Potent Reversible Inhibitors of the Protein Tyrosine Phosphatase CD45

Regioselective synthesis of 4-arylamino-1,2-naphthoquinones in eutectogel as a confined reaction medium using LED light

Predicting selectivity and conversion in a confined reaction medium under photochemical conditions is highly challenging as compared to the corresponding conventional synthesis. Herein, we report the use of a simple carbohydrate-derived eutectogel to facilitate LED-light-induced regioselective synthesis of 4-arylamino-1,2-naphthoquinones in good yield. This methodology, by including a reusable reaction medium, proved to have the potential of affording the regioselective formation of various desired products in good yields.

Distinct early role of PTEN regulation during HCMV infection of monocytes

Human cytomegalovirus (HCMV) infection of monocytes is essential for viral dissemination and persistence. We previously identified that HCMV entry/internalization and subsequent productive infection of this clinically relevant cell type is distinct when compared to other infected cells. We showed that internalization and productive infection required activation of epidermal growth factor receptor (EGFR) and integrin/c-Src, via binding of viral glycoprotein B to EGFR, and the pentamer complex to β1/β3 integrins. To understand how virus attachment drives entry, we compared infection of monocytes with viruses containing the pentamer vs. those without the pentamer and then used a phosphoproteomic screen to identify potential phosphorylated proteins that influence HCMV entry and trafficking. The screen revealed that the most prominent pentamer-biased phosphorylated protein was the lipid- and protein-phosphatase phosphatase and tensin homolog (PTEN). PTEN knockdown with siRNA or PTEN inhibition with a PTEN inhibitor decreased pentamer-mediated HCMV entry, without affecting trimer-mediated entry. Inhibition of PTEN activity affected lipid metabolism and interfered with the onset of the endocytic processes required for HCMV entry. PTEN inactivation was sufficient to rescue pentamer-null HCMV from lysosomal degradation. We next examined dephosphorylation of a PTEN substrate Rab7, a regulator of endosomal maturation. Inhibition of PTEN activity prevented dephosphorylation of Rab7. Phosphorylated Rab7, in turn, blocked early endosome to late endosome maturation and promoted nuclear localization of the virus and productive infection.

Bioinformatics-led discovery of liver-specific genes and macrophage infiltration in acute liver injury

Background

Acute liver injury (ALI) is an important global health concern, primarily caused by widespread hepatocyte cell death, coupled with a complex immune response and a lack of effective remedies. This study explores the underlying mechanisms, immune infiltration patterns, and potential targets for intervention and treatment ALI.

Methods

The datasets of acetaminophen (APAP), carbon tetrachloride (CCl4), and lipopolysaccharide (LPS)-induced ALI were obtained from the GEO database. Differentially expressed genes (DEGs) were individually identified using the limma packages. Functional enrichment analysis was performed using KEGG, GO, and GSEA methods. The overlapping genes were extracted from the three datasets, and hub genes were identified using MCODE and CytoHubba algorithms. Additionally, PPI networks were constructed based on the String database. Immune cell infiltration analysis was conducted using ImmuCellAI, and the correlation between hub genes and immune cells was determined using the Spearman method. The relationship between hub genes, immune cells, and biochemical indicators of liver function (ALT, AST) was validated using APAP and triptolide (TP) -induced ALI mouse models.

Results

Functional enrichment analysis indicated that all three ALI models were enriched in pathways linked to fatty acid metabolism, drug metabolism, inflammatory response, and immune regulation. Immune analysis revealed a significant rise in macrophage infiltration. A total of 79 overlapping genes were obtained, and 10 hub genes were identified that were consistent with the results of the biological information analysis after screening and validation. Among them, Clec4n, Ms4a6d, and Lilrb4 exhibited strong associations with macrophage infiltration and ALI.

Comparative study of the ditrophic interaction between Beauveria bassiana and Plutella xylostella

In the present investigation, hyperparasitic interaction between B. bassiana, TM (MH590235) and P. xylostella was studied through scanning electron microscopy and chromatographic techniques. Dose-mortality responses showed an increase in mortality of larva with an increase in spore concentration. The LC₅₀ value for B. bassiana isolate TM (MH590235) was 2.4 × 10⁷ spores mL^-1. The ditrophic interaction between B. bassiana and P. xylostella after 24 h revealed the adherence of conidia on stemmata, sensory setae, maxillary palpi and legs. After 48 h post-infection (hpi), germination of the conidia and appressorium formation was observed. Formation of hyphae and initiation of fungal networking was observed at 72 hpi. Complete ramification by mycelia and conidiogenesis of B. bassiana was observed over the mycosed cadaver after 168 hpi. Subsequently, typical sympodial conidiophores of B. bassiana bearing secondary spores were also observed. The metabolome profile of healthy larvae of P. xylostella revealed the presence of non-volatile organic compounds (NVOCs) like docosene, nonadecene, palmitic acid and heneicosane. However, the NVOC profile was different in the P. xylostella larvae hyperparasitized by B. bassiana. The metabolites present in the infected cadaver were phthalate esters, hydroxyquebrachamine and lactones.

Targeted chemotherapy overcomes drug resistance in melanoma

In this study, Yue et al. describe a therapeutic strategy termed “targeted chemotherapy” that involves depleting PP2A or inhibiting it using a small molecule inhibitor, phendione, in drug-resistant melanoma. The authors show phendione induces DNA damage response without causing DNA breaks or inducing cellular dormancy, therefore blocking tumor growth of BRAF mutant and NRAS mutant melanomas.

The emergence of drug resistance is a major obstacle for the success of targeted therapy in melanoma. Additionally, conventional chemotherapy has not been effective as drug-resistant cells escape lethal DNA damage effects by inducing growth arrest commonly referred to as cellular dormancy. We present a therapeutic strategy termed “targeted chemotherapy” by depleting protein phosphatase 2A (PP2A) or its inhibition using a small molecule inhibitor (1,10-phenanthroline-5,6-dione [phendione]) in drug-resistant melanoma. Targeted chemotherapy induces the DNA damage response without causing DNA breaks or allowing cellular dormancy. Phendione treatment reduces tumor growth of BRAF^V600E-driven melanoma patient-derived xenografts (PDX) and diminishes growth of NRAS^Q61R-driven melanoma, a cancer with no effective therapy. Remarkably, phendione treatment inhibits the acquisition of resistance to BRAF inhibition in BRAF^V600E PDX highlighting its effectiveness in combating the advent of drug resistance.

Opportunities and challenges for the development of covalent chemical immunomodulators

Compounds that react irreversibly with cysteines have reemerged as potent and selective tools for altering protein function, serving as chemical probes and even clinically approved drugs. The exquisite sensitivity of human immune cell signaling pathways to oxidative stress indicates the likely, yet still underexploited, general utility of covalent probes for selective chemical immunomodulation. Here, we provide an overview of immunomodulatory cysteines, including identification of electrophilic compounds available to label these residues. We focus our discussion on three protein classes essential for cell signaling, which span the 'druggability' spectrum from amenable to chemical probes (kinases), somewhat druggable (proteases), to inaccessible (phosphatases). Using existing inhibitors as a guide, we identify general strategies to guide the development of covalent probes for selected undruggable classes of proteins and propose the application of such compounds to alter immune cell functions.

Napabucasin and Related Heterocycle-Fused Naphthoquinones as STAT3 Inhibitors with Antiproliferative Activity against Cancer Cells

Napabucasin (6) and its angularly anellated isomer (7), for which the synthesis is described, together with related plant-derived naphthoquinones, were evaluated in vitro against human breast cancer (MDA-MB-231) and chronic myelogenous leukemia (K562) cells. As observed for β-lapachone (3), the active naphthoquinones all induced apoptosis in a cell-cycle-independent fashion. In contrast to the pyran-fused β-lapachone (3), however, the most potent furan-fused naphthoquinones were able to redox cycle and generate superoxide in cell-based assays, which was independent of NAD(P)H:quinone oxido-reductase 1. In a homogeneous time-resolved fluorescence (HTRF) assays with MDA-MB-231 cells, both napabucasin (6) and isonapabucasin (7) were identified as targeting STAT3 phosphorylation. In addition, drug affinity responsive target stability assays were performed to validate a direct interaction of the naphthoquinones with STAT3. Isonapabucasin (7) turned out to be twice as potent against STAT3 as napabucasin (6) in the HTRF assay, with an EC₅₀ in the submicromolar range, which was in excellent agreement with the potency of both agents to inhibit the growth of MDA-MB-231 cells. Moreover, molecular docking experiments predicted different binding modes to the STAT3 SH2 domain for the linearly anellated napabucasin (6) and its angularly anellated isomer (7).

Inhibition of protein tyrosine phosphatase non-receptor type 2 by PTP inhibitor XIX: Its role as a multiphosphatase inhibitor

Protein tyrosine phosphatases (PTPs) play crucial roles in signal transduction and their functional alteration has been detected in many diseases. PTP inhibitors have been developed as therapeutic drugs for diseases that are related to the activity of PTPs. In this study, PTP inhibitor XIX, an inhibitor of CD45 and PTEN, was investigated whether it inhibits other PTPs. Protein tyrosine phosphatase non-receptor type 2 (PTPN2) was selectively inhibited by the inhibitor in a competitive manner. Drug affinity responsive target stability (DARTS) analysis showed that the inhibitor induces conformational changes in PTPN2. Phosphorylation levels of signal transducer and activator of transcription 3 (STAT3) at Tyr-705, a crucial site for STAT3 activation and target site of PTPN2, decreased upon exposure to the inhibitor. Our results suggest that PTP inhibitor XIX might be considered as an effective regulator of PTPN2 for treating diseases related to PTPN2.

CD45 in human physiology and clinical medicine

CD45 is an evolutionary highly conserved receptor protein tyrosine phosphatase exclusively expressed on all nucleated cells of the hematopoietic system. It is characterized by the expression of several isoforms, specific to a certain cell type and the developmental or activation status of the cell. CD45 is one of the key players in the initiation of T cell receptor signaling by controlling the activation of the Src family protein-tyrosine kinases Lck and Fyn. CD45 deficiency results in T- and B-lymphocyte dysfunction in the form of severe combined immune deficiency. It also plays a significant role in autoimmune diseases and cancer as well as in infectious diseases including fungal infections. The knowledge collected on CD45 biology is rather vast, but it remains unclear whether all findings in rodent immune cells also apply to human CD45. This review focuses on human CD45 expression and function and provides an overview on its ligands and role in human pathology.

Copper(0)/Selectfluor System-Promoted Oxidative Carbon-Carbon Bond Cleavage/Annulation of o-Aryl Chalcones: An Unexpected Synthesis of 9,10-Phenanthraquinone Derivatives

A general and efficient protocol for the synthesis of 9,10-phenanthraquinone derivatives has been successfully developed involving a copper(0)/Selectfluor system-promoted oxidative carbon-carbon bond cleavage/annulation of o-aryl chalcones. A variety of substituted 9,10-phenanthraquinones were synthesized in moderate to good yields under mild reaction conditions.

Mannose receptor induces T-cell tolerance via inhibition of CD45 and up-regulation of CTLA-4

The mannose receptor (MR) is an endocytic receptor involved in serum homeostasis and antigen presentation. Here, we identify the MR as a direct regulator of CD8(+) T-cell activity. We demonstrate that MR expression on dendritic cells (DCs) impaired T-cell cytotoxicity in vitro and in vivo. This regulatory effect of the MR was mediated by a direct interaction with CD45 on the T cell, inhibiting its phosphatase activity, which resulted in up-regulation of cytotoxic T-lymphocyte-associated Protein 4 (CTLA-4) and the induction of T-cell tolerance. Inhibition of CD45 prevented expression of B-cell lymphoma 6 (Bcl-6), a transcriptional inhibitor that directly bound the CTLA-4 promoter and regulated its activity. These data demonstrate that endocytic receptors expressed on DCs contribute to the regulation of T-cell functionality.

Phosphatase Inhibitors Function as Novel, Broad Spectrum Botulinum Neurotoxin Antagonists in Mouse and Human Embryonic Stem Cell-Derived Motor Neuron-Based Assays

There is an urgent need to develop novel treatments to counter Botulinum neurotoxin (BoNT) poisoning. Currently, the majority of BoNT drug development efforts focus on directly inhibiting the proteolytic components of BoNT, i.e. light chains (LC). Although this is a rational approach, previous research has shown that LCs are extremely difficult drug targets and that inhibiting multi-serotype BoNTs with a single LC inhibitor may not be feasible. An alternative approach would target neuronal pathways involved in intoxication/recovery, rather than the LC itself. Phosphorylation-related mechanisms have been implicated in the intoxication pathway(s) of BoNTs. However, the effects of phosphatase inhibitors upon BoNT activity in the physiological target of BoNTs, i.e. motor neurons, have not been investigated. In this study, a small library of phosphatase inhibitors was screened for BoNT antagonism in the context of mouse embryonic stem cell-derived motor neurons (ES-MNs). Four inhibitors were found to function as BoNT/A antagonists. Subsequently, we confirmed that these inhibitors protect against BoNT/A in a dose-dependent manner in human ES-MNs. Additionally, these compounds provide protection when administered in post-intoxication scenario. Importantly, the inhibitors were also effective against BoNT serotypes B and E. To the best of our knowledge, this is the first study showing phosphatase inhibitors as broad-spectrum BoNT antagonists.

Studies of C-terminal naphthoquinone dipeptides as 20S proteasome inhibitors

The ubiquitin proteasome pathway is crucial in regulating many processes in the cell. Modulation of proteasome activities has emerged as a powerful strategy for potential therapies against much important pathologies. In particular, specific inhibitors may represent a useful tool for the treatment of tumors. Here, we report studies of a new series of peptide-based analogues bearing a naphthoquinone pharmacophoric unit at the C-terminal position. Some derivatives showed inhibition in the µM range of the post-acidic-like and chymotrypsin-like active sites of the proteasome.

Discovery of benzo[f]indole-4,9-dione derivatives as new types of anti-inflammatory agents

Certain benzo[f]indole-4,9-dione derivatives were synthesized and evaluated for their inhibitory effects on superoxide anion generation and neutrophil elastase (NE) release in formyl-l-methionyl-l-leucyl-l-phenylalanine (fMLF)-activated human neutrophils. Results indicated that (Z)-1-benzyl-4-(hydroxyimino)-1H-benzo[f]indol-9(4H)-one (10) showed a potent dual inhibitory effect on NE release and superoxide anion generation with IC50 value of 2.78 and 2.74 μM respectively. The action mechanisms of 10 in human neutrophils were further investigated. Our results showed that compound 10 did not alter fMLF-induced phosphorylation of Src (Src family Y416). Notably, phosphorylation of Akt (S473) and mobilization of [Ca2+]i caused by fMLF was inhibited by compound 10. Further structural optimization of 10 is ongoing.

Allosteric noncompetitive small molecule selective inhibitors of CD45 tyrosine phosphatase suppress T-cell receptor signals and inflammation in vivo

CD45 is a receptor-like member of the protein tyrosine phosphatase (PTP) family. We screened in silico for small molecules binding at a predicted allosteric pocket unique to the CD45 intracellular domain, and validated inhibitors by in vitro phosphatase assays. Compound 211 exhibited a CD45 IC50 value of 200 nM and had >100-fold selectivity over six related PTPs. The relevance of the allosteric pocket was verified through site-directed mutagenesis. Compound 211 has a noncompetitive mechanism of action, and it is extremely effective at preventing dephosphorylation of substrate Lck phosphotyrosine (pY)-505 versus preventing dephosphorylation of Lck pY-393. In cultured primary T cells, compound 211 prevents T-cell receptor-mediated activation of Lck, Zap-70, and mitogen-activated protein kinase, and interleukin-2 production. In a delayed-type hypersensitivity reaction in vivo, compound 211 abolished inflammation. This work demonstrates a novel approach to develop effective allosteric inhibitors that can be expanded to target the corresponding allosteric domains of other receptor PTPs.

Astragaloside II triggers T cell activation through regulation of CD45 protein tyrosine phosphatase activity

AIM

To investigate the immunomodulating activity of astragalosides, the active compounds from a traditional tonic herb Astragalus membranaceus Bge, and to explore the molecular mechanisms underlying the actions, focusing on CD45 protein tyrosine phosphatase (CD45 PTPase), which plays a critical role in T lymphocyte activation.

METHODS

Primary splenocytes and T cells were prepared from mice. CD45 PTPase activity was assessed using a colorimetric assay. Cell proliferation was measured using a [(3)H]-thymidine incorporation assay. Cytokine proteins and mRNAs were examined with ELISA and RT-PCR, respectively. Activation markers, including CD25 and CD69, were analyzed using flow cytometry. Activation of LCK (Tyr505) was detected using Western blot analysis. Mice were injected with the immunosuppressant cyclophosphamide (CTX, 80 mg/kg), and administered astragaloside II (50 mg/kg).

RESULTS

Astragaloside I, II, III, and IV concentration-dependently increased the CD45-mediated of pNPP/OMFP hydrolysis with the EC50 values ranged from 3.33 to 10.42 μg/mL. Astragaloside II (10 and 30 nmol/L) significantly enhanced the proliferation of primary splenocytes induced by ConA, alloantigen or anti-CD3. Astragaloside II (30 nmol/L) significantly increased IL-2 and IFN-γ secretion, upregulated the mRNA levels of IFN-γ and T-bet in primary splenocytes, and promoted CD25 and CD69 expression on primary CD4(+) T cells upon TCR stimulation. Furthermore, astragaloside II (100 nmol/L) promoted CD45-mediated dephosphorylation of LCK (Tyr505) in primary T cells, which could be blocked by a specific CD45 PTPase inhibitor. In CTX-induced immunosuppressed mice, oral administration of astragaloside II restored the proliferation of splenic T cells and the production of IFN-γ and IL-2. However, astragaloside II had no apparent effects on B cell proliferation.

CONCLUSION

Astragaloside II enhances T cell activation by regulating the activity of CD45 PTPase, which may explain why Astragalus membranaceus Bge is used as a tonic herb in treating immunosuppressive diseases.

Identification of small molecule inhibitors of PTPσ through an integrative virtual and biochemical approach

PTPσ is a dual-domain receptor type protein tyrosine phosphatase (PTP) with physiologically important functions which render this enzyme an attractive biological target. Specifically, loss of PTPσ has been shown to elicit a number of cellular phenotypes including enhanced nerve regeneration following spinal cord injury (SCI), chemoresistance in cultured cancer cells, and hyperactive autophagy, a process critical to cell survival and the clearance of pathological aggregates in neurodegenerative diseases. Owing to these functions, modulation of PTPσ may provide therapeutic value in a variety of contexts. Furthermore, a small molecule inhibitor would provide utility in discerning the cellular functions and substrates of PTPσ. To develop such molecules, we combined in silico modeling with in vitro phosphatase assays to identify compounds which effectively inhibit the enzymatic activity of PTPσ. Importantly, we observed that PTPσ inhibition was frequently mediated by oxidative species generated by compounds in solution, and we further optimized screening conditions to eliminate this effect. We identified a compound that inhibits PTPσ with an IC₅₀ of 10 µM in a manner that is primarily oxidation-independent. This compound favorably binds the D1 active site of PTPσ in silico, suggesting it functions as a competitive inhibitor. This compound will serve as a scaffold structure for future studies designed to build selectivity for PTPσ over related PTPs.

Small molecule tools for functional interrogation of protein tyrosine phosphatases

The importance of protein tyrosine phosphatases (PTPs) in the regulation of cellular signalling is well established. Malfunction of PTP activity is also known to be associated with cancer, metabolic syndromes and autoimmune disorders, as well as neurodegenerative and infectious diseases. However, a detailed understanding of the roles played by the PTPs in normal physiology and in pathogenic conditions has been hampered by the absence of PTP-specific small molecule agents. In addition, the therapeutic benefits of modulating this target class are underexplored as a result of a lack of suitable chemical probes. Potent and specific PTP inhibitors could significantly facilitate functional analysis of the PTPs in complex cellular signal transduction pathways and may constitute valuable therapeutics in the treatment of several human diseases. We highlight the current challenges to and opportunities for developing PTP-specific small molecule agents. We also review available selective small molecule inhibitors developed for a number of PTPs, including PTP1B, TC-PTP, SHP2, lymphoid-specific tyrosine phosphatase, haematopoietic protein tyrosine phosphatase, CD45, PTPβ, PTPγ, PTPRO, Vaccinia H1-related phosphatase, mitogen-activated protein kinase phosphatase-1, mitogen-activated protein kinase phosphatase-3, Cdc25, YopH, mPTPA and mPTPB.

CD45 regulates homing and engraftment of immature normal and leukemic human cells in transplanted immunodeficient mice

Bone marrow homing and engraftment by clinically transplanted hematopoietic stem and progenitor cells is a complex process that is not fully understood. We report that the pan-leukocyte CD45 phosphatase plays an essential role in trafficking and repopulation of the bone marrow by immature human CD34(+) cells and leukemic cells in transplanted nonobese diabetic severe combined immunodeficient mice. Inhibiting CD45 function by blocking antibodies or a CD45 inhibitor impaired the motility of both normal and leukemic human cells. Blocking CD45 inhibited homing and repopulation by immature human CD34(+) cells as well as homing of primary patient leukemic cells. In addition, CD45 inhibition negatively affected development of hematopoietic progenitors in vitro and their recovery in transplanted recipients in vivo, revealing the central role of CD45 in the regulation of hematopoiesis. Moreover, CD45 blockage induced a hyperadhesive phenotype in immature human progenitor cells as well as in murine leukocytes, leading to their defective adhesion interactions with endothelial cells. This phenotype was further manifested by the ability of CD45 blockage to prevent breakdown of adhesion interactions in the BM, which inhibited murine progenitor mobilization. The substantial effects of a direct CD45 inhibition point at its essential roles in cell trafficking, including murine progenitor cell mobilization and both normal immature and leukemic human hematopoietic cells as well as regulation of hematopoiesis and engraftment potential.

Discovery of a novel series of inhibitors of lymphoid tyrosine phosphatase with activity in human T cells

The lymphoid tyrosine phosphatase LYP, encoded by the PTPN22 gene, is a critical regulator of signaling in T cells and recently emerged as a candidate target for therapy of autoimmune diseases. Here, by library screening, we identified a series of noncompetitive inhibitors of LYP that showed activity in primary T cells. Kinetic analysis confirmed that binding of the compounds to the phosphatase is nonmutually exclusive with respect to a known bidentate competitive inhibitor. The mechanism of action of the lead inhibitor compound 4e was studied by a combination of hydrogen/deuterium-exchange mass spectrometry and molecular modeling. The results suggest that the inhibitor interacts critically with a hydrophobic patch located outside the active site of the phosphatase. Targeting of secondary allosteric sites is viewed as a promising yet unexplored approach to develop pharmacological inhibitors of protein tyrosine phosphatases. Our novel scaffold could be a starting point to attempt development of "nonactive site" anti-LYP pharmacological agents.

Galectin-8 tandem-repeat structure is essential for T-cell proliferation but not for co-stimulation

Gal (galectin)-8 is a tandem-repeat Gal containing N-CRDs (Nterminal carbohydrate-recognition domains) and C-CRDs (C-terminal carbohydrate-recognition domains) with differential glycan-binding specificity fused by a linker peptide. Gal-8 has two distinct effects on CD4 T-cells: at high concentrations it induces antigen-independent proliferation, whereas at low concentrations it co-stimulates antigen-specific responses. Associated Gal-8 structural requirements were dissected in the present study. Recombinant homodimers N–N (two N-terminal CRD chimaera) and C–C (two C-terminal CRD chimaera), but not single C-CRDs or N-CRDs, induced proliferation; however, single domains induced co-stimulation. These results indicate that the tandem-repeat structure was essential only for the proliferative effect, suggesting the involvement of lattice formation, whereas co-stimulation could be mediated by agonistic interactions. In both cases, C–C chimaeras displayed higher activity than Gal-8, indicating that the C-CRD was mainly involved, as was further supported by the strong inhibition of proliferation and co-stimulation in the presence of blood group B antigen, specifically recognized by this domain. Classic Gal inhibitors (lactose and thiodigalactoside) prevented proliferation but not co-stimulatory activity, which was inhibited by 3-O-β-D-galactopyranosyl-D-arabinose. Interestingly, Gal-8 induced proliferation of naïve human CD4 T-cells, varying from non- to high-responder individuals, whereas it promoted cell death of phytohaemagglutinin or CD3/CD28 pre-activated cells. The findings of the present study delineate the differential molecular requirements for Gal-8 activities on T-cells, and suggest a dual activity relying on activation state.

Synthesis and biological evaluation of naphthoquinone analogs as a novel class of proteasome inhibitors

Screening of the NCI Diversity Set-1 identified PI-083 (NSC-45382) a proteasome inhibitor selective for cancer over normal cells. Focused libraries of novel compounds based on PI-083 chloronaphthoquinone and sulfonamide moieties were synthesized to gain a better understanding of the structure-activity relationship responsible for chymotrypsin-like proteasome inhibitory activity. This led to the demonstration that the chloronaphthoquinone and the sulfonamide moieties are critical for inhibitory activity. The pyridyl group in PI-083 can be replaced with other heterocyclic groups without significant loss of activity. Molecular modeling studies were also performed to explore the detailed interactions of PI-083 and its derivatives with the beta5 and beta6 subunits of the 20S proteasome. The refined model showed an H-bond interaction between the Asp-114 and the sulfonamide moiety of the PI-083 in the beta6 subunit.

Solvent-free production of singlet oxygen at the gas-solid interface: visible light activated organic-inorganic hybrid microreactors including new cyanoaromatic photosensitizers

We synthesized new cyanoaromatics, benzo[b]triphenylene-9,14-dicarbonitrile (DBTP) 1a and a graftable derivative, 9,14-dicyanobenzo[b]triphenylene-3-carboxylic acid (DBTP-COOH) 1b, easily prepared from commercial reagents. Their photosensitizing properties were investigated. Hybrid porous silica monoliths loaded with encapsulated 1a or grafted 1b were prepared, and their adsorption, spectroscopic and photosensitizing properties, as well as stability, were compared. Solvent-free, efficient oxidation of dimethylsulfide (DMS) was observed at the gas-solid interface under visible light irradiation. Quantum yields of formation of 1O2 inside the porous monoliths are comparable to those of phenalenone. Singlet oxygen lifetimes (approximately 25 micros) were found to be longer in silica monoliths than in usual polar solvents such as methanol or ethanol. This new class of hybrid materials work as porous, transparent, and highly efficient microreactors for oxidation reactions under visible light.

Activation of maxi-anion channel by protein tyrosine dephosphorylation

The maxi-anion channel with a large single-channel conductance of >300 pS, and unknown molecular identity, is functionally expressed in a large variety of cell types. The channel is activated by a number of experimental maneuvers such as exposing cells to hypotonic or ischemic stress. The most effective and consistent method of activating it is patch membrane excision. However, the activation mechanism of the maxi-anion channel remains poorly understood at present. In the present study, involvement of phosphorylation/dephosphorylation in excision-induced activation was examined. In mouse mammary fibroblastic C127 cells, activity of the channel was suppressed by intracellular application of Mg-ATP, but not Mg-5'-adenylylimidodiphosphate (AMP-PNP), in a concentration-dependent manner. When a cocktail of broad-spectrum tyrosine phosphatase inhibitors was applied, channel activation was completely abolished, whereas inhibitors of serine/threonine protein phosphatases had no effect. On the other hand, protein tyrosine kinase inhibitors brought the channel out of an inactivated state. In mouse adult skin fibroblasts (MAFs) in primary culture, similar maxi-anion channels were found to be activated on membrane excision, in a manner sensitive to tyrosine phosphatase inhibitors. In MAFs isolated from animals deficient in receptor protein tyrosine phosphatase (RPTP)zeta, activation of the maxi-anion channel was significantly slower and less prominent compared with that observed in wild-type MAFs; however, channel activation was restored by transfection of the RPTPzeta gene. Thus it is concluded that activation of the maxi-anion channel involves protein dephosphorylation mediated by protein tyrosine phosphatases that include RPTPzeta in mouse fibroblasts, but not in C127 cells.

Galectin-8 provides costimulatory and proliferative signals to T lymphocytes

Galectin (Gal) constitute a family of carbohydrate-recognizing molecules ubiquitously expressed in mammals. In the immune system, they regulate many processes such as inflammation, adhesion, and apoptosis. Here, we report the expression in the spleen of the two same Gal-8 splice variants described previously in the thymus. Gal-8 was found to induce two separate biological activities on T lymphocytes: a robust naive CD4(+) T cell proliferation in the absence of antigen and notably, a costimulatory signal that synergized the cognate OVA peptide in DO11.10 mice transgenic for TCR(OVA). The antigen-independent proliferation induced by Gal-8 displayed increased expression of pro- and anti-inflammatory cytokines, thus suggesting the polyclonal expansion of Th1 and Th2 clones. The costimulatory effect on antigen-specific T cell activation was evidenced when the Gal and the peptide were assayed at doses suboptimal to induce T cell proliferation. By mass spectra analysis, several integrins and leukocyte surface markers, including CD45 isoforms, as well as other molecules specific to macrophages, neutrophils, and platelets, were identified as putative Gal-8 counter-receptors. Gal-8 triggered pZAP70 and pERK1/2. Moreover, pretreatment with specific inhibitors of CD45 phosphatase or ERK1/2 prevented its antigen-dependent and -independent T cell-proliferative activities. This seems to be associated with the agonistic binding to CD45, which lowers the activation threshold of the TCR signaling pathway. Taken together, our findings support a distinctive role for locally produced Gal-8 as an enhancer of otherwise borderline immune responses and also suggest that Gal-8 might fuel the reactivity at inflammatory foci.

Reduced expression of CD45 protein-tyrosine phosphatase provides protection against anthrax pathogenesis

The modulation of cellular processes by small molecule inhibitors, gene inactivation, or targeted knockdown strategies combined with phenotypic screens are powerful approaches to delineate complex cellular pathways and to identify key players involved in disease pathogenesis. Using chemical genetic screening, we tested a library of known phosphatase inhibitors and identified several compounds that protected Bacillus anthracis infected macrophages from cell death. The most potent compound was assayed against a panel of sixteen different phosphatases of which CD45 was found to be most sensitive to inhibition. Testing of a known CD45 inhibitor and antisense phosphorodiamidate morpholino oligomers targeting CD45 also protected B. anthracis-infected macrophages from cell death. However, reduced CD45 expression did not protect anthrax lethal toxin (LT) treated macrophages, suggesting that the pathogen and independently added LT may signal through distinct pathways. Subsequent, in vivo studies with both gene-targeted knockdown of CD45 and genetically engineered mice expressing reduced levels of CD45 resulted in protection of mice after infection with the virulent Ames B. anthracis. Intermediate levels of CD45 expression were critical for the protection, as mice expressing normal levels of CD45 or disrupted CD45 phosphatase activity or no CD45 all succumbed to this pathogen. Mechanism-based studies suggest that the protection provided by reduced CD45 levels results from regulated immune cell homeostasis that may diminish the impact of apoptosis during the infection. To date, this is the first report demonstrating that reduced levels of host phosphatase CD45 modulate anthrax pathogenesis.

The cytoplasmic tail of CD45 is released from activated phagocytes and can act as an inhibitory messenger for T cells

CD45 is the prototypic transmembrane protein tyrosine phosphatase (PTP), which is expressed on all nucleated hematopoietic cells and plays a central role in the integration of environmental signals into immune cell responses. Here we report an alternative function for the intracellular domain of CD45. We dis-covered that CD45 is sequentially cleaved by serine/metalloproteinases and γ-secretases during activation of human monocytes and granulocytes by fungal stimuli or phorbol 12-myristate 13-acetate but not by other microbial stimuli. Proteolytic processing of CD45 occurred upon activation of monocytes or granulocytes but not of T cells, B cells, or dendritic cells and resulted in a 95-kDa fragment of the cytoplasmic tail of CD45 (ct-CD45). ct-CD45 was released from monocytes and granulocytes upon activation-induced cell death. Binding studies with ct-CD45 revealed a counter-receptor on preactivated T cells. Moreover, T-cell proliferation induced by dendritic cells or CD3 antibodies was inhibited in the presence of ct-CD45. Taken together, the results of our study demonstrate that fragments of the intracellular domain of CD45 from human phagocytes can function as intercellular regulators of T-cell activation.

Lateral compartmentalization of T cell receptor versus CD45 by galectin-N-glycan binding and microfilaments coordinate basal and activation signaling

Lateral compartmentalization of membrane proteins into microdomains regulates signal transduction; however, structural determinants are incompletely understood. Membrane glycoproteins bind galectins in proportion to the number (i.e. NX(S/T) sites) and degree of GlcNAc branching within attached N-glycans, forming a molecular lattice that negatively regulates T cell function and autoimmunity. We find that in resting T cells, partition of CD45 inside and T cell receptor (TCR)/CD4-Lck/Zap-70 outside microdomains is positively and negatively regulated by the galectin lattice and actin cytoskeleton, respectively. In the absence of TCR ligands, the galectin lattice counteracts F-actin to retain CD45 in microdomains while concurrently blocking TCR/CD4-Lck/Zap-70 partition to microdomains by preventing a conformational change in the TCR that recruits Nck/Wiscott Aldrich Syndrome (WASp)/SLP76/F-actin/CD4 to TCR. The counterbalancing activities of the galectin lattice and actin cytoskeleton negatively and positively regulate Lck activity in resting cells and CD45 versus TCR clustering and signaling at the early immune synapse, respectively. Microdomain-localized CD45 inactivates Lck and inhibits TCR signaling at the early immune synapse. Thus, the galectin lattice and actin cytoskeleton interact on opposing sides of the plasma membrane to control microdomain structure and function, coupling basal growth signaling with thresholds to activation.

An Efficient and Scalable Synthesis of Substituted Phenanthrenequinones by Intramolecular Friedel−Crafts Reaction of Imidazolides

An efficient synthesis of 9,10-phenanthrenequinones is described. The two carbonyl groups were introduced by an orthoselective intermolecular Friedel-Crafts reaction of 3-methoxyphenol with ethyl chlorooxoacetate. The formation of a biaryl bond by Suzuki-Miyaura coupling reaction, followed by the hydrolysis of the ester, gave a biaryloxoacetic acid. Treatment of this acid with CDI gave the corresponding imidazolide. The ring closure to the desired phenanthrenequinone was accomplished by intramolecular Friedel-Crafts reaction of the imidazolide promoted by TiCl(4).

Chemical knockdown of protein-tyrosine phosphatase 1B by 1,2-naphthoquinone through covalent modification causes persistent transactivation of epidermal growth factor receptor

1,2-Naphthoquinone (1,2-NQ), an atmospheric contaminant, causes the contraction of guinea pig trachea through the activation of epidermal growth factor receptor (EGFR) by inhibiting protein-tyrosine phosphatases (PTPs). Phosphorylation of EGFR is negatively regulated by PTPs, but details of the mechanism by which 1,2-NQ inhibits PTPs have not been elucidated. Results described in this report demonstrate that 1,2-NQ forms covalent bonds with PTP1B after exposure to human epithelial A431 cells. In this study, a concentration-dependent phosphorylation of EGFR was found to be coupled to the reduction of PTP activity in the cells. The reduction in PTP activity was due to the irreversible modification of PTP1B, and when PTP1B was overexpressed by the cells, the 1,2-NQ-mediated EGFR phosphorylation was suppressed. Studies with purified PTP1B and 1,2-NQ showed that the reduction in enzyme activity was due to a nucleophilic attack by the quinone on the enzyme, to form covalent bonds. Matrix-assisted laser desorption and ionization time-of-flight mass spectrometry analysis and mutation experiments revealed that PTP1B inactivation was primarily due to covalent attachment of the quinone to Cys-121 of the enzyme, with binding to His-25 and Cys-215 as well. Collectively, the results show that covalent attachment of 1,2-NQ to PTP1B is at least partially responsible for the reduction of PTP activity, which leads to prolonged transactivation of EGFR in the cells.

Structure-based discovery of new small molecule inhibitors of low molecular weight protein tyrosine phosphatase

The application of a fully integrated and automated virtual screening method for identifying potential and novel inhibitors of bovine lmwPTP is described. The protocol makes extensive use of our recently introduced LINGO tools, which allow the extraction of the implicit chemical information present in SMILES representations. Nine out of 34 compounds selected from a database of almost 500,000 commercially available compounds were experimentally confirmed to be competitive inhibitors of lmwPTP, two of them showing K(i) values around 10microM. The best inhibitors previously described had K(i) values higher than 1mM. These results constitute an experimental validation of our virtual screening algorithm and provide a basis for the optimization of pharmacologically interesting lmwPTP inhibitors.

Collagen-mediated survival signaling is modulated by CD45 in Jurkat T cells

T cell activation is a critical step in the development of a proper immune response to infection and inflammation. This dynamic process requires efficient T cell receptor signaling, which in turn is modulated by integrin receptor activation and the actin cytoskeleton. CD45 is a key player in T cell receptor mediated signal transduction. However, its exact role in integrin mediated signaling in T cells remains to be elucidated. The present study addresses the relationship between CD45 and beta1-integrin mediated survival signaling in the human T leukemic cell line Jurkat, in which collagen receptors alpha1 beta1 and alpha2 beta1 integrins are localized. Wild type (WT)-Jurkat T cells treated with collagen demonstrated increased cell proliferation and survival. Monitoring the intracellular signaling pathways activated by collagen in WT-Jurkat cells revealed increased focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK) activation. Moreover, examination of the actin cytoskeleton of WT-Jurkat T cells treated with collagen demonstrated the presence of an organized cortical actin structure, reminiscent of the survival phenotype. This is in contrast to CD45-deficient J45.01 T cells, where collagen treatment failed to enhance cell proliferation/survival and was unable to stimulate FAK and ERK activity. In addition, the actin cytoskeleton of collagen treated J45.01 T cells was disorganized with cortical actin aggregates present throughout. The importance of an organized actin cytoskeleton to proper cell signaling and survival was further demonstrated by the inability of collagen treated WT-Jurkat cells to activate the FAK and ERK survival pathway in the presence of cytochalasin D, a cytoskeleton-disrupting drug. Consistently, addition of the CD45 specific inhibitor abolished collagen-stimulated FAK and ERK activation in WT-Jurkat cells, further depicting CD45 as the key mediator. Furthermore, collagen-mediated T cell signaling alone was able to activate IL-2 gene transcription devoid of concomitant T cell receptor activation. Taken together, these results are the first to demonstrate that CD45 is important in promoting cell survival by modulating integrin-mediated FAK/ERK signaling in Jurkat T cells and is involved in a distinct signal transduction pathway, separate from T cell receptor signaling, influencing T cell immune responses. Hence, this study will help further our knowledge about beta1-integrin mediated signaling in T cells, which may prove to be essential for the regulation of various T cell mediated immune responses.

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.

Natural compounds as a source of protein tyrosine phosphatase inhibitors: application to the rational design of small-molecule derivatives

Reversible phosphorylation of tyrosine residues is a key regulatory mechanism for numerous cellular events. Protein tyrosine kinases and protein tyrosine phosphatases (PTPs) have a pivotal role in regulating both normal cell physiology and pathophysiology. Accordingly, deregulated activity of both protein tyrosine kinases and PTPs is involved in the development of numerous congenitically inherited and acquired human diseases, prompting obvious pharmaceutical and academic research interest. The development of compound libraries with higher selective PTP inhibitory activity has been bolstered by the realization that many natural products have such activity and thus are interesting biologically lead compounds, which properties are widely exploited. In addition, more rational approaches have focused on the incorporation of phosphotyrosine mimetics into specific peptide templates (peptidomimetic backbones). Additional factors furthering discovery as well as therapeutic application of new bioactive molecules are the integration of functional genomics, cell biology, structural biology, drug design, molecular screening and chemical diversity. Together, all these factors will lead to new avenues to treat clinical disease based on PTP inhibition.

Targeting the PTPome in human disease

Protein tyrosine phosphatases (PTPs) play vital roles in numerous cellular processes and are implicated in a growing number of human diseases, ranging from cancer to cardiovascular, immunological, infectious, neurological and metabolic diseases. There are at least 107 genes in the human genome, collectively referred to as the human 'PTPome'. Here the authors review the involvement of PTPs in human disease, discuss their potential as drug targets, and current efforts to develop PTP inhibitors for the treatment of human disease. Finally, the authors present their view of the future for PTPs as drug targets.

A naphthoquinone derivative, shikonin, has insulin-like actions by inhibiting both phosphatase and tensin homolog deleted on chromosome 10 and tyrosine phosphatases

The 1,4-naphthoquinone derivative, shikonin, has been shown to increase glucose uptake by adipocytes and myocytes with minor effects on protein tyrosine phosphorylation in the cells (Biochem Biophys Res Commun 292:642-651, 2002). The present study was performed to examine the mechanism of this action of shikonin. Shikonin inhibited the phosphatidylinositol 3,4,5-triphosphate (PtdIns-3,4,5-P3) phosphatase activity of recombinant phosphatase and tensin homolog deleted on chromosome 10 (PTEN) with an IC50 value of 2.7 microM. Shikonin induced marked accumulation of PtdIns-3,4,5-P3 and activation of protein kinase B (PKB) in Chinese hamster ovary cells expressing insulin receptors. In addition to its effect on PTEN, shikonin was found to inhibit several protein phosphatases in cell-free systems. Its effect on tyrosine phosphorylation in intact cells was far weaker than that of pervanadate, a widely used tyrosine phosphatase inhibitor, despite the observation that the effect of shikonin on PKB was more potent than that of pervanadate. These results suggested that the inhibition of PTEN provides a clue to its potent insulin-like actions. We also found that naphthoquinones, including 1,2-naphthoquinone, inhibit PTEN in the cell-free system, which suggested that the effect on PTEN (and thus the effect on phosphatidylinositol 3-kinase signaling) should be taken into account when examining the pharmacological actions of naphthoquinone derivatives.

HIV-1 gp120-mediated apoptosis of T cells is regulated by the membrane tyrosine phosphatase CD45

The molecular mechanism of the human immunodeficiency virus type 1 (HIV-1) gp120-induced apoptosis of bystander T cells is not well defined. Here, we demonstrate that CD45, a key component of the T cell receptor pathway, plays a crucial role in apoptosis induced by HIV-1 gp120. We observed that HIV-1 gp120-induced apoptosis was significantly reduced in a CD45-deficient cell line and that reconstitution of CD45 in these cells restored gp120-induced apoptosis. However, expression of a chimeric protein containing only the intracellular phosphatase domain was not able to restore the apoptotic function in the CD45-negative clone, indicating an important role for the extracellular domain of CD45 in this function. The role of CD45 in gp120-induced apoptosis was further confirmed in T cell lines and peripheral blood mononuclear cells using a selective CD45 inhibitor as well as CD45-specific small interfering RNA. We also observed that gp120 treatment induced CD45 association with the HIV coreceptor CXCR4. Further elucidation of downstream signaling events revealed that CD45 modulates HIV-1 gp120-induced apoptosis by regulating Fas ligand induction and activation of the phosphoinositide 3-kinase/Akt pathway. These results suggest a novel CD45-mediated mechanism for the HIV envelope-induced apoptosis of T cells.