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Affiliation(s)
- A D Levinson
- Genentech, Inc., South San Francisco, CA 94080, USA
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Ricketts MH, Durrheim GA, North HM, van der Merwe MJ, Levinson AD. Positive and negative modulation of H-ras transforming potential by mutations of phenylalanine-28. Mol Biol Rep 1996; 23:109-17. [PMID: 8983024 DOI: 10.1007/bf00424436] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Conserved amino-acids of H-ras from residues 25 to 34 were mutated in human H-ras cDNA with a pre-existing valine-12 activating mutation ([V12]p21), and built into SV40-driven expression vectors. The influence of the introduced mutations was initially screened by transfection of Rat-1 cells to score foci of transformed cells. Non-conservative mutations of amino-acids 25 (tryptophan for glutamine), 27 (asparagine for histidine) and 34 (alanine for proline) did not abrogate the transforming potential of [V12]p21. The conservative mutation of phenylalanine-28 to tryptophan ([V12W28]p21) was also still transforming. Significantly, in the absence of the valine-12 activating mutation, tryptophan-28-ras ([W28]p21) was weakly transforming while, in contrast, [V12D28]p21 was unable to transform Rat-1 cells and retarded cell growth. Analysis of the binding and dissociation of GTP and GDP to normal and mutated p21 expressed in Escherichia coli showed that [V12D28]p21 and [D28]p21 do not bind GTP. The dissociation rate of both GTP and GDP bound to [W28]p21 is increased, suggesting a mechanism for its transforming potential in Rat-1 cells. These studies illustrate the importance of phenylalanine-28 in guanine nucleotide binding by p21H-ras. The mutations described could be valuable tools in investigations of cellular signal transduction involving small GTP-binding proteins.
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Affiliation(s)
- M H Ricketts
- Department of Psychiatry, UMDNJ, Robert Wood Johnson Medical School, Piscataway 08854, USA
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Shelton DL, Sutherland J, Gripp J, Camerato T, Armanini MP, Phillips HS, Carroll K, Spencer SD, Levinson AD. Human trks: molecular cloning, tissue distribution, and expression of extracellular domain immunoadhesins. J Neurosci 1995; 15:477-91. [PMID: 7823156 PMCID: PMC6578290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Using molecular cloning techniques, human homologs of the known members of the trk family of neurotrophin receptors have been cloned and sequenced. Overall, there is a high degree of similarity between the human sequences and those from other mammals; however, there are differences in splicing patterns. There are two spliced forms of the extracellular domain of trkC in the human, a finding that has not been described in other species. In contrast, fewer spliced forms were detected of the intracellular domains of human trkB and trkC than has been described in other mammals. Northern analysis and in situ hybridization experiments indicate that the human trks are expressed in a similar pattern to that described in other mammals. Expression of the trk extracellular domains as fusion proteins with IgG heavy chain yields soluble molecules that mimic intact trks in their binding specificity and affinity. These soluble chimeras block the biological activity of their cognate neurotrophin(s) in vitro.
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Affiliation(s)
- D L Shelton
- Department of Neuroscience, Genentech, Inc., South San Francisco, California 94080
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Cohen JB, Snow JE, Spencer SD, Levinson AD. Suppression of mammalian 5' splice-site defects by U1 small nuclear RNAs from a distance. Proc Natl Acad Sci U S A 1994; 91:10470-4. [PMID: 7937977 PMCID: PMC45042 DOI: 10.1073/pnas.91.22.10470] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
One of the earliest events in the process of intron removal from mRNA precursors is the establishment of a base-pairing interaction between U1 small nuclear (sn) RNA and the 5' splice site. Mutations at the 5' splice site that prevent splicing can often be suppressed by coexpression of U1 snRNAs with compensatory changes, but in yeast, accurate splicing is not restored when the universally conserved first intron base is changed. In our mammalian system as well, such a mutation could not be suppressed, but the complementary U1 caused aberrant splicing 12 bases downstream. This result is reminiscent of observations in yeast that aberrant 5' splice sites can be activated by U1 snRNA from a distance. Using a rapid, qualitative protein expression assay, we provide evidence that 5' splice-site mutations can be suppressed in mammalian cells by U1 snRNAs with complementarity to a range of sequences upstream or downstream of the site. Our approach uncouples in vivo the commitment-activation step of mammalian splicing from the process of 5' splice-site definition and as such will facilitate the genetic characterization of both.
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Affiliation(s)
- J B Cohen
- Department of Molecular Genetics and Biochemistry, University of Pittsburgh, School of Medicine, PA 15261
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Hoeffler WK, Levinson AD, Bauer EA. Activation of c-Jun transcription factor by substitution of a charged residue in its N-terminal domain. Nucleic Acids Res 1994; 22:1305-12. [PMID: 8165146 PMCID: PMC523657 DOI: 10.1093/nar/22.7.1305] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
C-Jun is a cellular transcription factor that can control gene expression in response to treatment of cells with phorbol esters, growth factors, and expression of some oncogenes. The ability of c-Jun to catalyze the transcription of certain genes is controlled, in part, by changes in the phosphorylation state of specific amino acids in c-Jun. One of the major sites that is phosphorylated during signal response is Ser73. Here we show that substitution of a negatively charged aspartic acid residue at 73 constitutively increased transcriptional activity of c-Jun. The Asp73 substitution also enhanced its availability to bind to DNA in a whole cell extract without altering its intrinsic DNA binding activity since the intrinsic activity was unaltered for the c-Jun mutant proteins expressed in a bacterial system. The negatively charged Asp substitution may mimic the negative charge of a phosphorylated serine at 73. The substitution of an uncharged alanine at 73 resulted in lowered activities. The N-terminal end of c-Jun containing these substitutions was fused to the DNA-binding region of the bovine papilloma virus E2 protein, and was able to confer the same activation properties to the fusion protein at the heterologous E2 DNA-binding site. Ser73 lies in a region of c-Jun previously proposed to bind an uncharacterized inhibitor, perhaps related to a protein of approximately 17.5 kD that coprecipitates along with our c-Jun or the JunE2 fusion products.
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Affiliation(s)
- W K Hoeffler
- Department of Dermatology, Stanford University Medical School, CA 94305
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Crowley C, Spencer SD, Nishimura MC, Chen KS, Pitts-Meek S, Armanini MP, Ling LH, McMahon SB, Shelton DL, Levinson AD. Mice lacking nerve growth factor display perinatal loss of sensory and sympathetic neurons yet develop basal forebrain cholinergic neurons. Cell 1994; 76:1001-11. [PMID: 8137419 DOI: 10.1016/0092-8674(94)90378-6] [Citation(s) in RCA: 795] [Impact Index Per Article: 26.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Homologous recombination was utilized to generate mice with a deletion in the coding sequence of the nerve growth factor (NGF) gene. Animals homozygous for NGF disruption failed to respond to noxious mechanical stimuli, and histological analysis revealed profound cell loss in both sensory and sympathetic ganglia. Within dorsal root ganglia, effects of the mutation appeared to be restricted to small and medium peptidergic neurons. These observations confirm the critical dependence of sensory and sympathetic neurons on NGF and demonstrate that other neurotrophins are not able to compensate for the loss of NGF action on these cells. Examination of the central nervous system revealed that, in marked contrast with neurons of sensory and sympathetic ganglia, basal forebrain cholinergic neurons differentiate and continue to express phenotypic markers for the life span of the null mutant mice. Thus, differentiation and initial survival of central NGF-responsive neurons can occur in the absence of NGF.
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Affiliation(s)
- C Crowley
- Department of Cell Genetics, Genentech, Incorporated, South San Francisco, California 94080
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James GL, Goldstein JL, Brown MS, Rawson TE, Somers TC, McDowell RS, Crowley CW, Lucas BK, Levinson AD, Marsters JC. Benzodiazepine peptidomimetics: potent inhibitors of Ras farnesylation in animal cells. Science 1993; 260:1937-42. [PMID: 8316834 DOI: 10.1126/science.8316834] [Citation(s) in RCA: 530] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Oncogenic Ras proteins transform animal cells to a malignant phenotype only when modified by farnesyl residues attached to cysteines near their carboxyl termini. The farnesyltransferase that catalyzes this reaction recognizes tetrapeptides of the sequence CAAX, where C is cysteine, A is an aliphatic amino acid, and X is a carboxyl-terminal methionine or serine. Replacement of the two aliphatic residues with a benzodiazepine-based mimic of a peptide turn generated potent inhibitors of farnesyltransferase [50 percent inhibitory concentration (IC50) < 1 nM]. Unlike tetrapeptides, the benzodiazepine peptidomimetics enter cells and block attachment of farnesyl to Ras, nuclear lamins, and several other proteins. At micromolar concentrations, these inhibitors restored a normal growth pattern to Ras-transformed cells. The benzodiazepine peptidomimetics may be useful in the design of treatments for tumors in which oncogenic Ras proteins contribute to abnormal growth, such as that of the colon, lung, and pancreas.
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Affiliation(s)
- G L James
- Department of Molecular Genetics, University of Texas Southwestern Medical Center, Dallas 75235
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Abstract
The plasminogen activator urokinase (u-PA) mediates proteolysis by a variety of human tumor cells. Competitive displacement of u-PA from cellular binding sites results in decreased proteolysis in vitro, suggesting that the cell surface is the preferred site for u-PA-mediated protein degradation. We studied the effect of u-PA receptor blockade on the metastatic capacity of human PC3 prostate carcinoma cells, using transfectants which expressed chloramphenicol acetyl-transferase (CAT). Eight weeks after subcutaneous inoculation of these cells into nude mice, CAT activity was detected in regional lymph nodes, femurs, lungs, and brain, thereby mimicking the organ tropism observed for naturally occurring metastases of prostate cancer. In a second transfection, CAT-expressing PC3 cells received cDNA encoding a mutant u-PA (Ser356-->Ala) which lacks enzymatic activity but which retains full receptor binding affinity. Three mutant u-PA expressors, each with < 5% of wild-type cell-associated u-PA activity, were compared in vivo with independently derived controls. Primary tumor growth was similar in each group of animals and all tumors expressed comparable CAT activity. In contrast, metastasis (as assessed by CAT activity) was markedly inhibited when cell surface u-PA activity was blocked. Levels of CAT activity were reduced by a factor of > 300 in regional lymph nodes, 40-100 in brain tissue, and 10-20 in lung tissue. Metastatic capacity was inhibited similarly when animals were given intermittent intraperitoneal injections of a u-PA/IgG fusion protein capable of displacing u-PA activity from the tumor cell surface. Our results indicate that cell surface u-PA activity is essential to the metastatic process. In addition, the assay system employed in these experiments may be generally useful in testing other therapeutic modalities to limit the spread of primary tumors.
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Affiliation(s)
- C W Crowley
- Department of Cell Genetics, Genentech, Inc., South San Francisco, CA 94080
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Cohen JB, Broz SD, Levinson AD. U1 small nuclear RNAs with altered specificity can be stably expressed in mammalian cells and promote permanent changes in pre-mRNA splicing. Mol Cell Biol 1993; 13:2666-76. [PMID: 7682651 PMCID: PMC359637 DOI: 10.1128/mcb.13.5.2666-2676.1993] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Pre-mRNA 5' splice site activity depends, at least in part, on base complementarity to U1 small nuclear RNA. In transient coexpression assays, defective 5' splice sites can regain activity in the presence of U1 carrying compensatory changes, but it is unclear whether such mutant U1 RNAs can be permanently expressed in mammalian cells. We have explored this issue to determine whether U1 small nuclear RNAs with altered specificity may be of value to rescue targeted mutant genes or alter pre-mRNA processing profiles. This effort was initiated following our observation that U1 with specificity for a splice site associated with an alternative H-ras exon substantially reduced the synthesis of the potentially oncogenic p21ras protein in transient assays. We describe the development of a mammalian complementation system that selects for removal of a splicing-defective intron placed within a drug resistance gene. Complementation was observed in proportion to the degree of complementarity between transfected mutant U1 genes and different defective splice sites, and all cells selected in this manner were found to express mutant U1 RNA. In addition, these cells showed specific activation of defective splice sites presented by an unlinked reporter gene. We discuss the prospects of this approach to permanently alter the expression of targeted genes in mammalian cells.
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Affiliation(s)
- J B Cohen
- Department of Cell Genetics, Genentech, Inc., South San Francisco, California 94080
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Ferrara N, Winer J, Burton T, Rowland A, Siegel M, Phillips HS, Terrell T, Keller GA, Levinson AD. Expression of vascular endothelial growth factor does not promote transformation but confers a growth advantage in vivo to Chinese hamster ovary cells. J Clin Invest 1993; 91:160-70. [PMID: 8423215 PMCID: PMC330010 DOI: 10.1172/jci116166] [Citation(s) in RCA: 132] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Vascular endothelial growth factor (VEGF) is a mitogen with a specificity for endothelial cells in vitro and an angiogenic inducer in vivo. We tested the hypothesis that VEGF may confer on expressing cells a growth advantage in vivo. Dihydrofolatereductase--Chinese hamster ovary cells were transfected with expression vectors which direct the constitutive synthesis of VEGF. Neither the expression nor the exogenous administration of VEGF stimulated anchorage-dependent or anchorage-independent growth of Chinese hamster ovary cells in vitro. However, VEGF-expressing clones, unlike control cells, demonstrated an ability to proliferate in nude mice. Histologic examination revealed that the proliferative lesions were compact, well vascularized, and nonedematous. Ultrastructural analysis revealed that capillaries within the lesions were of the continuous type. These findings indicate that the expression of VEGF may confer on cells the ability to grow in vivo in the absence of transformation by purely paracrine mechanisms. Since VEGF is a widely distributed protein, this property may have relevance for a variety of physiological and pathological proliferative processes.
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Affiliation(s)
- N Ferrara
- Genentech, Inc., South San Francisco, California 94080
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Pelletier AJ, Bodary SC, Levinson AD. Signal transduction by the platelet integrin alpha IIb beta 3: induction of calcium oscillations required for protein-tyrosine phosphorylation and ligand-induced spreading of stably transfected cells. Mol Biol Cell 1992; 3:989-98. [PMID: 1421580 PMCID: PMC275660 DOI: 10.1091/mbc.3.9.989] [Citation(s) in RCA: 83] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
We demonstrate an example of signal transduction by an integrin and have begun to define the pathway through which this signaling is achieved. We constructed a stably transfected derivative of 293 cells (ATCC 1573) that expresses the platelet integrin GPIIbIIIa (alpha IIb beta 3). This cell line, clone B, adheres to and spreads on fibrinogen, a ligand for alpha IIb beta 3, while the parent cell line does not. Stimulation of these cells either by adhesion to fibrinogen or with antiserum directed against alpha IIb beta 3 results in induction of calcium oscillations, followed by tyrosine phosphorylation of at least one protein of molecular weight approximately 125 kDa. We establish that this phosphorylation, as well as the morphological rearrangements, requires the mobilization of calcium.
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Affiliation(s)
- A J Pelletier
- Genentech Inc., South San Francisco, California 94080
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Cohen RL, Xi XP, Crowley CW, Lucas BK, Levinson AD, Shuman MA. Effects of urokinase receptor occupancy on plasmin generation and proteolysis of basement membrane by human tumor cells. Blood 1991; 78:479-87. [PMID: 1648983] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
The goal of the present study was to assess the relative importance of receptor-bound and secreted plasminogen activator urokinase (u-PA) in generating cell-surface plasmin and fostering destruction of normal tissue by tumor cells. We first showed that active site-inhibited u-PA could displace endogenous u-PA from the surface of the human colon adenocarcinoma cell line HCT 116. We then prepared expression vectors for u-PA and for a mutant molecule in which the codon for the active site serine residue was changed to encode alanine. Expression of non-functional mutant u-PA decreased the level of cell-bound active u-PA by more than 95% via a mechanism that involved competition for receptor sites. Decreased cell-surface u-PA activity was associated with a decrease in cell-bound plasmin activity to undetectable levels, suggesting that receptor-bound u-PA plays an important role in the generation of plasmin on the cell surface. Transfectants that secreted eightfold to 20-fold elevated levels of active wild-type u-PA showed approximately 50% increases in cell-associated u-PA and only twofold to fourfold increases in cell-associated plasmin, suggesting that the role of secreted u-PA in generating cell-surface plasmin activity was relatively minor. In parent cells and both types of transfectants there was a good correlation between the amount of plasmin bound to the tumor cell surface and the extent to which a basement membrane substrate was degraded. These studies show that receptor-bound u-PA provides an efficient mechanism for plasmin generation on the surface of tumor cells, which, in turn, contributes significantly to their degradative potential.
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Affiliation(s)
- R L Cohen
- Cancer Research Institute, University of California-San Francisco 94143
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Wakefield LM, Winokur TS, Hollands RS, Christopherson K, Levinson AD, Sporn MB. Recombinant latent transforming growth factor beta 1 has a longer plasma half-life in rats than active transforming growth factor beta 1, and a different tissue distribution. J Clin Invest 1990; 86:1976-84. [PMID: 2254455 PMCID: PMC329834 DOI: 10.1172/jci114932] [Citation(s) in RCA: 236] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Transforming growth factor beta 1 (TGF-beta 1) is a key regulator of cell growth and differentiation. Under normal physiological conditions, it is made as a biologically latent complex whose significance is unknown. Previous work has indicated that active TGF-beta 1 has a very short plasma half-life in rats (Coffey, R. J., L. J. Kost, R. M. Lyons, H. L. Moses, and N. F. La-Russo. 1987. J. Clin. Invest. 80:750-757). We have investigated the possibility that latent complex formation may extend the plasma half-life of TGF-beta 1 and alter its organ distribution. Radiolabeled latent TGF-beta 1 was formed by noncovalent association of 125I-TGF-beta 1 with the TGF-beta 1 precursor "pro" region from recombinant sources. TGF-beta 1 in this latent complex had a greatly extended plasma half-life (greater than 100 min) in rats compared with active TGF-beta 1 (2-3 min). Whereas active TGF-beta 1 was rapidly taken up by the liver, kidneys, lungs, and spleen and degraded, TGF-beta 1 in the latent complex was largely confined to the circulation, and was less than 5% degraded after 90 min. The pharmacokinetics of TGF-beta 1 in the latent complex were shown to be critically dependent on the degree of sialylation of the complex. The results suggest that formation of latent complexes may switch endogenous TGF-beta 1 from an autocrine/paracrine mode of action to a more endocrine mode involving target organs distant from the site of synthesis.
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Affiliation(s)
- L M Wakefield
- Laboratory of Chemoprevention, National Cancer Institute, Bethesda, Maryland 20892
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Wallick SC, Figari IS, Morris RE, Levinson AD, Palladino MA. Immunoregulatory role of transforming growth factor beta (TGF-beta) in development of killer cells: comparison of active and latent TGF-beta 1. J Exp Med 1990; 172:1777-84. [PMID: 2258706 PMCID: PMC2188774 DOI: 10.1084/jem.172.6.1777] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Using recombinant DNA technology, we have generated Chinese hamster ovary (CHO) cell lines that synthesize latent transforming growth factor beta 1 (TGF-beta 1) to study immune regulation by TGF-beta 1. In vitro, latent TGF-beta 1 synthesized by transfectants or added exogenously as a purified complex after activation inhibited CTL generation to a similar extent as seen with acid-activated recombinant human (rHu) TGF-beta 1. In vivo, serum from nu/nu mice bearing CHO/TGF-beta 1 tumors contained significant levels of latent TGF-beta 1 in addition to depressed natural killer (NK) activity in spleens which paralleled that seen in C3H/HeJ mice treated with acid-activated rHuTGF-beta 1. rHuTGF-beta 1 treatment of mice receiving heart allografts resulted in significant enhancement of organ graft survival. Because of possible regulated tissue-specific activation, administration of latent rather than active TGF-beta may provide a better route to deliver this powerful immunosuppressive agent in vivo.
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Affiliation(s)
- S C Wallick
- Department of Immunology Research and Assay Technologies Genetech, Inc., South San Francisco, California 94080
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Abstract
Within the past three years there has been a rapid expansion in our knowledge of the role TGF-beta mediates in regulating immune responses in vitro. Whether the TGF-beta will be clinically useful to suppress immune responses to transplanted organs or autoimmune responses is unknown. However, now that highly purified quantities of TGF-beta are available through recombinant DNA technologies, questions concerning the in vivo immunosuppressive activities of TGF-beta can be answered.
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Affiliation(s)
- M A Palladino
- Genentech, Inc., South San Francisco, California 94080
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18
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Abstract
Native and recombinant forms of transforming growth factor-beta 1 (TGF-beta 1) are synthesized predominantly as biologically latent complexes. Physicochemical analysis demonstrates that the more recently described TGF-beta 2 and TGF-beta 3 are also latent, and reveals a common series of sharply defined parameters for activation. Human recombinant latent TGF-beta's 1 and 2 show identical profiles of activation by acid and base; the transition from latency occurs between pH 4.1 and 3.1, and between pH 11.0 and 11.9. The profile for chicken recombinant latent TGF-beta 3 is slightly shifted with activation between pH 3.1 and 2.5, and between pH 10.0 and 12.3. Thermal activation of native and recombinant latent TGF-beta 1 occurs over the temperature ranges of 75-100 degrees C and 65-100 degrees C, respectively, with complete activation after 5 min at 80 degrees C. Temperatures above 90 degrees C result in thermal denaturation of TGF-beta 1 itself. Recombinant latent TGF-beta's 2 and 3 are also activated over this temperature range; however, maximum activation occurs at 100 degrees C. These results suggest common elements in latent complex structure despite differences between the TGF-beta subtypes in pro-region primary sequence.
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Affiliation(s)
- P D Brown
- Laboratory of Chemoprevention, National Cancer Institute, Bethesda, Maryland 20892
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Abstract
Adenovirus VAI-RNA is a small virally encoded RNA that is required for efficient protein synthesis at late times of adenoviral infection. We show that in transient transfection assays VAI-RNA promotes not only an increased level of protein encoded by a co-transfected marker (CAT) plasmid, but also a marked accumulation of its transcript. The increases in CAT protein and RNA levels reflect an enhanced stability of the cytoplasmic RNA as shown by primer extension analyses of RNA isolated from transfected cells upon transcriptional arrest. Surprisingly, the ability of VAI to activate expression of CAT requires the translation of a substantial portion of the RNA: when translation is prevented by elimination of the initiator AUG codon or by introduction of stop codons 5' to codon 107, VAI-RNA is no longer capable of increasing CAT RNA levels; the introduction of stop codons 3' of codon-135, on the other hand, does not significantly impair VAI-RNA function. We conclude that in addition to its role as a specific activator of translation, adenovirus VA genes function to regulate the stability of ribosome-bound RNA.
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Affiliation(s)
- R Strijker
- Department of Cell Genetics, Genentech Inc., South San Francisco, CA 94080
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Abstract
We previously demonstrated that a point mutation in the last intron of the human H-ras oncogene causes a significant increase in its expression and transforming efficiency. Here we establish the basis of this phenomenon. Using gene reconstruction experiments, we have identified a negative-acting element in the intron that is completely inactivated by the mutation. The effects of other nucleotide alterations introduced into this region suggested that the negative element might constitute an alternative exon. Transcripts containing this putative exon were identified and S1 nuclease analysis confirmed that the mutation prevents their synthesis. The abundance of these transcripts is low, apparently due to message instability and/or defective processing. The predicted product of the alternative transcript is suggested to lack transforming potential. Our findings demonstrate that alternative splicing normally operates to suppress p21H-ras expression and that this negative control is abolished by a variety of mutations that interfere with this process.
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Affiliation(s)
- J B Cohen
- Department of Cell Genetics, Genentech, Inc., South San Francisco, California 94080
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Cohen RL, Niclas J, Lee WM, Wun TC, Crowley CW, Levinson AD, Sadler JE, Shuman MA. Effects of cellular transformation on expression of plasminogen activator inhibitors 1 and 2. Evidence for independent regulation. J Biol Chem 1989; 264:8375-83. [PMID: 2498314] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Expression of plasminogen activators (PA) has been reported to be associated with invasive tumor growth and increased metastatic ability. In order to delineate changes in PA and PA inhibitor (PAI) expression that accompany cellular transformation, we studied oncogene-containing variants of the Rat-1 cell line. We report here that transfection of the oncogenes v-src, erbB, c-myc, v-myc, N-myc, and EJras into these cells does not result in detectable PA activity in conditioned media or cell extracts. In addition, Northern blot analysis fails to demonstrate urokinase mRNA in Rat-1 cells or transfectants. Moreover, cells transformed by EJras and v-src but not other oncogenes secrete an active placental-type PAI, PAI-2. Using inducible EJras constructs, we find that increased PAI-2 gene expression is detectable within 6-12 h after treatment with the inducing agent. Peak expression of PAI-2 mRNA is increased 10-15-fold over base line, and high levels are maintained for at least 72 h. In contrast to the results with PAI-2, secretion of endothelial-type PAI-1 into conditioned media is sharply down-regulated by several oncogenes. Thus, we have found that PAI-1 and PAI-2 are independently regulated in transformed variants of Rat-1 cells. The specific induction of PAI-2 in cells transformed by oncogenic ras and src suggests that this protease inhibitor may have a previously unsuspected role in malignancy.
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Affiliation(s)
- R L Cohen
- Cancer Research Institute, University of California, San Francisco 94143
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Cohen RL, Niclas J, Lee WMF, Wun TC, Crowley CW, Levinson AD, Sadler JE, Shuman MA. Effects of cellular transformation on expression of plasminogen activator inhibitors 1 and 2. J Biol Chem 1989. [DOI: 10.1016/s0021-9258(18)83192-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Wakefield LM, Smith DM, Broz S, Jackson M, Levinson AD, Sporn MB. Recombinant TGF-beta 1 is synthesized as a two-component latent complex that shares some structural features with the native platelet latent TGF-beta 1 complex. Growth Factors 1989; 1:203-18. [PMID: 2629880 DOI: 10.3109/08977198908997997] [Citation(s) in RCA: 90] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The entire coding region of the human transforming growth factor beta 1 (TGF-beta 1) precursor cDNA has been stably expressed in a human renal carcinoma cell line. Like platelet TGF-beta 1, the recombinant TGF-beta 1 is secreted in a biologically latent form. Immunoblot analysis and gel-filtration indicate that the recombinant latent TGF-beta 1 is a 100-kDa complex in which active 25-kDa TGF-beta 1 is noncovalently associated with the remaining 75 kDa of the processed precursor. Unlike the platelet latent complex, the recombinant latent complex contains no 135-kDa component. Thus, the processed precursor peptide alone is sufficient to confer latency on active TGF-beta 1, and the 135-kDa platelet component has a different role. The processed precursor is similarly glycosylated in recombinant and platelet complexes, and in both has an exposed heparin binding site that may be involved in targeting of the latent complex. Finally, acid activation of recombinant and platelet complexes is reversible, suggesting that the activation process does not cause major structural modifications in the components of the latent complex.
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Affiliation(s)
- L M Wakefield
- Laboratory of Chemoprevention, National Cancer Institute, Bethesda, MD 20892
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25
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Jakobovits EB, Schlokat U, Vannice JL, Derynck R, Levinson AD. The human transforming growth factor alpha promoter directs transcription initiation from a single site in the absence of a TATA sequence. Mol Cell Biol 1988; 8:5549-54. [PMID: 2907605 PMCID: PMC365660 DOI: 10.1128/mcb.8.12.5549-5554.1988] [Citation(s) in RCA: 29] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Transforming growth factor alpha (TGF-alpha) is a transformation-responsive mitogenic polypeptide that is expressed in the brain, epithelial cells, and activated macrophages. We isolated and characterized the TGF-alpha promoter and localized the 5' end of the TGF-alpha transcript to a unique position. Surprisingly, no apparent TATA box was present in the promoter sequence, suggesting that transcription from mammalian genes can initiate at unique and specific positions from promoters lacking this sequence motif.
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Affiliation(s)
- E B Jakobovits
- Department of Cell Genetics, Genentech, Inc., South San Francisco, California 94080
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26
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Kuzumaki N, Fujita H, Dosaka H, Katabami M, Levinson AD. Transplantation resistance to a Rous sarcoma virus-induced tumor in mice immunized with v-src protein. J Natl Cancer Inst 1988; 80:959-62. [PMID: 2840516 DOI: 10.1093/jnci/80.12.959] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
It is of great interest in tumor immunology to know whether oncogene products could be used not only as tumor markers for cancer diagnosis, but also as immunogens for cancer therapy. BALB/c mice immunized with syngeneic fibroblasts, Escherichia coli cells producing p60v-src, or the purified p60v-src protein extracted from the E. coli producer cells showed transplantation resistance to a Rous sarcoma virus-induced tumor but not a Kirsten sarcoma virus-induced tumor. In contrast, mice immunized with cells not producing p60v-src or their derived proteins or with chicken ovalbumin did not show any significant resistance. These findings suggest that p60v-src can act as a specific transplantation rejection antigen in mice.
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Affiliation(s)
- N Kuzumaki
- Laboratory of Molecular Genetics, Hokkaido University School of Medicine, Sapporo, Japan
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27
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Cohen JB, Levinson AD. A point mutation in the last intron responsible for increased expression and transforming activity of the c-Ha-ras oncogene. Nature 1988; 334:119-24. [PMID: 3133569 DOI: 10.1038/334119a0] [Citation(s) in RCA: 117] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
The T24/EJ allele of the Ha-ras proto-oncogene owes its powerful oncogenic activity not merely to the well documented mutation that perturbs the structure of the encoded polypeptide, but in addition to a second single nucleotide alteration in an intron that causes a tenfold increase in expression. This effect on expression is maintained upon transfer of the surrounding DNA to a heterologous gene, and as such defines a novel regulatory element.
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Affiliation(s)
- J B Cohen
- Department of Cell Genetics, Genentech Inc., South San Francisco, California 94080
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28
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Abstract
The genome of human hepatitis B virus (HBV) contains an enhancer element within a 360-base-pair transcribed region located between sequences encoding the virus surface and core antigens. Beyond the usual properties associated with enhancers (i.e., activity 5' or 3' of a heterologous promoter and relative orientation independence), DNA sequences encompassing this enhancer exhibited unexpected characteristics. Using gene expression assays in both stably and transiently transfected cells, we found that the HBV enhancer element, when located in a transcribed region of chimeric genes, dramatically increased expression levels of genes controlled by the simian virus 40 promoter/enhancer. This synergism was not observed, however, when the HBV enhancer was located outside of the transcribed region. When these transcribed sequences were reversed in orientation, expression levels decreased significantly. These data suggest that RNA stability and transcriptional activity may be affected by sequences associated with this DNA region. In contrast to the findings of others, we found that the HBV enhancer activated transcription in a relatively cell-type-independent manner when the enhancer was located either 5' of the promoter or in the 3' untranslated region of gene constructs. The implications of these and other properties of the HBV enhancer region on viral gene expression and its life cycle are discussed.
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Affiliation(s)
- J L Vannice
- Department of Molecular Biology, Genentech, Inc., South San Francisco, California 94080
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29
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Abstract
Rat-1 cells were transfected with plasmids encoding normal (Gly-12), nonactivated (Pro-12), and activated (Val-12 and Ile-12) p21H-ras in the presence of an amplifiable dihydrofolate reductase marker. The introduced DNA was amplified by selection in methotrexate to establish the relationship between p21H-ras expression and various hallmarks of cellular transformation. The maximum level of p21H-ras (Gly-12) consistent with cell viability was approximately 0.13% of total cell protein (approximately 60,000 molecules per cell); this is 44-fold greater than the level of the endogenous protein. The maximum tolerated level of a second nontransforming form of p21H-ras (pro-12) was about half of this. Amplification in Rat-1 cells of H-ras genes encoding the highly oncogenic Val-12 and Ile-12 forms of p21H-ras could not be achieved by methotrexate selection, providing strong evidence that synthesis of activated p21H-ras above a certain threshold (about 0.02% of total protein) in Rat-1 cells is incompatible with cell viability. Individual cell lines were isolated and their morphology, anchorage-independent growth, tumorigenicity, and response to and production of growth factors were studied. We report that cell lines expressing near-maximum tolerated levels of either the normal or pro-12 form of p21H-ras were not as transformed as cells expressing much more modest levels of the highly oncogenic (Val-12) form, suggesting that the complete elaboration of the transformed phenotype by ras depends, at least in part, on mutations that distinguish the cellular and viral proteins. We found that cells expressing elevated levels of the normal p21(H-ras) could be fully transformed by the activated (Val-12) form and that such cells continued to overexpress p21(H-ras) (Gly-12), arguing against a role for normal ras genes in suppression of the oncogenic potential of their mutationally activated counterparts.
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Affiliation(s)
- M H Ricketts
- Department of Cell Genetics, Genetech Inc., South San Francisco, California 94080
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30
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Simonsen CS, Walter M, Levinson AD. Expression of the plasmid-encoded type I dihydrofolate reductase gene in cultured mammalian cells: a novel selectable marker. Nucleic Acids Res 1988; 16:2235-46. [PMID: 3357775 PMCID: PMC338212 DOI: 10.1093/nar/16.5.2235] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
A recombinant plasmid has been designed to express the gene encoding a type I methotrexate-resistant dihydrofolate reductase, derived from the bacterial plasmid R483, in DHFR- Chinese hamster ovary cells. Vectors containing the wild type gene, whose coding sequence initiates with a GTG codon, fail to direct the synthesis of detectable levels of protein. Substitution of the GTG codon by an AG codon using in vitro mutagenesis overcomes this block; cells transfected with the modified vector synthesize a functional prokaryotic protein that sustains the growth of these cells in the presence of dihydrofolic acid in the culture media. This property is consistent with the inability of the type I enzyme to reduce folate to dihydrofolate, and enabled the development of a selection strategy whereby prokaryotic and mammalian DHFRs genes could be used sequentially as independently selectable markers.
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Affiliation(s)
- C S Simonsen
- Department of Molecular Biology, Genentech, Inc., San Francisco, CA 94080
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31
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Abstract
The biological role of amino acid differences between the human 21-kDa Ha-ras protein (p21) and the human 23-kDa R-ras protein (p23) was investigated by engineering mutant Ha-ras p21 molecules containing divergent amino acid sequences from R-ras p23. Variant amino acids from R-ras p23 regions 1-30, 52-57, 67-78, 1-30 and 67-78 together, and 112-124 were substituted for the corresponding Ha-ras p21 amino acid regions 1-4, 26-31, 41-52, 1-4 and 41-52 together, and 86-98, respectively. Rat fibroblasts transfected with genes encoding these position-12 valine-substituted chimeric Ha-ras proteins displayed the same properties of morphological transformation and anchorage-independent growth as Ha-ras T24 oncogene-transformed fibroblasts. However, substitution of variant amino acids from the 80 C-terminal residues (amino acids 138-218) of R-ras p23 for the corresponding p21 amino acids (residues 112-189) inactivated the transforming activity of position-12 valine-substituted p21. The converse substitution of Ha-ras p21 C-terminal residues into R-ras p23 did not result in transformation by position-38 valine-substituted p23. These data are discussed in terms of the structure of ras proteins and the nature of interactions determining the specificity of effector function.
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Affiliation(s)
- D G Lowe
- Department of Molecular Biology, Genentech, Inc., South San Francisco, CA 94080
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32
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Cohen JB, Walter MV, Levinson AD. A repetitive sequence element 3' of the human c-Ha-ras1 gene has enhancer activity. J Cell Physiol Suppl 1987; Suppl 5:75-81. [PMID: 3316256 DOI: 10.1002/jcp.1041330415] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Efficient expression of the human c-Ha-ras1 gene requires sequences 3' of those specifying the polyadenylation of its transcripts. These sequences can stimulate the expression of heterologous genes in a manner largely independent of position and orientation, arguing that they possess a transcriptional enhancing activity that regulates the c-Ha-ras1 promoter. As this element is associated with a repetitive domain that is highly polymorphic, it is possible that the activity of this enhancer is variable within the human population.
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Affiliation(s)
- J B Cohen
- Department of Molecular Biology, Genentech, Inc., South San Francisco, California 94080
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33
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Sullivan KA, Liao YC, Alborzi A, Beiderman B, Chang FH, Masters SB, Levinson AD, Bourne HR. Inhibitory and stimulatory G proteins of adenylate cyclase: cDNA and amino acid sequences of the alpha chains. Proc Natl Acad Sci U S A 1986; 83:6687-91. [PMID: 3092218 PMCID: PMC386574 DOI: 10.1073/pnas.83.18.6687] [Citation(s) in RCA: 135] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The G protein family of signal transducers includes five heterotrimers, which are most clearly distinguished by their different alpha chains. The family includes Gs and Gi, the stimulatory and inhibitory GTP-binding regulators of adenylate cyclase; Go, a protein of unknown function abundant in brain; and transducin 1 and transducin 2, proteins involved in retinal phototransduction. Using a bovine alpha t1 cDNA as a hybridization probe, we have isolated mouse cDNAs that encode alpha chains of two G proteins. One encodes a polypeptide of 377 amino acids (Mr 43,856), identified as alpha s because it specifically fails to hybridize with any transcript in an alpha s-deficient S49 mouse lymphoma mutant, cyc-; the other encodes a polypeptide of 355 amino acids (Mr 40,482), presumed to be alpha i. These alpha chains and those of the retinal transducins exhibit impressive sequence homology. Of the four, alpha t1 and alpha t2 are most alike (81% identical amino acid residues), whereas the presumptive alpha i is more similar than alpha s to alpha t1 (63% vs. 38% identical residues). Sequence homologies with p21ras and elongation factor Tu identify regions of the alpha chains that form the site for GTP binding and hydrolysis. Further comparison of the alpha-chain sequences suggests additional regions that may contribute to interactions with beta gamma subunits and the receptor and effector components of different signal transduction systems.
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34
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Abstract
Single amino acid changes were introduced into normal (non-oncogenic) and activated forms of the human H-ras protein at a position (residue 116) proposed on structural grounds to represent a contact site with guanine nucleotides. Substitutions at this site could significantly reduce the ability of both forms to bind and hydrolyze guanosine 5'-triphosphate; these substitutions, however, did not necessarily diminish the transforming capacity of activated derivatives. One substitution that severely impairs these functions activated the transforming potential of the otherwise normal polypeptide.
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35
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Patzer EJ, Nakamura GR, Simonsen CC, Levinson AD, Brands R. Intracellular assembly and packaging of hepatitis B surface antigen particles occur in the endoplasmic reticulum. J Virol 1986; 58:884-92. [PMID: 3517385 PMCID: PMC252996 DOI: 10.1128/jvi.58.3.884-892.1986] [Citation(s) in RCA: 103] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
Hepatitis B surface antigen (HBsAg) particles are secreted by Chinese hamster ovary cells that are stably transfected with the S gene of hepatitis B virus. The assembly of HBsAg into cylindrical and spherical particles occurred intracellularly within the endoplasmic reticulum. HBsAg particles accumulated within large dilated areas of the endoplasmic reticulum and remained within these structures for most of the time prior to secretion from the cells. Once the particles were formed, the HBsAg polypeptides did not appear to become associated with subsequent intracellular organelle membranes or the plasma membrane. HBsAg within the dilated structures did not bind wheat germ agglutinin, indicating that its oligosaccharide chains had not yet been processed to the complex form (containing terminal sialic acid-N-acetylglucosamine residues). The oligosaccharide chains of HBsAg are processed to the complex form and can be detected on the HBsAg after secretion, but this event was not detected within cells. In addition, HBsAg was not observed on the cell surface by indirect immunofluorescence or immunoprecipitation, although immunoelectron microscopy revealed some staining at or near the cell surface. These results suggested that HBsAg was either secreted from cells without being incorporated into the plasma membrane, or that the levels of HBsAg in the plasma membrane were below the limits of detection.
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36
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Abstract
We expressed six forms of p21-ras polypeptides in Escherichia coli with differing transformation potentials resulting from amino acid substitutions at position 12. The ability of the encoded p21's to autophosphorylate, bind guanine nucleotides, and hydrolyze GTP was assessed. All versions of p21 bound GTP equivalently; the kinase activity, while dependent upon residue 12, did not correlate with the transforming potential of the polypeptide. All transforming versions exhibited an impaired GTPase activity, while a novel nontransforming derivative [p21(pro-12)] possessed an enhanced GTPase activity. These results provide strong support for the proposal that an impairment of the cellular p21 GTPase activity can unmask its transforming potential.
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37
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Abstract
We expressed normal and activated human cellular Ha-ras cDNAs which encode 21,000-dalton polypeptides (p21s) in Saccharomyces cerevisiae by their insertion into a 2 micron-based replicating plasmid vector under 3-phosphoglycerate kinase promoter control. We found that newly synthesized p21 in S. cerevisiae was produced as a soluble precursor (pro-p21) which matured into a form electrophoretically indistinguishable from the processed form (p21) observed in mammalian cells. Coincident with the processing event was translocation to a membrane component, suggesting a coupling of the two events. Using vectors that direct the synthesis of p21 variants possessing the ability to autophosphorylate in vitro, we found that processing of p21 did not significantly affect this autophosphorylation reaction. In contrast to Escherichia coli, marked phenotypic changes were observed in S. cerevisiae as a consequence of the synthesis of p21, including reduction in growth rate and induction of flocculation. Accompanying these phenotypic alterations was a significant elevation of adenylate cyclase activity.
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38
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Snyder MA, Bishop JM, McGrath JP, Levinson AD. A mutation at the ATP-binding site of pp60v-src abolishes kinase activity, transformation, and tumorigenicity. Mol Cell Biol 1985; 5:1772-9. [PMID: 3927152 PMCID: PMC367296 DOI: 10.1128/mcb.5.7.1772-1779.1985] [Citation(s) in RCA: 53] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
We constructed a mutant, called RSV-SF2, at the ATP-binding site of pp60v-src. In this mutant, lysine-295 is replaced with methionine. SF2 pp60v-src was found to have a half-life similar to that of wild-type pp60v-src and was localized in the membranous fraction of the cell. Rat cells expressing SF2 pp60v-src were morphologically untransformed and do not form tumors. The SF2 pp60v-src isolated from these cells lacked kinase activity with either specific immunoglobulin or other substrates, and expression of SF2 pp60v-src failed to cause an increase of total phosphotyrosine in the proteins of infected cells. Wild-type pp60v-src was phosphorylated on serine and tyrosine in infected cells, and the analogous phosphorylations could also be carried out in vitro. Phosphorylation of serine was catalyzed by a cyclic AMP-dependent protein kinase, and phosphorylation of tyrosine was perhaps catalyzed by pp60v-src itself. By contrast, SF2 pp60v-src could not be phosphorylated on serine or tyrosine either in infected cells or in vitro. These findings strengthen the belief that the phosphotransferase activity of pp60v-src is required for neoplastic transformation by the protein and suggest that the binding of ATP to pp60v-src elicits an allosteric change required for phosphorylation of serine in the protein.
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39
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Abstract
Vertebrate genomes contain proto-oncogenes whose enhanced expression or alteration by mutation seems to be involved in the development of naturally occurring tumours. These activated genes, usually assayed by their ability to induce the malignant transformation of NIH 3T3 cells, are frequently related to the ras oncogene of Harvey (Ha-ras) or Kirsten (Ki-ras) murine sarcoma viruses, or a third member of this family (N-ras). Activation involves point mutation which often affect codon 12 (refs 16-26) of the encoded 21,000-molecular weight polypeptide (p21). To provide insight into structural requirements involved in p21 activation, we have now constructed 20 mutant c-Ha-ras1 genes by in vitro mutagenesis, each encoding a different amino acid at codon 12. Analysis of rat fibroblasts transfected with these altered genes demonstrates that all amino acids except glycine (which is encoded by normal cellular ras genes) and proline at position 12 activate p21, suggesting a requirement for an alpha-helical structure in this region of the polypeptide. The morphological phenotype of cells transformed by the activated genes can, however, depend on the particular amino acid at this position.
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40
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Abstract
Human Ha-ras1 cDNAs encoding normal and activated p21 polypeptides have been efficiently expressed in Escherichia coli and the biochemical activities associated with each polypeptide compared. In addition to the guanine nucleotide binding activity, normal p21 displays a GTPase activity which is selectively impaired by a mutation which activates its oncogenic potential.
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41
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Abstract
Initiation of translation of eukaryotic mRNAs typically occurs at the first AUG triplet from the 5' end of the message, although several notable exceptions have been described. Using vectors which efficiently express the gene encoding the surface antigen of hepatitis B virus in monkey cells, we have studied the consequences of inserting ATG triplets in all three reading frames upstream of the usual translational initiation codon of this gene. In agreement with the scanning model for eukaryotic translation initiation, these additional codons can severely depress the initiation of translation at the 'authentic' start codon, although the extent of inhibition depends on sequences flanking the upstream AUG. Such inhibition can, however, be at least partially suppressed by the presence of a translation termination codon in-frame with the upstream AUG. These results raise the possibility that mammalian ribosomes can reinitiate translation at an AUG codon after previously initiating, and terminating, at an upstream site.
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42
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Simonsen CC, Levinson AD. Analysis of processing and polyadenylation signals of the hepatitis B virus surface antigen gene by using simian virus 40-hepatitis B virus chimeric plasmids. Mol Cell Biol 1983; 3:2250-8. [PMID: 6318092 PMCID: PMC370096 DOI: 10.1128/mcb.3.12.2250-2258.1983] [Citation(s) in RCA: 76] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
We examined the transcription of the hepatitis B virus surface antigen (HBsAg) gene in COS cells transfected with simian virus 40-based recombinant plasmids. When positioned behind the simian virus 40 late promoter, three transcripts were identified which hybridized to the HBsAg gene: a 2,000-nucleotide transcript colinear with a gene, a 1,100-nucleotide transcript representing a spliced molecule in which a major portion of the sequences encoding HBsAg were deleted, and an 800-nucleotide transcript derived primarily from sequences 3' to the HBsAg gene. The splice acceptor site utilized by the 1,100-nucleotide transcript is located immediately upstream of an open reading frame of unknown function contained within the 3' nontranslated region of the HBsAg gene. The HBsAg-specific mRNA species terminate 12 to 19 base pairs 3' of the sequence UAUAAA, similar to the concensus hexanucleotide which is thought to promote polyadenylation (AAUAAA). We constructed a series of plasmids with progressive deletions from the region surrounding where these transcripts terminate. Analysis of mRNA produced by cells transfected with these plasmids indicated that the signal hexanucleotide is in itself unable to promote the efficient processing of mRNA in the absence of downstream hepatitis B virus sequences. Processing proceeds properly, however, from plasmids containing an additional 30 nucleotides 3' of this signal.
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43
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Alitalo K, Ramsay G, Bishop JM, Pfeifer SO, Colby WW, Levinson AD. Identification of nuclear proteins encoded by viral and cellular myc oncogenes. Nature 1983; 306:274-7. [PMID: 6316149 DOI: 10.1038/306274a0] [Citation(s) in RCA: 200] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The myelocytomatosis viruses are a family of replication-defective avian retroviruses that cause a variety of tumours in chickens and transform both fibroblasts and macrophages in culture through the activity of their oncogene v-myc. A closely related gene (c-myc) is found in vertebrate animals and is thought to be the progenitor of v-myc. Changes in the expression and perhaps the structure of c-myc have been implicated in the genesis of avian, murine and human tumours (for a review, see ref. 15). Elucidation of the mechanisms by which v-myc and c-myc might elicit tumorigenesis requires identification of the proteins encoded by these genes. To this end, we have expressed a portion of v-myc in a bacterial host and used the resulting protein to raise antisera that react with myc proteins. We report here that v-myc and c-myc encode closely related proteins with molecular weights (MWs) of approximately 58,000. Integration of retroviral DNA near or within c-myc in avian lymphomas apparently enhances expression of the gene. Here we have used cells from one such tumour to identify the protein encoded by c-myc and find that the coding domain for the gene is probably intact.
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44
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Simonsen CC, Chen EY, Levinson AD. Identification of the type I trimethoprim-resistant dihydrofolate reductase specified by the Escherichia coli R-plasmid R483: comparison with procaryotic and eucaryotic dihydrofolate reductases. J Bacteriol 1983; 155:1001-8. [PMID: 6411680 PMCID: PMC217792 DOI: 10.1128/jb.155.3.1001-1008.1983] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
We have isolated and determined the nucleotide sequence of a 1,626-base-pair fragment from R-plasmid R483 which encodes a trimethoprim-resistant dihydrofolate reductase. Analysis of the nucleotide sequence of this fragment revealed the presence of two open reading frames, each sufficient to encode polypeptides of approximately 17,000 daltons. Both open regions are preceded by sequences conforming closely to the canonical description of procaryotic promoters. A 490-base-pair HpaI fragment spanning one of the potential coding regions was inserted into a plasmid vector under the transcriptional control of the trp promoter. Cells transformed with this plasmid were trimethoprim resistant and produced dihydrofolate reductase activity which in vitro was resistant to moderate levels of trimethoprim. Analysis of the predicted amino acid sequence of this protein indicated that the R483-encoded trimethoprim-resistant enzyme was distantly related to the trimethoprim-sensitive bacterial homologs. The conserved amino acids were localized primarily to the region of the enzyme previously shown to comprise the hydrophobic substrate binding pocket.
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45
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McGrath JP, Capon DJ, Smith DH, Chen EY, Seeburg PH, Goeddel DV, Levinson AD. Structure and organization of the human Ki-ras proto-oncogene and a related processed pseudogene. Nature 1983; 304:501-6. [PMID: 6308466 DOI: 10.1038/304501a0] [Citation(s) in RCA: 282] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Analysis of the organization and nucleotide sequence of two human loci related to the transforming gene of Kirsten murine sarcoma virus establishes one as a functional gene and the other as a processed pseudogene. The two final coding exons of the functional gene seem to have arisen by duplication. Differentially spliced mRNAs incorporating one or other of the duplicated exons probably served as the intermediates by which the viral transforming gene and the pseudogene were generated. This suggests that the functional gene may specify either of two related polypeptides depending on the pattern of RNA splicing.
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46
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Capon DJ, Seeburg PH, McGrath JP, Hayflick JS, Edman U, Levinson AD, Goeddel DV. Activation of Ki-ras2 gene in human colon and lung carcinomas by two different point mutations. Nature 1983; 304:507-13. [PMID: 6308467 DOI: 10.1038/304507a0] [Citation(s) in RCA: 442] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Kirsten (Ki)-ras cDNA clones were prepared from human lung and colon carcinoma cell lines expressing an activated c-Ki-ras2 gene. DNA sequence analysis and transfection studies indicate that different point mutations at the same codon can activate the gene; that most human c-Ki-ras2 mRNA uses sequences from a fourth coding exon distinct from that of its viral counterpart; and that at least one cell line is functionally homozygous for the activated gene.
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47
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Klempnauer KH, Ramsay G, Bishop JM, Moscovici MG, Moscovici C, McGrath JP, Levinson AD. The product of the retroviral transforming gene v-myb is a truncated version of the protein encoded by the cellular oncogene c-myb. Cell 1983; 33:345-55. [PMID: 6305504 DOI: 10.1016/0092-8674(83)90416-6] [Citation(s) in RCA: 169] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Avian myeloblastosis virus (AMV) is an oncogenic retrovirus that rapidly causes myeloblastic leukemia in chickens and transforms myeloid cells in culture. AMV carries an oncogene, v-myb, that is derived from a cellular gene, c-myb, found in the genomes of vertebrate species. We constructed a plasmid vector that allows expression of a portion of the coding region for v-myb in a procaryotic host. We then used the myb-encoded protein produced in bacteria to immunize rabbits. The antisera obtained permitted identification of the proteins encoded by both v-myb and chicken c-myb. The molecular weights of the products of v-myb and c-myb (45,000 and 75,000 respectively) indicate that the v-myb protein is an appreciably truncated version of the c-myb protein.
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Hitzeman RA, Chen CY, Hagie FE, Patzer EJ, Liu CC, Estell DA, Miller JV, Yaffe A, Kleid DG, Levinson AD, Oppermann H. Expression of hepatitis B virus surface antigen in yeast. Nucleic Acids Res 1983; 11:2745-63. [PMID: 6344021 PMCID: PMC325921 DOI: 10.1093/nar/11.9.2745] [Citation(s) in RCA: 124] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
The structural gene of Hepatitis B virus surface protein (HBsAg) was introduced into a plasmid capable of autonomous replication and selection in both the yeast Saccharomyces cerevisiae and E. coli. In this plasmid transcription of the HBsAg is initiated by the 5'-flanking sequence of the yeast 3-phosphoglycerate kinase (PGK) gene and terminated by the 3'-flanking region of the yeast TRP1 gene. Yeast cells containing this plasmid produce a new major species of mRNA of 1200 nucleotides in length coding for HBsAg. Viral surface antigen is made in nonglycosylated form at a level of about 1-2 percent of total yeast protein. A small fraction of this polypeptide (2-5 percent) is found in aggregated form upon yeast cell disruption by glass beads. This material is similar in size, density, and shape to the 22nm particle, isolated from the plasma of human hepatitis carriers, and induced comparable levels of HBsAg antibodies in mice when compared with the natural particle.
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Abstract
We have constructed a cDNA library from a murine cell line expressing high levels of a dihydrofolate reductase (tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3) that displays an abnormally low affinity for methotrexate. From this library we have isolated a cDNA clone similar to, but distinguishable from, a cDNA clone previously demonstrated to encode the wild-type enzyme. Analysis of the nucleotide sequence of this cDNA clone allows us to predict that the altered dihydrofolate reductase differs from the wild-type enzyme at a single amino acid, reflecting the substitution of an arginine for a leucine residue in a region of the polypeptide thought to form a hydrophobic pocket essential for inhibitor binding. To confirm that this substitution was responsible for the altered properties of the enzyme, we genetically localized the region of the cDNA that specified resistance to methotrexate by in vitro recombination. These results reveal that a single nucleotide change in the codon specifying amino acid 22 of the enzyme was sufficient to alter the methotrexate sensitivity of the enzyme. We demonstrate that this altered gene can be employed as a dominant selectable marker in cultured cells expressing normal levels of wild-type dihydrofolate reductase.
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Abstract
Avian erythroblastosis virus (AEV) induces both erythroblastosis and fibrosarcomas in susceptible birds. A locus, v-erbB, within the viral genome has been implicated in AEV-mediated oncogenesis. We report here the detection and partial characterization of the protein product of the v-erbB oncogene in AEV-transformed cells. We obtained the antisera necessary for our analysis by expressing a portion of the molecularly cloned v-erbB locus in Escherichia coli and immunizing rabbits with the resulting bacterial erbB polypeptide. Antisera directed against the bacterial polypeptide reacted with v-erbB proteins obtained from virus-infected avian cells. By three criteria--tunicamycin inhibition, lectin binding and metabolic labeling with radioactive sugar precursors--the product of the v-erbB gene appears to be a glycoprotein.
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