PubMed Health⌕ Search

Biomedical subjects

M A Horton

Publications and source records attributed to M A Horton.

At least 19 recordsLinked to original sources
PubMed1992

A nonradioactive biochemical characterization of membrane proteins using enhanced chemiluminescence.

Here we demonstrate a nonradioactive immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) technique which replaces the standard practice of isotopic protein labeling by iodination or metabolic tagging in the analysis of membrane proteins. The technique has proved extremely valuable in the biochemical analysis of small quantities of frozen, pathological tissue. Membranes were prepared from Dx3 (a human melanoma cell line), C6 (a rat glial cell line), and osteoclastoma (a human giant cell tumor of bone). The membranes were labeled with biotin and immunoprecipitated with a variety of antibodies to the vitronectin receptor (VNR). The VNR proteins were resolved by SDS-PAGE and immunoblotted onto nitrocellulose paper. The biotinylated protein was visualized using streptavidin horseradish peroxidase and enhanced chemiluminescence (ECL). Film exposures ranged from 15 min to 16 h. Good visualization of the VNR, yielding the typical heterodimeric receptor of 90 and 150 kDa, was given. Signals generated were high and background noise low with a 30-min film exposure. An overnight exposure increased the detection of weaker bands. In conclusion, biotinylation of membrane proteins proved a satisfactory label for immunoprecipitation and SDS-PAGE analysis. The ECL development stage was extremely flexible with visualization of strong and weak signals. The method has several advantages over a conventional radioactive immunoprecipitation in that it is relatively inexpensive, simple, quick and nonhazardous.

Biotin↗
PubMed1992

Rat osteoclasts adhere to a wide range of RGD (Arg-Gly-Asp) peptide-containing proteins, including the bone sialoproteins and fibronectin, via a beta 3 integrin.

The ligand binding ability of rat osteoclast adhesion receptors was investigated in an attachment assay using osteoclasts disaggregated from bone. Osteoclasts adhered well to the Arg-Gly-Asp (RGD)-containing proteins osteopontin (bone sialoprotein I) and BSP (bone sialoprotein II), vitronectin, fibrinogen, von Willebrand factor, and fibronectin. Osteoclasts also adhered, but less strongly, to type I collagen. No attachment of osteoclasts was observed to thrombospondin, tenascin, laminin, or a range of non-RGD-containing bone proteins and proteins from other sources. The attachment of osteoclasts to all ligands was abolished in the presence of GRGDSP peptide, indicating the involvement of the RGD cell binding sequence in ligand binding. Attachment of osteoclasts to all substrates, with the exception of type I collagen, was also strongly inhibited by the addition of monoclonal antibody F11 to the beta 3 integrin subunit, indicating that a beta 3 integrin, probably the vitronectin receptor, was involved. Attachment to type I collagen was blocked by EDTA chelation of divalent cations and was not significantly affected by anti-beta 3 or anti-beta 1 antibodies; when taken with the inhibition by RGD peptide, this suggests the involvement of various receptors, possibly including nonintegrin collagen receptors, in the binding of osteoclasts to this protein. These results define the wide range of ligands for extracellular matrix receptors in osteoclasts in vitro. It remains to be established which of these proteins are important in osteoclast adhesion and osteoclastic bone resorption in vivo.

Amino Acid Sequence↗
PubMed1992

Integrins on rat osteoclasts: characterization of two monoclonal antibodies (F4 and F11) to rat beta 3.

Two monoclonal antibodies, F4 and F11, were raised to newborn rat bone cell suspensions. These antibodies are shown by immunocytochemistry on tissue sections to recognize an antigen shared between osteoclasts, megakaryocytes, and platelets. Immunoprecipitation analysis of the antigen from C6 rat glial cells followed by SDS-PAGE showed a heterodimeric molecule with a characteristic integrin-like shift in apparent molecular mass upon reduction (137/78 kD nonreduced; 118/100 kD reduced); the low-molecular-mass band comigrates with the beta 3 subunit precipitated with polyclonal antihuman vitronectin receptor antiserum, and the high-molecular-mass band comigrates with the alpha v subunit precipitated with a polyclonal antiserum to a C-terminal amino acid sequence of human alpha v. Antibody F4 strongly cross-reacts with human cells and is shown in cross-blocking experiments and immunoprecipitation analysis with a human melanoma cell line DX3 to recognize a seemingly identical molecule as identified by anti-alpha v beta 3 monoclonal antibody 23C6. Expression of F4 and F11 is reduced in platelets from a patient heterozygous for Glanzmann's thrombasthenia. Taken together, these results indicate that F4 and F11 recognize rat CD61, the integrin beta 3 chain, which, as was confirmed with polyclonal anti CD61 antisera, is highly expressed in rat osteoclasts. These antibodies may be useful tools in investigating the biochemical nature and biologic function of beta 3 integrins in rat osteoclasts. Additionally, because high expression of beta 3 in vivo is restricted to osteoclasts, megakaryocytes, and platelets, these antibodies may be used to help identify osteoclasts in tissue sections and bone cell suspensions.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

An assessment of the ability of human bone marrow cultures to generate osteoclasts.

Several groups have successfully generated osteoclasts in cultures of murine haemopoietic cells. This approach would clearly be useful in the analysis of mechanisms of regulation of human osteoclast formation if analogous results could be obtained in cultures of human bone marrow. This communication describes independent attempts by three groups to generate unequivocally defined osteoclasts from bone marrow obtained from human iliac crest, femoral neck, rib, and from foetuses. The haemopoietic tissue was incubated using techniques described by others for production of osteoclast-like cells, and with variants of this technique using strategies based on our experiences with murine osteoclastogenesis. Haemopoietic cells were incubated with calcium regulating hormones, cytokines, osteoblastic supernatants, and osteoblastic or bone marrow stromal cell layers. Formation of cells capable of excavation of bone slices was rarely seen. Despite the paucity of bone resorbing cells, multinucleate cells (MNCs) developed with similar characteristics to the MNCs that have been interpreted as osteoclast-like in human bone marrow cultures. The MNCs were, however, calcitonin-receptor (CTR) negative, and did not show the typical pattern of reactivity with osteoclast-specific antibodies. They possessed instead an antigenic profile characteristic of macrophage polykaryons. We conclude that the MNCs which consistently generate in human bone marrow cultures do not possess phenotypic characteristics specific for osteoclasts and appear to be macrophage polykaryons. The conditions required for osteoclast generation in cultures of human haemopoietic cells remain to be defined.

Bone Marrow Cells↗
PubMed1992

Adhesion receptors are differentially expressed on developing thymocytes and epithelium in human thymus.

The thymic microenvironment consists of a network of interrelated cells of epithelial, fibroblastic, endothelial, and hemopoietic origin. Within this environment, the development of specific T-lymphocyte subpopulations partially depends on the selective interaction of T-cell precursors with such cells. Human thymic epithelial cell strains, generated with a defective retroviral vector containing simian virus 40 (SV40) large T antigen and the neomycin resistance gene or by transfection with an SV40 plasmid defective in the origin of replication, provide useful tools for understanding the mechanisms contributing to the control of T-cell maturation. Because interepithelial, epithelial-macrophage, and lymphocyte-epithelial cell interactions are important for thymocyte differentiation, the distribution of integrin and nonintegrin adhesion receptors on these cells and on developing thymocytes in vivo and in vitro has been examined in detail. Our results indicate that the transformed human thymic epithelial cell strains express the common very late antigen (VLA)-beta 1 receptor and unique alpha chains VLA-2, VLA-3, and VLA-6. The cells are also positive for LFA-3 and ICAM-1 and weakly express beta 3, beta 4, and VNR alpha. They do not express the Leu-cellular adhesion molecules (CAM). This phenotypic profile on cultured thymic epithelium generally corresponds to the distribution of integrin and other receptor molecules on thymic epithelial cells in tissue sections. The majority of thymocytes also express the integrin VLA-beta 1 and -beta 2 chains as well as VLA-4, VLA-6, and LFA-1 alpha(L). Three-color flow cytometric analyses show differential levels of expression of these adhesion receptors on human thymocyte subsets. Taken together with the immunohistochemical localization of extracellular matrix molecules, these studies suggest that both the distribution of receptor-ligand pairs and the level of expression of adhesion molecules may influence T-cell development within the thymus.

Antigens, Polyomavirus Transforming↗
PubMed1991

Integrin expression in human melanoma cell lines: heterogeneity of vitronectin receptor composition and function.

Ten human melanoma cell lines were examined for integrin-receptor expression using a panel of antibodies directed against different integrin subunits. Considerable heterogeneity was detected for levels of expression of 7 integrins, including the alpha v beta 3 vitronectin receptor where a correlation between tumorigenic capacity in athymic nude mice and alpha v beta 3 levels was found. Detailed analysis of the vitronectin receptor on these lines revealed heterogeneity of composition. In one cell line, VUP, an alpha v beta 1 association was detected and, by antibody-inhibition studies, this receptor was shown to bind vitronectin as its ligand. In another line, DX3, evidence was obtained which indicated that apart from the alpha v beta 3 receptor the alpha v was able to associate with another beta subunit which was not beta 3. The existence of these alternative forms of the vitronectin receptor in this small sample of tumours of common origin might explain why the capacity to bind to fibrinogen and vitronectin substrates by these cells did not necessarily correlate with alpha v beta 3 levels.

Animals↗
PubMed1991

Characterization of integrin chains in normal and neoplastic human pancreas.

Integrins are a complex family of non-covalently linked heterodimeric glycoproteins which function as cell adhesion molecules, interacting with extracellular matrix molecules such as laminin, fibronectin, vitronectin, and collagen, and also having a role in intercellular adhesion. Each integrin subfamily is characterized by a common beta chain associated with variable alpha chains. We have examined, using immunohistological methods, the expression of the VLA (very late activation) family comprising beta 1 in association with alpha 1-6, and also alpha 6 in association with beta 4, the LFA beta chain beta 2, and the vitronectin receptor, in association with beta 1 or beta 5 and as the complex alpha v beta 3. Cryostat sections of normal pancreas, pancreatic adenocarcinomas, and ampullary tumours were studied together with six pancreatic carcinoma cell lines. Normal pancreas showed expression of beta 1 in all parenchyma. alpha 2 and alpha 6 had a similar distribution whereas alpha 3 expression was confined to ducts, including the very smallest radicles. Staining along the basement membranes of ducts was seen with beta 4 and the anti-vitronectin alpha v chain receptor antibody 13C2. Islet cells failed to stain with any antibody. No staining of epithelial components was seen with antibodies to alpha 1, alpha 4, alpha 5, or to the alpha v beta 3 form of the vitronectin receptor (beta 3 and alpha v beta 3 using the antibody 23C6). Pancreatic adenocarcinomas and ampullary tumours showed expression of alpha 2, alpha 3, alpha 6, beta 1, beta 4, and the vitronectin receptor (alpha v associated with beta 1 or beta 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Basement Membrane↗
PubMed1991

Co-ordinate expression of the alpha-6 integrin laminin receptor sub-unit and laminin in breast cancer.

Interactions between cells and extracellular matrices are mediated in part by a family of heterodimeric molecules known as integrins. We have investigated, using immunohistology, the distribution of six integrin alpha sub-units in normal breast tissue and 26 breast carcinomas. Alpha-1 integrin (collagen/laminin receptor sub-unit) was detected in myoepithelium, but not in luminal epithelium nor in most (20/26) carcinomas. Its expression on fibroblasts was enhanced in desmoplastic stroma. Both benign and malignant epithelium showed uniform positive staining for alpha-2 (collagen receptor sub-unit) and for alpha-3 (collagen/fibronectin/laminin receptor sub-unit). All epithelium was negative for alpha-4 (sub-unit of a fibronectin receptor). Epithelial staining for alpha-5 (fibronectin receptor sub-unit) was weak in all samples. Alpha-6 (sub-unit of two integrin laminin receptors) showed conspicuous changes in all invasive carcinomas. In normal tissues, there was weak staining of epithelial cytoplasm with alpha-6 antibody and moderate cell membrane staining. Strongest staining was present in a basement membrane distribution. In carcinomas, loss of cytoplasmic and cell membrane staining was variable, but basal membrane staining was diminished or absent in all tumours. Loss of basal membrane staining for alpha-6 integrin corresponded closely to loss of immunoreactivity for its ligand laminin in invasive breast cancer.

Adenofibroma↗
PubMed1991

Arg-Gly-Asp (RGD) peptides and the anti-vitronectin receptor antibody 23C6 inhibit dentine resorption and cell spreading by osteoclasts.

Studies with a range of monoclonal and polyclonal antisera to components of the human, rat, and chick vitronectin receptor, alpha V beta 3, and the VLA beta 1 chain show that chick and rat osteoclasts express similar integrin receptors to those described in man. Biochemical analysis with monoclonal antibody 23C6 confirmed the presence on chick osteoclasts of a vitronectin receptor heterodimer of similar size (110/95 kDa reduced) to that immunoprecipitated from human osteoclastoma giant cells. The synthetic peptide GRGDSP, corresponding to the cell adhesion sequence in fibronectin, but not GRGESP peptide, induced significant (P less than 0.005) osteoclast retraction in chick and rat osteoclasts at IC50s (+/- SEM) of 210.0 +/- 14.4 and 191.4 +/- 13.7 microM, respectively; monoclonal anti-vitronectin receptor alpha V beta 3 complex antibody, 23C6, produced similar changes in chick osteoclasts (IC50 = 1.45 +/- 0.22 microM). Antibody 23C6 inhibited the number of pits resorbed in dentine by chick osteoclasts over a concentration range of 4.4 to 88 micrograms/ml; a significant 76% reduction (P = 0.03) was observed at a final concentration of 88 micrograms/ml (6 microM). The effect of peptides upon dentine resorption was less dramatic. No consistent inhibition was seen using chick osteoclasts. Inhibitory effects on resorption by rat osteoclasts were, however, observed; significant reduction in resorption occurred with both GRGDSP (78%; P less than 0.01) and GRGESP (67%; P = 0.02) peptides at 400 microM peptide concentration. These data demonstrate that osteoclast function can be disrupted by low concentrations of the anti-vitronectin receptor antibody, 23C6. The inhibitory effects of the peptides used in this study produced effects on dentine resorption which were generally weaker and variable, although osteoclast cell adhesion was consistently inhibited in an Arg-Gly-Asp (RGD)-dependent manner. We conclude that the vitronectin receptor may play an important role in effecting resorption of mineralized tissues by osteoclasts.

Amino Acid Sequence↗
PubMed1991

Immunocytochemical demonstration of PTHrP protein in neoplastic tissue of HTLV-1 positive human adult T cell leukaemia/lymphoma: implications for the mechanism of hypercalcaemia.

The infiltrated tissues from seven West Indian patients with HTLV-1 positive adult T cell lymphoma/leukaemia (ATLL) have been analysed by immunocytochemical techniques for the presence of immunoreactive parathyroid hormone-related protein (PTHrP), a hormonal mediator of humoral hypercalcaemia of malignancy. Six of the seven were hypercalcaemic at some stage of the course of their disease. Four of the six evaluable patients showed evidence of specific cellular and extracellular expression of PTHrP protein in neoplastic tissues. This finding suggests that PTHrP may be involved in the production of hypercalcaemia in at least some cases of T cell lymphoma - proof of a causal relationship however must await the demonstration of tissue release of PTHrP resulting in raised circulating hormone levels.

Adult↗
PubMed1991

Vitronectin receptor has a role in bone resorption but does not mediate tight sealing zone attachment of osteoclasts to the bone surface.

During bone resorption, osteoclasts form a tight attachment, the sealing zone, around resorption lacunae. Vitronectin receptor has previously been shown to be expressed in osteoclasts and it has been suggested that it mediates the tight attachment at the sealing zone. In this study we have shown that glycine-arginine-glycine-aspartic acid-serine pentapeptide inhibits bone resorption by isolated osteoclasts and drastically changes the morphology of the osteoclasts. When the vitronectin receptor was localized by immunofluorescence in rat and chicken osteoclasts cultured on bone slices, it was found to be distributed throughout the osteoclast cell membrane except in the sealing zone areas. Immunoperoxidase staining of rat bone sections at the light microscopical level also revealed intense staining of the cell membrane with occasional small unstained areas, probably corresponding to the sealing zones. Immunoelectron microscopy confirmed the results obtained by light microscopy showing specific labeling only at the ruffled borders and basolateral membranes (0.82 and 2.43 gold particles/microns of membrane, respectively), but not at the sealing zone areas (0.06 gold particles/microns of membrane). Both alpha v and beta 3 subunits of the vitronectin receptor were similarly localized. These results strongly suggest that, although the vitronectin receptor is important in the function of osteoclasts, it is not mediating the final sealing zone attachment of the osteoclasts to the mineralized bone surface.

Animals↗
PubMed1991

Familial mastocytosis: a clinical, immunophenotypic, light and electron microscopic study.

A women and her daughter both developed diffuse cutaneous mastocytosis in early infancy. The immunophenotypes of the cutaneous mast cells in the two cases were shown to be identical: leucocyte common antigen (CD45) and macrophage/monocyte marker EBM11 were both strongly positive, HLA-DR was positive and CD25 was weakly positive. The peripheral lymphocytes of the patients were analysed by flow cytometry and this revealed that there was no increase in the activation markers HLA-DR and CD25, contrary to recent claims that lymphocytes have a contributory role in driving mast-cell proliferation. Mast-cell granules in both cases were found on electron microscopy to have an abnormal ultrastructure. The close similarity between the two cases at clinical, immunophenotypic and ultrastructural levels strongly suggests that genetic factors are important in the development of this type of mastocytosis.

Adult↗
PubMed1991

Immunohistochemical detection of parathyroid hormone-related protein in human fetal epithelia.

PTH-related protein (PTHrP) is commonly produced by squamous cell carcinomata and is the mediator of the PTH-like features of humoral hypercalcemia of malignancy. It has also been implicated in calcium regulation during fetal development. In this study immunohistochemical techniques, using rabbit polyclonal antibodies to synthetic PTHrP peptides, have been used to localize PTHrP in human fetal tissues from one fetus of 7 weeks and two of approximately 18 and 20 weeks gestation, respectively, in order to identify sites of potential functional significance. PTHrP immunoreactivity was identified in epithelia from many sources, including skin, bronchus, pancreas, pharynx, gut, stomach, and renal pelvis. Thyroid and parathyroid glands, which develop from epithelial origins, also stained positive for PTHrP, as did kidney collecting tubules, adrenal tissue, and skeletal and smooth muscle. PTHrP immunoreactivity was also located in developing long bones and calvaria, where it may have relevance in bone turnover during fetal development. The role of PTHrP at these locations remains to be elucidated, but the identification of specific PTHrP immunoreactivity in fetal epithelia is consistent with PTHrP production by cancers of epithelial origin and supports the hypothesis that PTHrP may have a role in epithelial growth and differentiation.

Bronchi↗
PubMed1990

Expression of the VLA family of integrins in human intestine.

The distribution of cells expressing the integrins VLA-1 to 6 in human intestine was examined by alkaline phosphatase immunohistochemistry using monoclonal antibodies specific for the individual alpha-chains of the VLA heterodimer. VLA-2,3, and 6 were expressed on all epithelial cells in the small and large bowel. VLA-1 was expressed on crypt cells in the small and large bowel, but was only weakly expressed or was absent on villus epithelial cells in the small bowel and colonic surface epithelial cells. All epithelia were negative for VLA-4 and VLA-5. Intraepithelial lymphocytes were VLA-1+ and VLA-4+. VLA-1,3, and 5 were expressed uniformly by muscularis propria, muscularis mucosae, pericrypt cells, and smooth muscle fibres within the villi. By contrast, VLA-2 and 4 were present only in pericrypt cells and fibres within the villi; they were absent from the muscularis mucosae. VLA-1,3,5, and 6 were expressed by endothelium. Staining of muscle fibres and endothelium in the lamina propria made it difficult to determine the extent of VLA expression on lamina propria lymphocytes. However, VLA-1+ cells with lymphoid morphology were only rarely seen. All mononuclear cells in the lamina propria were VLA-4+.

Antibodies, Monoclonal↗
PubMed1990

New sites of cellular vitronectin receptor immunoreactivity detected with osteoclast-reacting monoclonal antibodies 13C2 and 23C6.

The immunohistochemical profile of osteoclast-reacting monoclonal antibodies, 13C2 and 23C6, known to detect the alpha-chain of the vitronectin receptor, is described. Both antibodies reacted with several cell types apart from osteoclasts including megakaryocytes, smooth muscle cells, endothelial cells, thyroid follicular epithelium, renal glomeruli and tubular epithelium, myoepithelial and epithelial cells in the breast and prostate, and both cytotrophoblast and syncytiotrophoblast. In addition, macrophage polykaryons, synovial lining cells, a small number of mononuclear cells in buffy coats, and a few macrophage-like cells in the stroma of various tissues were also stained. The epitopes recognized by these antibodies are thus not osteoclast-specific and are present on other cells of the mononuclear phagocyte system. The implications of these results for osteoclast ontogeny, the nature of the antigens described and the question of osteoclast-specific antibodies are discussed.

Antibodies, Monoclonal↗
PubMed1990

Blood leukocytes bind platelet glycoprotein (IIb-IIIa)' but do not express the vitronectin receptor.

Within the integrin family of Arg-Gly-Asp(RGD)-binding adhesion receptors, the subfamily defined by the beta chain known as beta-3 or glycoprotein (GP)IIIa is known to contain two individual receptors. These are the GPIIb-IIIa complex of platelets, where the alpha chain of the heterodimer is GPIIb, and the vitronectin receptor (VnR) containing the alpha V subunit. The presence of either GPIIb-IIIa and/or the VnR on blood leukocytes has been controversial. We have investigated this problem by performing immunoprecipitation and immunoblotting studies with rabbit and monoclonal antibodies (mAb) to each of the subunits of GPIIb-IIIa and the VnR. On cultured cells of different origin, it was established that almost all expressed the VnR but none had GPIIb-IIIa, and the only polypeptide associated with beta 3 was alpha V. Platelets expressed predominantly GPIIb-IIIa, and weakly, the VnR. Monocytes and neutrophils freshly isolated from blood did not express the VnR but bore on their surface a modified form of GPIIb-IIIa. This molecule appeared identical to GPIIb-IIIa but an epitope on GPIIb was masked on the intact cell and was only revealed after immunoblotting. We have termed this modified form of GPIIb-IIIa, GP(IIb-IIIa)'. With differentiation in culture, monocytes rapidly lost surface GP(IIb-IIIa)' and concurrently began to express the VnR. Evidence is presented that GP(IIb-IIIa)' is derived from particles released by activated platelets and is bound firmly to the leukocyte membrane. Its primary function does not seem to be to mediate attachment to matrix proteins; thus, although U937 cells bearing platelet-derived GP(IIb-IIIa)' bound fibrinogen in an RGD-dependent manner, isolated blood monocytes did not. It is suggested that this transfer of membrane proteins from platelets to monocytes and neutrophils may regulate the expression of the leukocyte VnR and also serve as a means of facilitating leukocyte procoagulant activity.

Amino Acid Sequence↗
PubMed1979

Characteristics and genetic control of NK-cell-mediated cytotoxicity activated by naturally acquired infection in the mouse.

Most and perhaps all natural-cell-mediated cytotoxicity (NCMC) may be activated by a response to exogenous infections. Specific-pathogen-free (SPF) mice have little or no natural killer (NK) cell activity, but when they are relocated in conventional conditions, they develop strong NCMC within 2 to 3 days. Unlike other SPF animals, hypothymic nude mice display good NCMC which is further augmented upon their entry into a pathogenic environment. The ontogeny, genetic control and other features of pathogen-activated NCMC resemble those previously described for NK cells. An H2-D region NCMC regulatory gene is active in either a homozygous or heterozygous state, but to be operative seems to require the presence of an additional complementing locus, which maps outside the H-2 complex. It is proposed that H-2 influences NCMC levels by affecting the expression or immunogenicity of NK cell-activating determinants. Recently activated NK cells were non-adherent and lacked Ia and Thy-1 determinants. NCMC was not affected by treatment with monoclonal high-titer Thy-1.2 antisera and complement. However, an Ly-6.2 antiserum did contain anti-NK cytotoxic activity, which was shown by absorption analysis to be distinct from anti-Ly-6.2 activity. The NK antigen has a strain distribution pattern distinct from Ly-5 and other Ly markers, but may be related or identical to NK-1.

Animals↗