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Biomedical subjects

W J Dower

Publications and source records attributed to W J Dower.

At least 19 recordsLinked to original sources
PubMed1998

Identification of a 13 amino acid peptide mimetic of erythropoietin and description of amino acids critical for the mimetic activity of EMP1.

To obtain information about the functional importance of amino acids required for effective erythropoietin (EPO) mimetic action, the conserved residues of a peptide mimetic of EPO, recently discovered by phage display, were subjected to an alanine replacement strategy. Further, to identify a minimal mimetic peptide sequence, a series of truncation peptides has been generated. One EPO mimetic peptide sequence, EMP1, was targeted and more than 25 derivatives of this sequence were evaluated for their ability to compete with [125I]EPO for receptor binding and for their ability to support the proliferation of two EPO-responsive cell lines. Two hydrophobic amino acids, Tyr4 and Trp13, appear essential for mimetic action, and aromatic residues appear to be important at these sites. These findings are consistent with the previously reported X-ray crystal structure of EMP1 complexed with the extracellular domain of the EPO receptor (EPO binding protein; EBP). In our efforts to define the structural elements required for EPO mimetic action, a 13 amino acid peptide was identified which possesses mimetic properties and contains a minimal agonist epitope. The ability of this peptide to effectively serve as a mimetic capable of the induction of EPO-responsive cell proliferation appears to reside within a single residue, equivalent to position Tyr4 of EMP1, when present in a sequence that includes the cyclic core peptide structure. Although these peptides are less potent than EPO, they should serve as an excellent starting point for the design of compounds with EPO mimetic activity.

Alanine↗
PubMed1998

Peptide agonists of the thrombopoietin receptor.

We have screened a variety of L-amino acid peptide libraries against the extracellular domain of the human thrombopoietin (HuTPO) receptor, c-Mpl. A large number of peptide ligands were recovered and categorized into two families. Peptides from each family compete with the binding of HuTPO and with the binding of peptides from the other familiy. Representative peptides were synthesized and found to activate the full-length HuTPO receptor expressed in Ba/F3 cells to promote proliferation. These peptide families show no apparent homology to the primary sequence of TPO. We have focused our optimization efforts on one of the peptides, a linear 14-mer (IEGPTLRQWLAARA) with an IC50 of 2 nM in a competition binding assay and an EC50 of 400 nM in the proliferation assay. In order to enhance the potency of the compound, we constructed dimeric peptides by linking the carboxy-termini of the 14-mers to a lysine branch. These molecules exhibited slightly higher affinity (0.5 nM) and greatly increased potency (0.1 nM). The EC50 of the dimeric peptide was equivalent to that of the 332 aa form of baculovirus-expressed recombinant HuTPO. As previously shown for the erythropoietin-mimetic peptides, the TPO-mimetic peptides probably activate the TPO receptor by binding and inducing receptor dimerization. This supposition is supported by the observation that covalent dimerization of the peptide enhances its potency by 4,000-fold over that of the monomer. The peptide dimer is also active in stimulating in vitro proliferation of progenitors and maturation of megakaryocytes from human bone marrow, and in promoting an increase in platelet count when administered to normal mice.

Amino Acid Sequence↗
PubMed1998

Targeting growth factor and cytokine receptors with recombinant peptide libraries.

The single-transmembrane-spanning receptors of cytokines and growth factors have historically proven resistant to the small-molecule screening efforts of the pharmaceutical industry. Advances in combinatorial library approaches to ligand discovery have begun to show success with these targets. There are several recent reports of peptides, derived from randomly assembled collections of L-peptides expressed in recombinant display vectors, that are high-affinity antagonists and even agonists of these receptors. These results indicate that molecules much smaller than the natural protein factors can interact effectively with these receptors, and this may lead the way to the discovery of even smaller nonpeptidic agents.

Amino Acid Sequence↗
PubMed1997

Peptide agonist of the thrombopoietin receptor as potent as the natural cytokine.

Two families of small peptides that bind to the human thrombopoietin receptor and compete with the binding of the natural ligand thrombopoietin (TPO) were identified from recombinant peptide libraries. The sequences of these peptides were not found in the primary sequence of TPO. Screening libraries of variants of one of these families under affinity-selective conditions yielded a 14-amino acid peptide (Ile-Glu-Gly-Pro-Thr-Leu-Arg-Gln-Trp-Leu-Ala-Ala-Arg-Ala) with high affinity (dissociation constant approximately 2 nanomolar) that stimulates the proliferation of a TPO-responsive Ba/F3 cell line with a median effective concentration (EC50) of 400 nanomolar. Dimerization of this peptide by a carboxyl-terminal linkage to a lysine branch produced a compound with an EC50 of 100 picomolar, which was equipotent to the 332-amino acid natural cytokine in cell-based assays. The peptide dimer also stimulated the in vitro proliferation and maturation of megakaryocytes from human bone marrow cells and promoted an increase in platelet count when administered to normal mice.

Amino Acid Sequence↗
PubMed1997

Increased potency of an erythropoietin peptide mimetic through covalent dimerization.

We have synthesized a chemically defined, dimeric form of an erythropoietin mimetic peptide (EMP) that displays 100-fold increased affinity for the erythropoietin receptor (EPOR) and correspondingly elevated potency in cell-based assays and in mice. The dimeric EMP1 was synthesized using a C-terminal lysine residue as a branch point. A beta-alanine residue was coupled to the main-chain (alpha) amino group of the lysine residue in order to provide a pseudosymmetrical scaffold where both the side-chain and main-chain were of approximately equal length. Using an orthogonal protection system, independently disulphide-cylized EMP1 moieties were synthesized upon this scaffold. The proposed mechanism of increased potency of the dimer over the parental compound EMP1 is consistent with the structure of a cocrystal of EMP1 and the extracellular domain of the EPOR in which a noncovalent peptide dimer is seen spanning the cleft between two molecules of the EPOR extracellular domain.

Amino Acid Sequence↗
PubMed1996

Small peptides as potent mimetics of the protein hormone erythropoietin.

Random phage display peptide libraries and affinity selective methods were used to isolate small peptides that bind to and activate the receptor for the cytokine erythropoietin (EPO). In a panel of in vitro biological assays, the peptides act as full agonists and they can also stimulate erythropoiesis in mice. These agonists are represented by a 14- amino acid disulfide-bonded, cyclic peptide with the minimum consensus sequence YXCXXGPXTWXCXP, where X represents positions allowing occupation by several amino acids. The amino acid sequences of these peptides are not found in the primary sequence of EPO. The signaling pathways activated by these peptides appear to be identical to those induced by the natural ligand. This discovery may form the basis for the design of small molecule mimetics of EPO.

Amino Acid Sequence↗
PubMed1996

Functional mimicry of a protein hormone by a peptide agonist: the EPO receptor complex at 2.8 A.

The functional mimicry of a protein by an unrelated small molecule has been a formidable challenge. Now, however, the biological activity of a 166-residue hematopoietic growth hormone, erythropoietin (EPO), with its class 1 cytokine receptor has been mimicked by a 20-residue cyclic peptide unrelated in sequence to the natural ligand. The crystal structure at 2.8 A resolution of a complex of this agonist peptide with the extracellular domain of EPO receptor reveals that a peptide dimer induces an almost perfect twofold dimerization of the receptor. The dimer assembly differs from that of the human growth hormone (hGH) receptor complex and suggests that more than one mode of dimerization may be able to induce signal transduction and cell proliferation. The EPO receptor binding site, defined by peptide interaction, corresponds to the smaller functional epitope identified for hGH receptor. Similarly, the EPO mimetic peptide ligand can be considered as a minimal hormone, and suggests the design of nonpeptidic small molecule mimetics for EPO and other cytokines may indeed be achievable.

Amino Acid Sequence↗
PubMed1996

High affinity type I interleukin 1 receptor antagonists discovered by screening recombinant peptide libraries.

Two families of peptides that specifically bind the extracellular domain of the human type I interleukin I (IL-1) receptor were identified from recombinant peptide display libraries. Peptides from one of these families blocked binding of IL-lalpha to the type I IL-1 receptor with IC50 values of 45-140 microM. Affinity-selective screening of variants of these peptides produced ligands of much higher affinity (IC50 approximately 2 nM). These peptides block IL-1-driven responses in human and monkey cells; they do not bind the human type II IL-1 receptor or the murine type I IL-1 receptor. This is the first example (that we know of) of a high affinity peptide that binds to a cytokine receptor and acts as a cytokine antagonist.

Animals↗
PubMed1996

Toward cell-targeting gene therapy vectors: selection of cell-binding peptides from random peptide-presenting phage libraries.

Ideal gene therapy vectors would be delivered intravenously to transfect only specific cells. Existing vectors only transfect cells in vivo in a manner determined by blood flow and the site of introduction. As a general and systematic approach for generating cell-targeting ligands for gene therapy vectors, we have used peptide-presenting phage libraries to select peptides that bind and enter several different cell types. Because of their small size, cell-binding peptides such as these could be incorporated into biological or physical gene therapy vectors. In addition, peptide-presenting phage themselves may also be candidates for gene therapy vectors.

Amino Acid Sequence↗
PubMed1995

A generic method for expression and use of "tagged" soluble versions of cell surface receptors.

A general method for expression, purification, immobilization, detection and radiolabeling of extracellular domains (ECD) of type I membrane proteins. The type I interleukin-1 receptor (IL-1RtI), the alpha-subunit of interleukin-2 receptor (IL-2R alpha) and E-selectin are used as illustrative examples of cell surface receptors. DNA encoding the ECD of the proteins are fused at their 3' end to a chimeric DNA which serves to generically "tag" the recombinant ECD. The resulting fusion protein contains a substrate sequence for protein kinase-A (PKA) adjacent to the signal sequence from human placental alkaline phosphatase (HPAP), The HPAP signal sequence directs the formation of the phosphatidylinositol-glycan (PI-G) anchorage of the protein at the cell surface. When these chimeric genes are expressed in CHO cells, the ECDs are detected on the cell surface and can be released by treatment with phosphatidylinositol-specific phospholipase-C (PI-PLC). Based on protein processing known to occur for native HPAP, twenty amino acids from the HPAP signal sequence remain at the C-terminus of the ECD. A high affinity monoclonal antibody was generated against this common epitope. This antibody can be used to detect, purify and immobilize the ECDs. In addition, the ECDs can be radiolabeled with 32P by treatment with PKA and maintain the ability to bind their natural ligands. This "tagging" method has been successfully applied to many other type I proteins which serve as cell surface receptors.

Alkaline Phosphatase↗
PubMed1994

An in vitro polysome display system for identifying ligands from very large peptide libraries.

We have used an in vitro protein synthesis system to construct a very large library of peptides displayed on polysomes. A pool of DNA sequences encoding 10(12) random decapeptides was incubated in an Escherichia coli S30 coupled transcription/translation system. Polysomes were isolated and screened by affinity selection of the nascent peptides on an immobilized monoclonal antibody specific for the peptide dynorphin B. The mRNA from the enriched pool of polysomes was recovered, copied into cDNA, and amplified by the polymerase chain reaction (PCR) to produce template for the next round of in vitro synthesis and selection. A portion of the amplified template from each round was cloned into a filamentous phagemid vector to determine the specificity of peptide binding by phage ELISA and to sequence the DNA. After four rounds of affinity selection, the majority of clones encoded peptides that bound specifically to the antibody and contained a consensus sequence that is similar to the known epitope for the antibody. Synthetic peptides corresponding to several of these sequences have binding affinities ranging from 7 to 140 nM. The in vitro system described here has the potential to screen peptide libraries that are three to six orders of magnitude larger than current biological peptide display systems.

Amino Acid Sequence↗
PubMed1994

Synthetic peptide ligands of the antigen binding receptor induce programmed cell death in a human B-cell lymphoma.

Peptide ligands for the antigen binding site of the surface immunoglobulin receptor of a human B-cell lymphoma cell line were identified with the use of filamentous phage libraries displaying random 8- and 12-amino acid peptides. Corresponding synthetic peptides bound specifically to the antigen binding site of this immunoglobulin receptor and blocked the binding of an anti-idiotype antibody. The ligands, when conjugated to form dimers or tetramers, induced cell death by apoptosis in vitro with an IC50 between 40 and 200 nM. This effect was associated with specific stimulation of intracellular protein tyrosine phosphorylation.

Amino Acid Sequence↗