Phosphotyrosine Phosphatase Inhibitor Research Articles

Bombyxin-stimulated ecdysteroidogenesis in relation to sugar transporter/trehalase expressions in Bombyx prothoracic glands

Our previous studies showed that bombyxin stimulated ecdysteroidogenesis in Bombyx mori prothoracic glands (PGs) during a long-term incubation period in a phosphatidylinositol 3-kinase (PI3K)/Akt-dependent manner. In the present study, we further investigated the downstream signaling cascade in bombyxin-stimulated PGs. Our results showed that upon treatment with bombyxin, expression levels of the sugar transport 1 (St1) and St4 genes and trehalase 1 (Treh1) gene, but not ecdysteroid biosynthesis genes were greatly enhanced compared to the controls. Treatment with LY294002 (an inhibitor of PI3K) reduced the enhanced St1 and Treh1 expression levels, clearly indicating the involvement of PI3K. Treatment with 1 mM of mpV(pic) (a potent inhibitor of protein phosphotyrosine phosphatase and activator of insulin receptor (InR) kinase) also stimulated expression levels of the St1 and Treh1 genes, thus further confirming the involvement of the InR. Determining Treh enzyme activity showed that bombyxin treatment stimulated Treh enzyme activity in time- and PI3K-dependent manners. Validamycin A (a Treh inhibitor) blocked bombyxin-stimulated Treh enzyme activity and partly decreased bombyxin-stimulated ecdysteroidogenesis. A specific sugar transport inhibitor (cytochalasin B) and a glycolysis inhibitor (2-deoxy-D-glucose (2-DG)) also reduced bombyxin-stimulated ecdysteroidogenesis. Taken together, these results indicated that increased expressions of Sts and Treh1 and enhanced Treh enzyme activity downstream of InR/PI3K are involved in bombyxin-stimulated ecdysteroidogenesis in B. mori PGs.

High T3 Induces β-Cell Insulin Resistance via Endoplasmic Reticulum Stress.

Hyperthyroidism can cause glucose metabolism disorders and insulin resistance. Insulin resistance in muscle and adipose tissues has been extensively studied, whereas investigations on β-cell insulin resistance are limited. This study preliminarily explored the effects of high T3 levels on β-cell line (MIN6) insulin resistance, as well as the roles of endoplasmic reticulum stress (ERS). In this study, we treated β-cell line with T3, with or without an inhibitor of phosphotyrosine phosphatases (PTPs, sodium vanadate) or ERS inhibitor (4-PBA). The results indicated that high levels of T3 significantly inhibited insulin secretion in β-cell line. In addition, we observed an upregulation of p-IRS-1ser307 and downregulation of Akt. These results can be corrected by sodium vanadate. Moreover, high T3 levels upregulate the ERS-related proteins PERK, IRE1, ATF6, and GRP78, as well as ERS-related apoptosis CHOP and caspase-12. Similarly, this change can be corrected by 4-PBA. These results suggest that high T3 levels can induce insulin resistance in β-cell line by activating ERS and the apoptotic pathway.

SOCS2 Binds to and Regulates EphA2 through Multiple Mechanisms

Suppressors of cytokine signaling (SOCS) proteins inhibit signaling by serving as substrate receptors for the Cullin5-RING E3 ubiquitin ligase (CRL5) and through a variety of CRL5-independent mechanisms. CRL5, SOCS2 and SOCS6 are implicated in suppressing transformation of epithelial cells. We identified cell proteins that interact with SOCS2 and SOCS6 using two parallel proteomics techniques: BioID and Flag affinity purification mass spectrometry. The receptor tyrosine kinase ephrin type-A receptor 2 (EphA2) was identified as a SOCS2-interacting protein. SOCS2-EphA2 binding requires the SOCS2 SH2 domain and EphA2 activation loop autophosphorylation, which is stimulated by Ephrin A1 (EfnA1) or by phosphotyrosine phosphatase inhibition. Surprisingly, EfnA1-stimulated EphA2-SOCS2 binding is delayed until EphA2 has been internalized into endosomes. This suggests that SOCS2 binds to EphA2 in the context of endosomal membranes. We also found that SOCS2 overexpression decreases steady state levels of EphA2, consistent with increased EphA2 degradation. This effect is indirect: SOCS2 induces EfnA1 expression, and EfnA1 induces EphA2 down-regulation. Other RTKs have been reported to bind, and be regulated by, over-expressed SOCS proteins. Our data suggest that SOCS protein over-expression may regulate receptor tyrosine kinases through indirect and direct mechanisms.

Phosphotyrosine phosphatase inhibitor bisperoxovanadium endows myogenic cells with enhanced muscle stem cell functions via epigenetic modulation of Sca-1 and Pw1 promoters.

Understanding the regulation of the stem cell fate is fundamental for designing novel regenerative medicine strategies. Previous studies have suggested that pharmacological treatments with small molecules provide a robust and reversible regulation of the stem cell program. Previously, we showed that treatment with a vanadium compound influences muscle cell fatein vitro In this study, we demonstrate that treatment with the phosphotyrosine phosphatase inhibitor bisperoxovanadium (BpV) drives primary muscle cells to a poised stem cell stage, with enhanced function in muscle regenerationin vivofollowing transplantation into injured muscles. Importantly, BpV-treated cells displayed increased self-renewal potentialin vivoand replenished the niche in both satellite and interstitial cell compartments. Moreover, we found that BpV treatment induces specific activating chromatin modifications at the promoter regions of genes associated with stem cell fate, includingSca-1andPw1 Thus, our findings indicate that BpV resets the cell fate program by specific epigenetic regulations, such that the committed myogenic cell fate is redirected to an earlier progenitor cell fate stage, which leads to an enhanced regenerative stem cell potential.-Smeriglio, P., Alonso-Martin, S., Masciarelli, S., Madaro, L., Iosue, I., Marrocco, V., Relaix, F., Fazi, F., Marazzi, G., Sassoon, D. A., Bouché, M. Phosphotyrosine phosphatase inhibitor bisperoxovanadium endows myogenic cells with enhanced muscle stem cell functionsviaepigenetic modulation of Sca-1 and Pw1 promoters.

The Canadian Diabetes Association names Dr. Barry I. Posner as the 2015 Clinical & Scientific Section Lifetime Achievement Award Recipient.

The Canadian Diabetes Association names Dr. Barry I. Posner as the 2015 Clinical & Scientific Section Lifetime Achievement Award Recipient.

Redox-regulated pathway of tyrosine phosphorylation underlies NF-κB induction by an atypical pathway independent of the 26S proteasome.

Alternative redox stimuli such as pervanadate or hypoxia/reoxygenation, induce transcription factor NF-κB by phospho-tyrosine-dependent and proteasome-independent mechanisms. While considerable attention has been paid to the absence of proteasomal regulation of tyrosine phosphorylated IκBα, there is a paucity of information regarding proteasomal regulation of signaling events distinct from tyrosine phosphorylation of IκBα. To delineate roles for the ubiquitin-proteasome pathway in the phospho-tyrosine dependent mechanism of NF-κB induction, we employed the proteasome inhibitor, Aclacinomycin, and the phosphotyrosine phosphatase inhibitor, pervanadate (PV). Results from these studies demonstrate that phospho-IκBα (Tyr-42) is not subject to proteasomal degradation in a murine stromal epithelial cell line, confirming results previously reported. Correspondingly, proteasome inhibition had no discernable effect on the key signaling intermediaries, Src and ERK1/2, involved in the phospho-tyrosine mechanisms regulating PV-mediated activation of NF-κB. Consistent with previous reports, a significant redox imbalance leading to the activation of tyrosine kinases, as occurs with pervanadate, is required for the induction of NF-κB. Strikingly, our studies demonstrate that proteasome inhibition can potentiate oxidative stress associated with PV-stimulation without impacting kinase activation, however, other cellular implications for this increase in intracellular oxidation remain to be fully delineated.

The effect of systemic PTEN antagonist peptides on axon growth and functional recovery after spinal cord injury

Knockout studies suggest that PTEN limits the regenerative capacities of CNS axons as a dominant antagonist of PI3 kinase, but the transgenic approach is not feasible for treating patients. Although application of bisperoxovanadium may block PTEN function, it is a general inhibitor of phosphotyrosine phosphatases and may target enzymes other than PTEN, causing side effects and preventing firm conclusions about PTEN inhibition on regulating neuronal growth. A pharmacological method to selectively suppress PTEN post-injury could be a valuable strategy for promoting CNS axon regeneration. We identified PTEN antagonist peptides (PAPs) by targeting PTEN critical functional domains and evaluated their efficacy for promoting axon growth. Four PAPs (PAP 1–4) bound to PTEN protein expressed in COS7 cells and blocked PTEN signaling in vivo. Subcutaneous administration of PAPs initiated two days after dorsal over-hemisection injury significantly stimulated growth of descending serotonergic fibers in the caudal spinal cord of adult mice. Systemic PAPs induce significant sprouting of corticospinal fibers in the rostral spinal cord and limited growth of corticospinal axons in the caudal spinal cord. More importantly, PAP treatment enhanced recovery of locomotor function in adult rodents with spinal cord injury. This study may facilitate development of effective therapeutic agents for CNS injuries.

Mercury alters B-cell protein phosphorylation profiles.

Environmental exposure to mercury is suggested to contribute to human immune dysfunction. To shed light on the mechanism, we identified changes in the phosphoproteomic profile of the WEHI-231 B cell line after intoxication with Hg(2+). These changes were compared to changes in the phosphoproteome that were induced by pervanadate or okadaic acid exposure. Both 250 μM HgCl2 and pervanadate, a known phosphotyrosine phosphatase inhibitor, caused an increase in the number of proteins identified after TiO2 affinity selection and LC-MS/MS analysis. Pervanadate treatment had a larger effect than Hg(2+) on the number of Scansite motifs that were tyrosine-phosphorylated, 17, and Ingenuity canonical signaling pathways activated, 4, with score >5.0. However, Hg(2+) had a more focused effect, primarily causing tyrosine-phosphorylation in src homology 2 domains in proteins that are in the B cell receptor signaling pathway. The finding that many of the changes induced by Hg(2+) overlap with those of pervanadate, indicates that at high concentrations Hg(2+) inhibits protein tyrosine phosphatases.

The Streptococcus thermophilus protein Wzh functions as a phosphotyrosine phosphatase

Amino acid residues that are important for metal binding and catalysis in Gram-positive phosphotyrosine phosphatases were identified in the Wzh protein of Streptococcus thermophilus MR-1C by using sequence comparisons. A His-tagged fusion Wzh protein was purified from Escherichia coli cultures and tested for phosphatase activity against synthetic phosphotyrosine and phosphoserine-threonine peptides. Purified Wzh released 2316.5 ± 138.7 pmol PO4·min(-1)·μg(-1) from phosphotyrosine peptide-1 and 2345.7 ± 135.2 pmol PO4·min(-1)·μg(-1) from phosphotyrosine peptide-2. The presence of the phosphotyrosine phosphatase inhibitor sodium vanadate decreased purified Wzh activity by 45%-50% at 1 mmol·L(-1), 74%-84% at 5 mmol·L(-1), and by at least 88% at 10 mmol·L(-1). Purified Wzh had no detectable activity against the phosphoserine-threonine peptide. These results clearly establish that S. thermophilus MR-1C Wzh functions as a phosphotyrosine phosphatase that could function to remove phosphate groups from proteins involved in exopolysaccharide biosynthesis, including the protein tyrosine kinase Wze and priming glycosyltransferase.

Phospho-tyrosine phosphatase inhibitor Bpv(Hopic) enhances C2C12 myoblast migration in vitro. Requirement of PI3K/AKT and MAPK/ERK pathways

Muscle progenitor cell migration is an important step in skeletal muscle myogenesis and regeneration. Migration is required for muscle precursors to reach the site of damage and for the alignment of myoblasts prior to their fusion, which ultimately contributes to muscle regeneration. Limited spreading and migration of donor myoblasts are reported problems of myoblast transfer therapy, a proposed therapeutic strategy for Duchenne Muscular Dystrophy, warranting further investigation into different approaches for improving the motility and homing of these cells. In this article, the effect of protein phospho-tyrosine phosphatase and PTEN inhibitor BpV(Hopic) on C2C12 myoblast migration and differentiation was investigated. Applying a wound healing migration model, it is reported that 1μM BpV(Hopic) is capable of enhancing the migration of C2C12 myoblasts by approximately 40% in the presence of myotube conditioned media, without significantly affecting their capacity to differentiate and fuse into multinucleated myotubes. Improved migration of myoblasts treated with 1μM BpV(Hopic) was associated with activation of PI3K/AKT and MAPK/ERK pathways, while their inhibition with either LY294002 or UO126, respectively, resulted in a reduction of C2C12 migration back to control levels. These results propose that bisperoxovanadium compounds may be considered as potential tools for enhancing the migration of myoblasts, while not reducing their differentiation capacity and underpin the importance of PI3K/AKT and MAPK/ERK signalling for the process of myogenic progenitor migration.

Fluoride Effects: The Two Faces of Janus

The behavior of fluoride ions in the human organism is a classic example of double-edged sword. On the one hand the daily supplementation with fluoride is undoubtedly an important preventing factor in protecting teeth from caries, and, as an important mitogenic stimulus for osteoblasts, it may enhance mineral deposition in bone, but on the other hand fluoride, above a threshold concentration, has been demonstrated to be toxic. We present here a brief review of fluoride metabolism and exposure, its use in caries prevention and its effects on bone, followed by an updating about the main hypotheses concerning its mechanism of action and toxicity. The effects of fluoride have been related mainly to its ability to evoke the activation of G proteins and the inhibition of phosphotyrosine phosphatases, leading to an intracellular increase of tyrosine phosphorylation and activation of the mitogen-activated protein kinase pathway, and its capacity to cause generation of reactive oxygen species. We present also a unifying hypothesis accounting for these apparently different effects, although the available experimental models and conditions are highly variable in the literature. A lot of experiments still need to be performed to clarify the positive and negative effects of fluoride. Finding the mechanisms accounting for fluoride toxicity is an important point: indeed, the use of fluoride has been proposed in the preparation of new biomaterials to be inserted in the bone, in order to improve their stable and safe integration.

Distinct Phosphatase Activity Profiles in Two Strains of Trypanosoma cruzi

Phosphorylation of parasite proteins plays a key role in the process of cell invasion by Trypanosoma cruzi, the etiologic agent of Chagas' disease. In this sense, characterization of parasite kinases and phosphatases could open new possibilities for the rational design of chemotherapeutic agents for the treatment of Chagas' disease. In this work, we analyzed phosphatase activities in T. cruzi homogenates from 2 strains belonging to different lineages and with different resistance to oxidative stress. Tulahuen 2 cells (Lineage I) showed higher phosphatase activities and specificity constants when compared to the Y strain (Lineage II). Tulahuen 2 had an optimum phosphatase activity at pH 4.0 and the Y strain at pH 7.0. In both cases, neutral–basic, but not acid, phosphatase activities were increased in the presence of Mg2+. Although calcium had an inhibitory effect at a pH of 7.0 and 8.0 in the Y strain, this inhibition was restricted to pH 8.0 in the other strain. Different substrates and acid phosphotyrosine and alkaline phosphatase inhibitors exhibited distinct effects on the phosphatase activity of both strains. Our results provide a better understanding of T. cruzi phosphatases and reinforce the notion of heterogeneity among T. cruzi populations.

Involvement of the c-jun N-terminal kinases JNK1 and JNK2 in complement-mediated cell death

Cell death and survival signals activated by the complement membrane attack complex C5b-9 play important roles in complement-associated diseases and in antibody-based cancer therapy. Here, we investigated the involvement of the JNK mitogen-activated protein kinase in C5b-9-induced cell lysis. Necrotic-type cell death regulation by JNK1 and JNK2 was selectively studied in mouse fibroblasts and human K562, HeLa and 293T cells. C5b-9 induced higher JNK activation than C5b-8. Pretreatment with a JNK inhibitor reduced cell sensitivity to complement-mediated lysis. KO cells deficient in either JNK1 or JNK2 were less sensitive to lysis than WT cells. This correlated with lower C3 and C5b-9 deposition on KO cells. Furthermore, silencing of JNK1 or JNK2 expression by RNA interference decreased cell lysis by complement. Reconstitution of JNK2 into JNK2−/− cells and over expression of JNK2 in WT cells increased C3 and C5b-9 deposition as well as cell sensitivity to complement-mediated lysis. Pretreatment of cells with the phosphotyrosine phosphatase inhibitor phenylarsine oxide increased JNK activation and JNK-dependent complement-mediated necrotic death of WT and JNK2−/− KO cells but not of JNK1−/− KO cells. The JNK inhibitor and PAO had no effect on complement-mediated lysis in cells lacking Bid, suggesting involvement of Bid in the JNK lytic pathway. Our results demonstrate that complement C5b-9 induce a JNK/Bid-dependent and JNK-independent necrotic cell death. Both JNK1 and JNK2 have cytotoxic potential, however JNK2 is the primary signal transducer.

Growth Factors Outside of the Platelet-derived Growth Factor (PDGF) Family Employ Reactive Oxygen Species/Src Family Kinases to Activate PDGF Receptor α and Thereby Promote Proliferation and Survival of Cells

The vitreous contains a plethora of growth factors that are strongly implicated in the formation of fibroproliferative diseases such as proliferative vitreoretinopathy. Although platelet-derived growth factors (PDGFs) are present in the vitreous, vitreal growth factors outside of the PDGF family activated the PDGF alpha receptor (PDGFRalpha) and promoted disease progression in a rabbit model of proliferative vitreoretinopathy (H. Lei, G. Velez, P. Hovland, T. Hirose, D. Gilbertson, and A. Kazlauskas (2008) submitted for publication.) In this report we investigated the mechanism by which non-PDGFs activated PDGFRalpha. We found that non-PDGFs increased the cellular level of reactive oxygen species (ROS) and that this event was necessary and sufficient for phosphorylation of PDGFRalpha. We speculated that the underlying mechanism was ROS-mediated inhibition of phosphotyrosine phosphatases, which antagonize receptor auto-phosphorylation. However, this did not appear to be the case. Non-PDGFs promoted tyrosine phosphorylation of catalytically inactive PDGFRalpha, and thereby indicated that at least one additional tyrosine kinase was involved. Indeed, preventing expression or blocking the kinase activity of Src family kinases suppressed non-PDGF-dependent tyrosine phosphorylation of PDGFRalpha. Thus non-PDGFs increased the level of ROS, which activated Src family kinases and resulted in phosphorylation of PDGFRalpha. Finally, although non-PDGFs induced only modest phosphorylation of PDGFRalpha, proliferation and survival of cells in response to non-PDGFs was significantly enhanced by expression of PDGFRalpha. These studies reveal a novel mechanism for activation of PDGFRalpha that appears capable of enhancing the responsiveness of cells to growth factors outside of the PDGF family.

Giardia lamblia: Characterization of ecto-phosphatase activities

Ecto-phosphatase activities of Giardia lamblia were characterized in intact cells, which are able to hydrolyze the artificial substrate p-nitrophenylphosphate ( p-NPP) to p-nitrophenol ( p-NP) at a rate of 8.4 ± 0.8 nmol p-NP/h/10 7 cells. The ecto-phosphatase activities were inhibited at high pH as well as by classical inhibitors of acid phosphatases, such as sodium fluoride and sodium molybdate and by inorganic phosphate, the final product of the reaction. Experiments using a classical inhibitor of phosphotyrosine phosphatase, sodium orthovanadate, also showed that the ecto-phosphatase activity was inhibited in a dose-dependent manner. Different phosphorylated amino acids were used as substrates for the G. lamblia ecto-phosphatase activities the highest rate of phosphate release was achieved using phosphotyrosine. Not only p-NPP hydrolysis but also phosphotyrosine hydrolysis was inhibited by sodium orthovanadate. Phosphotyrosine but not phospho-serine or phospho-threonine inhibited the p-nitrophenylphosphatase activity. We also observed a positive correlation between the ecto-phosphatase activity and the capacity to encystation of G. lamblia trophozoites.

Genistein stimulates myocardial contractility in guinea pigs by different subcellular mechanisms

The purpose of this study was to investigate the mechanisms involved in the excitatory effect induced by genistein in isolated guinea pig left ventricular papillary muscles and to determine relationship of genistein action with the tyrosine kinase pathway and phosphatidylinositol 3-kinase (PI3K) activity, the cyclic adenosine 5′-monophosphate (cAMP) signal system and the sarcoplasmic reticulum Ca 2+ mobilization. Genistein (1–100 μM) significantly increased contraction of left ventricular papillary muscles from male and female guinea pigs in a concentration-dependent manner and its action had no obvious gender differences. Prior treatment with an L-type Ca 2+ channel blocker verapamil hydrochloride, β-adrenoceptor inhibitors propranolol and atenolol, an inhibitor of Na +–Ca 2+ reverse exchanger Kb-r7943 or the blocker of estrogen receptor ICI 182,780 failed to alter the positive inotropic effect induced by genistein in papillary muscles. However, tyrosine phosphatase inhibitor, sodium orthovanadate or a potent phosphotyrosine phosphatase inhibitor bpV (phen) could partly but significantly reduce the stimulatory action of genistein. Interestingly, insulin-like growth factor-1, a known PI3K activator could also decrease the stimulatory action of genistein obviously, but the PI3K inhibitor LY294002 had no significant effect on the stimulatory action of genistein. The excitatory effect of genistein was markedly attenuated not only after treatment with an inhibitor of cAMP synthesis Sq 22536, carbachol or an inhibitor of specific protein kinase A H-89, but also after the inhibition of sarcoplasmic reticulum Ca 2+ mobilization by ruthenium red, ryanodine or the inhibitor of sarcoplasmic reticulum Ca 2+-ATPase thapsigargin. All these results indicate that the excitatory effects of genistein in papillary muscles are due to the inhibition of tyrosine kinase pathway and PI3K activity, thereby locally activating cAMP signal transduction and facilitating intracellular Ca 2+ mobilization, but are not related to the activation of β-adrenoceptor, the Na +–Ca 2+ reverse exchange and the estrogen receptor.

Compartmentalization and in vivo insulin‐induced translocation of the insulin‐signaling inhibitor Grb14 in rat liver

The molecular adaptor Grb14 binds in vitro to the activated insulin receptor (IR) and inhibits IR signaling. In this study, we have used rat liver subcellular fractionation to analyze in vivo insulin effects on Grb14 compartmentalization and IR phosphorylation and activity. In control rats, Grb14 was recovered mainly in microsomal and cytosolic fractions, but was also detectable at low levels in plasma membrane and Golgi/endosome fractions. Insulin injection led to a rapid and dose-dependent increase in Grb14 content, first in the plasma membrane fraction, and then in the Golgi/endosome fraction, which paralleled the increase in IR beta-subunit tyrosine phosphorylation. Upon sustained in vivo IR tyrosine phosphorylation induced by high-affinity insulin analogs, in vitro IR dephosphorylation by endogenous phosphatases, and in vivo phosphorylation of the IR induced by injection of bisperoxo(1,10 phenanthroline)oxovanadate, a phosphotyrosine phosphatase inhibitor, we observed a striking correlation between IR phosphorylation state and Grb14 content in both the plasma membrane and Golgi/endosome fractions. In addition, coimmunoprecipitation experiments provided evidence that Grb14 was associated with phosphorylated IR beta-subunit in these fractions. Altogether, these data support a model whereby insulin stimulates the recruitment of endogenous Grb14 to the activated IR at the plasma membrane, and induces internalization of the Grb14-IR complex in endosomes. Removal of Grb14 from fractions of insulin-treated rats by KCl treatment led to an increase of in vivo insulin-stimulated IR tyrosine kinase activity, indicating that endogenous Grb14 exerts a negative feedback control on IR catalytic activity. This study thus demonstrates that Grb14 is a physiological regulator of liver insulin signaling.

N-Glycans in cancer progression

N-Glycan branching in the medial-Golgi generates ligands for lattice-forming lectins (e.g., galectins) that regulate surface levels of glycoproteins including epidermal growth factor (EGF) and transforming growth factor-beta (TGF-beta) receptors. Moreover, functional classes of glycoproteins differ in N-glycan multiplicities (number of N-glycans/peptide), a genetically encoded feature of glycoproteins that interacts with metabolic flux (UDP-GlcNAc) and N-glycan branching to differentially regulate surface levels. Oncogenesis increases beta1,6-N-acetylglucosaminyltransferase V (encoded by Mgat5) expression, and its high-affinity galectin ligands promote surface retention of growth receptors with a reduced dependence on UDP-GlcNAc. Mgat5(-/-) tumor cells are less metastatic in vivo and less responsive to cytokines in vitro, but undergo secondary changes that support tumor cell proliferation. These include loss of Caveolin-1, a negative regulator of EGF signaling, and increased reactive oxygen species, an inhibitor of phosphotyrosine phosphatases. These studies suggest a systems approach to cancer treatment where the surface distribution of receptors is targeted through metabolism and N-glycan branching to induce growth arrest.

Bisperoxovanadium, a phospho‐tyrosine phosphatase inhibitor, reprograms myogenic cells to acquire a pluripotent, circulating phenotype

Satellite cells are the main source of myogenic progenitors in postnatal skeletal muscle, but their use in cell therapy for muscle disorders is limited because these cells cannot be delivered through circulation and they are rapidly exhausted in severe myopathies. The search for alternative donor cells is ongoing, but none of the candidates so far show all the features required for successful colonization and repair of diseased muscle. In this study, we show that bisperoxovanadium, a phospho-tyrosine phosphatase inhibitor, induces myogenic cells to acquire a gene expression profile and a differentiation potential consistent with the phenotype of a circulating precursors, while maintaining their myogenic potential. These effects are mediated, at least in part, by NF-kappaB activation through the Tyr42-IkappaB-alpha phosphorylation, as shown by the expression of the dominant negative mutant form of the p50 NF-kappaB subunit. Moreover, when bisperoxovanadium-treated cells are injected into the femoral artery of alpha-sarcoglican null dystrophic mice, they are able to circulate and to reach muscle tissue; importantly, they contribute to muscle regeneration, as shown by the expression of alpha-sarcoglican in some fibers. Our observations indicate that bisperoxovanadium, or similar compounds, may prove very valuable to obtain and to expand, from committed cells, multipotent cell populations suitable for gene-cell therapy applications and may help to understand the molecular basis of genome reprogramming and "stem-ness."

Entamoeba histolytica: An ecto-phosphatase activity regulated by oxidation–reduction reactions

In this work, an ecto-phosphatase activity of Entamoeba histolytica was characterized using intact cells. This activity presented the following biochemical characteristics: (i) it hydrolyzes p-NPP with V max of 8.00 ± 0.22 nmol p-NP × h −1 × 10 −5 cells and K m of 2.68 ± 0.25 mM; (ii) it is inhibited by acid phosphatase inhibitors, such as sodium molybdate ( K i = 1.70 ± 0.24 μM) and sodium fluoride ( K i = 0.25 ± 0.02 mM); (iii) it also showed high sensitivity to phosphotyrosine phosphatase inhibitors, such as sodium orthovanadate ( K i = 1.07 ± 0.14 μM), bpV-PHEN ( K i = 0.38 ± 0.02 μM) and mpV-PIC ( K i = 0.39 ± 0.04 μM). Zn 2+, an oxidizing agent, decreased the enzymatic activity in 50%. DTT and GSH, two reducing agents, enhanced the activity twofold. The non-invasive E. histolytica and free-living E. moshkovskii were less efficient in hydrolyzing p-NPP than the pathogenic E. histolytica suggesting that this enzyme could represent a virulence marker for this cell.