PubMed Health⌕ Search

Biomedical subjects

I Trowbridge

Publications and source records attributed to I Trowbridge.

17 recordsLinked to original sources
PubMed1995

Role of CD44 cytoplasmic domain in hyaluronan binding.

The hyaluronan (HA) binding activity of mutant CD44 constructs expressed in AKR1 T-lymphoma cells was evaluated by flow cytometry using fluorescein-conjugated HA (Fl-HA). Previous studies showed that wild-type hematopoietic CD44 bound Fl-HA when expressed in AKR1, but that truncated "tailless" CD44, lacking all but six amino acids of the cytoplasmic domain, did not bind. Here, we show that a disulfide-bonded dimer of CD44, formed by substituting the transmembrane region of CD3 zeta chain for that of CD44, binds Fl-HA, even when the cytoplasmic domain of the CD44 dimer is absent. We conclude that dimerization of CD44 abrogates the requirement for the cytoplasmic domain, suggesting that the cytoplasmic domain of CD44 may contribute to HA binding by promoting CD44 clustering. These results suggest that changes in the distribution of CD44 on the cell surface, induced by molecular interactions either from within the cell or from outside, may regulate its role as a receptor. Further studies sought to localize the region of the CD44 cytoplasmic domain contributing to HA binding by the construction of a series of cytoplasmic domain truncation mutants and internal deletion mutants. All of the mutant CD44 molecules bound Fl-HA similarly to wild-type CD44. Thus, it was not possible to assign the function mediating HA binding to a specific region of the cytoplasmic domain, suggesting either that multiple regions of the cytoplasmic domain can promote enhancement of HA binding, or that the role of the cytoplasmic domain in mediating this function does not require a specific amino acid sequence.

Amino Acid Sequence↗
PubMed1991

Differential expression of the alternatively spliced exons of murine CD45 in Th1 and Th2 cell clones.

Antigen-specific murine CD4+ T cell clones can be divided into functionally distinct subsets known as Th1 and Th2. To date these cells have been indistinguishable by surface phenotype. This report identifies two anti-CD45R monoclonal antibodies (14.8 and C363.16A) that bind preferentially to Th2 cells. Further analysis of the CD45-specific mRNA in Th1 and Th2 cells shows clear differences between these two cell types. Th1 cell clones express mRNA for the two smallest forms of CD45 containing none or only one of the alternatively splices exons. In contrast, Th2 cell clones express predominantly the high molecular weight isoforms of CD45 containing two or three of the alternatively spliced exons.

Animals↗
PubMed1991

Regulation of CD45 expression in human leukemia cells.

The CD45 antigen cluster identifies a family of transmembrane glycoprotein tyrosine phosphatases (PTPases) present on nearly all hemopoietic cells. Recent studies suggest that CD45 may play a role in the control of receptor mediated blood cell responses, and that expression of the CD45 gene varies during bone marrow cell maturation. However, relatively little is known of the mechanisms controlling CD45 expression and function. Here we show that the induction of granulocyte or monocyte differentiation of HL60 leukemia cells is accompanied by a rapid increase in CD45 antigen expression and CD45 PTPase activity. In contrast, other leukemia cell lines induced for monocyte/macrophage differentiation did not show increased CD45. Immunoprecipitation of radiolabelled CD45 glycoprotein from dimethyl sulphoxide (DMSO) treated HL60 cells indicated that the cells expressed 200 and 180 kD isoforms. Northern blots of steady-state RNA from HL60 cells showed a 4-11-fold increase in CD45 transcripts after DMSO treatment, but no alteration in the half-life of CD45 mRNA. Nuclear transcription assays showed that CD45 expression was controlled at the level of gene transcription. Namalwa Burkitt leukemia cells expressing the heterologous epidermal growth factor (EGF) receptor protein tyrosine kinase were used to assess the specificity of CD45 PTPase activity. Co-clustering of CD45 and the EGF receptor with specific monoclonal antibodies failed to alter the EGF stimulated tyrosine phosphorylation of the EGF receptor. These studies indicate that CD45 increases during myeloid maturation, and the expression of the CD45 gene is controlled at the level of gene transcription. Preliminary studies suggest that CD45 does not alter the protein tyrosine kinase activity of the EGF receptor in intact cells, suggesting substrate specificity in vivo.

Antigens, CD↗
PubMed1987

Structural studies of T200 glycoprotein and the IL-2 receptor.

Immunological analysis of the cell surface of hematopoietic cells has led to the identification of many different cell membrane molecules, some of which have well-defined functions as receptors. In general, however, the role of most lymphocyte cell surface molecules remains ill-defined even in cases in which antibody inhibition studies have given some insight into the biological processes in which they participate. Here we describe molecular and biochemical studies of T200 glycoprotein (leukocyte-common antigen) and the IL-2 receptor which illustrate the kinds of approaches that can be currently used to characterize individual molecules. T200 glycoprotein is a large Mr glycoprotein found exclusively on leukocytes. However, the exact Mr varies in a cell-type-specific fashion and this property is conserved between different species. Comparison of the rat, mouse and human cDNA sequences show that the large cytoplasmic portion of the molecule is well-conserved, approximately 90%, whereas the exterior portion is only about 50% homologous. Cell-type-specific differences in the primary sequence of the molecule have been identified in the N-terminal portion of the molecules. In contrast to T200, the function of the IL-2 receptor is well-known. The interaction of IL-2 with its receptor provides a growth signal that determines the magnitude and duration of T-cell responses. Limited proteolysis studies provide the first direct biochemical evidence that the external region of the IL-2 receptor consists of two independent domains. 125I-labeled IL-2 has been chemically crosslinked to the receptor and proteolytic cleavage of the crosslinked product indicates that IL-2 is selectively bound to the N-terminal domain of the receptor.

Animals↗
PubMed1987

Regulation of transferrin receptor expression in myeloid leukemia cells.

Surface transferrin (Tf) receptors are displayed by cultured human hematopoietic cells and provide Fe required for cell growth. Cell cycle status, cell density in culture, exposure to Fe, and differentiation alter Tf receptor display by myeloid leukemia cells. To investigate mechanisms controlling Tf receptor expression, rates of receptor synthesis and steady-state mRNA levels were measured in HL60 promyelocytic cells grown in serum and serum-free media or after differentiation in response to dimethylsulfoxide (DMSO). Although surface binding sites were unchanged during the first three days in culture with serum or in serum-free media containing Tf, by the third day, rates of receptor biosynthesis and steady-state mRNA levels declined, consistent with cell density-dependent, receptor regulation. Cells grown with soluble Fe instead of Tf showed reduced Tf binding sites, rates of receptor synthesis, and Tf receptor mRNA. When cells grown with Fe were subcultured, Tf receptor mRNA levels increased within 15 minutes and peaked by 24 hours. This was followed by a decline in receptor and gene expression so that by three days cells grown in the presence of Fe expressed approximately four times fewer receptors and had half the rates of Tf receptor synthesis and mRNA levels of cells grown in serum or Tf. Cells treated with DMSO showed a rapid decline in surface receptors, receptor synthesis, and steady-state mRNA levels. Modulation of Tf receptor expression was not due to redistribution between the cell surface and an internal receptor pool. In each instance, concurrent assessment of N-ras transcripts showed that changes in Tf receptor mRNA levels were not due to generalized alterations in protein synthesis. Exposure of cells grown in Fe or treated with DMSO to cycloheximide did not alter Tf receptor mRNA levels, thereby suggesting that receptor expression was not regulated by posttranscriptional processes dependent on protein synthesis. Actinomycin D inhibition of Tf receptor mRNA was compatible with a transcript half-life of approximately 2.2 hours. Nuclear transcription studies showed reduced rates of Tf receptor transcription after culture with Fe or exposure to DMSO. The present studies show complex patterns of Tf receptor gene regulation in cultured myeloid leukemia cells and demonstrate that transcriptional regulation is a major mechanism controlling Tf receptor gene expression in response to Fe and differentiation.

Animals↗
PubMed1983

Effects of anti-transferrin receptor antibodies on growth of normal and malignant myeloid cells.

The effects of three monoclonal antibodies (B3/25, 43/31, and 42/6) reactive with human transferrin (Tf) receptors on growth of normal and malignant myeloid cells were examined using in vitro culture techniques. When added directly to cultures, all three antibodies caused dose-dependent inhibition of normal granulocyte/macrophage progenitor (CFU-GM) growth. Monoclonal antibody 42/6 was by far the most potent of the three, with an ID50 of less than 5 micrograms/ml. Identical effects were seen on CFU-GM from three patients with chronic myelogenous leukemia. Growth of colonies from two myeloid leukemia cells lines (KG-I, HL60) was also inhibited by all three antibodies, and these cells were generally more sensitive than normal CFU-GM. Blast colony-forming cells from three patients with acute non-lymphocytic leukemia were relatively resistant to the antibodies, and CFU-GM from a patient with myeloid metaplasia were resistant (ID50 greater than 50 micrograms/ml) to 42/6. In liquid culture, growth of the leukemic cell lines was inhibited by saturating concentrations of the three antibodies, although in both liquid and colony culture recovery was seen even after exposure to antibody for periods of up to 72 h. Analysis of the cell-cycle status of these cells showed that the antibodies did not cause accumulation of cells in any particular phase of the cell cycle. Addition to cultures of large quantities of human Tf failed to reverse the inhibitory effects of the antibodies. Competitive binding studies on the leukemia cell lines showed that only 42/6 inhibited binding of Tf to its receptor, although all three antibodies inhibited cell growth. Addition of Fe chelate (as ferric nitriloacetic acid, FeNTA) failed to reverse the inhibitory effects of the antibodies on CFU-GM and HL60 cells, but had variable effects on KG-I cell growth. FeNTA fully reversed inhibitory effects of 42/6 on KG-I cells. We conclude that monoclonal antibodies to Tf receptors can inhibit growth of both normal and malignant myeloid cells. Overall, no selectivity for malignant vs normal cells is apparent, although malignant cells from one individual were more sensitive to colony inhibition by 43/31 monoclonal antibody than normal CFU-GM.

Animals↗
PubMed1983

The major histocompatibility complex-restricted antigen receptor on T cells in mouse and man: identification of constant and variable peptides.

The variability of the MHC restricted receptor on murine T cells was examined by comparing tryptic peptide fingerprints of the receptor isolated fom three T cell hybridomas and a T cell tumor. Both variable and constant peptides were seen. Constant peptides were most apparent when comparing receptors from the same mouse strain. Peptide fingerprints of receptors from two independent T cell hybridomas with the same idiotype and specificity were identical. We also describe a molecule detected on the surface of a human T cell leukemia whose properties were identical to those reported for the MHC receptor on normal human T cells. The molecule was a dimer of 85,000-90,000 MW containing a 46,000 MW acidic alpha-chain and an unrelated 40,000 MW neutral beta-chain.

Animals↗
PubMed1983

Inhibition of human lymphocyte proliferation by monoclonal antibody to transferrin receptor.

A monoclonal antibody, 42/6, which blocks the binding of transferrin to its receptor on the cell membrane, inhibits proliferation of human lymphocytes stimulated by phytohemagglutinin. Anti-receptor antibody B3/25, which does not block transferrin binding, does not alter the mitogenic response. Addition of soluble iron, in the form of ferric nitrilotriacetic acid, results in partial reversal of inhibition. Lymphocytes in the quiescent phase of the cell cycle at the time of 42/6 antibody addition are unable to traverse S phase, whereas cells actively proliferating when antibody is added are sensitive to its inhibitory effects throughout all phases of the cell cycle. Inhibition is static rather than cidal, since it can be reversed by removal of antibody after up to 48 hr of exposure.

Antibodies, Monoclonal↗
PubMed1981

Two complementation classes of T200 (Ly-5) glycoprotein-negative mutants.

Mutants of murine lymphomas have been isolated which express less than 1 percent of wild-type levels of T200 (Ly-5) glycoprotein on their cell surface but express wild-type levels of other cell-surface antigens tested. These mutants define two genetic complementation classes. The Class A mutant does not synthesize detectable amounts of T200 glycoprotein and is a mutant in either the structural gene coding for the T200 glycoprotein or in a gene acting in cis position to regulate this structural gene. The Class B mutant synthesizes very low levels of T200 glycoprotein and is most simply interpreted as a mutant in a gene acting at some post-transcriptional step necessary for expression of the T200 glycoprotein on the cell surface.--The isolation of T200- mutants by cytotoxic immunoselection suggests that this method is a general way of studying the biosynthesis, regulation and function of cell-surface molecules.

Animals↗
PubMed1980

Cell surface molecules of Friend erythroleukemias: decrease in T200 glycoprotein expression after induction.

Monoclonal antibodies against the Thy-1 and T200 glycoproteins were used to study the expression of cell surface molecules on mouse hematopoietic cell lines. Friend erythroleukemias express T200 glycoprotein but do not express significant amounts of Thy-1 glycoprotein on their cell surface. The rate of T200 glycoprotein synthesis in maximally-induced Friend erythroleukemia 745.6 cells is less than 10% that in noninduced cells, although total protein synthesis shows only a twofold decline and induced cells express 2-6-fold less T200 glycoprotein on their surface compared to noninduced cells. T200 glycoprotein expression is reduced in a variant cell line obtained by selection for growth in dimethylsulfoxide, showing that the reduction in T200 glycoprotein synthesis characteristic of induced cells is an event that can be dissociated from commitment and hemoglobin synthesis. Analysis of T200 glycoprotein negative cell lines, isolated by cytotoxic immunoselection against T200 glycoprotein, indicates that the presence of T200 glycoprotein on the cell surface is not necessary for induction of hemoglobin synthesis and terminal differentiation of Friend erythroleukemias.

Animals↗
PubMed1979

Correlated expression of a B-lymphocyte-specific glycoprotein (gp27/35) and the EBV receptor/C3 receptor complex in sublines from the same Burkitt lymphoma.

A series of virus-producer and non-producer sublines, derived from the Burkitt lymphoma line Jijoye and its P3HR-1 clone, were previously found to differ in the expression of EBV receptors and, in parallel, C3 receptors. The differences could be related to an "internal selection" caused by the cytopathic P3HR-1 virus variant, favouring the growth of receptor-negative cells. We have now analyzed the same lines for the expression of a B-lymphocyte-specific glycoprotein (gp27/35). A close parallellism was found between the expression of the EBV receptor-complement receptor complex and the glycoprotein, measured by quantitative absorption. The results favour a relationship between gp27/35 and EBV/C3 receptor expression.

Antigen-Antibody Complex↗
PubMed1978

Localization of T25 glycoprotein in wild-type and Thy 1- mutant cells by immunofluorescence and immunoelectron microscopy.

The wild-type BW5147 (Thy 1+) cell line and its Thy 1- mutant derivative BW5147 (Thy 1-a) were examined by immunofluorescence and immunoelectron microscopy for the presence of T25, the glycoprotein which bears the Thy 1 alloantigen. The wild-type cell had T25 predominantly localized on the cell surface. In the mutant cell line, T25 accumulated intracellularly and was present in a clustered distribution throughout the cytoplasm. T25 was not present on the surface of the mutant cell line in significant amount.

Animals↗
PubMed1978

Participation of histocompatibility antigens in capping of molecularly independent cell surface components by their specific antibodies.

The antibody-induced capping of several cell surface components has been investigated by immunofluorescence methods using two mouse cell lines, a parental C58 thymoma line and a mutant derived from it lacking TL and H-2 antigens. Other cell surface components were present in approximately equal amounts on the two cells. Parental cells treated with rabbit antibodies to T200, a major surface glycoprotein, rapidly formed caps containing T200, but the mutant cells similarly treated showed a uniform surface distribution of T200. On the other hand, with a secondary antibody treatment, the T200 on both cells capped equally well. When the indirect T200 caps were examined using a second immunofluorescent stain for H-2, TL, or Thy-1 antigens, it was found that on parental cells all three of these antigens were co-capped with T200; on mutant cells no staining was found for H-2 or TL, as expected, and essentially uniform distribution of Thy-1 was observed. The co-capping of H-2, TL, and Thy-1 antigens with T200 on the parent cell is remarkable, because the first three components are known to be molecularly independent in lymphocyte cell surfaces. The indirect capping of the viral glycoprotein gp 69/71 similarly induced a co-capping of H-2 and TL antigens on the parent cell. These results demonstrate that H-2 and related molecules may co-cap with a variety of independent cell surface antigens. Such co-capping of histocompatibility components could play an important role in a proposed dual recognition mechanism for cell-mediated cytotoxicity reactions and other immunologically important cell-cell interactions.

Antibodies, Neoplasm↗
PubMedDate not supplied

Selection and properties of a mouse L-cell transformant expressing human transferrin receptor.

Transferrin receptors are expressed in large quantities on tissues with high requirements for iron such as maturing erythroid cells and placenta. In addition, they are found in abundance on proliferating cells from other normal tissues as well as on a variety of tumours. Recent genetic analysis has shown that structural genes for the transferrin receptor, probably transferrin itself and for p97, a melanoma-associated antigen that exhibits primary sequence homology with transferrin and that can bind ferric iron, each map in man to chromosome 3 (refs 9-12). On this basis it has been suggested that there may be a region on chromosome 3 containing genes involved in Fe transport and that rearrangements in this region of chromosome 3 may in some circumstances be associated with malignant transformation. Furthermore, it is unresolved whether all cell types express structurally identical transferrin receptors. To study these problems, and as an initial step towards cloning the transferrin receptor gene, we describe here the derivation of mouse L-cell transformants expressing the human transferrin receptor.

Animals↗