MC-26 colon cancer tumors in mice. These results designate TPI-1 and the analogs as novel SHP-1 inhibitors with anti-tumor activity likely via an immune mechanism, supporting SHP-1 as a novel target for cancer treatment.

PRL-2 increases Epo and IL-3 responses in hematopoietic cells

Dual specificity protein tyrosine phosphatase PRL-2 is overexpressed in pediatric acute myeloid leukemia (AML) and is located at human chromosome 1p35, a region often rearranged or amplified in malignant lymphoma and B-cell chronic lymphocytic leukemia (B-CLL). Little is known of the significance of PRL-2 expression in hematopoietic malignancies. Herein we demonstrated that ectopic expression of PRL-2 in murine pre-B-cell line Baf3ER and mouse bone marrow cells induced key features associated with malignant progression and metastasis. PRL-2-transfected Baf3ER cells had augmented growth responses to hematopoietic growth factors Epo or IL-3 with shortened cell cycle, reduced requirement (5x) for Epo in cell survival, increased cell migration (3x), reduced cell adhesion (5x), and conversion to an immature cell morphology in association with increased expression (3x) of stem cell marker Bmi-1. When transduced into mouse bone marrow cells, PRL-2 increased Epo-induced colony formation (4x) and gave rise to larger colonies. These observations provide evidences implicating PRL-2 as a pathogenic molecule in hematopoietic malignancies and suggest its potential as a novel therapeutic target.

HVCN1 modulates BCR signal strength via regulation of BCR-dependent generation of reactive oxygen species

Voltage-gated proton currents regulate generation of reactive oxygen species (ROS) in phagocytic cells. In B cells, stimulation of the B cell antigen receptor (BCR) results in the production of ROS that participate in B cell activation, but the involvement of proton channels is unknown. We report here that the voltage-gated proton channel HVCN1 associated with the BCR complex and was internalized together with the BCR after activation. BCR-induced generation of ROS was lower in HVCN1-deficient B cells, which resulted in attenuated BCR signaling via impaired BCR-dependent oxidation of the tyrosine phosphatase SHP-1. This resulted in less activation of the kinases Syk and Akt, impaired mitochondrial respiration and glycolysis and diminished antibody responses in vivo. Our findings identify unanticipated functions for proton channels in B cells and demonstrate the importance of ROS in BCR signaling and downstream metabolism.

Interferon-gamma is induced in human peripheral blood immune cells in vitro by sodium stibogluconate/interleukin-2 and mediates its antitumor activity in vivo

Sodium stibogluconate (SSG), an inhibitor of SHP-1 that negatively regulates cytokine signaling and immunity, suppressed growth of murine Renca tumors in combination with interleukin-2 (IL-2) via a T-cell-dependent mechanism. The ability of SSG to interact with IL-2 in activating primary human immune cells was evaluated herein by assessing its induction of interferon (IFN)-gamma(+) TH1 cells in human peripheral blood in vitro. The significance of IFN-gamma(+) cells was also investigated by assessing SSG/IL-2 antitumor activity in wild-type and IFN-gamma(-/-) mice. IFN-gamma(+) cells but not IL-5(+) cells were induced markedly (9.1x) in healthy peripheral blood by SSG/IL-2 in contrast to the modest induction by SSG alone (2.1x) at its clinically achievable dose (20 microg/mL) or by IL-2 (3.1x) at its C(max) of low-dose schedule (30 IU/mL). SSG at a higher dose (100 microg/mL) was less effective alone (1.5x) or in combination with IL-2 (7.8x). Peripheral IFN-gamma(+) cells were induced after 4 or 16 h treatment with SSG/IL-2 within CD4(+) and CD8(+) lymphocytes coincided with heightened CD69 expression (approximately 3-4x). SSG/IL-2 was also more effective than the single agents in inducing IFN-gamma(+) cells in the peripheral blood of melanoma patients, whose basal IFN-gamma(+) cell levels were approximately 5% of healthy controls. Renca tumor growth was inhibited by SSG/IL-2 in wild-type but not IFN-gamma(-/-) mice. These results demonstrate SSG interactions with IL-2 in vitro to activate key antitumor immune cells in peripheral blood of healthy and melanoma donors, providing further evidence for proof of concept clinical trials for effecting augmentation of IL-2 through inhibiting negative regulatory protein tyrosine phosphatases.

Leukocyte Ig-like receptor B4 (LILRB4) is a potent inhibitor of FcgammaRI-mediated monocyte activation via dephosphorylation of multiple kinases

The leukocyte immunoglobulin-like receptor (LILR) B4 belongs to a family of cell surface receptors that possesses cytoplasmic immunoreceptor tyrosine-based inhibitory motifs (ITIMs). LILRB4 is believed to down-regulate activation signals mediated by non-receptor tyrosine kinase cascades through the recruitment of SHP-1. However, the exact mechanisms of LILRB4-mediated inhibition are not fully elucidated. In this study, we demonstrate high level surface expression of LILRB4 on THP-1 cells and primary peripheral blood monocytes, which profoundly inhibited production of a key pro-inflammatory cytokine (TNFalpha) induced by FcgammaRI (CD64). We also report that LILRB4 aggregated to sites of activation upon co-ligation with CD64 and that this may enhance its inhibitory effects. Cross-linking of CD64 on THP-1 cells markedly increased phosphorylation of multiple proteins including tyrosine kinases and signaling molecules (Lck, Syk, LAT, and Erk), an adaptor protein that targets protein-tyrosine kinases for degradation (c-Cbl) and a protein involved in the formation of actin cytoskeletal rearrangement (alpha-actinin-4). Co-ligation of LILRB4 considerably reduced CD64-mediated phosphorylation of Lck, Syk, LAT, Erk, and c-Cbl but not alpha-actinin-4, suggesting selective inhibition of signaling molecules. Treatment of cells with a broad-spectrum phosphatase inhibitor, sodium pervanadate (SP), significantly reversed LILRB4-mediated inhibition of TNFalpha production and protein tyrosine phosphorylation. In comparison, treatment with an SHP-1 specific inhibitor, sodium stibogluconate (SS) has no effects indicating involvement of phosphatase(s) other than SHP-1 in LILRB4 signaling. Collectively, our data show LILRB4 is a potent inhibitor of monocytes activation. This may provide a new potential therapeutic strategy for inflammatory conditions characterized by excessive TNFalpha production.

Treatment of non-Hodgkin's lymphoma xenografts with the HB22.7 anti-CD22 monoclonal antibody and phosphatase inhibitors improves efficacy

PURPOSE

To examine the role of phosphatase inhibition on anti-CD22, HB22.7-mediated lymphomacidal effects.

EXPERIMENTAL DESIGN

CD22 is a cell-surface molecule expressed on most B cell lymphomas (NHL). HB22.7 is an anti-CD22 monoclonal antibody that binds a unique CD22-epitope, blocks ligand binding, initiates signaling, and has demonstrated lymphomacidal activity. The SHP-1 tyrosine phosphatase is associated with the cytoplasmic domain of CD22. Sodium orthovanadate (NaV) is a phosphatase inhibitor. The SHP-1-CD22 interaction presents an opportunity to manipulate CD22-mediated signaling effects. In vitro cell culture assays and in vivo human NHL xenograft studies were used to assess the effects of phosphatase inhibition.

RESULTS

NaV caused dose dependent killing of NHL cells in vitro; when HB22.7 was given with NaV, antibody-mediated cell death was augmented. Flow cytometry showed that NaV-pretreatment resulted in less CD22 internalization after ligation with HB22.7 than did control cells. Studies in mice bearing Raji NHL xenografts showed that the combination of NaV and HB22.7 shrank NHL tumors more rapidly, had a higher complete response rate (80%), and produced the best survival compared to controls; no toxicity was detected. Studies using Raji cells stably transfected with SHP-1DN confirmed that these observations were due to SHP-1 inhibition.

CONCLUSION

The relatively specific association of SHP-1 with CD22 suggests that CD22-specific signal augmentation by phosphatase inhibitors can improve the clinical outcome of anti-CD22 based immunotherapy.

Macrophage interleukin-6 and tumour necrosis factor-alpha are induced by coronavirus fixation to Toll-like receptor 2/heparan sulphate receptors but not carcinoembryonic cell adhesion antigen 1a

A rapid antiviral immune response may be related to viral interaction with the host cell leading to activation of macrophages via pattern recognition receptors (PPRs) or specific viral receptors. Carcinoembryonic cell adhesion antigen 1a (CEACAM1a) is the specific receptor for the mouse hepatitis virus (MHV), a coronavirus known to induce acute viral hepatitis in mice. The objective of this study was to understand the mechanisms responsible for the secretion of high-pathogenic MHV3-induced inflammatory cytokines. We report that the induction of the pro-inflammatory cytokines interleukin (IL)-6 and tumour necrosis factor (TNF)-alpha in peritoneal macrophages does not depend on CEACAM1a, as demonstrated in cells isolated from Ceacam1a(-/-) mice. The induction of IL-6 and TNF-alpha production was related rather to the fixation of the spike (S) protein of MHV3 on Toll-like receptor 2 (TLR2) in regions enriched in heparan sulphate and did not rely on viral replication, as demonstrated with denatured S protein and UV-inactivated virus. High levels of IL-6 and TNF-alpha were produced in livers from infected C57BL/6 mice but not in livers from Tlr2(-/-) mice. The histopathological observations were correlated with the levels of those inflammatory cytokines. Depending on mouse strain, the viral fixation to heparan sulfate/TLR2 stimulated differently the p38 mitogen-activated protein kinase (MAPK) and nuclear factor (NF)-kappaB in the induction of IL-6 and TNF-alpha. These results suggest that TLR2 and heparan sulphate receptors can act as new viral PPRs involved in inflammatory responses.

Pentavalent antimonials: new perspectives for old drugs

Pentavalent antimonials, including meglumine antimoniate and sodium stibogluconate, have been used for more than half a century in the therapy of the parasitic disease leishmaniasis. Even though antimonials are still the first-line drugs, they exhibit several limitations, including severe side effects, the need for daily parenteral administration and drug resistance. The molecular structure of antimonials, their metabolism and mechanism of action are still being investigated. Some recent studies suggest that pentavalent antimony acts as a prodrug that is converted to active and more toxic trivalent antimony. Other works support the direct involvement of pentavalent antimony. Recent data suggest that the biomolecules, thiols and ribonucleosides, may mediate the actions of these drugs. This review will summarize the progress to date on the chemistry and biochemistry of pentavalent antimony. It will also present the most recent works being done to improve antimonial chemotherapy. These works include the development of simple synthetic methods for pentavalent antimonials, liposome-based formulations for targeting the Leishmania parasites responsible for visceral leishmaniasis and cyclodextrin-based formulations to promote the oral delivery of antimony.

Respiratory syncytial virus impairs macrophage IFN-alpha/beta- and IFN-gamma-stimulated transcription by distinct mechanisms

Macrophages are the primary lung phagocyte and are instrumental in maintenance of a sterile, noninflamed microenvironment. IFNs are produced in response to bacterial and viral infection, and activate the macrophage to efficiently counteract and remove pathogenic invaders. Respiratory syncytial virus (RSV) inhibits IFN-mediated signaling mechanisms in epithelial cells; however, the effects on IFN signaling in the macrophage are currently unknown. We investigated the effect of RSV infection on IFN-mediated signaling in macrophages. RSV infection inhibited IFN-beta- and IFN-gamma-activated transcriptional mechanisms in primary alveolar macrophages and macrophage cell lines, including the transactivation of important Nod-like receptor family genes, Nod1 and class II transactivator. RSV inhibited IFN-beta- and IFN-gamma-mediated transcriptional activation by two distinct mechanisms. RSV impaired IFN-beta-mediated signal transducer and activator of transcription (STAT)-1 phosphorylation through a mechanism that involves inhibition of tyrosine kinase 2 phosphorylation. In contrast, RSV-impaired transcriptional activation after IFN-gamma stimulation resulted from a reduction in the nuclear STAT1 interaction with the transcriptional coactivator, CBP, and was correlated with increased phosphorylation of STAT1beta, a dominant-negative STAT1 splice variant, in response to IFN-gamma. In support of this concept, overexpression of STAT1beta was sufficient to repress the IFN-gamma-mediated expression of class II transactivator. These results demonstrate that RSV inhibits IFN-mediated transcriptional activation in macrophages, and suggests that paramyxoviruses modulate an important regulatory mechanism that is critical in linking innate and adaptive immune mechanisms after infection.

IL-10 interferes directly with TCR-induced IFN-gamma but not IL-17 production in memory T cells

IL-10 is a potent immunoregulatory and anti-inflammatory cytokine. However, therapeutic trials in chronic inflammation have been largely disappointing. It is well established that IL-10 can inhibit Th1 and Th2 cytokine production via indirect effects on APC. Less data are available about the influence of IL-10 on IL-17 production, a cytokine which has been recently linked to chronic inflammation. Furthermore, there are only few reports about a direct effect of IL-10 on T cells. We demonstrate here that IL-10 can directly interfere with TCR-induced IFN-gamma production in freshly isolated memory T cells in the absence of APC. This effect was independent of the previously described effects of IL-10 on T cells, namely inhibition of IL-2 production and inhibition of CD28 signaling. In contrast, IL-10 did not affect anti-CD3/anti-CD28-induced IL-17 production from memory T cells even in the presence of APC. This might have implications for the interpretation of therapeutic trials in patients with chronic inflammation where Th17 cells contribute to pathogenesis.

Leishmanicidal effect of LLD-3 (1), a nor-triterpene isolated from Lophanthera lactescens

Leishmanicidal activity of 6alpha, 7alpha, 15beta, 16beta, 24-pentacetoxy-22alpha-carbometoxy-21beta,22beta-epoxy-18beta-hydroxy-27,30-bisnor-3,4-secofriedela-1,20 (29)-dien-3,4 R-olide (LLD-3 (1)) isolated from Lophanthera lactescens Ducke, a member of the Malpighiaceae, was demonstrated against intramacrophage amastigote forms (IC(50) of 0.41mug/mL). The in vitro leishmanicidal effect of Glucantime, the first choice drug for leishmaniasis treatment, was increased by LLD-3 (1) association. The leishmanicidal effect of LLD-3 (1) was not due to stimulation of nitric oxide production by macrophages. LLD-3 (1) was also not cytotoxic for mouse peritoneal macrophages or B cells as assessed by the XTT and Trypan blue exclusion assays. LLD-3 (1) was unable to affect proliferation of naïve or activated B and T cells, as well as the B cells immunoglobulin synthesis. Cellularity of different tissues, liver and kidney functions were not altered in mice treated with LLD-3 (1), as well as the histology pattern of different organs. Our results add LLD-3 (1) as a potential drug candidate for treatment of leishmaniasis.

Jak2 inhibition deactivates Lyn kinase through the SET-PP2A-SHP1 pathway, causing apoptosis in drug-resistant cells from chronic myelogenous leukemia patients

Chronic myelogenous leukemia (CML) patients treated with imatinib mesylate (IM) become drug resistant by mutations within the kinase domain of Bcr-Abl, and by other changes that cause progression to advanced stage (blast crisis) and increased expression of the Lyn tyrosine kinase, the regulation of which is not understood yet. In Bcr-Abl+ cells inhibition of Jak2, a downstream target of Bcr-Abl, by either Jak2 inhibitors or Jak2-specific short interfering RNA (siRNA) reduced the level of the SET protein, and increased PP2A Ser/Thr phosphatase and Shp1 tyrosine phosphatase activities, which led to decreased levels of activated Lyn. Activation of PP2A combined with Jak2 inhibition enhanced the reduction of activated Lyn kinase compared with Jak2 inhibition alone. In contrast, inhibition of either PP2A or Shp1 combined with Jak2 inhibition interfered with the loss of Lyn kinase activation more so than Jak2 inhibition alone, indicating the involvement of PP2A and Shp1 in the inactivation of the Lyn kinase caused by Jak2 inhibition. Inhibition of Jak2 induced apoptosis and reduced colony formation in IM-sensitive and -resistant Bcr-Abl mutant cell lines. Jak2 inhibition also induced apoptosis in CML cells from blast crisis patients but not in normal hematopoietic cells. These results indicate that Lyn is downstream of Jak2, and Jak2 maintains activated Lyn kinase in CML through the SET-PP2A-Shp1 pathway.

The role and target potential of protein tyrosine phosphatases in cancer

Protein tyrosine phosphatases (PTPases) are attractive targets for developing novel cancer therapeutics. Activated via gain-of-function point mutations or overexpression, several PTPases have been identified as critical oncogenic molecules in human malignancies that may be targeted with small chemical inhibitors as a therapeutic strategy. Tumor suppressor PTPases have also been discovered as contributing factors in cancer development that may be targeted via intervention of downstream signaling events for therapeutic purposes. In addition, PTPases have been identified as key negative regulators of cytokines or immune cells. Targeting these negative PTPases may improve the efficacy of cytokine therapy and immunotherapy, which currently have modest response rates and limited survival benefit. Inhibitors of selective PTPases have demonstrated significant preclinical antitumor activity, leading to early-phase clinical trials. Further research and development could lead to PTPase-targeted cancer therapeutics in the near future.

Surfactant proteins A and D suppress alveolar macrophage phagocytosis via interaction with SIRP alpha

RATIONALE

Efficient removal of apoptotic cells is essential for the resolution of acute pulmonary inflammation. Alveolar macrophages ingest apoptotic cells less avidly than other professional phagocytes at rest but overcome this defect during acute inflammation. Surfactant protein (SP)-A and SP-D are potent modulators of macrophage function and may suppress clearance of apoptotic cells through activation of the transmembrane receptor signal inhibitory regulatory protein alpha (SIRP alpha).

OBJECTIVES

To investigate whether binding of SP-A and SP-D to SIRP alpha on alveolar macrophages suppresses apoptotic cell clearance.

METHODS

Phagocytosis of apoptotic cells was assessed using macrophages pretreated with SP-A, SP-D, or the collectin-like molecule C1q. Binding of SP-A and SP-D to SIRP alpha was confirmed in vitro using blocking antibodies and fibroblasts transfected with active and mutant SIRP alpha. The effects of downstream molecules SHP-1 and RhoA on phagocytosis were studied using SHP-1-deficient mice, sodium stibogluconate, and a Rho kinase inhibitor. Lipopolysaccharide was given to chimeric mice to study the effects of SP-A and SP-D binding on inflammatory macrophages.

MEASUREMENTS AND MAIN RESULTS

Preincubation of macrophages with SP-A or SP-D suppressed apoptotic cell clearance. Surfactant suppression of macrophage phagocytosis was reversed by blocking SIRP alpha and inhibiting downstream molecules SHP-1 and RhoA. Macrophages from inflamed lungs ingested apoptotic cells more efficiently than resting alveolar macrophages. Recruited mononuclear phagocytes with low levels of SP-A and SP-D mediated this effect.

CONCLUSIONS

SP-A and SP-D tonically inhibit alveolar macrophage phagocytosis by binding SIRP alpha. During acute pulmonary inflammation, defects in apoptotic cell clearance are overcome by recruited mononuclear phagocytes.

Modulation of gene expression in human macrophages treated with the anti-leishmania pentavalent antimonial drug sodium stibogluconate

Within the mammalian host, Leishmania donovani is an obligatory intracellular protozoan parasite that resides and multiplies exclusively in the phagolysosomes of macrophages. Leishmania control relies primarily on chemotherapy, with the mainstay being pentavalent antimony (SbV) complexed to carbohydrates in the form of sodium stibogluconate (Pentostam) or meglumine antimoniate (Glucantime). The mode of action of SbV is still not known precisely. To explore the effect of SbV on macrophage gene expression, a microarray analysis was performed using Affymetrix focus arrays to compare gene expression profiles in noninfected and L. donovani-infected THP-1 monocytic cells treated or not treated with sodium stibogluconate. Under our experimental conditions, SbV changed the expression of a few host genes, and this was independent of whether cells were infected or not infected with Leishmania. Leishmania infection had a greater effect on the modulation of host gene expression. Statistical analyses have indicated that the expression of eight genes was modified by at least twofold upon SbV treatment, with six genes upregulated and two genes downregulated. One gene whose expression was affected by SbV was the heme oxygenase gene HMOX-1, and this change was observed both in the monocytic cell line THP-1 and in primary human monocyte-derived macrophages. Another pathway that was affected was the glutathione biosynthesis pathway, where the expression of the glutamate-cysteine ligase modifier subunit was increased upon SbV treatment. Our analysis has suggested that, under our experimental conditions, the expression of a few genes is altered upon SbV treatment, and some of these encoded proteins may be implicated in the yet-to-be-defined mode of action of SbV.

Vanillic acid derivatives from the green algae Cladophora socialis as potent protein tyrosine phosphatase 1B inhibitors

A novel vanillic acid derivative (1) and its sulfate adduct (2) were isolated from a green algae, Cladophora socialis. The structures of 1 and 2 were elucidated from NMR and HRESIMS experiments. Both compounds showed potent inhibitory activity against protein tyrosine phosphatase 1B (PTP1B), an enzyme involved in the regulation of insulin cell signaling. Compounds 1 and 2 had IC50 values of 3.7 and 1.7 microM, respectively.

Tratamento da Leishmaniose Tegumentar Americana

A leishmaniose tegumentar americana é doença infecciosa da pele e mucosa, cujo agente etiológico é um protozoário do gênero Leishmania. Seu tratamento é desafio porque as drogas disponíveis apresentam elevada toxicidade, e nenhuma delas é bastante eficaz. A recidiva, a falha terapêutica em pacientes imunodeprimidos e a resistência ao tratamento são fatores que motivam a busca de uma droga ideal.

Molecular mechanisms of antimony resistance in Leishmania

Leishmaniasis causes significant morbidity and mortality worldwide. The disease is endemic in developing countries of tropical regions, and in recent years economic globalization and increased travel have extended its reach to people in developed countries. In the absence of effective vaccines and vector-control measures, the main line of defence against the disease is chemotherapy. Organic pentavalent antimonials [Sb(V)] have been the first-line drugs for the treatment of leishmaniasis for the last six decades, and clinical resistance to these drugs has emerged as a primary obstacle to successful treatment and control. A multiplicity of resistance mechanisms have been described in resistantLeishmaniamutants developedin vitroby stepwise increases of the concentration of either antimony [Sb(III)] or the related metal arsenic [As(III)], the most prevalent mechanism being upregulated Sb(III) detoxification and sequestration. With the availability of resistant field isolates, it has now become possible to elucidate mechanisms of clinical resistance. The present review describes the mechanisms of antimony resistance inLeishmaniaand highlights the links between previous hypotheses and current developments in field studies. Unravelling the molecular mechanisms of clinical resistance could allow the prevention and circumvention of resistance, as well as rational drug design for the treatment of drug-resistantLeishmania.

Possibility of membrane modification as a mechanism of antimony resistance in Leishmania donovani

Resistance to antimonials has become a clinical threat in the treatment of visceral leishmaniasis (VL). Unravelling the resistance mechanism needs attention to circumvent the problem of drug resistance. In one of the resistant isolates, we earlier identified a gene (PG1) implicated in antimony resistance whose localization in the present study was confirmed on the pellicular plasma membrane of the parasite thereby indicating towards membrane modification as a mechanism of resistance in this resistant isolate.

Efficacy of SSG and SSG/IFNalpha2 against human prostate cancer xenograft tumors in mice: a role for direct growth inhibition in SSG anti-tumor action

BACKGROUND

Pre-clinical activity of SSG against melanoma and renal cancer has been identified recently although the drug's mechanism of action and activity against tumors of additional histological-types remain undefined.

METHODS

The effects of SSG and SSG combination with other agents on DU145 human prostate carcinoma xenograft tumors in mice and on DU145 cell subpopulations of differential SSG sensitivities were evaluated.

RESULTS

DU145 tumor growth was inhibited by SSG (69%), IFNalpha2 (33%) or the combination (80%) that induced complete regression of WM9 human melanoma tumors. DU145 cells in culture were also partially growth inhibited by SSG at killing doses (200-800 mug/ml) for WM9 cells, indicating a correlation of SSG inhibition of cancer cell growth in vitro and in vivo. DU145 cells formed multiple micro tumors in mice treated with SSG or SSG/IFNalpha2 in contrast to the single large tumors in the control or IFNalpha2-treated mice, suggesting the existence of an SSG-resistant subpopulation in DU145 cells. Indeed, DU145 but not WM9 cells formed colonies (approximately 4% frequency) when cultured in the presence of SSG. Single cell clone (DU145-7) isolated from DU145 cells showed SSG-resistant growth in culture, unassociated with cross-resistance to IFNalpha2 and converted to SSG-responsive cells by BSO that inhibited intracellular glutathione levels.

CONCLUSIONS

These results implicate a role for direct growth inhibition in SSG anti-tumor action, provide novel insights into the mechanism of tumor resistance to the drug and suggest a therapeutic potential for SSG and its combinations with IFNalpha2 or BSO for prostate cancer that warrants further investigation.

Inhibitors of protein tyrosine phosphatases: next-generation drugs?

The protein tyrosine phosphatases (PTPs) constitute a family of closely related key regulatory enzymes that dephosphorylate phosphotyrosine residues in their protein substrates. Malfunctions in PTP activity are linked to various diseases, ranging from cancer to neurological disorders and diabetes. Consequently, PTPs have emerged as promising targets for therapeutic intervention in recent years. In this review, general aspects of PTPs and the development of small-molecule inhibitors of PTPs by both academic research groups and pharmaceutical companies are discussed. Different strategies have been successfully applied to identify potent and selective inhibitors. These studies constitute the basis for the future development of PTP inhibitors as drugs.

Bifunctional role of the leishmanial antimonate reductase LmACR2 as a protein tyrosine phosphatase

LmACR2 is the first identified antimonate reductase responsible for the reduction of pentavalent antimony in pentostam to the active trivalent form of the drug in Leishmania. LmACR2 is a homologue of the yeast arsenate reductase Acr2p and Cdc25 phosphatases and has the HC[X]5R phosphatase motif. Purified LmACR2 exhibited phosphatase activity in vitro and was able to dephosphorylate a phosphotyrosine residue from a synthetic peptide. This phosphatase activity was inhibited by classical inhibitors such as orthovanadate. LmACR2-catalyzed phosphatase activity was inhibited by either antimonate or arsenate. Site-directed mutagenesis experiments showed that the H74C[X]5R81 motif was involved in catalysis. This is the first report of a metalloid reductase with a bifunctional role in protein tyrosine phosphatase activity. Leishmania is never exposed to metalloids during its life cycle. It is therefore unlikely that it would evolve an enzyme exclusively for drug activation. We propose that the physiological function of LmACR2 is to dephosphorylate phosphotyrosine residues in leishmanial proteins.

Discovery of protein phosphatase inhibitor classes by biology-oriented synthesis

Protein phosphatases have very recently emerged as important targets for chemical biology and medicinal chemistry research, and new phosphatase inhibitor classes are in high demand. The underlying frameworks of natural products represent the evolutionarily selected fractions of chemical space explored by nature so far and meet the criteria of relevance to nature and biological prevalidation most crucial to inhibitor development. We refer to synthesis efforts and compound collection development based on these criteria as biology-oriented synthesis. For the discovery of phosphatase inhibitor classes by means of this approach, four natural product-derived or -inspired medium-sized compound collections were synthesized and investigated for inhibition of the tyrosine phosphatases VE-PTP, Shp-2, PTP1B, MptpA, and MptpB and the dual-specificity phosphatases Cdc25A and VHR. The screen yielded four unprecedented and selective phosphatase inhibitor classes for four phosphatases with high hit rates. For VE-PTP and MptpB the first inhibitors were discovered. These results demonstrate that biology-oriented synthesis is an efficient approach to the discovery of new compound classes for medicinal chemistry and chemical biology research that opens up new opportunities for the study of phosphatases, which may lead to the development of new drug candidates.

Sodium antimony gluconate induces generation of reactive oxygen species and nitric oxide via phosphoinositide 3-kinase and mitogen-activated protein kinase activation in Leishmania donovani-infected macrophages

Pentavalent antimony complexes, such as sodium stibogluconate and sodium antimony gluconate (SAG), are still the first choice for chemotherapy against various forms of leishmaniasis, including visceral leishmaniasis, or kala-azar. Although the requirement of a somewhat functional immune system for the antileishmanial action of antimony was reported previously, the cellular and molecular mechanism of action of SAG was not clear. Herein, we show that SAG induces extracellular signal-regulated kinase 1 (ERK-1) and ERK-2 phosphorylation through phosphoinositide 3-kinase (PI3K), protein kinase C, and Ras activation and p38 mitogen-activated protein kinase (MAPK) phosphorylation through PI3K and Akt activation. ERK-1 and ERK-2 activation results in an increase in the production of reactive oxygen species (ROS) 3 to 6 h after SAG treatment, while p38 MAPK activation and subsequent tumor necrosis factor alpha release result in the production of nitric oxide (NO) 24 h after SAG treatment. Thus, this study has provided the first evidence that SAG treatment induces activation of some important components of the intracellular signaling pathway, which results in an early wave of ROS-dependent parasite killing and a stronger late wave of NO-dependent parasite killing. This opens up the possibility of this metalloid chelate being used in the treatment of various diseases either alone or in combination with other drugs and vaccines.

Adenosine downregulates DPPIV on HT-29 colon cancer cells by stimulating protein tyrosine phosphatase(s) and reducing ERK1/2 activity via a novel pathway

The multifunctional cell-surface protein dipeptidyl peptidase IV (DPPIV/CD26) is aberrantly expressed in many cancers and plays a key role in tumorigenesis and metastasis. Its diverse cellular roles include modulation of chemokine activity by cleaving dipeptides from the chemokine NH(2)-terminus, perturbation of extracellular nucleoside metabolism by binding the ecto-enzyme adenosine deaminase, and interaction with the extracellular matrix by binding proteins such as collagen and fibronectin. We have recently shown that DPPIV can be downregulated from the cell surface of HT-29 colorectal carcinoma cells by adenosine, which is a metabolite that becomes concentrated in the extracellular fluid of hypoxic solid tumors. Most of the known responses to adenosine are mediated through four different subtypes of G protein-coupled adenosine receptors: A(1), A(2A), A(2B), and A(3). We report here that adenosine downregulation of DPPIV from the surface of HT-29 cells occurs independently of these classic receptor subtypes, and is mediated by a novel cell-surface mechanism that induces an increase in protein tyrosine phosphatase activity. The increase in protein tyrosine phosphatase activity leads to a decrease in the tyrosine phosphorylation of ERK1/2 MAP kinase that in turn links to the decline in DPPIV mRNA and protein. The downregulation of DPPIV occurs independently of changes in the activities of protein kinases A or C, phosphatidylinositol 3-kinase, other serine/threonine phosphatases, or the p38 or JNK MAP kinases. This novel action of adenosine has implications for our ability to manipulate adenosine-dependent events within the solid tumor microenvironment.

Loss of SPARC-mediated VEGFR-1 suppression after injury reveals a novel antiangiogenic activity of VEGF-A

VEGF-A promotes angiogenesis in many tissues. Here we report that choroidal neovascularization (CNV) incited by injury was increased by excess VEGF-A before injury but was suppressed by VEGF-A after injury. This unorthodox antiangiogenic effect was mediated via VEGFR-1 activation and VEGFR-2 deactivation, the latter via Src homology domain 2-containing (SH2-containing) tyrosine phosphatase-1 (SHP-1). The VEGFR-1-specific ligand placental growth factor-1 (PlGF-1), but not VEGF-E, which selectively binds VEGFR-2, mimicked these responses. Excess VEGF-A increased CNV before injury because VEGFR-1 activation was silenced by secreted protein, acidic and rich in cysteine (SPARC). The transient decline of SPARC after injury revealed a temporal window in which VEGF-A signaling was routed principally through VEGFR-1. These observations indicate that therapeutic design of VEGF-A inhibition should include consideration of the level and activity of SPARC.

Sodium Stibogluconate Interacts with IL-2 in Anti-Renca Tumor Action via a T Cell-Dependent Mechanism in Connection with Induction of Tumor-Infiltrating Macrophages

IL-2 therapy results in 10-20% response rates in advanced renal cell carcinoma (RCC) via activating immune cells, in which the protein tyrosine phosphatase Src homology 2 domain-containing phosphatase 1 (SHP-1) is a key negative regulator. Based on finding that sodium stibogluconate (SSG) inhibited SHP-1, the anti-RCC potential and action mechanism of SSG and SSG/IL-2 in combination were investigated in a murine renal cancer model (Renca). Despite its failure to inhibit Renca cell proliferation in cultures, SSG induced 61% growth inhibition of Renca tumors in BALB/c mice coincident with an increase (2-fold) in tumor-infiltrating macrophages (Mphi). A combination of SSG and IL-2 was more effective in inhibiting tumor growth (91%) and inducing tumor-infiltrating Mphi (4-fold), whereas IL-2 alone had little effect. Mphi increases were also detected in the spleens of mice treated with SSG (3-fold) or SSG/IL-2 in combination (6-fold), suggesting a systemic Mphi expansion similar to those in SHP-deficient mice. T cell involvement in the anti-Renca tumor action of the combination was suggested by the observations that the treatment induced spleen IFN-gamma T cells in BALB/c mice, but failed to inhibit Renca tumor growth in athymic nude mice and that SSG treatment of T cells in vitro increased production of IFN-gamma capable of activating tumoricidal Mphi. The SSG and SSG/IL-2 combination treatments were tolerated in the mice. These results together demonstrate an anti-Renca tumor activity of SSG that was enhanced in combination with IL-2 and functions via a T cell-dependent mechanism with increased IFN-gamma production and expansion/activation of Mphi. Our findings suggest that SSG might improve anti-RCC efficacy of IL-2 therapy by enhancing antitumor immunity.

The tumor suppressor PP2A is functionally inactivated in blast crisis CML through the inhibitory activity of the BCR/ABL-regulated SET protein

The oncogenic BCR/ABL kinase activity induces and maintains chronic myelogenous leukemia (CML). We show here that, in BCR/ABL-transformed cells and CML blast crisis (CML-BC) progenitors, the phosphatase activity of the tumor suppressor PP2A is inhibited by the BCR/ABL-induced expression of the PP2A inhibitor SET. In imatinib-sensitive and -resistant (T315I included) BCR/ABL+ cell lines and CML-BC progenitors, molecular and/or pharmacological activation of PP2A promotes dephosphorylation of key regulators of cell proliferation and survival, suppresses BCR/ABL activity, and induces BCR/ABL degradation. Furthermore, PP2A activation results in growth suppression, enhanced apoptosis, restored differentiation, impaired clonogenic potential, and decreased in vivo leukemogenesis of imatinib-sensitive and -resistant BCR/ABL+ cells. Thus, functional inactivation of PP2A is essential for BCR/ABL leukemogenesis and, perhaps, required for blastic transformation.

The Tyrosine Phosphatase, SHP-1, Is a Negative Regulator of Endothelial Superoxide Formation

OBJECTIVES

We investigated the role of SH2-domain containing phosphatase-1 (SHP-1) in endothelial reduced nicotinamide adenine dinucleotide (phosphate) (NAD[P]H)-oxidase-dependent oxidant production.

BACKGROUND

Superoxide (O2*-) generation by endothelial NAD(P)H-oxidase promotes endothelial dysfunction and atherosclerosis. Signaling pathways that regulate NAD(P)H-oxidase activity are, however, poorly understood.

METHODS

SH2-domain containing phosphatase-1 was inhibited using site-directed magnetofection of antisense oligodesoxynucleotides (AS-ODN) or short interfering ribonucleic acid (siRNA) in vitro in human umbilical vein endothelial cells (HUVEC) and in isolated hamster arteries; O2*- was measured by cytochrome c reduction in vitro. Activities of NAD(P)H-oxidase activity, phosphatidyl-inositol-3-kinase (PI3K), and SHP-1 were assessed by specific assays; Rac1 activation was assessed by a pull-down assay.

RESULTS

Basal endothelial O2*- release was enhanced after inhibition of endothelial SHP-1 (p < 0.01), which could be prevented by specific inhibition of NAD(P)H-oxidase (p < 0.01); SHP-1 activity was high under basal conditions, further increased by vascular endothelial growth factor (10 ng/ml, p < 0.05), and abolished by SHP-1 AS-ODN treatment (p < 0.01), which also increased NAD(P)H-oxidase activity 3.3-fold (p < 0.01). Vascular endothelial growth factor also induced O2*- release (p < 0.01), which was even more enhanced when SHP-1 was knocked down (p < 0.05). The effect of SHP-1 was mediated by inhibition of PI3K/Rac1-dependent NAD(P)H-oxidase activation (p < 0.01); SHP-1 AS-ODN augmented tyrosine phosphorylation of the p85 regulatory subunit of PI3K (p < 0.05) and Rac1 activation. The latter was prevented by wortmannin, a blocker of PI3K.

CONCLUSIONS

In HUVEC, SHP-1 counteracts basal and stimulated NAD(P)H-oxidase activity by negative regulation of PI3K-dependent Rac1 activation; SHP-1 thus seems to be an important part of endothelial antioxidative defense controlling the activity of the O2(*-)-producing NAD(P)H-oxidase.

Leishmania donovani engages in regulatory interference by targeting macrophage protein tyrosine phosphatase SHP-1

Protozoan parasites of the genus leishmania are obligate intracellular parasites of monocytes and macrophages. These pathogens have evolved to invade the mammalian immune system and typically survive for long periods of time. Leishmania have developed a variety of remarkable strategies to prevent their elimination by both innate and acquired immune effector mechanisms. One particular strategy of interest involves manipulation of host cell regulatory pathways so as to prevent macrophage activation required for efficient microbicidal activity. These interference mechanisms are the main focus of this review. Several lines of evidence have been developed to show that the Src homology-2 domain containing tyrosine phosphatase-1 (SHP-1) becomes activated in leishmania-infected cells and that this contributes to disease pathogenesis. Recent studies aimed at understanding the mechanism responsible for the change in activation state of SHP-1 led to the identification of leishmania EF-1alpha as an SHP-1 binding protein and SHP-1 activator. This was a surprising finding given that this ubiquitous and highly conserved protein plays an essential role in protein translation in both prokaryotic and eukaryotic cells. The role of leishmania EF-1alpha as an SHP-1 activator and its contribution to pathogenesis are reviewed with particular attention to the properties that distinguish it from host EF-1alpha.

Normal neutrophil maturation is associated with selective loss of MAP kinase activation by G-CSF

Although both GM-CSF and G-CSF activate p42/44 MAPK in neutrophil progenitors, the ability of G-CSF to cause MAPK activation is lost in mature neutrophils, while GM-CSF exposure still causes activation. The mechanism of this differential effect related to maturation status has not been explored. We verified that G-CSF and GM-CSF receptors remain functional on purified mature neutrophils by demonstrating that both cytokines caused phosphorylation of STAT3. However, only GM-CSF was capable of activating MAPK as assessed by gel shift and in vitro kinase assay. Both G-CSF and GM-CSF caused activation of p21 ras in neutrophils, demonstrating that early events in the ras-MAPK pathway remain functional after stimulation by either cytokine. Inhibition of tyrosine phosphatase activity by pervanadate restored the ability of G-CSF to activate MAPK in mature neutrophils. Specific inhibition of the SHP-1 phosphatase, known to be activated by G-CSF but not GM-CSF also restored the ability of G-CSF to activate MAPK in neutrophils. These studies suggest that G-CSF activation of SHP-1 may be an important regulatory step for permitting optimal terminal differentiation during neutrophil production and add to our knowledge of the instructional role of G-CSF and GM-CSF for balancing proliferation and differentiation of neutrophil progenitor cells. This information may prove useful for the understanding of conditions in which neutrophil proliferative/differentiative balancing is dysregulated, such as myeloid leukemia and myelodysplastic disorders.

INHIBITION OF LEISHMANIA DONOVANI PROMASTIGOTE DNA TOPOISOMERASE I AND HUMAN MONOCYTE DNA TOPOISOMERASES I AND II BY ANTIMONIAL DRUGS AND CLASSICAL ANTITOPOISOMERASE AGENTS

We have compared the inhibitor sensitivities of DNA topoisomerase I (TOPI) from Leishmania donovani promastigotes and TOPs I and II of human monocytes using pentavalent and trivalent antimonials (SbV, SbIII) and classical TOP inhibitors. Bis-benzimidazoles (Hoechst-33258 and -33342) were potent inhibitors of both parasite and human TOPI, but Hoechst-33342 was markedly less cytotoxic to promastigotes than to monocytes in vitro. Leishmania donovani was also considerably less sensitive than monocytes to camptothecin, both at enzyme and cellular levels. Sodium stibogluconate (SSG) was the only antimonial to inhibit TOPI, exhibiting a significant (P < 0.05) 3-fold greater potency against the L. donovani enzyme but showed low cytotoxicities against intact promastigotes. The SbV meglumine antimoniate failed to inhibit TOPI and showed negligible cytotoxicities, whereas SbIII drugs were lethal to parasites and monocytes yet poor inhibitors of TOPI. Monocyte TOPII was inhibited by bis-benzimidazoles and insensitive to antimonials and camptothecin. The disparity between the high leishmanicidal activity and low anti-TOPI potency of SbIII indicates that in vivo targeting of L. donovani TOPI by the reductive pathway of antimonial activation is improbable. Nevertheless, the potent direct inhibition of TOPI by SSG and the differential interactions of camptothecin with L. donovani and human TOPI support the possibility of developing parasite-specific derivatives.

Structure-based Design of Selective and Potent Inhibitors of Protein-tyrosine Phosphatase β

Protein-tyrosine phosphatases (PTPs) are considered important therapeutic targets because of their pivotal role as regulators of signal transduction and thus their implication in several human diseases such as diabetes, cancer, and autoimmunity. In particular, PTP1B has been the focus of many academic and industrial laboratories because it was found to be an important negative regulator of insulin and leptin signaling, and hence a potential therapeutic target in diabetes and obesity. As a result, significant progress has been achieved in the design of highly selective and potent PTP1B inhibitors. In contrast, little attention has been given to other potential drug targets within the PTP family. Guided by x-ray crystallography, molecular modeling, and enzyme kinetic analyses with wild type and mutant PTPs, we describe the development of a general, low molecular weight, non-peptide, non-phosphorus PTP inhibitor into an inhibitor that displays more than 100-fold selectivity for PTPbeta over PTP1B. Of note, our structure-based design principles, which are based on extensive bioinformatics analyses of the PTP family, are general in nature. Therefore, we anticipate that this strategy, here applied to PTPbeta, in principle can be used in the design and development of selective inhibitors of many, if not most PTPs.

Directed evolution of a yeast arsenate reductase into a protein-tyrosine phosphatase

Arsenic, which is ubiquitous in the environment and comes from both geochemical and anthropogenic sources, has become a worldwide public health problem. Every organism studied has intrinsic or acquired mechanisms for arsenic detoxification. In Saccharomyces cerevisiae arsenate is detoxified by Acr2p, an arsenate reductase. Acr2p is not a phosphatase but is a homologue of CDC25 phosphatases. It has the HCX5R phosphatase motif but not the glycine-rich phosphate binding motif (GXGXXG) that is found in protein-tyrosine phosphatases. Here we show that creation of a phosphate binding motif through the introduction of glycines at positions 79, 81, and 84 in Acr2p resulted in a gain of phosphotyrosine phosphatase activity and a loss of arsenate reductase activity. Arsenate likely achieved geochemical abundance only after the atmosphere became oxidizing, creating pressure for the evolution of an arsenate reductase from a protein-tyrosine phosphatase. The ease by which an arsenate reductase can be converted into a protein-tyrosine phosphatase supports this hypothesis.

Dendritic cell-based immunotherapy combined with antimony-based chemotherapy cures established murine visceral leishmaniasis

Dendritic cells (DCs) have been proposed to play a critical role as adjuvants in vaccination and immunotherapy. In this study we evaluated the combined effect of soluble Leishmania donovani Ag (SLDA)-pulsed syngeneic bone marrow-derived DC-based immunotherapy and antimony-based chemotherapy for the treatment of established murine visceral leishmaniasis. Three weekly injections of SLDA-pulsed DCs into L. donovani-infected mice reduced liver and splenic parasite burden significantly, but could not clear parasite load from these organs completely. Strikingly, the conventional antileishmanial chemotherapy (sodium antimony gluconate) along with injections of SLDA-pulsed DCs resulted in complete clearance of parasites from both these organs. Repetitive in vitro stimulation of splenocytes from uninfected or L. donovani-infected mice with SLDA-pulsed DCs led to the emergence of CD4(+) T cells with characteristics of Th1 cells. Our data indicate that DC-based immunotherapy enhances the in vivo antileishmanial potential of antimony or vice versa.

Molecular cloning, biochemical and structural analysis of elongation factor-1 alpha from Leishmania donovani: comparison with the mammalian homologue

The Src-homology 2 domain containing protein tyrosine phosphatase-1 (SHP-1) is involved in the pathogenesis of infection with Leishmania. Recently, we identified elongation factor-1 alpha (EF-1 alpha) from Leishmania donovani as a SHP-1 binding and activating protein [J. Biol. Chem. 277 (2002) 50190]. To characterize this apparent Leishmania virulence factor further, the cDNA encoding L. donovani EF-1 alpha was cloned and sequenced. Whereas nearly complete sequence conservation was observed amongst EF-1 alpha proteins from trypanosomatids, the deduced amino acid sequence of EF-1 alpha of L. donovani when compared to mammalian EF-1 alpha sequences showed a number of significant changes. Protein structure modeling-based upon the known crystal structure of EF-1 alpha for Saccharomyces cerevisiae-identified a hairpin loop present in mammalian EF-1 alpha and absent from the Leishmania protein which corresponded to a 12 amino acid deletion. Consistent with these structural differences, the sub-cellular distributions of L. donovani EF-1 alpha and host EF-1 alpha were strikingly different. Interestingly, infection of macrophages with L. donovani caused redistribution of host as well as pathogen EF-1 alpha. Since EF-1 alpha is essential for survival, the distinct biochemical and structural properties of Leishmania EF-1 alpha may provide a novel target for drug development.

Leishmania EF-1alpha activates the Src homology 2 domain containing tyrosine phosphatase SHP-1 leading to macrophage deactivation

The human leishmaniasis are persistent infections of macrophages caused by protozoa of the genus Leishmania. The chronic nature of these infections is in part related to induction of macrophage deactivation, linked to activation of the Src homology 2 domain containing tyrosine phosphatase-1 (SHP-1) in infected cells. To investigate the mechanism of SHP-1 activation, lysates of Leishmania donovani promastigotes were subjected to SHP-1 affinity chromatography and proteins bound to the matrix were sequenced by mass spectrometry. This resulted in the identification of Leishmania elongation factor-1alpha (EF-1alpha) as a SHP-1-binding protein. Purified Leishmania EF-1alpha, but not host cell EF-1alpha, bound directly to SHP-1 in vitro leading to its activation. Three independent lines of evidence indicated that Leishmania EF-1alpha may be exported from the phagosome thereby enabling targeting of host SHP-1. First, cytosolic fractions prepared from macrophages infected with [(35)S]methionine-labeled organisms contained Leishmania EF-1alpha. Second, confocal, fluorescence microscopy using Leishmania-specific antisera detected Leishmania EF-1alpha in the cytosol of infected cells. Third, co-immunoprecipitation showed that Leishmania EF-1alpha was associated with SHP-1 in vivo in infected cells. Finally, introduction of purified Leishmania EF-1alpha, but not the corresponding host protein into macrophages activated SHP-1 and blocked the induction of inducible nitric-oxide synthase expression in response to interferon-gamma. Thus, Leishmania EF-1alpha is identified as a novel SHP-1-binding and activating protein that recapitulates the deactivated phenotype of infected macrophages.

Role of the protein tyrosine phosphatase SHP-1 (Src homology phosphatase-1) in the regulation of interleukin-3-induced survival, proliferation and signalling

The tyrosine phosphatase SHP-1 (Src homology phosphatase-1) has been widely implicated as a negative regulator of signalling in immune cells. We have investigated in detail the role of SHP-1 in interleukin-3 (IL-3) signal transduction by inducibly expressing wild-type (WT), C453S (substrate-trapping) and R459M (catalytically inactive) forms of SHP-1 in the IL-3-dependent cell line BaF/3. Expression of WT SHP-1 had little impact on IL-3-induced proliferation, but enhanced apoptosis following IL-3 withdrawal. Expression of R459M SHP-1 increased the proliferative response of BaF/3 cells to IL-3 and increased cell survival at low doses of IL-3 and following IL-3 withdrawal. Investigation into the biochemical consequences resulting from expression of these SHP-1 variants demonstrated that the beta chain of the IL-3 receptor (Aic2A) was hypo-phosphorylated in cells expressing WT SHP-1 and hyper-phosphorylated in those expressing R459M SHP-1. Further, ectopic expression of the trapping mutant, C453S SHP-1, protected Aic2A from dephosphorylation, suggesting that Aic2A is a SHP-1 substrate in BaF/3 cells. Examination of overall levels of tyrosine phosphorylation demonstrated that they were not perturbed in these transfectants. Activation-specific phosphorylation of STAT (signal transducer and activator of transcription) 5a/b, protein kinase B and ERK (extracellular-signal-regulated kinase)-1 and -2 was also unaffected by expression of WT or R459M SHP-1. However, overall levels of IL-3-induced tyrosine phosphorylation of STAT5 were reduced upon expression of WT SHP-1 and increased when R459M SHP-1 was expressed, consistent with STAT5 being a potential SHP-1 substrate. These results demonstrate that SHP-1 acts to negatively regulate IL-3-driven survival and proliferation, potentially via regulation of tyrosine phosphorylation of Aic2A and STAT5.