Sphingomyelinase treatment of low density lipoprotein and cultured cells results in enhanced processing of LDL which can be modulated by sphingomyelin.

The addition of neutral sphingomyelinase from S. aureus to the medium of rat intestinal epithelial cell cultures (IEC-6) containing added human low density lipoprotein (LDL) resulted in two- to fivefold increases in LDL uptake and degradation. This overall effect was shown to be the combined result of sphingomyelinase activity on the composition of the LDL particle and a separate action directly on the cells when native LDL was incubated with sphingomyelinase from S. aureus followed by removal of the sphingomyelinase. Analysis of sphingomyelinase-treated LDL showed that > 95% of the sphingomyelin (SM) was hydrolyzed, but no changes were observed in all the other components of the LDL particle. This modified LDL particle (SM(-)LDL) was also bound and degraded at higher rates than control LDL in a variety of cell lines, e.g., HepG2, GM-43, and CHO-K1 cells. No evidence of increased aggregation of SM(-)LDL could be observed. The increased processing of SM(-)LDL was due to enhanced affinity to LDL receptors and not to an increase in LDL receptor number. When sphingomyelinase from S. aureus was added to the medium of IEC-6 or GM-43 cells, which were processing SM(-)LDL, further increases in SM(-)LDL processing were observed, which were primarily due to greatly enhanced cellular degradation of SM(-)LDL, with little change in receptor binding and cell association. Since there was little sphingomyelin remaining in SM(-)LDL, it was assumed that the action of sphingomyelinase on the cells resulted in the enhanced degradation. In support of this concept, previous addition of sphingomyelin to cells growing in lipoprotein-deficient medium followed by addition of SM(-)LDL greatly inhibited the degradation of the apolipoprotein of SM(-)LDL. On the other hand, addition of sphingomyelin concomitantly with SM(-)LDL did not inhibit degradation. These results are interpreted to indicate that there may be two pathways for cellular processing of sphingomyelin, one of which may be a determinant in the lysosomal processing of the apolipoprotein of LDL. In support of this concept, addition of desipramine, an inhibitor of lysosomal sphingomyelinase, to IEC-6 cells in culture greatly inhibited the degradation of 125I-labeled LDL without affecting the receptor binding and cell association. Overall, these results suggest that sphingomyelin may play a modulatory role in cellular cholesterol homeostasis by regulating uptake of LDL as well as LDL processing.     

Alpha-actinin synthesis can be modulated by antisense probes and is autoregulated in non-muscle cells.

We used a 279 bp cDNA probe derived from a Dictyostelium alpha-actinin genomic sequence to assay the degree of homology between alpha-actinin from slime molds, mammalian and chicken cells. Recognition of this probe by vertebrate cells was shown in Southern and Northern blots, and by antisense RNA-induced depression of endogenous alpha-actinin synthesis in living cells. Micro-injection of Dictyostelium or chicken gizzard alpha-actinin resulted in incorporation of these proteins in stress fibers, peripheral microfilament belts and adhesion sites. Alpha-actinin-injected cells showed a marked, transient reduction of synthesis of the corresponding endogenous protein. These data emphasize the high degree of conservation of alpha-actinin during evolution and show for the first time autoregulation of synthesis for a microfilament protein.     

Alternagin-C, a nonRGD-disintegrin, induces neutrophil migration via integrin signaling.

Recently, a new protein containing a disintegrin domain, alternagin-C (Alt-C), was purified from Bothrops alternatus venom. Unlike other disintegrins, in Alt-C an ECD amino acid mogif takes the place of the RGD sequence. Most disintegrins contain an RGD/KGD sequence and are very potent inhibitors of platelet aggregation, as well as other cell interactions with the extracellular matrix, including tumor cell metastasis and angiogenesis. The present study investigated the effects of Alt-C on human neutrophil chemotaxis in vitro and the activation of integrin-mediated pathways. Alt-C showed a potent chemotactic effect for human neutrophils when compared to N-formyl-methionyl-leucyl-phenylalanine peptide (fMLP), a classic chemotactic agent. Moreover, preincubation of neutrophils with Alt-C significantly inhibited chemotaxis toward fMLP and itself. In addition, a peptide containing an ECD sequence presented a chemotactic activity and significantly inhibited chemotaxis induced by Alt-C and fMLP. A significant increase of F-actin content was observed in cells treated with Alt-C, showing that the chemotactic activity of Alt-C on neutrophils is driven by actin cytoskeleton dynamic changes. Furthermore, this protein was able to induce an increase of phosphotyrosine content triggering focal adhesion kinase activation and its association with phosphatidylinositol 3-kinase. Alt-C was also able to induce a significant increase in extracellular signal-regulated kinase 2 nuclear translocation. The chemotactic activity of Alt-C was partially inhibited by LY294002, a specific phosphatidylinositol 3-kinase inhibitor, and by PD98056, a Map kinase kinase inhibitor. These findings suggest that Alt-C can trigger human neutrophil chemotaxis modulated by intracellular signals characteristic of integrin-activated pathways and that these effects could be related to the ECD mogif present in disintegrin-like domain.     

Conjugative transfer can be inhibited by blocking relaxase activity within recipient cells with intrabodies

Horizontal transfer of antibiotic resistance genes carried by conjugative plasmids poses a serious health problem. As conjugative relaxases are transported to recipient cells during bacterial conjugation, we investigated whether blocking relaxase activity in the recipient cell might inhibit conjugation. For that purpose, we used an intrabody approach generating a single-chain Fv antibody library against the relaxase TrwC of conjugative plasmid R388. Recombinant single-chain Fv antibodies were engineered for cytoplasmic expression in Escherichia coli cells and either selected in vitro for their specific binding to TrwC, or in vivo by their ability to interfere with conjugation using a high-throughput mating assay. Several intrabody clones were identified showing specific inhibition against R388 conjugation upon cytoplasmic expression in the recipient cell. The epitope recognized by one of these intrabodies was mapped to a region of TrwC containing Tyr-26 and involved in the conjugative DNA-processing termination reaction. These findings demonstrate that the transferred relaxase plays an important role in the recipient cell and open a new approach to identify specific inhibitors of bacterial conjugation.     

F-actin capping by cap32/34 requires heterodimeric conformation and can be inhibited with PIP2.

The heterodimeric F-actin capping protein cap32/34 from Dictyostelium discoideum is a typical member of a widely distributed family of cytoskeletal proteins. To analyze its regulation and structure/function relationships we cloned and expressed the subunits separately in Escherichia coli using the ATG-expression vector pT7-7. Studies on the viscosity of F-actin solutions and the kinetics of actin polymerization in the presence of single subunits or the reconstituted protein showed that capping of F-actin absolutely requires the heterodimeric conformation. This activity can be inhibited by phosphatidyl bisphosphate (PIP2), an important component in signal transduction. The regulation of cap32/34 by PIP2 suggests an involvement of this protein in the re-organization of the actin cytoskeleton upon stimulation of D. discoideum cells with chemoattractant.     

Mitogenic effect of estradiol on MCF-7 human breast cancer cells can be modulated by serum

The MCF-7 human breast cancer cell line responds to estradiol stimulation in vitro by increased proliferation only if prolonged subcultures in dextran-coated charcoal-treated fetal calf serum have been made previously. This growth stimulation is not obtained when cells are grown in medium containing 5% untreated fetal calf serum. We describe here the culture conditions under which we obtain a reproducible estradiol effect on cell growth.     

Change in lactate production in Myc-transformed cells precedes apoptosis and can be inhibited by Bcl-2 overexpression

Interleukin-18 binding protein is a novel glycoprotein that we successfully cloned and expressed. First, murine interleukin-18 binding protein was purified from the sera of mice with endotoxin shock using ligand affinity chromatography. The murine interleukin-18 binding protein cDNA was cloned after RT-PCR using mixed primer pair sequences based on partial murine interleukin-18 binding protein amino acid sequence analysis. Subsequently, human interleukin-18 binding protein cDNA was cloned from cDNA libraries of normal human liver using murine interleukin-18 binding protein cDNA as a probe. Next, we transiently expressed recombinant human and murine interleukin-18 binding proteins in COS-1 cells and purified them from culture supernatants. Both recombinant interleukin-18 binding proteins did not exhibit species specificity and prevented interleukin-18 binding to its receptor. In addition, they inhibited interleukine-18 dependent IFN-gamma production from KG-1 cells effectively. These results suggest that the interleukin-18 binding protein may possess interleukine-18 antagonist activity.     

p53 DNA binding can be modulated by factors that alter the conformational equilibrium.

The p53 tumor suppressor protein is a dimer of dimers that binds its consensus DNA sequence (containing two half-sites) as a pair of clamps. We show here that after one wild-type dimer of a tetramer binds to a half-site on the DNA, the other (unbound) dimer can be in either the wild-type or the mutant conformation. An equilibrium state between these two conformations exists and can be modulated by two types of regulators. One type modifies p53 biochemically and determines the intrinsic balance of the equilibrium. The other type of regulator binds directly to one or both dimers in a p53 tetramer, trapping each dimer in one or the other conformation. In the wild-type conformation, the second dimer can bind to the second DNA half-site, resulting in drastically enhanced stability of the p53-DNA complex. Importantly, a genotypically mutant p53 can also be in equilibrium with the wild-type conformation, and when trapped in this conformation can bind DNA.     

Zinc induces apoptosis that can be suppressed by lanthanum in C6 rat glioma cells

Zinc ions have both essential and toxic effects on mammalian cells. Here we report the ability of zinc to act as an inducer of apoptosis in C6 rat glioma cells. Incubation with 150 to 300 microM ZnCl2 caused cell death that was characterized as apoptotic by internucleosomal DNA fragmentation, formation of apoptotic bodies, nuclear fragmentation and breakdown of the mitochondrial membrane potential. On the other hand, zinc deprivation by the membrane permeable chelator TPEN [N,N,N',N',-tetrakis (2-pyridyl-methyl)-ethylenediamine] also induced programmed death in this cell line, indicating the existence of intracellular zinc levels below and above which apoptosis is induced. Zinc-induced apoptosis in C6 cells was independent of major signaling pathways (protein kinase C, mitogen activated protein kinase and guanylate cyclase) and protein synthesis, but was increased by facilitating zinc uptake with the ionophore pyrithione. Lanthanum(III)chloride was also able to increase the net zinc uptake, but nevertheless apoptotic features and zinc toxicity were reduced. Remarkably, lanthanum suppressed the zinc-induced breakdown of the mitochondrial membrane potential. We conclude that in C6 cells lanthanum acts in two different ways, as a promoter of net zinc uptake and as a suppressor of zinc-induced apoptosis.     

Preferential migration of regulatory T cells mediated by gliomasecreted chemokines can be blocked with chemotherapy

Despite the immunogenicity of glioblastoma multiforme (GBM), immune-mediated eradication of these tumors remains deficient. Regulatory T cells (Tregs) in the blood and within the tumor microenvironment of GBM patients are known to contribute to their dismal immune responses. Here, we determined which chemokine secreted by gliomas can preferentially induce Treg recruitment and migration. In the malignant human glioma cell lines D-54, U-87, U-251, and LN-229, the chemokines CCL22 and CCL2 were detected by intracellular cytokine analysis. Furthermore, tumor cells from eight patients with GBM had a similar chemokine expression profile. However, only CCL2 was detected by enzyme-linked immunosorbent assay, indicating that CCL2 may be the principal chemokine for Treg migration in GBM patients. Interestingly, the Tregs from GBM patients had significantly higher expression levels of the CCL2 receptor CCR4 than did Tregs from healthy controls. Glioma supernatants and the recombinant human chemokines CCL2 and CCL22 induced Treg migration and were blocked by antibodies to the chemokine receptors. Production of CCL2 by glioma cells could also be mitigated by the chemotherapeutic agents temozolomide and carmustine [3-bis (2-chloroethyl)-1-nitrosourea]. Our results indicate that gliomas augment immunosuppression by selective chemokine-mediated recruitment of Tregs into the tumor microenvironment and that modulating this interaction with chemotherapy could facilitate the development of novel immunotherapeutics to malignant gliomas. Justin T. Jordan and Wei Sun are contributed equally to this work. An erratum to this article can be found at     

Embryo transfer induces a subclinical endometritis in recipient mares which can be prevented by treatment with non-steroid anti-inflammatory drugs

We tested the hypothesis that subclinical endometritis occurs after embryo transfer (ET) in the horse. Recipient mares were treated with meclofenamic acid (M) or flunixin meglumin (F) after ET or were left untreated (n=9 per group). Embryos were re-collected 4 days after transfer. Endometrial biopsies were taken for histology and analysis of cyclooxygenase-2 (COX-2) by immunohistochemistry and for PCR. Bacteriological swabs were collected from the uterus and lavage fluid of donor and recipient mares. Progesterone and prostaglandin F(2alpha) release was analysed in recipient mares after ET. Four days after ET, four embryos were recovered from group M and three from group F and untreated mares, each. The number of polymorph nuclear neutrophils was reduced in treated mares (p<0.05). Expression of mRNA for inflammatory cytokines did not differ between groups. In group M, expression of endometrial prostaglandin-E-synthase was higher than in group F (p<0.05). Three out of nine control mares unterwent preterm luteolysis (p<0.05 vs. treatment groups), prostaglandin release (p<0.05) and the number of COX-2 positive cells (p<0.01) were significantly higher than in treated mares. Only few bacteriological swabs were positive. In conclusion, treatment of embryo recipient mares with non-steroid anti-inflammatory drugs inhibits the inflammatory response of the endometrium after ET. Meclofenamic acid may have advantages in comparison to flunixin meglumin due to a different influence on prostaglandin synthesis that may not result in inhibition of embryonic mobility.     

Ultraviolet-C overexposure induces programmed cell death in Arabidopsis, which is mediated by caspase-like activities and which can be suppressed by caspase inhibitors, p35 and Defender against Apoptotic Death

Plants, animals, and several branches of unicellular eukaryotes use programmed cell death (PCD) for defense or developmental mechanisms. This argues for a common ancestral apoptotic system in eukaryotes. However, at the molecular level, very few regulatory proteins or protein domains have been identified as conserved across all eukaryotic PCD forms. A very important goal is to determine which molecular components may be used in the execution of PCD in plants, which have been conserved during evolution, and which are plant-specific. Using Arabidopsis thaliana, we have shown that UV radiation can induce apoptosis-like changes at the cellular level and that a UV experimental system is relevant to the study of PCD in plants. We report here that UV induction of PCD required light and that a protease cleaving the caspase substrate Asp-Glu-Val-Asp (DEVDase activity) was induced within 30 min and peaked at 1 h. This DEVDase appears to be related to animal caspases at the biochemical level, being insensitive to broad-range cysteine protease inhibitors. In addition, caspase-1 and caspase-3 inhibitors and the pan-caspase inhibitor p35 were able to suppress DNA fragmentation and cell death. These results suggest that a YVADase activity and an inducible DEVDase activity possibly mediate DNA fragmentation during plant PCD induced by UV overexposure. We also report that At-DAD1 and At-DAD2, the two A. thaliana homologs of Defender against Apoptotic Death-1, could suppress the onset of DNA fragmentation in A. thaliana, supporting an involvement of the endoplasmic reticulum in this form of the plant PCD pathway.     

Propionibacterium acnes GehA lipase, an enzyme involved in acne development, can be successfully inhibited by defined natural substances

Propionibacterium acnes, a usual inhabitant of human skin, plays an important role in acne development, related to the production of numerous enzymatic activities involved in the degradation of host molecules. Among these enzymes, P. acnes lipase (GehA, glycerol-ester hydrolase A) has been recognized as one of the major factors in the pathogenesis of acne, being responsible for the hydrolysis of sebum and the release of inflammatory compounds. Anti-acne treatments are based on the use of retinoids or benzoyl peroxide, frequently in combination with antibiotics. However, the low effectiveness of such treatments and the increasing antibiotic resistance has led to the development of alternative therapies such as Kampo formulations, containing traditional herbal drugs. Search for new anti-acne treatments led us to perform the cloning, characterization and inhibition of P. acnes GehA, considered an interesting pharmaceutical target for anti-acne therapies. The genetic, molecular and biochemical properties of the cloned lipase were analysed, and several inhibitor agents were tested, including natural substances like saponins, alkaloids or flavonoids. Among these, the flavonoids (±)-catechin and kaempferol were the most promising candidates for acne treatment, whereas saponins like glycyrrhicic acid and digitonin produced a lower inhibition of the enzyme. No inhibition by alkaloids was found. Therefore, the inhibition caused by (±)-catechin and kaempferol on GehA, together with their wide anti-acne properties and low toxicity, make them very suitable candidates for the treatment of acne and other P. acnes-related diseases.     

Induction of haptotactic migration of melanoma cells by neutrophil activating protein/interleukin-8

Natural or recombinant neutrophil activating cytokine (IL-8) induced migration across polycarbonate filters of human A 2058 melanoma cells. Anti-IL-8 antibodies blocked IL-8 induced melanoma cell migration. Checkerboard experiments revealed a gradient-dependent response of A2058 melanoma cells to IL-8. Filters exposed to IL-8 and washed supported melanoma cell migration, thus implying a haptotactic component in the response. The homologous polypeptide platelet factor 4 was inactive. The observation that IL-8 affects melanoma cells emphasizes the need for a comprehensive analysis of the spectrum of action of platelet factor 4-related peptides. The effect of the inflammatory cytokine IL-8 on melanoma cells may be relevant to augmented secondary localization of tumors at sites of inflammation.     

IgE-mediated 14C-serotonin release from rat mast cells modulated by morphine and endorphins

The formaldehyde method was used to examine the interaction of PGE₁ with morphine, β-endorphin and Met-enkephalin on rat mast cells by their effects on IgE-mediated ¹⁴C-serotonin release. PGE₁ (2×10^?8?2×10^?5 M) caused a dose-related inhibition of the mediator release 1 min after an antigen challenge, and morphine (3×10^?7?3×10^?5 M) reversed this PGE₁ effect dose-dependently and stereospecifically; naloxone (2×10^?4 M) antagonized this action of morphine. β-Endorphin (3×10^?7?10^?5 M) and Met-enkephalin (3×10^?6?10^?4 M) mimicked this morphine action dose-dependently and were antagonized by naloxone (2×10^?4 M). These results suggest that morphine and endorphins modulate immunological mediator release from rat mast cells through opioid receptors.     

Binding of neutrophil attractant/activation protein-1 (interleukin 8) to resident dermal cells.

Putative tissue receptors for leukocyte attractants, including neutrophil attractant/activation protein-1 (interleukin 8, NAP-1/IL-8), have been implicated in the regulation of neutrophil emigration into the tissues. An in-situ binding assay and an ex-vivo autoradiographic approach were used to investigate the binding of radiolabeled NAP-1/IL-8 to human and animal skin. These methods revealed the presence of saturable NAP-1/IL-8-binding sites on the endothelial cells of venules and veins but not arteries or capillaries of the dermis. In addition, the binding of NAP-1/IL-8 to dermal macrophages and perivascular mast cells was observed. We suggest that the NAP-1/IL-8-binding sites described here could be involved in the regulation of NAP-1/IL-8-induced neutrophil emigration.     

The Escherichia coli CysZ is a pH dependent sulfate transporter that can be inhibited by sulfite

The Escherichia coli inner membrane protein CysZ mediates the sulfate uptake subsequently utilized for the synthesis of sulfur-containing compounds in cells. Here we report the purification and functional characterization of CysZ. Using Isothermal Titration Calorimetry, we have observed interactions between CysZ and its putative substrate sulfate. Additional sulfur-containing compounds from the cysteine synthesis pathway have also been analyzed for their abilities to interact with CysZ. Our results suggest that CysZ is dedicated to a specific pathway that assimilates sulfate for the synthesis of cysteine. Sulfate uptake via CysZ into E. coli whole cells and proteoliposome offers direct evidence of CysZ being able to mediate sulfate uptake. In addition, the cysteine synthesis pathway intermediate sulfite can interact directly with CysZ with higher affinity than sulfate. The sulfate transport activity is inhibited in the presence of sulfite, suggesting the existence of a feedback inhibition mechanism in which sulfite regulates sulfate uptake by CysZ. Sulfate uptake assays performed at different extracellular pH and in the presence of a proton uncoupler indicate that this uptake is driven by the proton gradient.