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R B Pepinsky

Publications and source records attributed to R B Pepinsky.

At least 37 records · Page 2Linked to original sources
PubMed1998

Identification of a palmitic acid-modified form of human Sonic hedgehog.

During hedgehog biosynthesis, autocatalytic processing produces a lipid-modified amino-terminal fragment (residues 24-197 in the human Sonic hedgehog sequence) that is responsible for all known hedgehog signaling activity and that is highly conserved evolutionarily. Published in vitro biochemical studies using Drosophila hedgehog identified the membrane anchor as a cholesterol, and localized the site of attachment to the COOH terminus of the fragment. We have expressed full-length human Sonic hedgehog in insect and in mammalian cells and determined by mass spectrometry that, in addition to cholesterol, the human hedgehog protein is palmitoylated. Peptide mapping and sequencing data indicate that the palmitoyl group is attached to the NH2 terminus of the protein on the alpha-amino group of Cys-24. Cell-free palmitoylation studies demonstrate that radioactive palmitic acid is readily incorporated into wild type Sonic hedgehog, but not into variant forms lacking the Cys-24 attachment site. The lipid-tethered forms of hedgehog showed about a 30-fold increase in potency over unmodified soluble hedgehog in a cell- based (C3H10T1/2 alkaline phosphatase induction) assay, suggesting that the lipid tether plays an important role in hedgehog function. The observation that an extracellular protein such as Shh is palmitoylated is highly unusual and further adds to the complex nature of this protein.

Animals↗
PubMed1998

Structural and functional differences between glycosylated and non-glycosylated forms of human interferon-beta (IFN-beta).

PURPOSE: Two recombinant IFN-beta products have been approved for the treatment of multiple sclerosis, a glycosylated form with the predicted natural amino acid sequence (IFN-beta-1a) and a non-glycosylated form that has a Met-1 deletion and a Cys-17 to Ser mutation (IFN-beta-1b). The structural basis for activity differences between IFN-beta-1a and IFN-beta-1b, is determined. METHODS: In vitro antiviral, antiproliferative and immunomodulatory assays were used to directly compare the two IFN-beta products. Size exclusion chromatography (SEC), SDS-PAGE, thermal denaturation, and X-ray crystallography were used to examine structural differences. RESULTS: IFN-beta-1a was 10 times more active than IFN-beta-1b with specific activities in a standard antiviral assay of 20 x 10(7) IU/mg for IFN-beta-1a and 2 x 10(7) IU/mg for IFN-beta-1b. Of the known structural differences between IFN-beta-1a and IFN-beta-1b, only glycosylation affected in vitro activity. Deglycosylation of IFN-beta-1a produced a decrease in total activity that was primarily caused by the formation of an insoluble disulfide-linked IFN precipitate. Deglycosylation also resulted in an increased sensitivity to thermal denaturation. SEC data for IFN-beta-1b revealed large, soluble aggregates that had reduced antiviral activity (approximated at 0.7 x 10(7) IU/mg). Crystallographic data for IFN-beta-1a revealed that the glycan formed H-bonds with the peptide backbone and shielded an uncharged surface from solvent exposure. CONCLUSIONS: Together these results suggest that the greater biological activity of IFN-beta-1a is due to a stabilizing effect of the carbohydrate on structure.

Adjuvants, Immunologic↗
PubMed1998

The role of the very late antigen-4 and its counterligand vascular cell adhesion molecule-1 in the pathogenesis of experimental autoimmune neuritis of the Lewis rat.

We have investigated the functional role of very late antigen-4 [VLA-4 (alpha4/beta1) integrin] and vascular cell adhesion molecule-1 (VCAM-1) in experimental autoimmune neuritis (EAN), an animal model of the Guillain-Barré syndrome, using neutralizing monoclonal antibodies (mAbs) as probes. Disease was induced by intravenous adoptive transfer of P2 specific T cells (AT-EAN), or by immunization with bovine myelin (active EAN). Preventive treatment with 500 microg anti-VLA-4 mAb (TA-2) or with an isotype control antibody was given in AT-EAN 4 h before cell transfer and at day 3. Intravenous injection of 500 microg anti-VCAM-1 mAb (5F10) or a corresponding isotype control was given in AT-EAN 4 h before disease induction, and at days 2, 4 and 6. Preventive treatment of active EAN with mAb to VLA-4 or VCAM-1 was performed at days 5, 9 and 13. On immunohistochemical examination, VCAM-1 in sciatic nerve was found to be upregulated at early stages of EAN (days 3-5 after T-cell transfer), whilst no expression was noted in healthy controls. In both EAN models, blockade of VLA-4 markedly attenuated disease severity. Blockade of VCAM-1 also significantly ameliorated the disease course and diminished T-cell infiltration in sciatic nerve, but to a lesser degree. These experiments demonstrate the critical role of VLA-4 in the pathogenesis of EAN and show that upregulation of VCAM-1 expression contributes, at least in part, to the progression of the disease in the early stages. Future studies are needed to assess the potential contribution of other VLA-4 ligands.

Animals↗
PubMed1997

Glial cell line-derived neurotrophic factor-dependent RET activation can be mediated by two different cell-surface accessory proteins.

Glial cell line-derived neurotrophic factor (GDNF)-dependent activation of the tyrosine kinase receptor RET is necessary for kidney and enteric neuron development, and mutations in RET are associated with human diseases. Activation of RET by GDNF has been shown to require an accessory component, GDNFR-alpha (RETL1). We report the isolation and characterization of rat and human cDNAs for a novel cell-surface associated accessory protein, RETL2, that shares 49% identity with RETL1. Both RETL1 and RETL2 can mediate GDNF dependent phosphorylation of RET, but they exhibit different patterns of expression in fetal and adult tissues. The most striking differences in expression observed were in the adult central and peripheral nervous systems. In addition, the mechanisms by which the two accessory proteins facilitate the activation of RET by GDNF are quite distinct. In vitro binding experiments with soluble forms of RET, RETL1 and RETL2 demonstrate that while RETL1 binds GDNF tightly to form a membrane-associated complex which can then interact with RET, RETL2 only forms a high affinity complex with GDNF in the presence of RET. This strong RET dependence of the binding of RETL2 to GDNF was confirmed by FACS analysis on RETL1 and RETL2 expressing cells. Together with the recent discovery of a GDNF related protein, neurturin, these data raise the possibility that RETL1 and RETL2 have distinctive roles during development and in the nervous system of the adult. RETL1 and RETL2 represent new candidate susceptibility genes and/or modifier loci for RET-associated diseases.

Amino Acid Sequence↗
PubMed1997

Sequences flanking the core DNA-binding domain of bovine papillomavirus type 1 E2 contribute to DNA-binding function.

We have compared a series of molecular constructs that contain the minimal DNA-binding and dimerization domain of bovine papillomavirus type 1 (BPV-1) E2 alone or this binding domain plus the adjacent 16 or 40 amino acids to test the role of the flanking sequences in E2 function. The presence of these sequences resulted in an up to eightfold increase in the affinity of E2 for its target DNA and stabilized the protein against denaturation both in the absence of DNA and in the form of DNA-protein complexes. In addition, an aspartic acid-to-tyrosine mutation within the flanking region blocked DNA binding and function. These data demonstrate that sequences flanking the core domain contribute to E2 function and are, in fact, an integral part of the DNA-binding domain of BPV-1 E2.

Animals↗
PubMed1996

Pathophysiologic role of alpha 4 integrins in the lung.

Evidence for a central role for the integrins alpha 4 beta 1 and alpha 4 beta 7 in leukocyte pathophysiology is rapidly accumulating. Five distinct alpha 4 mAbs, each able to block alpha 4-dependent adhesion in vitro, show beneficial effects in vivo in six different species, and in a wide variety of organ systems, including colon, lung, skin, neural tissue, pancreas, peritoneum, and the vessel wall. In particular, a clear role for these integrins in lung pathophysiology is implied on the basis of in vivo studies in four different species. Although several issues remain to be resolved, including the relative importance of alpha 4 beta 1 and alpha 4 beta 7, and the relative roles of their counterligands, VCAM1, fibronectin, and MAdCAM, the data argue that alpha 4 integrins will likely be critical to both the normal physiology and pathology of the lung in man. To this end, we (Adams, Lin, Lobb, and Gill, unpublished data) and others have generated peptidomimetic small molecule antagonists of VLA4 based on the connecting segment 1 (CS1) peptide sequence of fibronectin that are potent blockers of integrin adhesive function in vitro and show efficacy in vivo. We have found that our inhibitors are excellent blockers of both murine contact hypersensitivity, and of the LPR and AHR in the sheep allergic airways model (Abraham, Lobb, Adams, and Gill, unpublished data), and are therefore possible candidates for clinical intervention in human asthma. The use of the VCAM-Ig fusion protein as a probe for high-affinity alpha 4 integrins has further enhanced our understanding of alpha 4 integrin function in the lung. While integrin upregulation in vitro has been observed many times, and high affinity (as opposed to avidity) of integrins seen in vitro in several systems, in vivo proof of integrin upregulation to a high-affinity state has been difficult to obtain in the absence of selective probes. Our data provide key information in this regard and strongly argue not only that integrin upregulation does indeed occur in vivo, but also that it is in fact obligatory for the leukocyte pathologies we have examined to date. Further studies are clearly warranted to further examine mechanisms of action, and to confirm and extend these studies, both with the alpha 4 integrins and with other integrin families. In summary, our studies of alpha 4 integrins continue to provide novel insights into the pathophysiology of integrin function and into future directions for drug discovery.

Animals↗
PubMed1996

The plasma and cytoplasmic forms of human gelsolin differ in disulfide structure.

Gelsolin is a widely distributed actin binding protein that regulates actin filament length. It exists in both an intracellular and an extracellular form that is derived from a single gene by alternative splicing. Both forms contain the six homologous domains that are responsible for function. Little is known regarding differences between the forms. We have used a combination of cysteine-specific modification with 4-vinylpyridine, HPLC peptide mapping methods, and mass spectrometry to analyze the disulfide structures of human plasma and cytoplasmic gelsolin. Of the five Cys residues in the human gelsolin sequence, all were present in the free thiol form in human cytoplasmic gelsolin, while only three of them were free thiols in the human plasma form. Cys residues 188 and 201 in domain 2 of plasma gelsolin were disulfide linked. Recombinant human plasma gelsolin that had been expressed intracellularly in Escherichia coli and as a secreted protein from Cos green monkey cells was also investigated. The E. coli product lacked the disulfide but could be converted to the plasma-like structure with mild oxidation while the mammalian product formed the correct disulfide prior to isolation. Structural differences were also detected by limited proteolysis with plasmin. The differences in proteolytic susceptibility were also due to perturbations in domain 2. These studies demonstrate that the intracellular and extracellular gelsolins are structurally distinct and suggest that at least some of the preparations of recombinant gelsolin that are being used to study structure/function may be improperly folded. The experiments also demonstrate a general method for the location of disulfide bonds in proteins.

Actins↗
PubMed1996

Lipocortin-1 (annexin-1) suppresses activation of autoimmune T cell lines in the Lewis rat.

Increased levels of lipocortins occur in the nervous system in multiple sclerosis, in experimental autoimmune encephalomyelitis and experimental neuritis at the height of disease and decrease thereafter, suggesting their potential involvement in recovery from disease. We therefore investigated whether lipocortins may suppress activation of autoimmune T cells. Antigen-specific and growth factor-mediated proliferation of T cell lines reactive with myelin basic protein (MBP) was measured in the presence of recombinant lipocortin-1, -2, and -5, and natural bovine lipocortin-1 using various concentrations and incubation periods. We also employed an N-terminal lipocortin-1 peptide spanning aa 1-26, a proteolytic fragment of lipocortin-1 where the respective N-terminal region was clipped off, tested blocking with a neutralizing antibody, and investigated the effect of alkaline phosphatase treatment. Both human recombinant and bovine lipocortin-1 had a marked suppressive effect on T cell activation by MBP and the respective immunogenic peptide. When added at 3 micrograms/ml we observed up to 90% inhibition of T cell proliferation between day 2 and 3, but not at earlier time points of activation. The inhibitory effect of human lipocortin-1 was blocked after addition of a neutralizing antibody directed against lipocortin-1. Lipocortin-2 and -5, and the N-terminal peptide of lipocortin-1 were ineffective, whereas the fragment spanning residues 27-345 of lipocortin-1 retained full activity. Treatment of bovine lipocortin-1 with alkaline phosphatase did not alter immunosuppressive properties.

Amino Acid Sequence↗
PubMed1996

Analysis of Rous sarcoma virus Gag protein by mass spectrometry indicates trimming by host exopeptidase.

We have used electrospray ionization-mass spectrometry to investigate Gag protein structure and processing in Rous sarcoma virus, the prototype of the avian sarcoma and leukemia viruses. Molecular masses determined for the mature virion proteins MA, CA, NC, and PR agree closely with those predicted by currently accepted models for their structures. However, the data for p10 imply that only about 10% of the product has the predicted mass while the remainder is missing the C-terminal methionine residue. Molecular masses also were obtained for products generated by PR cleavage in vitro of a Gag precursor polyprotein expressed in Escherichia coli. The data confirm the predicted Gag cleavage sites for PR. Thus, carboxypeptidase activity appears to be responsible for generating the des-Met form of p10. The same activity may account for the small amount of the mature des-Met CA, as previously reported. Analysis of cleavage products generated in vitro also serves to define the PR processing site separating the p2a and p2b peptides, Asn-164-Cys-165. In conjunction with published characterizations of these two peptides processed from the segment of Gag between MA and p10, these data suggest trimming of p2b by an aminopeptidase. Finally, the molecular masses determined for the MA-related species p19f, p23, and p35 now accurately define the structures of these proteins.

Amino Acid Sequence↗
PubMed1995

Vascular cell adhesion molecule-Ig fusion protein selectively targets activated alpha 4-integrin receptors in vivo. Inhibition of autoimmune diabetes in an adoptive transfer model in nonobese diabetic mice.

The alpha 4 beta 1-integrin (CD49d, CD29) constitutively expressed on leukocytes regulates cell migration to inflammatory sites, cell activation, and development through its interactions with two alternate ligands, vascular cell adhesion molecule-1 (VCAM-1; CD106) expressed on cytokine-activated endothelium, dendritic and stromal cells, and the extracellular matrix protein fibronectin. Another alpha 4-integrin receptor, alpha 4 beta 7, expressed on leukocytes also binds VCAM-1 and fibronectin (FN), and controls homing to mucosal tissues through its interactions with mucosal vascular addressin MAdCAM-1. In vitro studies have shown that alpha 4-dependent cell adhesion is regulated by the activation state of the cell and by divalent cations. However, the existence and role of cells with different alpha 4 activation states in vivo have not been defined. Herein we show that a soluble ligand with the two N-terminal domains of human VCAM-1 fused to a human IgG1 constant region, VCAM-Ig, binds selectively to activated alpha 4-receptors on murine cells, such as those induced by Mn2+ in vitro. To determine whether the cells identified by VCAM-Ig were required under physiologic conditions, we assessed its anti-inflammatory effect. We show that VCAM-Ig is not bound to the majority of murine alpha 4+ cells after in vivo administration, yet it significantly delays the onset of adoptively transferred autoimmune diabetes. Thus, soluble VCAM-Ig can modify alpha 4-dependent disease progression, apparently by its selective action on cells with activated alpha 4-integrin receptors, thereby providing evidence for distinct alpha 4 activation states in vivo.

Animals↗
PubMed1995

The crystal structure of an N-terminal two-domain fragment of vascular cell adhesion molecule 1 (VCAM-1): a cyclic peptide based on the domain 1 C-D loop can inhibit VCAM-1-alpha 4 integrin interaction.

Vascular cell adhesion molecule 1 (VCAM-1) represents a structurally and functionally distinct class of immunoglobulin superfamily molecules that bind leukocyte integrins and are involved in inflammatory and immune functions. X-ray crystallography defines the three-dimensional structure of the N-terminal two-domain fragment that participates in ligand binding. Residues in domain 1 important for ligand binding reside in the C-D loop, which projects markedly from one face of the molecule near the contact between domains 1 and 2. A cyclic peptide that mimics this loop inhibits binding of alpha 4 beta 1 integrin-bearing cells to VCAM-1. These data demonstrate how crystallographic structural information can be used to design a small molecule inhibitor of biological function.

Amino Acid Sequence↗
PubMed1995

Differential proteolytic processing leads to multiple forms of the CA protein in avian sarcoma and leukemia viruses.

The CA (capsid) protein of avian sarcoma and leukemia viruses occurs in multiple species. Only one form has been previously characterized biochemically. We have now determined that the mature CA protein of avian sarcoma and leukemia viruses exists as three species with different C termini, ending in amino acid residues A-476, A-478, and M-479 of the Gag precursor, respectively. These structures were deduced from a combination of cyanogen bromide peptide mapping, sequence analysis of tryptic peptides, and electrospray mass spectrometry. The three forms of CA were detected in the same ratios in Rous sarcoma virus and avian myeloblastosis virus and therefore are likely to represent a common feature of members of this genus of avian retroviruses. The only previously reported CA species, CAM-479, accounts for only about 36% of the total CA protein, while CAA-476 and CAA-478 account for 55 and 9%, respectively. From the analysis of peptides cleaved in vitro by PR, the viral protease, we infer that the cleavage site between A-476 and A-477 not only is recognized by PR but is the preferred site. We were unable to determine if A-478/A-479 is a cleavage site for PR or alternatively if CAA-478 results from further processing of CAM-479 by a carboxypeptidase. To study the biological significance of residues A-477 to M-479, we constructed genetically altered viruses in which deletions removed either residues 477 to 479 or 477 to 488. The resulting virus particles appeared to assembly with normal efficiencies, but the latter mutant showed slowed proteolytic processing. Neither of the mutants was infectious.

Amino Acid Sequence↗
PubMed1995

A direct binding assay for the vascular cell adhesion molecule-1 (VCAM1) interaction with alpha 4 integrins.

Vascular cell adhesion molecule-1 (VCAM1) is a member of the immunoglobulin (Ig) superfamily which interacts with the alpha 4 integrins alpha 4 beta 1 (very late antigen 4: VLA4) and alpha 4 beta 7, which are constitutively expressed on many leukocyte subsets and play a key role in cell trafficking and activation. Using a recombinant VCAM-IgG fusion protein (VCAM-Ig) as a soluble ligand for alpha 4 beta 1 we directly demonstrated by fluorescence analysis that the alpha 4 beta 1 receptor can exist in different affinity states on the cell surface, and that a high affinity state is induced by manganese ions or certain activating anti-beta 1 monoclonal antibodies (Jakubowski et al., 1995b). Here we have extended these observations by developing a rapid and reproducible assay using alkaline phosphatase (AP)-coupled VCAM-Ig (VCAM-Ig-AP) which measures the interaction between VCAM1 and alpha 4 integrins in a microtiter plate format. This assay has allowed us to evaluate directly the effects of metal ions, anti-beta 1 mAbs, and different cell types and species on the VCAM1/alpha 4 integrin interaction. Most importantly, the assay system provides a means to rapidly evaluate alpha 4 integrin-directed inhibitors without the complication of post-ligand binding events inherent in adhesion assays.

Animals↗
PubMed1994

Specific inhibition of a human papillomavirus E2 trans-activator by intracellular delivery of its repressor.

Papillomaviruses are the causative agents of benign and malignant epithelial tumors of the skin and mucosa. They encode a DNA-binding protein, E2, that regulates viral transcription and replication, making it an important therapeutic target. By deleting the amino-terminal trans-activation domain of human papillomavirus type 16 (HPV-16) E2 while retaining its carboxy-terminal DNA binding and dimerization domain, an E2 repressor (E2R) that efficiently inhibits transcriptional activation by full-length HPV E2 was generated. To deliver this repressor protein into animal cells, we have utilized the human immunodeficiency virus type 1 (HIV-1) Tat protein which itself is taken up efficiently into intact cells. Chimeras of E2R and the cellular uptake domain of Tat specifically inhibited E2-dependent reporter gene expression in COS-7 cells. Treatment of cervical intraepithelial neoplasia cells having episomally replicating HPV-31 DNA with this Tat-E2R protein led to a dose-dependent loss of HPV DNA copies and inhibition of cell growth. Tat-mediated delivery can be a valuable tool for assessing protein function and may allow the development of novel therapeutic proteins having intracellular targets.

Amino Acid Sequence↗
PubMed1993

The tryptophan bridge is a critical feature of the papillomavirus E2 DNA binding domain.

The papillomavirus E2 protein is a DNA binding protein that regulates viral transcription and replication. E2 binds DNA as a dimer. Recent crystallographic data for E2 complexed to DNA revealed that novel peptide structures in E2 mediated dimerization and DNA binding. To identify important features of these motifs we have used limited proteolysis and urea denaturation as biochemical probes for structure, applying these techniques to E2 alone, E2 bound to DNA, cross-linked products, and mutants that were targeted at Trp360, a contact point along the dimer interface. DNA binding stabilized E2 structure, shifting the point at which it denatures from 5 to 7.6 M urea. In contrast, Trp360 mutant proteins, while dimeric, were more sensitive to denaturation by urea when bound to DNA. The most striking results came from uv cross-linking studies in which Trp360 was targeted as the site of cross-linking. Ultraviolet cross-linking dramatically increased the resistance of E2 to proteolysis regardless of the protease tested and with no deleterious effect on the affinity of E2 for DNA. Cross-linking through Cys356 with bismaleimidohexane did not promote stabilization. The ability to stabilize or destabilize E2 by Trp360-targeted modifications demonstrates the importance of the Trp360-Trp360 interaction, which may represent a general feature of the beta-barrel motif.

Base Sequence↗
PubMed1993

Mullerian inhibiting substance requires its N-terminal domain for maintenance of biological activity, a novel finding within the transforming growth factor-beta superfamily.

Mullerian inhibiting substance (MIS)/anti-Mullerian hormone is a differentiation factor that causes regression of the Mullerian duct in the developing male fetus and an apparent sex reversal of the fetal ovary when inappropriately exposed to it. The purified product is a 140-kilodalton glycoprotein composed of two identical subunits. We show that a C-terminal fragment of MIS, which shares homology with transforming growth factor-beta, causes regression of the Mullerian duct and inhibits the biosynthesis of aromatase in the fetal ovary. However, both activities are enhanced dramatically by addition of the N-terminal portion of MIS. Under conditions where potentiation occurs, the N- and C-terminal domains of MIS reassociate. These results indicate that the N-terminus of MIS, unlike that of the other members of the transforming growth factor-beta family, plays a role in maintaining the biological activity of the C-terminus.

Animals↗
PubMed1992

Expression, purification and biochemical comparison of natural and recombinant human non-pancreatic phospholipase A2.

The gene coding for human non-pancreatic phospholipase A2 (npPLA2) was cloned in a eukaryotic expression vector and transfected into chinese hamster ovary (CHO) cells. A number of cell lines stably expressing npPLA2 were obtained. Northern analysis of these cell lines showed an abundant transcript of expected size 1200 nt. The recombinant enzyme was efficiently secreted in quantities up to 400 micrograms npPLA2 per liter culture medium in the most productive cell lines. npPLA2 was purified to homogeneity from conditioned medium as previously described (1). The recombinant npPLA2 migrated by SDS--PAGE as a single band with an apparent mass of 14,000. The recombinant enzyme displayed the pH-optimum, calcium dependence and substrate preference that were characteristic of the human platelet and synovial fluid enzymes.

Animals↗