A small-molecule, tight-binding inhibitor of the integrin alpha(4)beta(1) blocks antigen-induced airway responses and inflammation in experimental asthma in sheep.

The leukocyte integrin very late antigen-4 (alpha(4)beta(1), CD49d/CD29) is an adhesion receptor that plays an important role in allergic inflammation and contributes to antigen-induced late responses (LAR) and airway hyperresponsiveness (AHR). In this study, we show that single doses of a new small-molecule, tight-binding inhibitor of alpha(4), BIO-1211, whether given by aerosol or intravenously, either before or 1.5 h after antigen challenge blocks allergen- induced LAR and post-antigen-induced AHR in allergic sheep. Multiple treatments with doses of BIO-1211 that were ineffective when given singly, were protective. BIO-1211 also provided dose-dependent inhibition of the early airway response (EAR) to antigen. In conjunction with the functional protection against the antigen-induced LAR and AHR, sheep treated with BIO-1211 before challenge showed significantly reduced: (1) numbers of eosinophils in bronchoalveolar lavage (BAL), (2) BAL levels of the inflammatory marker tissue kallikrein, and (3) numbers of inflammatory cells (lymphocytes, eosinophils, metachromatic staining cells, and neutrophils) in bronchial biopsies obtained after challenge when compared with corresponding biopsies after vehicle treatment. More importantly, we show for the first time that an inhibitor of alpha(4) was able to reverse post-antigen-induced AHR, thereby decreasing the time of recovery from the normal period of > 9 d to 3 d. Our results show that effective inhibition of antigen-induced airway responses can be achieved with single doses of a potent small-molecule inhibitor of alpha(4) and that such agents may be used therapeutically, as well as prophylactically, to alleviate allergen- induced inflammatory events. These data provide further support and extend the evidence for the role of alpha(4) integrins in the pathophysiologic events that follow airway antigen challenge.

Tat-mediated protein delivery can facilitate MHC class I presentation of antigens.

We have previously shown that the tat protein of HIV-1 can be used as a carrier to promote the intracellular delivery of heterologous proteins. Here we have tested if the tat-delivery technology can be used to direct MHC class I presentation of native protein, using ovalbumin (OVA) as a model system. We show that a tat-ovalbumin conjugate (tatOVA) can be delivered into cells and that subsequent processing and presentation occurs, resulting in effective and specific killing of these target cells by an OVA specific cytotoxic T-lymphocyte (CTL) line. Comparison with the E.G7 line that expresses the OVA gene indicates that tat-mediated delivery is as efficient as endogenous expression in this system. Tat-mediated antigenic protein delivery may be useful both as a research technique and, potentially, as a therapeutic or prophylactic vaccine.

The exon 3 encoded sequence of the intracellular serine proteinase inhibitor plasminogen activator inhibitor 2 is a protein binding domain.

We have used a combination of biochemical and immunological methods to probe for proteins that interact with the cytoplasmic form of plasminogen activator inhibitor 2 (PAI-2) and to identify the structure in PAI-2 that mediates the binding. By affinity chromatography on immobilized PAI-2, we purified a collection of PAI-2-binding proteins. These proteins bound 125I-labeled PAI-2 in vitro (IC50, approximately 10-100 nM) in a calcium-independent reaction that did not abrogate the proteinase inhibitory function of PAI-2. Annexin I was identified among the eluted proteins, and purified annexins I, II, IV, and V, but not III and VI, possessed 125I-labeled PAI-2 binding activity. Immune precipitation by anti-PAI-2 monoclonal and polyclonal antibodies of metabolically labeled melanoma cells treated with a cleavable cross-linker prior to analysis revealed three prominent proteins with apparent masses of 100, 70, and 50 kDa. We localized the protein binding domain in PAI-2 between amino acid residues 66 and 98, as determined by using a PAI-2 mutant lacking this domain and a synthetic peptide spanning this region. This region of PAI-2 corresponds to exon 3 of the gene sequence thought to be critical for PAI-2 functions.

The role of alpha 4 integrins in lung pathophysiology.

The alpha 4 integrins are heterodimeric leucocyte cell surface molecules central to their cell and matrix adhesive interactions. The integrin alpha 4 beta 1 interacts with the immunoglobulin superfamily member vascular cell adhesion molecule-1 (VCAM-1), and with an alternatively spliced form of fibronectin. The integrin alpha 4 beta 7 binds not only VCAM-1 and fibronectin, but also the mucosal addressin cell adhesion molecule (MAdCAM). Certain monoclonal antibodies (MoAbs) to the alpha 4 chain of alpha 4 beta 1 and alpha 4 beta 7 can block their in vitro adhesive function. In vivo studies with these MoAbs in lung antigen challenge models in several species demonstrate that alpha 4 integrins play a key role in eosinophil and T-cell recruitment, in the late phase response, and in airways hyperresponsiveness. In particular, MoAb HP1/2 is efficacious in a sheep model of allergic airways challenge, whether given intravenously or as aerosol. To evaluate the mechanism of action of this MoAb, Fab fragments were generated and shown to be equipotent in vitro and as efficacious in vivo as the intact immunoglobulin G (IgG). These data demonstrate that the in vivo efficacy of monoclonal antibody HP1/2 is not due to indirect effects, such as antigen cross-linking, but rather to blockade of alpha 4 integrin adhesive function. Humanized monoclonal antibody or other alpha 4 integrin antagonists may provide novel therapeutics for asthma.

Structure of a functional fragment of VCAM-1 refined at 1.9 a resolution.

The crystal structure of the functional amino-terminal two-domain fragment of human vascular cell adhesion molecule 1 (VCAM-1) has been determined at 1.9 A resolution. The crystals contain two copies of the molecule in the asymmetric unit. The structure was solved by multiple isomorphous replacement, using lead and selenium derivatives. Anomalous scattering had to be used to resolve the phase ambiguity of a lead derivative. Since the selenium derivative has very small isomorphous differences, the local scaling algorithm had to be used to obtain an interpretable difference Patterson map. The initial phases were improved by non-crystallographic averaging, solvent flattening and histogram matching. The structure has been refined to a crystallographic R factor of 20.4% (15-1.9 A, F>/= 3sigma) and consists of two Ig domains (D1 and D2). The angle between these domains differs by 12 degrees between the two copies of the molecule in the crystallographic asymmetric unit, demonstrating that some movement is possible at the interface. In the amino-terminal domain D1 there is an 'extra' disulfide bond, in addition to the conserved cross-sheet disulfide bond, at the top of the molecule. This bond, a hallmark of the integrin-binding subclass of Ig superfamily proteins, makes the top of this domain very compact. The feature that projects most prominently from D1 is the CD loop, near the base of the domain. The key residue for integrin binding, Asp40, is located in this loop and is easily accessible.

Increased cellular uptake of the human immunodeficiency virus-1 Tat protein after modification with biotin.

The human immunodeficiency virus-1 Tat protein can efficiently enter cells when added exogenously in tissue culture. Using the transactivation activity of Tat as a measure of intracellular delivery, we found that the addition of hydrophobic groups to Tat potentiated its uptake. Biotin was the most promising of the reagents tested and we characterized this effect in more detail. When coupled through a cysteine thiol, the addition of a single biotin to Tat increased activity by about six-fold. Increased activity was only seen with reducible biotin analogs, as modification with noncleavable analogs is known to block Tat transactivation activity. Biotin had no effect on Tat uptake when mixed with Tat without cross-linking. Recently, Tat was used as a carrier to direct the uptake of heterologous proteins into cells. We have used RNase as a model system for studying Tat-mediated uptake and found that biotin also increased the delivery of a Tat37-58-RNase conjugate. The increased uptake of Tat and Tat conjugates by addition of hydrophobic groups may significantly enhance the usefulness of Tat as a delivery vehicle, and the approach may be applicable to other systems.

Crystallization and preliminary crystallographic analysis of the N-terminal two domain fragment of vascular cell adhesion molecule-1 (VCAM-1).

A molecular fragment comprising the first two domains of the human vascular cell adhesion molecule-1 (VCAM-1) has been crystallized by the vapor diffusion method. Two crystal forms have been examined by X-ray analysis: One crystal form belongs to the space group C2 with two molecules in the asymmetric unit and cell parameters: a = 122.1 A, b = 48.9 A, c = 73.4 A, and beta = 117.4 degrees. The other crystal form belongs to the space group P2(1) with one molecule in the asymmetric unit and cell parameters: a = 40.4 A, b = 45.7 A, c = 54.7 A, and beta = 100.5 degrees. Diffraction data up to 1.9 A resolution have been collected for the C2 crystal form.

Lipocortin 2 (annexin 2) is a major substrate for constitutive tyrosine kinase activity in chondrocytes.

Treatment of cultured bovine articular chondrocytes with 100 microM orthovanadate, in the absence of serum, results in the production of a single major tyrosine phosphorylated protein with an apparent molecular mass of 36 kDa (p36). Chondrocytes were found to contain proteins reactive with anti-lipocortin 1, 2, and 5 antibodies. p36 comigrated on SDS-polyacrylamide gels with lipocortin 2, but not with other members of the lipocortin family. The distribution of p36 between the particulate and soluble cell fractions was also similar to that of lipocortin 2. p36 that was purified on an anti-phosphotyrosine immunoaffinity column cross-reacted with anti-lipocortin 2 antibodies. Similarly, lipocortin 2 purified on an anti-lipocortin 2 immunoaffinity column reacted with anti-phosphotyrosine antibodies. Furthermore, cyanogen bromide cleavage fragments of purified lipocortin 2 and p36 were similar. These data demonstrate that the major constitutively tyrosine phosphorylated protein, in chondrocytes, is lipocortin 2. Tyrosine phosphorylated p36 required SDS buffers for extraction due to a loss of the tyrosine phosphate group under other solubilization conditions using Triton X-100 or sodium cholate. This study provides a system for the study of the effects of tyrosine phosphorylation on lipocortin 2 function. What role lipocortin 2 plays in chondrocyte biology remains to be determined.

Alpha 4-integrins mediate antigen-induced late bronchial responses and prolonged airway hyperresponsiveness in sheep.

Eosinophils and T lymphocytes are thought to be involved in allergic airway inflammation. Both cells express the alpha 4 beta 1-integrin, very late antigen-4 (VLA-4, CD49d/CD29); alpha 4-integrins can promote cellular adhesion and activation. Therefore, we examined the in vivo effects of a blocking anti-alpha 4 monoclonal antibody, HP 1/2, on antigen-induced early and late bronchial responses, airway hyperresponsiveness, inflammatory cell influx, and peripheral leukocyte counts in allergic sheep. Sheep blood lymphocytes, monocytes, and eosinophils expressed alpha 4 and bound HP 1/2. In control sheep, Ascaris antigen challenge produced early and late increases in specific lung resistance of 380 +/- 42% and 175 +/- 16% over baseline immediately and 7 h after challenge, respectively, as well as airway hyperresponsiveness continuing for 14 d after antigen challenge. Treatment with HP 1/2 (1 mg/kg, i.v.) 30 min before antigen challenge did not affect the early increase in specific lung resistance but inhibited the late-phase increase at 5-8 h by 75% (P < 0.05) and inhibited the post-antigen-induced airway hyperresponsiveness at 1, 2, 7, and 14 d (P < 0.05, for each time). Intravenous HP 1/2 given 2 h after antigen challenge likewise blocked late-phase airway changes and postchallenge airway hyperresponsiveness. Airway administration of HP 1/2 (16-mg dose) was also effective in blocking these antigen-induced changes. Response to HP 1/2 was specific since an isotypic monoclonal antibody, 1E6, was ineffective by intravenous and aerosol administration. Inhibition of leukocyte recruitment did not totally account for the activity of anti-alpha 4 antibody since HP 1/2 neither diminished the eosinopenia or lymphopenia that followed antigen challenge nor consistently altered the composition of leukocytes recovered by bronchoalveolar lavage. Because airway administration of HP 1/2 was also active, HP 1/2 may have inhibited cell activation. Reduction of platelet-activating factor-induced eosinophil peroxidase release from HP 1/2-treated eosinophils supports such a mechanism. These findings indicate a role for alpha 4-integrins in processes that lead to airway late phase responses and persisting airway hyperresponsiveness after antigen challenge.

Tat-mediated delivery of heterologous proteins into cells.

The Tat protein of human immunodeficiency virus 1 (HIV-1) can enter cells efficiently when added exogenously in tissue culture. To assess if Tat can carry other molecules into cells, we chemically cross-linked Tat peptides (residues 1-72 or 37-72) to beta-galactosidase, horseradish peroxidase, RNase A, and domain III of Pseudomonas exotoxin A (PE) and monitored uptake colorimetrically or by cytotoxicity. The Tat chimeras were effective on all cell types tested, with staining showing uptake into all cells in each experiment. In mice, treatment with Tat-beta-galactosidase chimeras resulted in delivery to several tissues, with high levels in heart, liver, and spleen, low-to-moderate levels in lung and skeletal muscle, and little or no activity in kidney and brain. The primary target within these tissues was the cells surrounding the blood vessels, suggesting endothelial cells, Kupffer cells, and/or splenic macrophages. Tat-mediated uptake may allow the therapeutic delivery of macromolecules previously thought to be impermeable to living cells.

Attenuation of colitis in the cotton-top tamarin by anti-alpha 4 integrin monoclonal antibody.

Recent studies have demonstrated the induced expression of endothelial adhesion molecules including E-selectin (also called endothelial leukocyte adhesion molecule-1), vascular cell adhesion molecule and intercellular adhesion molecule in actively involved mucosa of patients with ulcerative colitis and Crohn's disease. Similar induction has been demonstrated in the colon of the Cotton-top tamarin (CTT), a New World primate that experiences a spontaneous acute and chronic colitis resembling ulcerative colitis. To assess the potential importance of leukocyte adhesion as a necessary step in acute colitis, the effect of parenteral mAb directed against adhesion molecules on CTT colitis was evaluated in placebo-controlled blinded trials. Serial administration of either of two anti-E-selectin mAb designated BB11 and EH8 effectively coated endothelial surfaces expressing this vascular adhesion molecule. Although colitis activity was slightly diminished after the 10-d treatment period in CTT receiving either BB11 or EH8, this reduction was not significantly different than that seen in animals given a placebo control when assessed by a previously validated standardized scale of inflammatory activity: mean histologic activity grade 2.2 +/- 0.2 pretreatment vs 1.5 +/- 0.5 posttreatment in group receiving mAb and 2.1 +/- 0.1 pretreatment vs 1.3 +/- 0.5 posttreatment in the placebo group (P > 0.2). In contrast, administration of an anti-alpha 4 integrin mAb designated HP1/2 that binds VLA4 (alpha 4 beta 1) and presumably alpha 4 beta 7 integrins resulted in significant attenuation of acute colitis when compared to both pretreatment activity index (P = 0.005) and the placebo control group (P < 0.01): mean histologic activity grade 1.6 +/- 0.3 pretreatment vs 0.2 +/- 0.1 posttreatment in the group receiving HP1/2 and 1.8 +/- 0.5 pretreatment and 1.2 +/- 0.2 posttreatment in the placebo control group. These studies using a model of spontaneous colitis in the CTT demonstrate the feasibility of modulation of leukocyte-vascular adhesion and/or other integrin-mediated events possibly including T cell aggregation and T cell-stromal interactions, as well as lymphocyte homing. These results suggest both that these processes are important and possibly essential elements in sustaining acute colitis and that their disruption may result in therapeutic benefit.

Structure/function studies on vascular cell adhesion molecule-1.

Vascular cell adhesion molecule-1 (VCAM1) is a member of the immunoglobulin (Ig) superfamily which interacts with the integrin very late antigen-4 (VLA4). The VCAM1/VLA4 interaction mediates both adhesion and signal transduction and is thought to play an important role in inflammatory and immune responses in vivo. The major form of human VCAM1 contains seven extracellular Ig-like domains, with domain 1 designated as the most N-terminal. We have examined the relationship between human VCAM1 structure and function using a combination of domain truncation mutants and proteolytic fragmentation of recombinant soluble VCAM1. We have characterized two regions of VCAM1, localized to domains 4 and 5, which are highly sensitive to proteolytic cleavage, localized the epitope of the blocking monoclonal antibody 4B9 to domain 1, and found that domains 1-3 are sufficient for both its adhesive function and its ability to initiate T cell activation.

Cooperative binding of the E2 protein of bovine papillomavirus to adjacent E2-responsive sequences.

The DNA-binding properties of purified full-length E2 protein from bovine papillomavirus type 1 have been investigated by utilizing a quantitative gel shift analysis. By using a recombinant baculovirus which express the E2 open reading frame from the polyhedrin promoter, the full-length E2 protein was synthesized in insect cells and purified to homogeneity by using an E2 binding site (ACCGN4CGGT)-specific oligonucleotide column. The Kd of E2 binding to a 41-bp oligonucleotide containing a single binding site was found to be 2 x 10(-11) M. When two binding sites were included on an oligonucleotide, cooperative binding to these sites by the E2 protein was observed. A cooperativity parameter of 8.5 was determined for E2 binding to two sites. An 86-amino-acid peptide encompassing the C terminus of the protein retains the ability to bind E2 binding sites with a Kd of 4 x 10(-10) M but exhibits slight cooperativity of binding to two adjacent sites. A major determinant for cooperative binding of the full-length E2 protein is thus encoded by the N-terminal amino acids outside the minimal DNA binding domain.

Minimal antiproliferative effect of recombinant müllerian inhibiting substance on gynecological tumor cell lines and tumor explants.

Múllerian Inhibiting Substance (MIS) is a testicular hormone that promotes involution of the Múllerian duct during embryogenesis. The Múllerian duct gives rise to adult female reproductive ducts including the fallopian tubes, uterus, and upper vagina. Thus, testicular MIS ensures the regression of female sex organ primordia. Partially purified bovine MIS was reported to inhibit proliferation of tumor cells derived from human gynecological cancers. These observations suggest that MIS might be an effective anticancer agent for some human tumors. Recombinant human MIS (rHu-MIS) has recently become available. To assess the antiproliferative activity of rHu-MIS, we examined its effects on 11 ovarian, six endometrial, and two nongynecological human tumor cell lines. rHu-MIS had no effect on proliferation of these cell lines in five independent assays. Forty-three primary human tumor explants were also examined in human tumor colony forming assays, gel-supported primary culture assays, and subrenal capsule assays. rHu-MIS significantly inhibited the growth of five of these tumors including four ovarian and one small cell lung cancer explant. The four ovarian cancer responses include three of 13 (23%) explants tested in human tumor colony-forming assays and one of eight (12.5%) explants tested in gel-supported primary culture assays. We conclude that rHu-MIS may have antiproliferative activity against some human ovarian cancers.