PubMed Health⌕ Search

Biomedical subjects

P Vollmer

Publications and source records attributed to P Vollmer.

18 recordsLinked to original sources
PubMed2000

IL-6 receptor independent stimulation of human gp130 by viral IL-6.

The genome of human herpes virus 8, which is associated with Kaposi's sarcoma, encodes proteins with similarities to cytokines and chemokines including a homologue of IL-6. Although the function of these viral proteins is unclear, they might have the potential to modulate the immune system. For viral IL-6 (vIL-6), it has been demonstrated that it stimulates IL-6-dependent cells, indicating that the IL-6R system is used. IL-6 binds to IL-6R, and the IL-6/IL-6R complex associates with gp130 which dimerizes and initiates intracellular signaling. Cells that only express gp130 but no IL-6R cannot be stimulated by IL-6 unless a soluble form of the IL-6R is present. This type of signaling has been shown for hematopoietic progenitor cells, endothelial cells, and smooth muscle cells. In this paper we show that purified recombinant vIL-6 binds to gp130 and stimulates primary human smooth muscle cells. IL-6R fails to bind vIL-6 and is not involved in its signaling. A Fc fusion protein of gp130 turned out to be a potent inhibitor of vIL-6. Our data demonstrate that vIL-6 is the first cytokine which directly binds and activates gp130. This property points to a possible role of this viral cytokine in the pathophysiology of human herpes virus 8.

Aged↗
PubMed2000

Human herpes virus 8 interleukin-6 homologue triggers gp130 on neuronal and hematopoietic cells.

Human herpes virus-8 (HHV8) encodes a cytokine named viral interleukin-6 (vIL-6) that shares 25% amino-acid identity with its human homologue. Human IL-6 is known to be a growth and differentiation factor of lymphatic cells and plays a potential role in the pathophysiology of various lymphoproliferative diseases. vIL-6 is expressed in HHV8-associated-diseases including Kaposi's sarcoma, Body-cavity-based-lymphoma and Castleman's disease, suggesting a pathogenetic involvement in the malignant growth of B-cell associated diseases and other malignant tumours. We expressed vIL-6 in Escherichia coli as a fusion protein with recombinant periplasmic maltose binding protein. After cleavage from the maltose binding protein moiety and purification, vIL-6 was shown to be correctly folded using circular dichroism spectroscopy. A rabbit antiserum was raised against the recombinant vIL-6 protein. vIL-6 turned out to be active on cells that expressed gp130 but no IL-6 receptor (IL-6-R) suggesting that, in contrast to human IL-6, vIL-6 stimulated gp130 directly. Accordingly, vIL-6 activity could be inhibited by a soluble gp130 Fc Fusion protein. vIL-6 was shown to induce neuronal differentiation of rat pheochromocytoma cells and to stimulate colony formation of human hematopoietic progenitor cells. Thus, vIL-6 exhibits biologic activity that has only been observed for the IL-6/soluble IL-6-R complex but not for IL-6 alone. These properties are important for the evaluation of the pathophysiological potential of vIL-6.

Amino Acid Sequence↗
PubMed1999

Receptor recognition sites of cytokines are organized as exchangeable modules. Transfer of the leukemia inhibitory factor receptor-binding site from ciliary neurotrophic factor to interleukin-6.

Interleukin-6 (IL-6) and ciliary neurotrophic factor (CNTF) are "4-helical bundle" cytokines of the IL-6 type family of neuropoietic and hematopoietic cytokines. IL-6 signals by induction of a gp130 homodimer (e.g. IL-6), whereas CNTF and leukemia inhibitory factor (LIF) signal via a heterodimer of gp130 and LIF receptor (LIFR). Despite binding to the same receptor component (gp130) and a similar protein structure, IL-6 and CNTF share only 6% sequence identity. Using molecular modeling we defined a putative LIFR binding epitope on CNTF that consists of three distinct regions (C-terminal A-helix/N-terminal AB loop, BC loop, C-terminal CD-loop/N-terminal D-helix). A corresponding gp130-binding site on IL-6 was exchanged with this epitope. The resulting IL-6/CNTF chimera lost the capacity to signal via gp130 on cells without LIFR, but acquired the ability to signal via the gp130/LIFR heterodimer and STAT3 on responsive cells. Besides identifying a specific LIFR binding epitope on CNTF, our results suggest that receptor recognition sites of cytokines are organized as modules that are exchangeable even between cytokines with limited sequence homology.

Animals↗
PubMed1999

Primary structure and biochemical characterization of yeast GTPase-activating proteins with substrate preference for the transport GTPase Ypt7p.

Small GTPases of the Ypt/Rab family are regulators of vesicular protein trafficking in exo-and endocytosis. GTPase-activating proteins (GAP) play an important role as down regulators of GTPases. We here report the molecular cloning of a novel GAP-encoding gene (GYP7, for GAP for Ypt7) by high expression from a Saccharomyces cerevisiae genomic library. The GYP7 gene encodes a hydrophilic protein with a molecular mass of 87 kDa. Comparison of its primary sequence with that of the three other known GAPs for transport GTPases, the yeast Gyp6 and Gyp1 proteins and the Rab3A-GAP from rat brain, shows similarity between the yeast GAPs only. Like GYP6 and GYP1, GYP7 is not essential for yeast cell viability. Gyp7p was able to most effectively accelerate the intrinsic GTPase activity of Ypt7p. It was also active, but to a lesser extent, on Ypt31p, Ypt32p and Ypt1p. Ypt6p, Sec4p and the human H-Ras protein did not serve as substrates. We also report the identification and cloning of a gene from the dimorphic yeast Yarrowia lipolytica that encodes a protein whose primary structure and biochemical activity are significantly related to those of Gyp7p from baker's yeast.

Amino Acid Sequence↗
PubMed1999

A role for the immunoglobulin-like domain of the human IL-6 receptor. Intracellular protein transport and shedding.

Interleukin (IL)-6, IL-11 and cililary neurotrophic factor (CNTF) belong to the same family of hematopoietic and neurotrophic cytokines. Their receptor complexes contain a cytokine-binding alpha receptor and the common glycoprotein (gp)130 subunit for signal transduction. The extracellular parts of the alpha-receptor subunits consist of a membrane-proximal cytokine-binding domain and an N-terminal immunoglobulin (Ig)-like domain with unknown function. We examined the role of the Ig-like domain of IL-6R by constructing deletion mutants lacking the Ig domain (IL-6RDeltaIg and soluble IL-6RDeltaIg). IL-6RDeltaIg was shed as effectively as wild-type IL-6R from transfected COS-7 cells upon 4beta-phorbol 12-myristate 13-acetate (PMA) treatment, whereas nonstimulated shedding of IL-6RDeltaIg was not observed. The shed sIL-6RDeltaIg from PMA-treated cells, as well as the transmembrane IL-6RDeltaIg, had the same biological activity as wild-type sIL-6R, as measured by the induction of haptoglobin secretion in HepG2-IL-6 cells and IL-6-dependent proliferation of IL-6RDeltaIg transfected BAF/gp130 cells. In COS-7 cells transfected with IL-6RDeltaIg or soluble IL-6RDeltaIg cDNA, transport of the deletion mutants through the secretory pathway appeared to be delayed because a sizeable proportion of the mutants was detected as an endo-beta-N-acetylglucosaminidase-sensitive intermediate, suggesting that transport and processing of the DeltaIg mutants on the secretory pathway were impaired. These experiments suggest that the Ig-like domain of the IL-6R is important for intracellular transport of IL-6R through the secretory pathway. Furthermore, the Ig-like domain is necessary for noninduced shedding of the IL-6R, whereas it has no function in PKC-dependent shedding of the IL-6R.

Animals↗
PubMed1996

Yeast expression of the cytokine receptor domain of the soluble interleukin-6 receptor.

The complex of the soluble interleukin-6 receptor (sIL-6R) and IL-6 (IL-6) is a potent agonist on cells expressing the signal transducing protein gp 130. In contrast, IL-6 alone only stimulates cells which express a membrane bound form of the IL-6R and gp 130. The natural occurring sIL-6R is generated by shedding of the membrane receptor and to a lesser extend by alternative splicing. We have inserted the coding sequence of the 323 amino acid residues of the human sIL-6R into an expression/secretion vector suitable for the methylotrophic yeast Pichia pastoris. We obtained, however, no detectable expression and secretion of the recombinant protein. When we used only the coding sequence of the cytokine receptor domain of the sIL-6R for the construction of an expression plasmid, this truncated version of the sIL-6R accumulated in the supernatant to 1-5 mg/l. The protein was purified by a single affinity chromatography step using a monoclonal antibody directed against the human IL-6R. Following the same approach, we expressed a truncated splice variant of the sIL-6R. Both, the secreted truncated sIL-6R and the splice variant showed full agonistic biological activity on human hepatoma cells. The described expression strategy will be useful for large scale production of biologically active sIL-6R and might be adapted for the expression of other members of the hematopoietic cytokine receptor family.

Antigens, CD↗
PubMed1996

Pore-forming toxins trigger shedding of receptors for interleukin 6 and lipopolysaccharide.

Cleavage of membrane-associated proteins with the release of biologically active macromolecules is an emerging theme in biology. However, little is known about the nature and regulation of the involved proteases or about the physiological inducers of the shedding process. We here report that rapid and massive shedding of the interleukin 6 receptor (IL-6R) and the lipopolysaccharide receptor (CD14) occurs from primary and transfected cells attacked by two prototypes of pore-forming bacterial toxins, streptolysin O and Escherichia coli hemolysin. Shedding is not induced by an streptolysin O toxin mutant which retains cell binding capacity but lacks pore-forming activity. The toxin-dependent cleavage site of the IL-6R was mapped to a position close to, but distinct from, that observed after stimulation with phorbol myristate acetate. Soluble IL-6R that was shed from toxin-treated cells bound its ligand and induced an IL-6-specific signal in cells that primarily lacked the IL-6R. Transsignaling by soluble IL-6R and soluble CD14 is known to dramatically broaden the spectrum of host cells for IL-6 and lipopolysaccharide, and is thus an important mechanism underlying their systemic inflammatory effects. Our findings uncover a novel mechanism that can help to explain the long-range detrimental action of pore-forming toxins in the host organism.

Animals↗
PubMed1996

Diverse cell surface protein ectodomains are shed by a system sensitive to metalloprotease inhibitors.

The extracellular domains of a diverse group of membrane proteins are shed in response to protein kinase C activators such as phorbol 12-myristate 13-acetate (PMA). The lack of sequence similarity in the cleavage sites suggests the involvement of many proteases of diverse specificity in this process. However, a mutant Chinese hamster ovary cell line recently isolated for being defective in PMA-activated shedding of the membrane-anchored growth factor transforming growth factor alpha precursor (proTGF-alpha) is concomitantly defective in the shedding of many other unrelated membrane proteins. Here we show that independent mutagenesis and selection experiments yield shedding mutants having the same recessive phenotype and belonging to the same genetic complementation group. Furthermore, two structurally distinct agents, TAPI-2 and 1,10-phenanthroline, which are known to inhibit metalloproteases, block PMA-activated shedding of proTGF-alpha, cell adhesion receptor L-selectin, interleukin 6 receptor alpha subunit, beta-amyloid precursor protein, and an entire set of anonymous Chinese hamster ovary cell surface proteins. Certain serine protease inhibitors prevent release of these proteins by interfering with their maturation and transport to the cell surface but do not inhibit ectodomain shedding from the cell surface. The results suggest the existence of a common system for membrane protein ectodomain shedding involving one or several proteolytic activities sensitive to metalloprotease inhibitors, whose ability to act can be disrupted by recessive mutations in a single gene.

Amyloid beta-Protein Precursor↗
PubMed1996

The function of the soluble interleukin 6 (IL-6) receptor in vivo: sensitization of human soluble IL-6 receptor transgenic mice towards IL-6 and prolongation of the plasma half-life of IL-6.

Interleukin 6 (IL-6) is considered an important mediator of acute inflammatory responses. Moreover, IL-6 functions as a differentiation and growth factor of hematopoietic precursor cells, B cells, T cells, keratinocytes, neuronal cells, osteoclasts, and endothelial cells. IL-6 exhibits its action via a receptor complex consisting of a specific IL-6 receptor (IL-6R) and a signal transducing subunit (gp130). Soluble forms of both receptor components are generated by shedding and are found in patients with various diseases such as acquired immune deficiency syndrome, rheumatoid arthritis, and others. The function of the soluble (s)IL-6R in vivo is unknown. Since human (h)IL-6 acts on human and murine target cells, but murine IL-6 on murine cells only, we constructed transgenic mice expressing the hsIL-6R. We report here that in the presence of hsIL-6R, mice are hypersensitized towards hIL-6, mounting an acute phase protein gene induction at significantly lower IL-6 dosages compared to control animals. Furthermore, in hsIL-6R transgenic mice, the detected acute phase response persists for a longer period of time. The IL-6/IL-6R complex prolongs markedly the Il-6 plasma half-life. Our results reinforce the role of the hsIL-6R as an agonistic protein, help to understand the function of the hsIL-6R in vivo, and highlight the significance of the receptor in the induction of the acute phase response.

Acute-Phase Reaction↗
PubMed1996

Novel pathogenic mechanism of microbial metalloproteinases: liberation of membrane-anchored molecules in biologically active form exemplified by studies with the human interleukin-6 receptor.

Certain membrane-anchored proteins, including several cytokines and cytokine receptors, can be released into cell supernatants through the action of endogenous membrane-bound metalloproteinases. The shed molecules are then able to fulfill various biological functions; for example, soluble interleukin-6 receptor (sIL-6R) can bind to bystander cells, rendering these cells sensitive to the action of IL-6. Using IL-6R as a model substrate, we report that the metalloproteinase from Serratia marcescens mimics the action of the endogenous shedding proteinase. Treatment of human monocytes with the bacterial protease led to a rapid release of sIL-6R into the supernatant. This effect was inhibitable with TAPI [N-(D,L-[2-(hydroxyaminocarbonyl)methyl]-4-methylpentanoyl) L-3-(2' naphthyl)-alanyl-L-alanine, 2-aminoethyl amide], a specific inhibitor of the membrane-bound intrinsic metalloproteinase, but not with other conventional proteinase inhibitors. sIL-6R-liberating activity was also detected in culture supernatants of Staphylococcus aureus, Pseudomonas aeruginosa, and Listeria monocytogenes, organisms that are known to produce metalloproteinases. sIL-6R released through the action of S. marcescens metalloproteinase retained biological activity and rendered IL-6-unresponsive human hepatoma cells sensitive to stimulation with IL-6. This was shown by Northern (RNA) blot detection of haptoglobin mRNA and by quantitative measurements of de novo-synthesized haptoglobin in cell supernatants. Analysis of immunoprecipitated, radiolabeled sIL-6R revealed that the bacterial protease cleaved IL-6R at a site distinct from that utilized by the endogenous protease. These studies show that membrane-anchored proteins can be released in active form through cleavage at multiple sites, and they uncover a novel mechanism via which microbial proteases possibly provoke long-range biological effects in the host organism.

Animals↗
PubMed1993

A yeast GTPase-activating protein that interacts specifically with a member of the Ypt/Rab family.

Members of the Ras superfamily of GTP-binding proteins are involved in a variety of cellular processes, including signal transduction, cytoskeletal organization and protein transport. GTP-binding proteins of the Ypt/Rab family direct vesicular protein transport in the secretory and endocytic pathways in the yeast Saccharomyces cerevisiae (Ypt proteins) and in mammalian systems (Rab proteins). The cellular activity of monomeric GTP-binding proteins is influenced by proteins that regulate GDP/GTP exchange and GTP hydrolysis. GTPase-activating proteins (GAPs) can increase the slow intrinsic GTPase activity of GTP-binding proteins by several orders of magnitude. As GAPs modulate the activity of GTP-binding proteins, they are thought to give a biochemical handle on the functioning of Ypt/Rab proteins in transport vesicle budding and docking or fusion at donor and acceptor membranes. We report here the first cloned GTPase-activating protein for the Ypt/Rab protein family. The gene, GYP6 (GAP of Ypt6 protein), encodes a protein of 458 amino acids which is highly specific for the Ypt6 protein and shows little or no cross-reactivity with other Ypt/Rab family members or with H-Ras p21.

Amino Acid Sequence↗
PubMed1991

Identification and partial purification of GTPase-activating proteins from yeast and mammalian cells that preferentially act on Ypt1/Rab1 proteins.

Two GTPase-activating proteins of apparent molecular mass of 100 kDa and 30 kDa have been partially purified from porcine liver cytosol using mammalian Ypt1/Rab1 protein as substrate. Both proteins act most efficiently on Ypt1/Rab1p, but are inactive with H-Ras p21. From the budding yeast Saccharomyces cerevisiae, a cytosolic 40 kDa yptGAP was partially purified. It accelerates the intrinsic GTPase activity of wild-type Ypt1p but not of H-Ras p21 or a mutant ypt1p with an amino acid substitution of the effector domain which renders the protein functionally inactive in yeast cells.

Animals↗
PubMed1981

High-performance liquid chromatographic determination of components of bleomycin preparations.

A fast and sensitive method was developed for the quantitative determination of at least 10 components of pharmaceutical bleomycin sulfate preparations. The method is based on the reversed-phase high-performance liquid chromatographic (HPLC) separation of the components on a muBondapak C18 column with a mobile phase having a linear gradient of 10--40% methanol in aqueous 0.005 M 1-pentanesulfonic acid at pH 4.3. With this assay, the average standard deviations for components A2 and B2 are 0.92 and 0.87, respectively, for a 7.5--22.5 x 10(-3)-mg sample. Regulatory agencies presently use the official Code of Federal Regulations (CFR) method, which is based on CM-Sephadex column chromatography. It was demonstrated that this CFR method does not separate the bleomycin A2 component from some other minor bleomycin components. After elution from the CM-Sephadex column, the "A2 component" was separated into five components by the HPLC method. Bleomycin A2 is stable under these HPLC conditions.

Bleomycin↗
PubMed1981

Nucleotide sequence changes in polyoma virus A gene mutants.

The mutational alterations in polyoma virus mutants ts-a and ts-25E which cause their large T-antigens to be thermolabile have been identified. In ts-a, a G leads to A transition at nucleotide 2193 causes the replacement of Ala (GCT) by Thr (ACT). In ts-25E, a G leads to T transversion at nucleotide 2883 causes the replacement of Gly (GGC) by Cys (TGC). Revertants of both mutants have been isolated and shown to have the original nucleotides restored at these positions.

Amino Acid Sequence↗