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T A Libermann

Publications and source records attributed to T A Libermann.

53 records · Page 3Linked to original sources
PubMed1990

Involvement of a second lymphoid-specific enhancer element in the regulation of immunoglobulin heavy-chain gene expression.

To determine whether enhancer elements in addition to the highly conserved octamer (OCTA)-nucleotide motif are important for lymphoid-specific expression of the immunoglobulin heavy-chain (IgH) gene, we have investigated the effect of mutating the binding site for a putative additional lymphoid-specific transcription factor, designated NF-microB, in the murine IgH enhancer. We demonstrate that the NF-microB-binding site plays a critical role in the IgH enhancer, because mutation of the microB DNA motif decreased transcriptional activity of the IgH enhancer in cells of the B-cell lineage but not in nonlymphoid cells. This effect was comparable to or even stronger than the effect of a mutation in the OCTA site. Moreover, combined mutation of both microB and OCTA sites further reduced enhancer activity in lymphoid cells. Interestingly, alteration of either the microB or E3 site in a 70-base-pair fragment of the IgH enhancer that lacks the binding site for OCTA abolished enhancer activity in lymphoid cells completely. Nevertheless, a multimer of the microB motif alone showed no enhancer activity. DNase footprinting analysis corroborated the functional data showing that a lymphoid-specific protein binds to the microB DNA motif. Our results suggest that the microB element is a new crucial element important for lymphoid-specific expression of the IgH gene but that interaction with another enhancer element is essential for its activity.

Animals↗
PubMed1988

Expression of messenger RNAs for platelet-derived growth factor and transforming growth factor-alpha and their receptors in human malignant glioma cell lines.

Formal proof for an involvement of autocrine stimulation in the disturbed growth of malignant cells has been difficult to obtain, in part due to lack of precise methods of assessing growth factor production and receptor occurrence. In this study we have analyzed the mRNA levels for two growth factors and the corresponding receptors in a number of established human malignant glioma cell lines. Twenty-one tested lines all contained transcripts for the platelet-derived growth factor (PDGF) A chain while 16-17 of 21 expressed the c-sis/PDGF B chain gene; these two genes were expressed independently of each other. PDGF receptor transcripts were present in 15-16 of the 21 lines. Transcripts for the epidermal growth factor receptor were found in all 15 tested lines, in 2 of them at high levels, and the corresponding ligand transforming growth factor-alpha was found in 11 of 15 lines. No amplification or structural rearrangements of the genes, as analyzed by Southern blot hybridization, could explain the varying expression of PDGF A and B chain transcripts or the elevated levels of epidermal growth factor receptor mRNA. A correlation was found between cell morphology and expression of growth factor and receptor mRNA in these lines. The highest amount of PDGF receptor transcripts was found in cells with fibroblast-like morphology, and c-sis/B chain transcripts were found in small cell types and in cells with astrocyte-like morphology, while no clear relationship was found between PDGF receptor and A chain transcript levels or between morphology and A chain transcripts. It is possible that the findings reflect a coordinated expression of these genes in the progenitor cells. In conclusion, the data imply the existence of two possible autocrine loops in human malignant glioma lines, affecting the PDGF and epidermal growth factor receptor pathways.

Cell Line↗
PubMed1987

An angiogenic growth factor is expressed in human glioma cells.

Progression to increased malignancy frequently occurs in human brain tumors of glial origin and usually involves neovascularization--a massive proliferation of endothelial cells into the tumor tissue. We have shown previously that subversion of a normal growth factor-related pathway is frequently associated with human gliomas. Here we show that human glioma cell lines express the gene encoding the angiogenic peptide endothelial cell growth factor (ECGF) or acidic fibroblast growth factor (a-FGF) and that an ECGF-like polypeptide is produced by these cells. The glioma-derived growth factor was partially purified from cell extracts by heparin-Sepharose affinity chromatography where it eluted at 1.5 M sodium chloride. On reversed-phase h.p.l.c., growth factor activity for endothelial cells was eluted at the same concentration of acetonitrile as found for bovine brain-ECGF, also a potent mitogen for endothelial cells. Moreover, human glioma cells possess specific cell surface receptors for ECGF and are mitogenically stimulated by exogenous addition of this growth factor. Glioma derived-ECGF may therefore have a dual influence: first, by autocrine growth-stimulation of human gliomas and, second, by paracrine-stimulation of endothelial cell proliferation which results in neovascularization of the tumor tissue.

Cell Line↗
PubMed1985

Tyrosine kinase receptor with extensive homology to EGF receptor shares chromosomal location with neu oncogene.

A novel potential cell surface receptor of the tyrosine kinase gene family has been identified and characterized by molecular cloning. Its primary sequence is very similar to that of the human epidermal growth factor receptor and the v-erbB oncogene product; the chromosomal location of the gene for this protein is coincident with the neu oncogene, which suggests that the two genes may be identical.

Animals↗
PubMed1985

The carbohydrate specificities of the monoclonal antibodies 29.1, 455 and 3C1B12 to the epidermal growth factor receptor of A431 cells.

Sixteen hybridoma-derived antibodies to the epidermal growth factor receptor of A431 cells were studied with respect to their reactions with blood group-related carbohydrate structures. Twelve of these were assessed as recognizing carbohydrate determinants on the basis of their immunostaining of reference blood group substances on nitrocellulose paper. Three of these antibodies were further investigated by inhibition of binding assays with glycoproteins and structurally defined oligosaccharides or by haemagglutination of erythrocytes before and after treatment with endo-beta-galactosidase. Two of the antibodies, 29.1 and 455, were shown to have blood group A-related specificities which differed from one another and from those of monoclonal anti-A antibodies described previously. The third antibody, 3C1B12, which was shown to recognize a determinant based on alpha 1----3 fucosylated Type 2 chains on linear and branched backbone sequences, also differs from previously described monoclonal antibodies of 3-fucosyl-N-acetyllactosamine type, such as anti-SSEA-1 (anti-mouse embryo) and several antibodies to human myeloid cells. While these antibodies are invaluable in providing structural information on the carbohydrate chains of the receptor glycoprotein and should help to elucidate their functions, their use as 'anti-receptor' reagents in cell biology will be influenced by the knowledge that the determinants they recognize are shared by other glycoproteins and glycolipids of diverse cell types.

Animals↗
PubMed1985

Amplification and overexpression of the EGF receptor gene in primary human glioblastomas.

The expression of epidermal growth factor (EGF) receptor in brain tumours of glial origin was studied at the protein, mRNA and genomic levels. Four out of 10 glioblastomas that overexpress EGF receptor also have gene amplification. The amplified genes appear to be rearranged, generating an aberrant mRNA in at least one of these tumours. Such receptor defects may be relevant to tumorigenesis of human glioblastomas.

Brain Neoplasms↗
PubMed1984

Antibodies to two defined regions of the transforming protein pp60src interact specifically with the epidermal growth factor receptor kinase system.

Antibodies generated against two synthetic peptides corresponding to two defined regions on the transforming protein of Rous sarcoma virus, pp60src, interact specifically with the epidermal growth factor (EGF)-receptor kinase. An antibody directed against a synthetic peptide corresponding to the major phosphorylation site of pp60src interacts specifically with EGF receptor and immunoprecipitates a functional EGF-receptor kinase. The second antibody, which binds close to a region on the src molecule that is required for its kinase activity, also binds to EGF-receptor kinase and prevents the autophosphorylation of the receptor molecules. Neither antibody binds to intact cells, but they do recognize various forms of the solubilized receptor. It is concluded that at least two cytoplasmic domains of the EGF receptor are antigenically and presumably also structurally related to specific domains on pp60src.

Amino Acid Sequence↗
PubMed1984

Expression of epidermal growth factor receptors in human brain tumors.

The expression of receptors for epidermal growth factor (EGF-R) was determined in 29 samples of brain tumors from 22 patients. Primary gliogenous tumors, of various degrees of cancer, five meningiomas, and two neuroblastomas were examined. Tissue samples were frozen in liquid nitrogen immediately after the operation and stored at -70 degrees until use. Cerebral tissue samples from 11 patients who died from diseases not related to the central nervous system served as controls. Immunoprecipitation of functional EGF-R-kinase complexes revealed high levels of EGF-R in all of the brain tumors of nonneuronal origin that were examined. The level of EGF-R varied between tumors from different patients and also between specimens prelevated from different areas of the same tumor. In contrast, the levels of EGF-R from control specimens were invariably low. The biochemical properties of EGF-R in brain tumor specimens were found to be indistinguishable from those of the well-characterized EGF-R from the A-431 cell line, derived from human epidermoid carcinomas. Human brain EGF-R displays a molecular weight of 170,000 by polyacrylamide-sodium dodecyl sulfate gel electrophoresis. It is phosphorylated mainly in tyrosine residues and shows a 2-dimensional phosphopeptide map similar to that obtained with the phosphorylated EGF-R from membranes of A-431 cells. Our observations suggest that induction of EGF-R expression may accompany the malignant transformation of human brain cells of nonneuronal origin.

Adult↗
PubMed1983

Biological role of epidermal growth factor-receptor clustering. Investigation with monoclonal anti-receptor antibodies.

Monoclonal anti-epidermal growth factor (EGF) receptor antibodies were used as a diagnostic tool for the investigation of the role of the receptor molecule in the transduction of the biological effects mediated by EGF. The specificity of the antibodies was established by immunoprecipitation of the receptor from biosynthetically labeled cells. The previously described (Schreiber, A. B., Lax, I., Yarden, Y., Eshhar, Z., and Schlessinger, J. (1981) Proc. Natl. Acad. Sci U. S. A. 78, 7535-7539) 2F2-IgM antibody binds to or close to the binding site of the growth factor on the receptor molecule; it induces receptor clustering and internalization and triggers early and delayed effects of EGF. A monovalent Fab fragment of the 2G2-IgM antibody stimulates the EGF-receptor sensitive protein kinase, but does not induce receptor clustering and DNA synthesis. When cell-bound 2G2-Fab fragments are cross-linked with anti-mouse Ig antibodies, both receptor clustering and mitogenic activity are restored. A second monoclonal antibody against EGF-receptor denoted TL5-IgG does not interfere with the binding of EGF to the receptor, fails to induce receptor clustering, and does not possess any intrinsic bioactivity. The cross-linking of cell-bound TL5-IgG with anti-mouse Ig antibodies leads to the stimulation of DNA synthesis. It is concluded that the EGF-receptor, when properly triggered, contains all the biochemical attributes necessary for the initiation of biological effects. Receptor clustering, even when mediated via domains distinct from the hormone binding site on the receptor molecule, appears as a necessary and sufficient signal for the induction of DNA synthesis.

Animals↗
PubMed1983

Monoclonal antibody reactive with the human epidermal-growth-factor receptor recognizes the blood-group-A antigen.

The hybridoma antibody TL5, which precipitates the EGF receptor from the human epidermoid carcinoma cell line A431, has been shown to recognize the blood-group-A carbohydrate structure. This conclusion has been reached from studies of (a) the binding of the antibody to glycoproteins and haemagglutination of erythrocytes with known blood-group-antigen activities and (b) the inhibition of binding of the antibody to a radiolabelled blood-group-A-active glycoprotein by structurally defined oligosaccharides.

ABO Blood-Group System↗
PubMed1983

Monoclonal antibodies against epidermal growth factor receptor induce prolactin synthesis in cultured rat pituitary cells (GH3).

The addition of epidermal growth factor (EGF) to cultured rat pituitary cells (GH3) leads to increased synthesis of prolactin and to partial inhibition of cell proliferation. Monoclonal antibodies generated against EGF receptor from human epidermoid carcinoma (A-431) cells were used to characterize the EGF receptor kinase system of GH3 cells and to investigate the role of the hormone-receptor complex in the expression of the prolactin gene in these cells. The EGF receptor of GH3 cells is a 170,000-dalton protein associated with a protein kinase. It is similar but not identical to the EGF receptor identified in other tissues. The immunoprecipitated membrane receptor is phosphorylated on both serine and tyrosine residues. The monoclonal antibody denoted 2G2-IgM binds to EGF receptor on GH3 cells. Like EGF, the monoclonal antibody induced the synthesis of prolactin and morphological changes in these cells. Hence, EGF receptor in GH3 cells, when properly triggered, contains all of the biological attributes necessary for the induction of EGF-induced gene expression and morphological changes in GH3 cells.

Animals↗
PubMed1980

Phosphorylation and dephosphorylation of spectrin from human erythrocyte ghosts under physiological conditions: autocatalysis rather than reaction with separate kinase and phosphatase.

The mechanism of phosphosylation and dephosphorylation of spectrin from human erythrocyte membranes has been examined under closely physiological conditions. The results support the hypothesis that spectrin is an autophosphorylating and dephosphorylating system. (i) Extraction from ghosts of up to 85% of the kinase (casein kinase) suggested to catalyze the reaction [see Fairbanks, G., Avruch, J., Dino, E. J. & Patel, V. P. (1978) J. Supramol. Struct. 9, 97--112] only slightly reduced spectrin component 2 phosphorylation and did not affect ATP-induced changes in the ghosts' shapes. (ii) A spectrin--actin complex isolated from endocytotic inside-out vesicles under hyperteonic conditions contained virtually no casein kinase activity and still exhibited a largely intact phosphorylation machinery. (iii) Photoaffinity labeling experiments indicated that spectrin component 2 fulfills the necessary prerequisite of the hypothesis--i.e., it contains its own ATP-binding site. (iv) Under various conditions, spectrin phosphorylation and dephospohrylation seem to be tightly coupled. The implications of these findings for the understanding of spectrin function and the maintenance of erythrocyte shape are discussed.

Actins↗
PubMedDate not supplied

Human epidermal growth factor receptor cDNA sequence and aberrant expression of the amplified gene in A431 epidermoid carcinoma cells.

The complete 1,210-amino acid sequence of the human epidermal growth factor (EGF) receptor precursor, deduced from cDNA clones derived from placental and A431 carcinoma cells, reveals close similarity between the entire predicted v-erb-B mRNA oncogene product and the receptor transmembrane and cytoplasmic domains. A single transmembrane region of 23 amino acids separates the extracellular EGF binding and cytoplasmic domains. The receptor gene is amplified and apparently rearranged in A431 cells, generating a truncated 2.8-kilobase mRNA which encodes only the extracellular EGF binding domain.

Amino Acid Sequence↗
PubMedDate not supplied

Amplification, enhanced expression and possible rearrangement of EGF receptor gene in primary human brain tumours of glial origin.

Epidermal growth factor (EGF), through interaction with specific cell surface receptors, generates a pleiotropic response that, by a poorly defined mechanism, can induce proliferation of target cells. Subversion of the EGF mitogenic signal through expression of a truncated receptor may be involved in transformation by the avian erythroblastosis virus (AEV) oncogene v-erb-B, suggesting that similar EGF receptor defects may be found in human neoplasias. Overexpression of EGF receptors has been reported on the epidermoid carcinoma cell line A431, in various primary brain tumours and in squamous carcinomas. In A431 cells the receptor gene is amplified. Here we show that 4 of 10 primary brain tumours of glial origin which express levels of EGF receptors that are higher than normal also have amplified EGF receptor genes. Amplified receptor genes were not detected in the other brain tumours examined. Further analysis of EGF receptor defects may show that such altered expression and amplification is a particular feature of certain human tumours.

Brain Neoplasms↗