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Biomedical subjects

P E Roberts

Publications and source records attributed to P E Roberts.

At least 19 recordsLinked to original sources
PubMed1999

Distribution and function of the adhesion molecule BEN during rat development.

It is well established that the notochord influences the development of adjacent neural and mesodermal tissue. Involvement of the notochord in the differentiation of the dorsal pancreas has been demonstrated. However, our knowledge of the signals involved in pancreatic development is still incomplete. In order to identify proteins potentially implicated during pancreatic differentiation, we raised and characterized monoclonal antibodies against previously established embryonic pancreatic ductal epithelial cell lines (BUD and RED). Using the MAb 2117, the cell surface antigen 2117 (Ag 2117) was cloned. The predicted sequence for Ag 2117 is the rat homologue of BEN. Initially reported as a protein expressed on epithelial cells of the chicken bursa of Fabricius, BEN is expressed in a variety of tissues during development and described as a marker for the developing central and peripheral chicken nervous systems. A role has been suggested for BEN in the adhesion of stem cells and progenitor cells to the blood-forming tissue microenvironment. In this study, we demonstrate that BEN, initially expressed exclusively in the notochord during the early development of rat, is implicated in pancreatic development. We show that Ag 2117 regulates the pancreatic epithelial cell growth through the ras and Jun kinase pathways. In addition, we demonstrate that Ag 2117 is able to regulate the expression of the transcription factor PDX1, required for insulin gene expression, in embryonic pancreas organ cultures.

Activated-Leukocyte Cell Adhesion Molecule↗
PubMed1999

Selective cloning of cell surface proteins involved in organ development: epithelial glycoprotein is involved in normal epithelial differentiation.

Coordinating the activities of neighboring cells during development in multicellular organisms requires complex cellular interactions involving secreted, cell surface, and extracellular matrix components. Although most cloning efforts have concentrated on secreted molecules, recent work has emphasized the importance of membrane-bound molecules during development. To identify developmental genes, we raised antibodies to normal embryonic pancreatic epithelial cell surface proteins. These antibodies were characterized and used to clone the genes coding for the proteins by a panning strategy. Using this approach, we cloned the rat homologue of the mouse epithelial glycoprotein (EGP). Our immunohistochemistry data, describing the expression of EGP during rat development, as well as our in vitro data, looking at the effect of the anti-EGP antibody and the extracellular domain of EGP on embryonic pancreatic epithelial cell number and volume, strongly suggest a role for EGP during pancreatic development.

Amino Acid Sequence↗
PubMed1998

Biological response to ErbB ligands in nontransformed cell lines correlates with a specific pattern of receptor expression.

The human epidermal growth factor receptor (HER or ErbB) family consists of four distinct members, including the epidermal growth factor (EGF) receptor (EGFR, HER1, or ErbB1), ErbB2 (HER2 or neu), ErbB3 (HER3), and ErbB4 (HER4). Activation of these receptors plays an important role in the regulation of cell proliferation, differentiation, and survival in several different tissues. Binding of a specific ligand to one of the ErbB receptors triggers the formation of specific receptor homo- and heterodimers, with ErbB2 being the preferred signaling partner. We analyzed the levels of various ErbB receptor messenger RNAs in a series of nontransformed cell lines by real time quantitative RT-PCR. The cell lines chosen were derived from a variety of tissues, including pancreas, lung, heart, and nervous system. Further, we measured biological responses in these cell lines upon treatment with EGF, betacellulin, and two types of neuregulins, heregulin and sensory and motor neuron-derived factor. All cell lines examined expressed detectable levels of ErbB2. High levels of expression of ErbB3 were correlated with responsiveness to heregulin and sensory and motor neuron-derived factor, whereas high levels of EGFR expression were correlated with responsiveness to EGF and betacellulin. Moreover, the sensitivity of a cell line to ErbB ligands was also correlated with the levels of expression of the appropriate ErbB receptors in that cell line. These results are consistent with our hypothesis that appropriate biological responsiveness to ErbB ligands is determined by the levels of expression of specific ErbB receptor combinations within a given tissue.

Animals↗
PubMed1996

Differential antibody recognition of FC27-like Plasmodium falciparum merozoite surface protein MSP2 antigens which lack 12 amino acid repeats.

Three alleles of the FC27-type allelic family of the MSP2 gene of the malaria parasite Plasmodium falciparum have been sequenced from parasites from the field (The Gambia and Tanzania). These alleles lack the 12 amino acid repeat units which are usual in this family of MSP2 alleles. We have investigated the recognition by sera from an endemic area (The Gambia) of three recombinant MSP2 proteins that have 5, 1 and no copies of this repeat region. Antibody recognition of these recombinant proteins varied according to the number of repeats present. High titre antibody levels were seen with most sera using the recombinant protein with 5 x 12-mer repeats, whereas only low responses were measured using proteins containing 1 or no 12-mer repeats. Several sera entirely failed to recognise the protein which lacked 12-mer repeats. The data suggest that variation in the number of tandem repeat sequences could allow the parasite to avoid high avidity antibody binding and this may allow escape from immune recognition.

Alleles↗
PubMed1994

Forskolin specifically inhibits the bacterial galactose-H+ transport protein, GalP.

Forskolin is a potent inhibitor of mammalian passive glucose transporters. Here we show that forskolin is a remarkably specific inhibitor of energized D-galactose transport by the GalP sugar-H+ symport protein of Escherichia coli. Surprisingly, it does not inhibit transport of L-arabinose or D-xylose by the related E. coli AraE and XylE transporters, even though the amino acid sequences of their proteins are 30-64% identical to GalP and to the mammalian GLUT family. However, unlike GLUT1, photoactivation of the [3H]forskolin-GalP complex fails to incorporate radioactivity covalently into the protein, in contrast to the effective incorporation of radioactivity from [3H]cytochalasin B into both proteins. However, 3-[125I]iodo-4-azidophenethylamido-7-O-succinyldesacetylforskol in ([125I]APS-forskolin), which labels GLUT1, is a potent labeling reagent for GalP and, to a lesser extent, for AraE. The appropriate sugar substrates of each transporter protect it against the [125I]APS-forskolin. Equilibrium binding studies using membranes from an E. coli strain that overexpresses GalP reveal a single set of high affinity binding sites for [3H]forskolin with a Kd of 1.3-1.4 microM, probably forming a 1:1 complex, compared with a value of 7.5 microM for GLUT1. Sugar substrates of GalP and cytochalasin B displace forskolin from the protein. The nonhomologous sugar-H+ symporters for L-rhamnose (RhaT), L-fucose (FucP) and lactose (LacY) in E. coli are insensitive to forskolin. Forskolin and [125I]APS-forskolin, therefore, constitute novel probes for exploring the structure-activity relationship of the bacterial GalP protein. GalP will provide an excellent model for the human glucose transporters and for elucidating the molecular basis of subtle differences in substrate and inhibitor recognition by individual members of this widespread family of transport proteins.

Affinity Labels↗
PubMed1993

Follistatin modulates activin activity in a cell- and tissue-specific manner.

The high affinity activin-binding protein, follistatin, has recently been shown to block activin-stimulated activities in several in vitro systems. In the present study we sought to extend these observations and investigate the effects of follistatin on the activity of activin in stimulating the re-aggregation of Sertoli cell monolayers and proliferation of testicular germ cells, as measured by incorporation of [3H]-thymidine in vitro. Germ-Sertoli cell cocultures prepared from 21 day old rats were treated with media alone or media containing recombinant human (rh) activin A or rh activin B with or without follistatin, the low affinity activin-binding protein, alpha 2 macroglobulin, or a monoclonal antibody (mAB) known to block activin B activity. Follistatin blocked the ability of activin A to stimulate reaggregation of Sertoli cell monolayers when present at a 2-fold ratio (wt/wt) to activin. However, in these same cultures, follistatin had no effect on the ability of activin A to stimulate [3H]-thymidine incorporation. In activin B-treated cultures, both responses could be blocked by the addition of a neutralizing mAB directed against activin B. These results suggest that follistatin can modulate activin action in a cell-type specific fashion, and that this protein may play an important role in regulating the bioavailability of activin.

Activins↗
PubMed1992

Characterization of the proteins from Melanoplus bivittatus that bind juvenile hormone, and a refined EFDA photolabeling technique.

1. Juvenile hormone (JH) is specifically bound by a protein from hemolymph and fat body cytosol of the grasshopper, Melanoplus bivittatus. 2. This protein has a native molecular weight of 331,000 and subunits of 77,000. 3. Proteins that bind JH were covalently photolabeled with a JH analog, epoxyfarnesyl diazoacetate (EFDA). Samples were irradiated in spot plates and hydroxyapatite was used to separate bound from free [3H]EFDA. Differential solubilization was used to extract unlinked [3H]EFDA and solubilize [3H]EFDA linked to protein. 4. Hemolymph proteins of M(r) 479,000, 240,000 and 77,000 also bound [3H]EFDA. 5. Proteins that bound [3H]EFDA were not vitellogenins.

Affinity Labels↗
PubMed1990

A new method of detecting hormone-binding proteins electroblotted onto glass fiber filter: juvenile hormone-binding proteins from grasshopper hemolymph.

We have developed a new method to identify juvenile hormone (JH)-binding proteins blotted onto glass fiber filter (GFF) after electrophoretic separation. Insect JH regulates reproduction in the two-striped grasshopper, Melanoplus bivittatus. A number of proteins are involved in the delivery of JH from its site of synthesis to the nuclei of fat body cells where it acts to induce vitellogenesis. To identify JH binding proteins, hemolymph was separated by PAGE, electroblotted onto GFF, and incubated in [10-3H]JH-III. The amount of hormone bound by blotted proteins increased with the amount of protein on the filter, was competitively displaced by excess non-labeled hormone, and was affiliated with individual bands on fluorograms of proteins blotted after electrophoretic separation. GFF etched with trifluoroacetic acid was better than nitrocellulose, Zeta Probe, cellulose acetate or unetched GFF. Phosphate (pH 6.0-7.3) or Tris buffers (pH 7.3-8.0) worked equally well for the procedure. Unbound hormone was easily removed by short washes in buffer, and adequate binding for detection was achieved in a 15 min incubation. Preliminary data suggest that this technique may be used to detect receptors, carriers, and binding proteins of steroid hormones.

Animals↗
PubMed1990

A novel epithelial cell from neonatal rat lung: isolation and differentiated phenotype.

A novel epithelial cell from normal neonatal rat lung has been isolated, established, and maintained for multiple passages in the absence of serum, without undergoing crisis or senescence. By careful manipulation of the nutrition/hormonal microenvironment, we have been able to select, from a heterogeneous population, a single epithelial cell type that can maintain highly differentiated features in vitro. This cell type has characteristics of bronchiolar epithelial cells. A clonal line, RL-65, has been selected and observed for greater than 2 yr in continuous culture. It has been characterized by ultrastructural, morphological, and biochemical criteria. The basal medium for this cell line is Ham's F12/Dulbecco's modified Eagle's (DME) medium plus insulin (1 micrograms/ml), human transferrin (10 micrograms/ml), ethanolamine (10(-4) M), phosphoethanolamine (10(-4) M), selenium (2.5 x 10(-8) M), hydrocortisone (2.5 x 10(-7) M), and forskolin (5 microM). The addition of 150 micrograms/ml of bovine pituitary extract to the defined basal medium stimulates a greater than 10-fold increase in cell number and a 50- to 100-fold increase in thymidine incorporation. The addition of retinoic acid results in further enhancement of cell growth and complete inhibition of keratinization. We have demonstrated a strategy that may be applicable to isolating other cell types from the lung and maintaining their differentiated characteristics for long-term culture in vitro. Such a culture system promises to be a useful model in which to study cellular events associated with differentiation and proliferation in the lung and to better understand the molecular mechanisms involved in these events.

Actin Cytoskeleton↗
PubMed1983

Juvenile hormone binding by components of fat body cytosol from vitellogenic locusts.

Binding of 3H-labeled juvenile hormone (JH) to cytosol components of fat body from adult female Locusta migratoria, a tissue in which JH stimulates vitellogenin synthesis, has been characterized. Protein-bound JH is separated from unbound hormone with hydroxyapatite, which is found to provide a more sensitive and less variable assay than use of dextran-coated charcoal. By chromatography on DEAE-cellulose, three JH-binding components have been separated from cytosol. BP-I exhibited relatively stable binding with little degradation of the hormone, gave a Kd for JH-I by Scatchard analysis of 1.69 X 10(-8) M, and binding of JH-I was competed by JH-I and several synthetic JH analogs in an order corresponding to their JH activities. These characteristics suggest that BP-I may be a cytoplasmic JH receptor. BP-II, a minor component, also bound JH-I stably, but competition by analogs was not correlated with their hormone activity. BP-III caused rapid degradation of JH to JH acid and may be an esterase.

Adipose Tissue↗
PubMed1980

Effects of juvenile hormone, ecdysterone, actinomycin D, and mitomycin C on the cuticular proteins of Tenebrio molitor.

Juvenile hormone (JH), ecdysterone and some antibiotics cause Tenebrio molitor to form a second pupa or pupal-adult intermediate. Incorporation of labelled leucine into the cuticular proteins of JH-induced second pupae did not differ from incorporation in normal pupae, and the soluble cuticular proteins from these young second pupae were indentical to those extracted from normal pupal exocuticle when analysed by SDS-polyacrylamide gel electrophoresis. However, as these second pupae aged, the major early bands did not undergo a normal decrease in staining intensity, indicating a JH effect on protein insolubilization (sclerotization). The transport of protein into the cuticle may also have been altered by JH; electrophoretic analysis of the new cuticle of treated animals showed intense staining of bands with RF's similar to those of blood proteins. The new exocuticle produced after treatment of pupae with ecdysterone had soluble proteins which were typical of normal pupae, but extracts from such animals aged prior to cuticle removal yielded bands characteristic of normal adults. Pupae treated with actinomycin D occasionally form new abdominal cuticle with characteristic pupal morphology. These cuticles yielded soluble proteins which, upon analysis, had pupal, pupal and adult, or adult banding patterns. Animals treated with mitomycin C, although retaining vestiges of pupal abdominal characters, had adult cuticular proteins.

Animals↗
PubMed1979

Characterization of the avian progesterone receptor through the use of inhibitors.

Several chemical agents have been identified which block interaction of the avian progesterone receptor with isolated nuclei, ATP-Sepharose, DNA-cellulose or phosphocellulose. Four of these inhibitors, rifamycin AF/103, o-phenanthroline, aurintricarboxylic acid and pyridoxal 5-phosphate appear to block directly binding of the activated receptor complex to the above "acceptors." Another inhibitor, sodium molybdate, only blocks receptor interactions when added before receptor activation and therefore appears to interfere with the activation process. When nuclear receptor complexes were formed in vivo and labeled by nuclear exchange with [3H]progesterone in vitro, these complexes could not be disrupted by incubation of the nuclei with inhibitors. Therefore, the receptor complex bound in nuclei appears to be modified or masked in a way which resists the action of these chemical agents. These results indicate the value of inhibitors as chemical probes for the analysis of steroid receptors.

Animals↗