PTP1B: a double agent in metabolism and oncogenesis

Early growth response-1 negative feedback regulates skeletal muscle postprandial insulin sensitivity via activating Ptp1b transcription

Postprandial insulin desensitization plays a critical role in maintaining whole-body glucose homeostasis by avoiding the excessive absorption of blood glucose; however, the detailed mechanisms that underlie how the major player, skeletal muscle, desensitizes insulin action remain to be elucidated. Herein, we report that early growth response gene-1 ( Egr-1) is activated by insulin in skeletal muscle and provides feedback inhibition that regulates insulin sensitivity after a meal. The inhibition of the transcriptional activity of Egr-1 enhanced the phosphorylation of the insulin receptor (InsR) and Akt, thus increasing glucose uptake in L6 myotubes after insulin stimulation, whereas overexpression of Egr-1 decreased insulin sensitivity. Furthermore, deletion of Egr-1 in the skeletal muscle improved systemic insulin sensitivity and glucose tolerance, which resulted in lower blood glucose levels after refeeding. Mechanistic analysis demonstrated that EGR-1 inhibited InsR phosphorylation and glucose uptake in skeletal muscle by binding to the proximal promoter region of protein tyrosine phosphatase-1B (PTP1B) and directly activating transcription. PTP1B knockdown largely restored insulin sensitivity and enhanced glucose uptake, even under conditions of EGR-1 overexpression. Our results indicate that EGR-1/PTP1B signaling negatively regulates postprandial insulin sensitivity and suggest a potential therapeutic target for the prevention and treatment of excessive glucose absorption.-Wu, J., Tao, W.-W., Chong, D.-Y., Lai, S.-S., Wang, C., Liu, Q., Zhang, T.-Y., Xue, B., Li, C.-J. Early growth response-1 negative feedback regulates skeletal muscle postprandial insulin sensitivity via activating Ptp1b transcription.

Double agents: genes with both oncogenic and tumor-suppressor functions

The role of genetic components in cancer development is an area of interest for cancer biologists in general. Intriguingly, some genes have both oncogenic and tumor-suppressor functions. In this study, we systematically identified these genes through database search and text mining. We find that most of them are transcription factors or kinases and exhibit dual biological functions, e.g., that they both positively and negatively regulate transcription in cells. Some cancer types such as leukemia are over-represented by them, whereas some common cancer types such as lung cancer are under-represented by them. Across 12 major cancer types, while their genomic mutation patterns are similar to that of oncogenes, their expression patterns are more similar to that of tumor-suppressor genes. Their expression profile in six human organs propose that they mainly function as tumor suppressor in normal tissue. Our network analyses further show they have higher network degrees than both oncogenes and tumor-suppressor genes and thus tend to be the hub genes in the protein–protein interaction network. Our mutation, expression spectrum, and network analyses might help explain why some cancer types are specifically associated with them. Finally, our results suggest that the functionally altering mutations in “double-agent” genes and oncogenes are the main driving force in cancer development, because non-silent mutations are biasedly distributed toward these two gene sets across all 12 major cancer types.

Inhibition of protein tyrosine phosphatase (PTP1B) and α-glucosidase by geranylated flavonoids from Paulownia tomentosa

Protein tyrosine phosphatase 1B (PTP1B) and α-glucosidase are important targets to treat obesity and diabetes, due to their deep correlation with insulin and leptin signalling, and glucose regulation. The methanol extract of Paulownia tomentosa fruits showed potent inhibition against both enzymes. Purification of this extract led to eight geranylated flavonoids (1-8) displaying dual inhibition of PTP1B and α-glucosidase. The isolated compounds were identified as flavanones (1-5) and dihydroflavonols (6-8). Inhibitory potencies of these compounds varied accordingly, but most of the compounds were highly effective against PTP1B (IC50 = 1.9-8.2 μM) than α-glucosidase (IC50 = 2.2-78.9 μM). Mimulone (1) was the most effective against PTP1B with IC50 = 1.9 μM, whereas 6-geranyl-3,3',5,5',7-pentahydroxy-4'-methoxyflavane (8) displayed potent inhibition against α-glucosidase (IC50 = 2.2 μM). All inhibitors showed mixed type Ι inhibition toward PTP1B, and were noncompetitive inhibitors of α-glucosidase. This mixed type behavior against PTP1B was fully demonstrated by showing a decrease in Vmax, an increase of Km, and Kik/Kiv ratio ranging between 2.66 and 3.69.

Kinetic characterization of the inhibition of protein tyrosine phosphatase-1B by Vanadyl (VO2+) chelates

Protein tyrosine phosphatases (PTPases) are a prominent focus of drug design studies because of their roles in homeostasis and disorders of metabolism. These studies have met with little success because (1) virtually all inhibitors hitherto exhibit only competitive behavior and (2) a consensus sequence H/V-C-X5-R-S/T characterizes the active sites of PTPases, leading to low specificity of active site directed inhibitors. With protein tyrosine phosphatase-1B (PTP1B) identifed as the target enzyme of the vanadyl (VO2+) chelate bis(acetylacetonato)oxidovanadium(IV) [VO(acac)2] in 3T3-L1 adipocytes [Ou et al. J Biol Inorg Chem 10: 874-886, 2005], we compared the inhibition of PTP1B by VO(acac)2 with other VO2+-chelates, namely, bis(2-ethyl-maltolato)oxidovanadium(IV) [VO(Et-malto)2] and bis(3-hydroxy-2-methyl-4(1H)pyridinonato)oxidovanadium(IV) [VO(mpp)2] under steady-state conditions, using the soluble portion of the recombinant human enzyme (residues 1-321). Our results differed from those of previous investigations because we compared inhibition in the presence of the nonspecific substrate p-nitrophenylphosphate and the phosphotyrosine-containing undecapeptide DADEpYLIPQQG mimicking residues 988-998 of the epidermal growth factor receptor, a relevant, natural substrate. While VO(Et-malto)2 acts only as a noncompetitive inhibitor in the presence of either subtrate, VO(acac)2 exhibits classical uncompetitive inhibition in the presence of DADEpYLIPQQG but only apparent competitive inhibition with p-nitrophenylphosphate as substrate. Because uncompetitive inhibitors are more potent pharmacologically than competitive inhibitors, structural characterization of the site of uncompetitive binding of VO(acac)2 may provide a new direction for design of inhibitors for therapeutic purposes. Our results suggest also that the true behavior of other inhibitors may have been masked when assayed with only p-nitrophenylphosphate as substrate.

Inhibition of protein tyrosine phosphatase 1B by flavonoids: A structure - activity relationship study

The classical non-transmembrane protein tyrosine phosphatase 1B (PTP1B) has emerged as a key negative regulator of insulin signaling pathways that leads to insulin resistance, turning this enzyme a promising therapeutic target in the management of type 2 diabetes mellitus (T2DM). In the present work, the in vitro inhibitory activity of a panel of structurally related flavonoids, for recombinant human PTP1B was studied and the type of inhibition of the most active compounds further evaluated. The majority of the studied flavonoids was tested in this work for the first time, including flavonoid C13, which was the most potent inhibitor. It was observed that the ability to inhibit PTP1B depends on the nature, position and number of substituents in the flavonoid structure, as the presence of both 7- and 8-OBn groups in the A ring, together with the presence of both 3' and 4'-OMe groups in the B ring and the 3-OH group in the C ring; these substituents increase the flavonoids' ability to inhibit PTP1B. In conclusion, some of the tested flavonoids seem to be promising PTP1B inhibitors and potential effective agents in the management of T2DM, by increasing insulin sensitivity.

Protein tyrosine phosphatase 1B deficiency in podocytes mitigates hyperglycemia-induced renal injury

OBJECTIVE

Diabetic nephropathy is one of the most devastating complications of diabetes, and growing evidence implicates podocyte dysfunction in disease pathogenesis. The objective of this study was to investigate the contribution of protein tyrosine phosphatase 1B (PTP1B) in podocytes to hyperglycemia-induced renal injury.

METHODS

To determine the in vivo function of PTP1B in podocytes we generated mice with podocyte-specific PTP1B disruption (hereafter termed pod-PTP1B KO). Kidney functions were determined in control and pod-PTP1B KO mice under normoglycemia and high-fat diet (HFD)- and streptozotocin (STZ)-induced hyperglycemia.

RESULTS

PTP1B expression increased in murine kidneys following HFD and STZ challenges. Under normoglycemia control and pod-PTP1B KO mice exhibited comparable renal functions. However, podocyte PTP1B disruption attenuated hyperglycemia-induced albuminuria and renal injury and preserved glucose control. Also, podocyte PTP1B disruption was accompanied with improved renal insulin signaling and enhanced autophagy with decreased inflammation and fibrosis. Moreover, the beneficial effects of podocyte PTP1B disruption in vivo were recapitulated in E11 murine podocytes with lentiviral-mediated PTP1B knockdown. Reconstitution of PTP1B in knockdown podocytes reversed the enhanced insulin signaling and autophagy suggesting that they were likely a consequence of PTP1B deficiency. Further, pharmacological attenuation of autophagy in PTP1B knockdown podocytes mitigated the protective effects of PTP1B deficiency.

CONCLUSIONS

These findings demonstrate that podocyte PTP1B deficiency attenuates hyperglycemia-induced renal damage and suggest that PTP1B may present a therapeutic target in renal injury.

Punicalagin, a PTP1B inhibitor, induces M2c phenotype polarization via up-regulation of HO-1 in murine macrophages

Current data have shown that punicalagin (PUN), an ellagitannin isolated from pomegranate, possesses anti-inflammatory and anti-oxidant properties; however, its direct targets have not yet been reported. This is the first report that PTP1B serves as a direct target of PUN, with IC₅₀ value of 1.04μM. Results from NPOI further showed that the K_on and K_off of PUN-PTP1B complex were 3.38e2M^-1s^-1 and 4.13e-3s^-1, respectively. The active site Arg24 of PTP1B was identified as a key binding site of PUN by computation simulation and point mutation. Moreover, inhibition of PTP1B by PUN promoted an M2c-like macrophage polarization and enhanced anti-inflammatory cytokines expression, including IL-10 and M-CSF. Based on gene expression profile, we elucidated that PUN treatment significantly up-regulated 275 genes and down-regulated 1059 genes. M1-like macrophage marker genes, such as Tlr4, Irf1/2, Hmgb1, and Stat1 were down-regulated, while M2 marker genes, including Tmem171, Gpr35, Csf1, Il1rn, Cebpb, Fos, Vegfα, Slc11a1, and Bhlhe40 were up-regulated in PUN-treated macrophages. Hmox-1, a gene encoding HO-1 protein, was preferentially expressed with 16-fold change. Inhibition of HO-1 obviously restored PUN-induced M2 polarization and IL-10 secretion. In addition, phosphorylation of both Akt and STAT3 contributed to PUN-induced HO-1 expression. This study provided new insights into the mechanisms of PUN-mediated anti-inflammatory and anti-oxidant activities and provided new therapeutic strategies for inflammatory diseases.

Differential oxidation of protein-tyrosine phosphatases during zebrafish caudal fin regeneration

Zebrafish have the capacity to regenerate lost tissues and organs. Amputation of the caudal fin results in a rapid, transient increase in H₂O₂ levels emanating from the wound margin, which is essential for regeneration, because quenching of reactive oxygen species blocks regeneration. Protein-tyrosine phosphatases (PTPs) have a central role in cell signalling and are susceptible to oxidation, which results in transient inactivation of their catalytic activity. We hypothesized that PTPs may become oxidized in response to amputation of the caudal fin. Using the oxidized PTP-specific (ox-PTP) antibody and liquid chromatography-mass spectrometry, we identified 33 PTPs in adult zebrafish fin clips of the total of 44 PTPs that can theoretically be detected based on sequence conservation. Of these 33 PTPs, 8 were significantly more oxidized 40 min after caudal fin amputation. Surprisingly, Shp2, one of the PTPs that were oxidized in response to caudal fin amputation, was required for caudal fin regeneration. In contrast, Rptpα, which was not oxidized upon amputation, was dispensable for caudal fin regeneration. Our results demonstrate that PTPs are differentially oxidized in response to caudal fin amputation and that there is a differential requirement for PTPs in regeneration.

SENP1 regulates IFN-γ-STAT1 signaling through STAT3-SOCS3 negative feedback loop

Interferon-γ (IFN-γ) triggers macrophage for inflammation response by activating the intracellular JAK-STAT1 signaling. Suppressor of cytokine signaling 1 (SOCS1) and protein tyrosine phosphatases can negatively modulate IFN-γ signaling. Here, we identify a novel negative feedback loop mediated by STAT3-SOCS3, which is tightly controlled by SENP1 via de-SUMOylation of protein tyrosine phosphatase 1B (PTP1B), in IFN-γ signaling. SENP1-deficient macrophages show defects in IFN-γ signaling and M1 macrophage activation. PTP1B in SENP1-deficient macrophages is highly SUMOylated, which reduces PTP1B-induced de-phosphorylation of STAT3. Activated STAT3 then suppresses STAT1 activation via SOCS3 induction in SENP1-deficient macrophages. Accordingly, SENP1-deficient macrophages show reduced ability to resist Listeria monocytogenes infection. These results reveal a crucial role of SENP1-controlled STAT1 and STAT3 balance in macrophage polarization.

Inhibition of PTP1B disrupts cell-cell adhesion and induces anoikis in breast epithelial cells

Protein tyrosine phosphatase 1B (PTP1B) is a well-known inhibitor of insulin signaling pathways and inhibitors against PTP1B are being developed as promising drug candidates for treatment of obesity. PTP1B has also been linked to breast cancer both as a tumor suppressor and as an oncogene. Furthermore, PTP1B has been shown to be a regulator of cell adhesion and migration in normal and cancer cells. In this study, we analyzed the PTP1B expression in normal breast tissue, primary breast cells and the breast epithelial cell line D492. In normal breast tissue and primary breast cells, PTP1B is widely expressed in both epithelial and stromal cells, with highest expression in myoepithelial cells and fibroblasts. PTP1B is widely expressed in branching structures generated by D492 when cultured in 3D reconstituted basement membrane (3D rBM). Inhibition of PTP1B in D492 and another mammary epithelial cell line HMLE resulted in reduced cell proliferation and induction of anoikis. These changes were seen when cells were cultured both in monolayer and in 3D rBM. PTP1B inhibition affected cell attachment, expression of cell adhesion proteins and actin polymerization. Moreover, epithelial to mesenchymal transition (EMT) sensitized cells to PTP1B inhibition. A mesenchymal sublines of D492 and HMLE (D492M and HMLEmes) were more sensitive to PTP1B inhibition than D492 and HMLE. Reversion of D492M to an epithelial state using miR-200c-141 restored resistance to detachment induced by PTP1B inhibition. In conclusion, we have shown that PTP1B is widely expressed in the human breast gland with highest expression in myoepithelial cells and fibroblasts. Inhibition of PTP1B in D492 and HMLE affects cell–cell adhesion and induces anoikis-like effects. Finally, cells with an EMT phenotype are more sensitive to PTP1B inhibitors making PTP1B a potential candidate for further studies as a target for drug development in cancer involving the EMT phenotype.

Discovery and evaluation of the hybrid of bromophenol and saccharide as potent and selective protein tyrosine phosphatase 1B inhibitors

Protein tyrosine phosphatase 1B (PTP1B) is a key negative regulator of insulin signaling pathway. Inhibition of PTP1B is expected to improve insulin action. Appropriate selectivity and permeability are the gold standard for excellent PTP1B inhibitors. In this work, molecular hybridization-based screening identified a selective competitive PTP1B inhibitor. Compound 10a has IC₅₀ values of 199 nM against PTP1B, and shows 32-fold selectivity for PTP1B over the closely related phosphatase TCPTP. Molecule docking and molecular dynamics studies reveal the reason of selectivity for PTP1B over TCPTP. Moreover, the cell permeability and cellular activity of compound 10a are demonstrated respectively.

MenaINV dysregulates cortactin phosphorylation to promote invadopodium maturation

Invadopodia, actin-based protrusions of invasive carcinoma cells that focally activate extracellular matrix-degrading proteases, are essential for the migration and intravasation of tumor cells during dissemination from the primary tumor. We have previously shown that cortactin phosphorylation at tyrosine residues, in particular tyrosine 421, promotes actin polymerization at newly-forming invadopodia, promoting their maturation to matrix-degrading structures. However, the mechanism by which cells regulate the cortactin tyrosine phosphorylation-dephosphorylation cycle at invadopodia is unknown. Mena, an actin barbed-end capping protein antagonist, is expressed as various splice-isoforms. The Mena^INV isoform is upregulated in migratory and invasive sub-populations of breast carcinoma cells, and is involved in tumor cell intravasation. Here we show that forced Mena^INV expression increases invadopodium maturation to a far greater extent than equivalent expression of other Mena isoforms. Mena^INV is recruited to invadopodium precursors just after their initial assembly at the plasma membrane, and promotes the phosphorylation of cortactin tyrosine 421 at invadopodia. In addition, we show that cortactin phosphorylation at tyrosine 421 is suppressed by the phosphatase PTP1B, and that PTP1B localization to the invadopodium is reduced by Mena^INV expression. We conclude that Mena^INV promotes invadopodium maturation by inhibiting normal dephosphorylation of cortactin at tyrosine 421 by the phosphatase PTP1B.

Dietary Zinc Regulates Apoptosis through the Phosphorylated Eukaryotic Initiation Factor 2α/Activating Transcription Factor-4/C/EBP-Homologous Protein Pathway during Pharmacologically Induced Endoplasmic Reticulum Stress in Livers of Mice

BACKGROUND

Several in vitro studies have shown that zinc deficiency could induce endoplasmic reticulum (ER) stress, resulting in activation of the unfolded protein response.

OBJECTIVE

We aimed to determine whether consumption of a zinc-deficient diet (ZnD) triggers ER stress and to understand the impact of dietary zinc intake on ER stress-induced apoptosis using a mouse model.

METHODS

Young adult (8-16 wk of age) male mice of strain C57BL/6 were fed either a ZnD (<1 mg/kg diet), or a zinc-adequate diet (ZnA; 30 mg/kg diet). After 2 wk, liver, pancreas, and serum samples were collected and analyzed for indexes of ER stress. In another experiment, mice were fed either a ZnD, a ZnA, or a zinc-supplementation diet (ZnS; 180 mg/kg diet). After 2 wk, vehicle or tunicamycin (TM; 2 mg/kg body weight) was administered to mice to model ER stress. Liver and serum were analyzed for indexes of ER stress to evaluate the effects of zinc status.

RESULTS

Mice fed a ZnD did not activate the apoptotic and ER stress markers in the liver or pancreas. During the TM challenge, mice fed a ZnD showed greater C/EBP-homologous protein expression in the liver (3.8-fold, P < 0.01) than did ZnA-fed mice. TM-treated mice fed a ZnD also had greater terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling-positive cells in the liver (2.2-fold, P < 0.05), greater hepatic triglyceride accumulation (1.5-fold, P < 0.05), greater serum alanine aminotransferase activity (1.6-fold, P < 0.05), and greater protein-tyrosine phosphatase 1B activity (1.5-fold, P < 0.05), respectively, than did those fed a ZnA. No significant differences were observed in these parameters between mice fed ZnAs and ZnSs.

CONCLUSIONS

Consumption of a ZnD per se is not a critical factor for induction of ER stress in mice; however, once ER stress is triggered, adequate dietary zinc intake is required for suppressing apoptotic cell death and further insults in the liver of mice.

Design and synthesis of new potent PTP1B inhibitors with the skeleton of 2-substituted imino-3-substituted-5-heteroarylidene-1,3-thiazolidine-4-one: Part I

A new series of 2-substituted imino-3-substituted-5- heteroarylidene-1,3-thiazolidine-4-ones as the potent bidentate PTP1B inhibitors were designed and synthesized in this paper. All of the new compounds were characterized and identified by spectra analysis. The biological screening test against PTP1B showed that some of these compounds have the positive inhibitory activity against PTP1B. The activity of the compounds with 5-substituted pyrrole on 5-postion of 1,3-thiazolidine-4-one are more potent than that of those compounds with 5-substituted pyridine group. Compound 14b, 14h and 14i showed IC50 values of 8.66 μM, 6.83 μM and 6.09 μM against PTP1B, respectively. Docking analysis of these active compounds with PTP1B showed the possible interaction modes of these biheterocyclic compounds with the active sites of PTP1B. The inhibition tests against oncogenetic CDC25B were also conducted on this set of compounds to evaluate the selectivity and possible anti-neoplastic activity. Compound 14b also showed the lowest IC50 of 1.66 μM against CDC25B among all the possible inhibitors, including 14g, 14h, 14i and 15c. Some pharmacological parameters including VolSurf, steric and electric descriptors of all the compounds were calculated to give some hints about the relative relationship with the biological activity. The result of this study might give some light on designing the possible anti-cancer drugs targeting at phosphatases. The most active compound 14i might be used as the lead compound for further structure modification of the new low molecular weight PTP1B inhibitors with the N-containing heterocyclic skeleton.

Protein tyrosine phosphatase 1B targets PITX1/p120RasGAP thus showing therapeutic potential in colorectal carcinoma

Protein tyrosine phosphatase 1B (PTP1B) is known to promote the pathogenesis of diabetes and obesity by negatively regulating insulin and leptin pathways, but its role associated with colon carcinogenesis is still under debate. In this study, we demonstrated the oncogenic role of PTP1B in promoting colon carcinogenesis and predicting worse clinical outcomes in CRC patients. By co-immunoprecipitation, we showed that PITX1 was a novel substrate of PTP1B. Through direct dephosphorylation at Y160, Y175 and Y179, PTP1B destabilized PITX1, which resulted in downregulation of the PITX1/p120RasGAP axis. Interestingly, we found that regorafenib, the approved target agent for advanced CRC patients, exerted a novel property against PTP1B. By inhibiting PTP1B activity, regorafenib treatment augmented the stability of PITX1 protein and upregulated the expression of p120RasGAP in CRC. Importantly, we found that this PTP1B-dependant PITX1/p120RasGAP axis determines the in vitro anti-CRC effects of regorafenib. The above-mentioned effects of regorafenib were confirmed by the HT-29 xenograft tumor model. In conclusion, we demonstrated a novel oncogenic mechanism of PTP1B on affecting PITX1/p120RasGAP in CRC. Regorafenib inhibited CRC survival through reserving PTP1B-dependant PITX1/p120RasGAP downregulation. PTP1B may be a potential biomarker predicting regorafenib effectiveness, and a potential solution for CRC.

Orchestrating cellular signaling pathways-the cellular "conductor" protein tyrosine phosphatase interacting protein 51 (PTPIP51)

The protein tyrosine phosphatase interacting protein 51 (PTPIP51) is thought to regulate crucial cellular functions such as mitosis, apoptosis, migration, differentiation and communication between organelles as a scaffold protein. These diverse functions are modulated by the tyrosine/serine phosphorylation status of PTPIP51. This review interconnects the insights obtained about the action of PTPIP51 in mitogen-activated protein kinase signaling, nuclear factor kB signaling, calcium homeostasis and chromosomal segregation and identifies important signaling hubs. The interference of PTPIP51 in such multiprotein complexes and their PTPIP51-modulated cross-talk makes PTPIP51 an ideal target for novel drugs such as the small molecule LDC-3. Graphical Abstract ᅟ.

Sesquiterpene Hydroquinones with Protein Tyrosine Phosphatase 1B Inhibitory Activities from a Dysidea sp. Marine Sponge Collected in Okinawa

Three new sesquiterpene hydroquinones, avapyran (1), 17-O-acetylavarol (2), and 17-O-acetylneoavarol (3), were isolated from a Dysidea sp. marine sponge collected in Okinawa together with five known congeners: avarol (4), neoavarol (5), 20-O-acetylavarol (6), 20-O-acetylneoavarol (7), and 3'-aminoavarone (8). The structures of 1-3 were assigned on the basis of their spectroscopic data. Compounds 1-3 inhibited the activity of protein tyrosine phosphatase 1B with IC50 values of 11, 9.5, and 6.5 μM, respectively, while known compounds 4-8 gave IC50 values of 12, >32, 10, 8.6, and 18 μM, respectively. In a preliminary investigation on structure-activity relationships, six ester and methoxy derivatives (9-14) were prepared from 4 and 5.

P21-activated kinase 2 (PAK2) regulates glucose uptake and insulin sensitivity in neuronal cells

P21-activated kinases (PAKs) are recently reported as important players of insulin signaling and glucose homeostasis in tissues like muscle, pancreas and liver. However, their role in neuronal insulin signaling is still unknown. Present study reports the involvement of PAK2 in neuronal insulin signaling, glucose uptake and insulin resistance. Irrespective of insulin sensitivity, insulin stimulation decreased PAK2 activity. PAK2 downregulation displayed marked enhancement of GLUT4 translocation with increase in glucose uptake whereas PAK2 over-expression showed its reduction. Treatment with Akti-1/2 and wortmannin suggested that Akt and PI3K are mediators of insulin effect on PAK2 and glucose uptake. Rac1 inhibition demonstrated decreased PAK2 activity while inhibition of PP2A resulted in increased PAK2 activity, with corresponding changes in glucose uptake. Taken together, present study demonstrates an inhibitory role of insulin signaling (via PI3K-Akt) and PP2A on PAK2 activity and establishes PAK2 as a Rac1-dependent negative regulator of neuronal glucose uptake and insulin sensitivity.

Identification and evaluation of magnolol and chrysophanol as the principle protein tyrosine phosphatase-1B inhibitory compounds in a Kampo medicine, Masiningan

ETHNOPHARMACOLOGICAL RELEVANCE

Masiningan is a traditional medicine consisting of six crude drugs that have been used for treating constipation and diabetes mellitus in both Japan and China. Masiningan has been reported to have significant PTP1B inhibitory activity and to affect cells in the insulin-signaling pathway. The aim of the present study is to identify the PTP1B inhibitory compounds in Masiningan.

MATERIALS AND METHODS

Bioactivity peaks were identified by analytical HPLC profiling and PTP1B inhibitory activity profiling of sub-fractions from Masiningan extract. The bioactive compounds were isolated by tracking two identified bioactive peaks, and the chemical structures were determined by spectroscopic analyses. The bioactive compounds were further investigated for their inhibitory effect against PTP1B by enzymatic kinetic analysis, molecular docking simulation, inhibitory selectivity against other PTPs, and cellular activity in the insulin signal transduction pathway.

RESULTS

From Masiningan, magnolol (1) and chrysophanol (2) were isolated as compounds that exhibited significant dose-dependent inhibitory activities against PTP1B, with IC50 values of 24.6 and 12.3μM, respectively. Kinetic analysis revealed that 1 is a non-competitive and that 2 is a competitive PTP1B inhibitor. In the molecular docking simulation, compound 2 was stably positioned in the active pocket of PTP1B, and the CDOCKER energy was calculated to be 24.3411kcal/mol. Both compounds demonstrated remarkably high selectivity against four PTPs and revealed cellular activity against the insulin signal transduction pathway.

CONCLUSIONS

Magnolol (1) and chrysophanol (2) were identified as the principle PTP1B inhibitory active compounds in Masiningan, and their actions were investigated in detail. These findings demonstrated the effectiveness of Masiningan on diabetes mellitus through the inhibition of PTP1B at a molecular level as well as the potential of magnolol (1) and chrysophanol (2) as lead compounds in future anti-diabetes drug development.

A novel role for protein tyrosine phosphatase 1B as a positive regulator of neuroinflammation

BACKGROUND

Protein tyrosine phosphatase 1B (PTP1B) is a member of the non-transmembrane phosphotyrosine phosphatase family. Recently, PTP1B has been proposed to be a novel target of anti-cancer and anti-diabetic drugs. However, the role of PTP1B in the central nervous system is not clearly understood. Therefore, in this study, we sought to define PTP1B's role in brain inflammation.

METHODS

PTP1B messenger RNA (mRNA) and protein expression levels were examined in mouse brain and microglial cells after LPS treatment using RT-PCR and western blotting. Pharmacological inhibitors of PTP1B, NF-κB, and Src kinase were used to analyze these signal transduction pathways in microglia. A Griess reaction protocol was used to determine nitric oxide (NO) concentrations in primary microglia cultures and microglial cell lines. Proinflammatory cytokine production was measured by RT-PCR. Western blotting was used to assess Src phosphorylation levels. Immunostaining for Iba-1 was used to determine microglial activation in the mouse brain.

RESULTS

PTP1B expression levels were significantly increased in the brain 24 h after LPS injection, suggesting a functional role for PTP1B in brain inflammation. Microglial cells overexpressing PTP1B exhibited an enhanced production of NO and gene expression levels of TNF-α, iNOS, and IL-6 following LPS exposure, suggesting that PTP1B potentiates the microglial proinflammatory response. To confirm the role of PTP1B in neuroinflammation, we employed a highly potent and selective inhibitor of PTP1B (PTP1Bi). In LPS- or TNF-α-stimulated microglial cells, in vitro blockade of PTP1B activity using PTP1Bi markedly attenuated NO production. PTP1Bi also suppressed the expression levels of iNOS, COX-2, TNF-α, and IL-1β. PTP1B activated Src by dephosphorylating the Src protein at a negative regulatory site. PTP1B-mediated Src activation led to an enhanced proinflammatory response in the microglial cells. An intracerebroventricular injection of PTP1Bi significantly attenuated microglial activation in the hippocampus and cortex of LPS-injected mice compared to vehicle-injected mice. The gene expression levels of proinflammatory cytokines were also significantly suppressed in the brain by a PTP1Bi injection. Together, these data suggest that PTP1Bi has an anti-inflammatory effect in a mouse model of neuroinflammation.

CONCLUSIONS

This study demonstrates that PTP1B is an important positive regulator of neuroinflammation and is a promising therapeutic target for neuroinflammatory and neurodegenerative diseases.

The Tyrosine Kinome Dictates Breast Cancer Heterogeneity and Therapeutic Responsiveness

Phospho-tyrosine signaling networks control numerous biological processes including cellular differentiation, cell growth and survival, motility, and invasion. Aberrant regulation of the tyrosine kinome is a hallmark of malignancy and influences all stages of breast cancer progression, from initiation to the development of metastatic disease. The success of specific tyrosine kinase inhibitors strongly validates the clinical relevance of tyrosine phosphorylation networks in breast cancer pathology. However, a significant degree of redundancy exists within the tyrosine kinome. Numerous receptor and cytoplasmic tyrosine kinases converge on a core set of signaling regulators, including adaptor proteins and tyrosine phosphatases, to amplify pro-tumorigenic signal transduction pathways. Mutational activation, amplification, or overexpression of one or more components of the tyrosine kinome represents key contributing events responsible for the tumor heterogeneity that is observed in breast cancers. It is this molecular heterogeneity that has become the most significant barrier to durable clinical responses due to the development of therapeutic resistance. This review focuses on recent literature that supports a prominent role for specific components of the tyrosine kinome in the emergence of unique breast cancer subtypes and in shaping breast cancer plasticity, sensitivity to targeted therapies, and the eventual emergence of acquired resistance. J. Cell. Biochem. 117: 1971-1990, 2016. © 2016 Wiley Periodicals, Inc.

PTP1B inhibitor promotes endothelial cell motility by activating the DOCK180/Rac1 pathway

Promoting endothelial cell (EC) migration is important not only for therapeutic angiogenesis, but also for accelerating re-endothelialization after vessel injury. Several recent studies have shown that inhibition of protein tyrosine phosphatase 1B (PTP1B) may promote EC migration and angiogenesis by enhancing the vascular endothelial growth factor receptor-2 (VEGFR2) signalling. In the present study, we demonstrated that PTP1B inhibitor could promote EC adhesion, spreading and migration, which were abolished by the inhibitor of Rac1 but not RhoA GTPase. PTP1B inhibitor significantly increased phosphorylation of p130Cas, and the interactions among p130Cas, Crk and DOCK180; whereas the phosphorylation levels of focal adhesion kinase, Src, paxillin, or Vav2 were unchanged. Gene silencing of DOCK180, but not Vav2, abrogated the effects of PTP1B inhibitor on EC motility. The effects of PTP1B inhibitor on EC motility and p130Cas/DOCK180 activation persisted in the presence of the VEGFR2 antagonist. In conclusion, we suggest that stimulation of the DOCK180 pathway represents an alternative mechanism of PTP1B inhibitor-stimulated EC motility, which does not require concomitant VEGFR2 activation as a prerequisite. Therefore, PTP1B inhibitor may be a useful therapeutic strategy for promoting EC migration in cardiovascular patients in which the VEGF/VEGFR functions are compromised.

Selective binding modes and allosteric inhibitory effects of lupane triterpenes on protein tyrosine phosphatase 1B

Protein Tyrosine Phosphatase 1B (PTP1B) has been recognized as a promising therapeutic target for treating obesity, diabetes, and certain cancers for over a decade. Previous drug design has focused on inhibitors targeting the active site of PTP1B. However, this has not been successful because the active site is positively charged and conserved among the protein tyrosine phosphatases. Therefore, it is important to develop PTP1B inhibitors with alternative inhibitory strategies. Using computational studies including molecular docking, molecular dynamics simulations, and binding free energy calculations, we found that lupane triterpenes selectively inhibited PTP1B by targeting its more hydrophobic and less conserved allosteric site. These findings were verified using two enzymatic assays. Furthermore, the cell culture studies showed that lupeol and betulinic acid inhibited the PTP1B activity stimulated by TNFα in neurons. Our study indicates that lupane triterpenes are selective PTP1B allosteric inhibitors with significant potential for treating those diseases with elevated PTP1B activity.

Glucose Uptake Activities of Bis (2, 3-Dibromo-4, 5-Dihydroxybenzyl) Ether, a Novel Marine Natural Product from Red Alga Odonthaliacorymbifera with Protein Tyrosine Phosphatase 1B Inhibition, In Vitro and In Vivo

BACKGROUND AND AIMS

Protein tyrosine phosphatase 1B (PTP1B) is a novel therapeutic target for type-2 diabetes, which negatively regulates the insulin signaling transduction. Bis (2, 3-dibromo-4, 5-dihydroxybenzyl) ether (BDDE), a novel bromophenol isolated from the Red Alga, is a novel PTP1B inhibitor. But the anti-diabetic effects are not clear. In the present study, we evaluated the in vitro and in vivo antidiabetic effects of BDDE.

METHODS

The insulin-resistant HepG2 cells were used to evaluate the in vitro antidiabetic effects of BDDE. MTT assay was used to determine the safety concentrations in HepG2 cells. Glucose assay kit was used to check glucose uptake after treated with BDDE. Western blotting assay was used to explore the potent mechanisms. The db/db mice were used to evaluate the in vivo antidiabetic effects of BDDE. Body weight, blood glucose, Glycated hemoglobin (HbA1c), lipid profile, and insulin level were checked at the respective time points. Gastrocnemii were dissected and used to analyze the PTP1B and insulin receptor β (IRβ) expression.

RESULTS

BDDE increased the insulin-resisted glucose uptake in HepG2 cells. BDDE also decreased the expression of PTP1B and activated the substrates and downstream signals in insulin signal pathway, such as IRβ, insulin receptor substrate-1/2 (IRS1/2), phosphoinositide 3-kinase (PI3K), and protein kinase B (PKB/Akt). In the db/db mice model, BDDE significantly decreased the blood glucose, HbA1c and triglyceride (TG) levels. BDDE also decreased the expression of PTP1B and activated the phosphorylation of IRβ in gastrocnemii. Moreover, BDDE at high doses downregulated the body weight without affecting food and water intake.

CONCLUSION

Our results suggest that BDDE as a new PTP1B inhibitor improves glucose metabolism by stimulating the insulin signaling and could be used in the treatment of type-2 diabetes mellitus.

Pathological Implications of Oxidative Stress in Patients and Animal Models with Schizophrenia: The Role of Epidermal Growth Factor Receptor Signaling

Proinflammatory cytokines perturb brain development and neurotransmission and are implicated in various psychiatric diseases, such as schizophrenia and depression. These cytokines often induce the production of reactive oxygen species (ROS) and regulate not only cell survival and proliferation but also inflammatory process and neurotransmission. Under physiological conditions, ROS are moderately produced in mitochondria but are rapidly scavenged by reducing agents in cells. However, brain injury, ischemia, infection, or seizure-like neural activities induce inflammatory cytokines and trigger the production of excessive amounts of ROS, leading to abnormal brain functions and psychiatric symptoms. Protein phosphatases, which are involved in the basal silencing of cytokine receptor activation, are the major targets of ROS. Consistent with this, several ROS scavengers, such as polyphenols and unsaturated fatty acids, attenuate both cytokine signaling and psychiatric abnormalities. In this review, we list the inducers, producers, targets, and scavengers of ROS in the brain and discuss the interaction between ROS and cytokine signaling implicated in schizophrenia and its animal models. In particular, we present an animal model of schizophrenia established by perinatal exposure to epidermal growth factor and illustrate the pathological role of ROS and antipsychotic actions of ROS scavengers, such as emodin and edaravone.

Phosphatases: Their Roles in Cancer and Their Chemical Modulators

Phosphatases are involved in basically all cellular processes by dephosphorylating cellular components such as proteins, phospholipids and second messengers. They counteract kinases of which many are established oncogenes, and therefore kinases are one of the most important drug targets for targeted cancer therapy. Due to this relationship between kinases and phosphatases, phosphatases are traditionally assumed to be tumour suppressors. However, research findings over the last years prove that this simplification is incorrect, as bona-fide and putative phosphatase oncogenes have been identified. We describe here the role of phosphatases in cancer, tumour suppressors and oncogenes, and their chemical modulators, and discuss new approaches and opportunities for phosphatases as drug targets.

Novel chromenedione derivatives displaying inhibition of protein tyrosine phosphatase 1B (PTP1B) from Flemingia philippinensis

Protein tyrosine phosphatase 1B (PTP1B) is an important target to treat obesity and diabetes due to its key roles in insulin and leptin signaling. The MeOH extracts of the root bark of Flemingia philippinensis yielded eight inhibitory molecules (1-8) capable of targeting PTP1B. Three of them were identified to be novel compounds, philippin A (1), philippin B (2), and philippin C (3) which have a rare 3-phenylpropanoyl chromenedione skeleton. The other compounds (4-8) were known prenylated isoflavones. All compounds (1-8) inhibited PTP1B in a dose dependent manner with IC50s ranging between 2.4 and 29.4μM. The most potent compound emerged to be prenylated isoflavone 5 (IC50=2.4μM). In kinetic studies, chromenedione derivatives (1-3) emerged to be reversible, competitive inhibitors, whereas prenylated isoflavones (5-8) were noncompetitive inhibitors.

Subcellular Partitioning of Protein Tyrosine Phosphatase 1B to the Endoplasmic Reticulum and Mitochondria Depends Sensitively on the Composition of Its Tail Anchor

The canonical protein tyrosine phosphatase PTP1B is an important regulator of diverse cellular signaling networks. PTP1B has long been thought to exert its influence solely from its perch on the endoplasmic reticulum (ER); however, an additional subpopulation of PTP1B has recently been detected in mitochondria extracted from rat brain tissue. Here, we show that PTP1B’s mitochondrial localization is general (observed across diverse mammalian cell lines) and sensitively dependent on the transmembrane domain length, C-terminal charge and hydropathy of its short (≤35 amino acid) tail anchor. Our electron microscopy of specific DAB precipitation revealed that PTP1B localizes via its tail anchor to the outer mitochondrial membrane (OMM), with fluorescence lifetime imaging microscopy establishing that this OMM pool contributes to the previously reported cytoplasmic interaction of PTP1B with endocytosed epidermal growth factor receptor. We additionally examined the mechanism of PTP1B’s insertion into the ER membrane through heterologous expression of PTP1B’s tail anchor in wild-type yeast and yeast mutants of major conserved ER insertion pathways: In none of these yeast strains was ER targeting significantly impeded, providing in vivo support for the hypothesis of spontaneous membrane insertion (as previously demonstrated in vitro). Further functional elucidation of the newly recognized mitochondrial pool of PTP1B will likely be important for understanding its complex roles in cellular responses to external stimuli, cell proliferation and diseased states.

Identification of Bidentate Salicylic Acid Inhibitors of PTP1B

PTP1B is a master regulator in the insulin and leptin metabolic pathways. Hyper-activated PTP1B results in insulin resistance and is viewed as a key factor in the onset of type II diabetes and obesity. Moreover, inhibition of PTP1B expression in cancer cells dramatically inhibits cell growth in vitro and in vivo. Herein, we report the computationally guided optimization of a salicylic acid-based PTP1B inhibitor 6, identifying new and more potent bidentate PTP1B inhibitors, such as 20h, which exhibited a > 4-fold improvement in activity. In CHO-IR cells, 20f, 20h, and 20j suppressed PTP1B activity and restored insulin receptor phosphorylation levels. Notably, 20f, which displayed a 5-fold selectivity for PTP1B over the closely related PTPσ protein, showed no inhibition of PTP-LAR, PRL2 A/S, MKPX, or papain. Finally, 20i and 20j displayed nanomolar inhibition of PTPσ, representing interesting lead compounds for further investigation.

Antihyperglycemic and antioxidant activities of twig extract from Cinnamomum osmophloeum

This is the first report concerning the α-glucosidase, α-amylase and protein tyrosine phosphatase 1B (PTP1B) inhibitory activities of cinnamon twig extracts. Comparing the antihyperglycemic activity of renewable plant parts, indigenous cinnamon (Cinnamomum osmophloeum; tǔ ròu guì) twig extracts (CoTE) showed better α-glucosidase and α-amylase activities than leaf, 2-cm branch and 5-cm branch extracts. Chemotype of C. osmophloeum has no influence on the antihyperglycemic activities and proanthocyanidin contents of CoTE. Among four soluble fractions obtained from CoTE by following bioactivity-guided fractionation procedure, the n-butanol soluble fraction (BSF) with abundant proanthocyanidins and condensed tannins, exhibited the best antihyperglycemic and PTP1B inhibitory activities. In addition, the BSF displayed the excellent DPPH free-radical scavenging and ferrous ion-chelating activities. The antihyperglycemic and antioxidant activities of all four soluble fractions from CoTE showed high correlation coefficient with their proanthocyanidin and condensed tannin contents. Furthermore, CoTE had no toxicity on 3T3-L1 preadiocytes. Results obtained demonstrated that CoTE has excellent antihyperglycemic, antioxidant and PTP1B inhibitory activities, and thus has great potential as a source for natural health products.

Inactivation of protein tyrosine phosphatases by dietary isothiocyanates

Isothiocyanates are bioactive dietary phytochemicals that react readily with protein thiol groups. We find that isothiocyanates are time-dependent inactivators of cysteine-dependent protein tyrosine phosphatases (PTPs). Rate constants for the inactivation of PTP1B and SHP-2 by allyl isothiocyanate and sulforaphane range from 2 to 16 M(-1)s(-1). Results in the context of PTP1B are consistent with a mechanism involving covalent, yet reversible, modification of the enzyme's active site cysteine residue.

Synthesis of novel 3-aryl-1-oxa-2,8-diazaspiro[4.5]dec-2-ene derivatives and their biological evaluation against protein tyrosine phosphatase 1B

A series of novel 3-aryl-1-oxa-2,8-diazaspiro[4.5]dec-2-ene derivatives were designed, synthesized, and evaluated as a new class of inhibitors against protein tyrosine phosphatase 1B. Among them, compound 6f displayed moderate inhibitory activity with IC50 of 2.87 ± 0.24 μm and can be used as a novel lead compound for the design of inhibitors of protein tyrosine phosphatase 1B.

Magnolia officinalis Extract Contains Potent Inhibitors against PTP1B and Attenuates Hyperglycemia in db/db Mice

Protein tyrosine phosphatase 1B (PTP1B) is an established therapeutic target for type 2 diabetes mellitus (T2DM) and obesity. The aim of this study was to investigate the inhibitory activity of Magnolia officinalis extract (ME) on PTP1B and its anti-T2DM effects. Inhibition assays and inhibition kinetics of ME were performed in vitro. 3T3-L1 adipocytes and C2C12 myotubes were stimulated with ME to explore its bioavailability in cell level. The in vivo studies were performed on db/db mice to probe its anti-T2DM effects. In the present study, ME inhibited PTP1B in a reversible competitive manner and displayed good selectivity against PTPs in vitro. Furthermore, ME enhanced tyrosine phosphorylation levels of cellular proteins, especially the insulin-induced tyrosine phosphorylations of insulin receptor β-subunit (IRβ) and ERK1/2 in a dose-dependent manner in stimulated 3T3-L1 adipocytes and C2C12 myotubes. Meanwhile, ME enhanced insulin-stimulated GLUT4 translocation. More importantly, there was a significant decrease in fasting plasma glucose level of db/db diabetic mice treated orally with 0.5 g/kg ME for 4 weeks. These findings indicated that improvement of insulin sensitivity and hypoglycemic effects of ME may be attributed to the inhibition of PTP1B. Thereby, we pioneered the inhibitory potential of ME targeted on PTP1B as anti-T2DM drug discovery.

Light-switched inhibitors of protein tyrosine phosphatase PTP1B based on phosphonocarbonyl phenylalanine as photoactive phosphotyrosine mimetic

Phosphopeptide mimetics containing the 4-phosphonocarbonyl phenylalanine (pcF) as a photo-active phosphotyrosine isoster are developed as potent, light-switchable inhibitors of the protein tyrosine phosphatase PTP1B. The photo-active inhibitors 6-10 are derived from phosphopeptide substrates and are prepared from the suitably protected pcF building block 12 by Fmoc-based solid phase peptide synthesis. All pcF-containing peptides are moderate inhibitors of PTP1B with KI values between 10 and 50μM. Irradiation of the inhibitors at 365nm in the presence of the protein PTP1B amplify the inhibitory activity of pcF-peptides up to 120-fold, switching the KI values of the best inhibitors to the sub-micromolar range. Photo-activation of the inhibitors results in the formation of triplet intermediates of the benzoylphosphonate moiety, which deactivate PTP1B following an oxidative radical mechanism. Deactivation of PTP1B proceeds without covalent crosslinking of the protein target with the photo-switched inhibitors and can be reverted by subsequent addition of reducing agent dithiothreitol (DTT).

Canthinone alkaloids are novel protein tyrosine phosphatase 1B inhibitors

Considerable attention has been paid to protein tyrosine phosphatase 1B (PTP1B) inhibitors as a potential therapy for diabetes. Screening of a natural compound library resulted in six canthinone alkaloids, namely, picrasidine L (1), 3,4-dimethyl-canthin-5,6-dione (2), 4-ethyl-3-methyl-canthin-5,6-dione (3), eurycomine E (4), 5-methoxy-canthin-6-one (5), and 5-acethoxy-canthin-6-one (6), as novel PTP1B inhibitors. Among these, 1 is the competitive PTP1B inhibitor with the best inhibitory selectivity between PTP1B and other PTPs and was shown to promote activity in the insulin signaling pathway in cell-based assays. Molecular docking simulations and structure-activity relationship analysis of 1 will add to its potential as a lead compound in future anti-insulin-resistant drug developments.

Protein topology determines cysteine oxidation fate: the case of sulfenyl amide formation among protein families

Cysteine residues have a rich chemistry and play a critical role in the catalytic activity of a plethora of enzymes. However, cysteines are susceptible to oxidation by Reactive Oxygen and Nitrogen Species, leading to a loss of their catalytic function. Therefore, cysteine oxidation is emerging as a relevant physiological regulatory mechanism. Formation of a cyclic sulfenyl amide residue at the active site of redox-regulated proteins has been proposed as a protection mechanism against irreversible oxidation as the sulfenyl amide intermediate has been identified in several proteins. However, how and why only some specific cysteine residues in particular proteins react to form this intermediate is still unknown. In the present work using in-silico based tools, we have identified a constrained conformation that accelerates sulfenyl amide formation. By means of combined MD and QM/MM calculation we show that this conformation positions the NH backbone towards the sulfenic acid and promotes the reaction to yield the sulfenyl amide intermediate, in one step with the concomitant release of a water molecule. Moreover, in a large subset of the proteins we found a conserved beta sheet-loop-helix motif, which is present across different protein folds, that is key for sulfenyl amide production as it promotes the previous formation of sulfenic acid. For catalytic activity, in several cases, proteins need the Cysteine to be in the cysteinate form, i.e. a low pK_a Cys. We found that the conserved motif stabilizes the cysteinate by hydrogen bonding to several NH backbone moieties. As cysteinate is also more reactive toward ROS we propose that the sheet-loop-helix motif and the constraint conformation have been selected by evolution for proteins that need a reactive Cys protected from irreversible oxidation. Our results also highlight how fold conservation can be correlated to redox chemistry regulation of protein function.

Cysteine oxidation is emerging as a relevant regulatory mechanism of enzymatic function in the cell. Many proteins are protected from over oxidation by reactive oxygen species by the formation of a cyclic sulfenyl amide. Understanding how cyclic sulfenyl amide is formed and its dependence on protein structure is not only a basic question but necessary to predict which proteins may auto protect from over oxidation We describe a structural motif, which includes cysteine residues with a constrained conformation in a “forbidden” region of the Ramachandran plot plus a Beta-Cys-loop-helix motif, which has a reactive low pK_a Cysteine and also enables to form the cyclic sulfenyl amide with a low activation barrier. Our QM/MM computations show that the cyclization reaction only occurs if the “forbidden” conformation is acquired by the Cysteine residue. This structural motif was identified at least in 7 PFAM families and 145 proteins with solved structure, showing that a large number of proteins could have the ability to go through such cyclic product preventing irreversible oxidation.

Effects of hepatic protein tyrosine phosphatase 1B and methionine restriction on hepatic and whole-body glucose and lipid metabolism in mice

AIMS

Methionine restriction (MR) and hepatic protein tyrosine phosphatase 1B (PTP1B) knockdown both improve hepatic insulin sensitivity by targeting different proteins within the insulin signaling pathway, as well as diminishing hepatic triglyceride content through decreasing hepatic lipogenesis. We hypothesized that a combined approach of hepatic PTP1B inhibition and methionine restriction could lead to a synergistic effect on improvements in glucose homeostasis and lipid metabolism.

METHODS

Male and female hepatic PTP1B knockout (Alb-Ptp1b(-/-)) and control wild-type (Ptp1b(fl/fl)) mice were maintained on control diet (0.86% methionine) or MR diet (0.172% methionine) for 8weeks. Body weight and food intake were recorded and physiological tests for whole-body glucose homeostasis were performed. Serum and tissues were analyzed biochemically.

RESULTS

MR decreased body weight and increased food intake in Ptp1b(fl/fl) mice as expected, without changing PTP1B protein expression levels or activity. In females, MR treatment alone improved glucose tolerance in Ptp1b(fl/fl) mice, which was further amplified with hepatic PTP1B deficiency. However, other markers of glucose homeostasis were similar between MR-fed groups. In males, MR improved glucose homeostasis in both, Alb-Ptp1b(-/-) and wild-type Ptp1b(fl/fl) mice to a similar extent. Hepatic PTP1B inhibition in combination with MR could not further enhance insulin-stimulated hepatic protein kinase B/Akt phosphorylation compared to MR treatment alone and therefore led to no further increase in hepatic insulin signaling. The combined treatment did not further improve lipid metabolism relative to MR diet alone.

CONCLUSIONS

Methionine restriction improves glucose and lipid homeostasis; however, adding hepatic PTP1B inhibition to MR is unlikely to yield any additional protective effects.

UBC9-dependent association between calnexin and protein tyrosine phosphatase 1B (PTP1B) at the endoplasmic reticulum

Calnexin is a type I integral endoplasmic reticulum (ER) membrane protein, molecular chaperone, and a component of the translocon. We discovered a novel interaction between the calnexin cytoplasmic domain and UBC9, a SUMOylation E2 ligase, which modified the calnexin cytoplasmic domain by the addition of SUMO. We demonstrated that calnexin interaction with the SUMOylation machinery modulates an interaction with protein tyrosine phosphatase 1B (PTP1B), an ER-associated protein tyrosine phosphatase involved in the negative regulation of insulin and leptin signaling. We showed that calnexin and PTP1B form UBC9-dependent complexes, revealing a previously unrecognized contribution of calnexin to the retention of PTP1B at the ER membrane. This work shows that the SUMOylation machinery links two ER proteins from divergent pathways to potentially affect cellular protein quality control and energy metabolism.

Voltage sensitive phosphatases: emerging kinship to protein tyrosine phosphatases from structure-function research

The transmembrane protein Ci-VSP from the ascidian Ciona intestinalis was described as first member of a fascinating family of enzymes, the voltage sensitive phosphatases (VSPs). Ci-VSP and its voltage-activated homologs from other species are stimulated by positive membrane potentials and dephosphorylate the head groups of negatively charged phosphoinositide phosphates (PIPs). In doing so, VSPs act as control centers at the cytosolic membrane surface, because they intervene in signaling cascades that are mediated by PIP lipids. The characteristic motif CX₅RT/S in the active site classifies VSPs as members of the huge family of cysteine-based protein tyrosine phosphatases (PTPs). Although PTPs have already been well-characterized regarding both, structure and function, their relationship to VSPs has drawn only limited attention so far. Therefore, the intention of this review is to give a short overview about the extensive knowledge about PTPs in relation to the facts known about VSPs. Here, we concentrate on the structural features of the catalytic domain which are similar between both classes of phosphatases and their consequences for the enzymatic function. By discussing results obtained from crystal structures, molecular dynamics simulations, and mutagenesis studies, a possible mechanism for the catalytic cycle of VSPs is presented based on that one proposed for PTPs. In this way, we want to link the knowledge about the catalytic activity of VSPs and PTPs.