The role of intracellular oxidative stress in the mechanism of action of phosphotyrosine phosphatase (PTP) inhibitors was studied using three vanadiumbased compounds. Sodium orthovanadate (Na 3 VO 4 ), sodium oxodiperoxo(1,10-phenanthroline)vanadate(V) (pV(phen), and bis(maltolato)-oxovanadium(IV) (BMOV) differentially induced oxidative stress in lymphocytes. Treatment with pV(phen), which caused intracellular oxidation, induced strong protein tyrosine phosphorylation compared with Na 3 VO 4 and BMOV. Syk family kinases and the mitogen-activated protein kinase erk2 were rapidly activated by pV(phen) but not by BMOV or Na 3 VO 4 . In contrast, both BMOV and pV(phen) strongly activated NF-B. The antioxidant pyrrolidine dithiocarbamate (PDTC) greatly diminished the intracellular oxidation and protein phosphotyrosine accumulation induced by pV(phen). Pretreatment of cells with PDTC reduced and delayed the activation of Syk kinases and erk2. However, NF-B activation by pV(phen) was markedly enhanced in lymphocytes pretreated with PDTC, and another antioxidant, N-acetylcysteine, did not prevent the activation of NF-B by BMOV. These results indicate a role for oxidative stress in the biological effects of some PTP inhibitors, whereas NF-B activation by PTP inhibitors is mediated by mechanisms independent of intracellular redox status.Lymphocyte signal transduction requires the activation of protein tyrosine kinases (PTKs), 1 with subsequent assembly of signaling complexes, generation of second messengers, activation of transcription factors, and gene expression (1, 2). The balance of protein tyrosine phosphorylation within the cell is controlled by the relative activities of the PTKs and PTPs in the signaling network (3). Besides dephosphorylating a variety of PTK substrates, PTPs have been shown to directly modulate the activities of PTKs (4, 5). Thus PTPs serve a crucial function in lymphocytes by controlling both the initiation and termination of receptor-based signals.The inhibition of PTPs reveals PTK substrates on which phosphotyrosine accumulates in the absence of receptor engagement (6). Some of these substrates are key phosphoproteins in lymphocyte signal transduction pathways, suggesting that PTKs involved in transmission of receptor signals are activated by the absence of PTP regulation (6 -9). However, many of the PTP inhibitors used thus far to explore lymphocyte signal transduction pathways are redox-active compounds. For example, phenylarsine oxide, a thiol-reactive compound, and H 2 O 2 , which generates hydroxyl radicals, both act as potent PTP inhibitors (6, 10). The role of intracellular oxidation in the mechanism of action of PTP inhibitors is unknown, a question this study addresses.Vanadium-based PTP inhibitors, which have been extensively studied as insulin mimetic agents, stimulate glucose uptake and fatty acid synthesis in adipocytes and mimic receptor-based signals in lymphocytes (11-15). The widely used PTP inhibitor pervanadate is a peroxovanadium compound generated by reaction of H 2 O 2 wi...

This study assessed the effects of selective inhibitors of 3 ,5 -cyclic nucleotide phosphodiesterases (PDEs) on adipocyte lipolysis. IC224, a selective inhibitor of type 1 phosphodiesterase (PDE1), suppressed lipolysis in murine 3T3-L1 adipocytes (69.6 ؎ 5.4% of vehicle control) but had no effect in human adipocytes. IC933, a selective inhibitor of PDE2, had no effect on lipolysis in either cultured murine 3T3-L1 adipocytes or human adipocytes. Inhibition of PDE3 with cilostamide moderately stimulated lipolysis in murine 3T3-L1 and rat adipocytes (397 ؎ 25% and 235 ؎ 26% of control, respectively) and markedly stimulated lipolysis in human adipocytes (932 ؎ 7.6% of control). Inhibition of PDE4 with rolipram moderately stimulated lipolysis in murine 3T3-L1 adipocytes (291 ؎ 13% of control) and weakly stimulated lipolysis in rat adipocytes (149 ؎ 7.0% of control) but had no effect on lipolysis in human adipocytes. Cultured adipocytes also responded differently to a combination of PDE3 and PDE4 inhibitors. Simultaneous exposure to cilostamide and rolipram had a synergistic effect on lipolysis in murine 3T3-L1 and rat adipocytes but not in human adipocytes. Hence, the relative importance of PDE3 and PDE4 in regulating lipolysis differed in cultured murine, rat, and human adipocytes. Adipose tissue functions as an energy storage organ in which excess calories are sequestered in the form of triglyceride (TG). TG contained in circulating chylomicrons and VLDL particles is hydrolyzed by extracellular lipoprotein lipase to yield glycerol and FFA. FFA is then taken up by adipocytes, converted to fatty acyl-CoA, and reesterified with glycerol-3-phosphate to form intracellular TG. The size of adipose TG stores is dynamically regulated by endocrine signals in response to energy intake and metabolic demands. Thus, anabolic hormones, such as insulin, stimulate adipocyte TG synthesis (lipogenesis), whereas catabolic hormones, such as epinephrine, glucagon, and corticotropin, stimulate hydrolysis of adipocyte TG to glycerol and FFA (lipolysis).Cyclic AMP is an important second messenger in the signaling pathways that mobilize fat stores (1). Catecholamines (epinephrine and norepinephrine) stimulate adipocyte lipolysis by binding to ␤ -adrenoceptors, which activate adenylyl cyclase (AC) via the stimulatory guanine nucleotide binding protein (G s ), leading to an increase in intracellular cAMP and activation of cAMP-dependent protein kinase (PKA). Initially, cAMP-mediated stimulation of lipolysis was thought to be attributable exclusively to PKA-dependent phosphorylation and activation of hormone-sensitive lipase (HSL), the primary neutral lipase in adipose tissue (2). However, adipocytes from HSL knockout mice retain considerable TG lipase activity, and lipolysis in these cells is partially responsive to the ␤ -adrenoceptor agonist isoproterenol (ISO), suggesting that other lipases besides HSL play a role in lipolysis (3-5). Another layer of regulation of lipolysis is revealed by the observation that lipolytic stimuli cau...

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CD19 is a B cell surface protein capable of forming non-covalent molecular complexes with a number of other B cell surface proteins including the CD21/CD81/Leu-13 complex as well as with surface immunoglobulin. CD19 tyrosine phosphorylation increases after B cell activation, and is proposed to play a role in signal transduction through its cytoplasmic domain, which contains nine tyrosine residues. Several second messenger proteins have been shown to immunoprecipitate with CD19, including p59 Fyn (Fyn), p59 Lyn (Lyn) and phosphatidylinositol-3 kinase (PI-3 kinase). These associations are predicted to occur via the src-homology 2 (SH2) domains of the second messenger proteins. Two of the cytoplasmic tyrosines in the CD19 cytoplasmic region contain the consensus binding sequence for the PI-3 kinase SH2 domain (YPO4-X-X-M). However, the reported consensus binding sequence for the Fyn and Lyn SH2 domains (YPO4-X-X-I/L) is not found in CD19. We investigated the capacity of CD19 cytoplasmic tyrosines to bind both Fyn and PI-3 kinase SH2-domain fusion proteins. In activated B cells, both Fyn and PI-3 kinase SH2-domain fusion proteins precipitate CD19. Using synthetic tyrosine-phosphorylated peptides comprising each of the CD19 cytoplasmic tyrosines and surrounding amino acids, we investigated the ability of the Fyn SH2 and PI-3 kinase SH2 fusion proteins to bind to the different CD19 cytoplasmic phosphotyrosine peptides. ELISA revealed that the two CD19 cytoplasmic tyrosine residues contained within the Y-X-X-M sequences (Y484 and Y515) bound preferentially to the PI-3 kinase SH2-domain fusion proteins. Two different tyrosines (Y405 and Y445) bound preferentially to the Fyn SH2-domain fusion protein via a novel sequence, Y-E-N-D/E, different from that previously reported for the Fyn SH2 domain. In precipitation studies, peptide Y484 was able to compete with tyrosine phosphorylated CD19 specifically for binding to the PI-3 kinase SH2 domain fusion proteins, while peptides Y405 and Y445 were able to compete specifically for binding to the Fyn SH2 domain fusion proteins. These results indicate that CD19 may be capable of binding both Fyn and PI-3 kinase concurrently, suggesting a mechanism for CD19 signal transduction, in which binding of PI-3 kinase to the Fyn SH3 domain results in activation of PI-3 kinase.

A human immunoglobulin G1 (IgG1) antibody oligomer was isolated from a transfected myeloma cell line that produced a monoclonal antibody to group B streptococci. Compared to the IgG1 monomer, the oligomer was significantly more effective at protecting neonatal rats from infection in vivo. The oligomer was also shown to cross the placenta and to be stable in neonatal rats. Immunochemical analysis and complementary DNA sequencing showed that the transfected cell line produced two distinct kappa light chains: a normal light chain (Ln) with a molecular mass of 25 kilodaltons and a 37-kilodalton species (L37), the domain composition of which was variable-variable-constant (V-V-C). Cotransfection of vectors encoding the heavy chain and L37 resulted in production of oligomeric IgG.

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Deoxyspergualin (DSG) is a potent immunosuppressive agent that is currently undergoing clinical trials for treatment of transplant rejection, preventive of human anti-mouse Ab response, and blocking autoimmune disease progression. The mechanism of action of DSG appears to be novel, with in vivo activity attributable to the suppression of both humoral and cell-mediated immunity. In this study we investigated the effect of DSG on the induction of lg expression in the 70Z/3 murine pre-B cell line. Treatment of 70Z/3 cells with DSG for 24, 48, or 72 h before LPS or IFN-gamma induction resulted in a time-dependent inhibition of surface lgM expression, with greater than 80% inhibition observed after 72 h of pretreatment. Inhibition of surface expression was specific for lgM, as neither MHC class I nor CD45 (B220) surface expression was affected by DSG pretreatment. Cyclosporin A was ineffective at suppressing surface igM induction. DSG pretreatment results in a 10-fold reduction in LPS- or IFN-gamma-induced kappa L chain protein and mRNA expression. No change was observed in either mu or beta-actin mRNA levels. Analysis of nuclear and cytoplasmic NF-kappa B expression using electrophoretic mobility shift analysis and Western analysis, revealed that DSG blocked LPS-induced NF-kappa B nuclear translocation, but had no effect on cytoplasmic NF-kappa B levels. We conclude that DSG may act to suppress humoral immune responses by blocking the transcriptional activation of kappa L chain expression during certain stages of B cell development.

Human IgG1 mAb dimers specific for either group B streptococci or Escherichia coli K1 bacteria were formed using chemical cross-linkers. The effect of antibody valency on biologic efficacy was investigated by comparing the IgG dimers against the corresponding IgG monomers. Binding activity and relative avidity were assessed using Ag binding and competition ELISA, and functional activity was analyzed using opsonophagocytic assays. These in vitro assays revealed that the dimers were greater than or equal to 50-fold more active than the monomers. A neonatal rat infection model showed the in vivo protective efficacy of the dimers was greater than or equal to 20-fold greater than that of the monomers. Enhancing the activity of mAb by chemical cross-linking may be a useful strategy for salvaging low affinity IgG mAb that possess poor functional properties.