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PubMed1985

Specific transforming potential of oncogenes encoding protein-tyrosine kinases.

Several chimeric murine retroviruses were constructed to test whether the gag sequence of Abelson murine leukemia virus (A-MuLV) could influence the in vitro specificity of two sarcoma-inducing oncogenes: src of Rous sarcoma virus and fps of Fujinami sarcoma virus. Although the src- or fps- containing chimerae could transform fibroblasts, they were unable to mimic the action of A-MuLV in causing lymphoid transformation in vitro. A-MuLV-derived gag sequences could, however, functionally replace the 5' end of src and restore the transformation potential of a 5'-truncated src gene. To investigate this functional similarity, we replaced the gag sequence of an A-MuLV virus with the 5' end of src. This recombinant virus behaved like the A-MuLV virus from which it was derived: it transformed both fibroblasts and lymphoid cells in vitro. Taken together, these results suggest that lymphoid transformation in vitro is a specific property of abl and not of src or fps. Furthermore, it shows that a functional homology exists between the gag sequence of A-MuLV and the 5' end of src.

Abelson murine leukemia virus↗
PubMed1996

Subtype-specific regulation of recombinant NMDA receptor-channels by protein tyrosine kinases of the src family.

1. Tyrosine kinases regulate NMDA receptor-channel activity in cultured neurons, and NMDA receptor subunits are tyrosine phosphorylated in the brain. 2. Heteromeric NMDA receptor-channels were transiently expressed in human embryonic kidney (HEK) 293 cells and glutamate (100 microM)-activated whole-cell currents (500 ms) were studied when tyrosine kinases of the src gene family were included in the pipette solution. 3. Glutamate-activated currents (evoked every 20 s for up to 20 min) were increased by src and fyn kinases without affecting the desensitization and deactivation kinetics in NR1-NR2A but the kinases had no effects in NR1-NR2B, NR1-NR2C and NR1-NR2D receptor-channels, suggesting that a phosphorylation site in NR2A is targeted. 4. In a mutant channel consisting of NR1 and a C-terminal deletion mutant of NR2A (NR2A delta C), src and fyn kinases lost their potentiating effects indicating that the phosphorylation of tyrosine(s) in the C-terminal domain of NR2A affects the current flux through native NMDA receptor-channels.

Cell Line↗
PubMed1990

Expression of the neuronal form of pp60c-src in neuroblastoma in relation to clinical stage and prognosis.

The expression of the protooncogene c-src has been studied in specimens of childhood tumors with special reference to neuroblastoma and other tumors of neuronal origin. For comparison c-src gene expression was studied in seven neuroblastoma and neuroepithelioma cell lines. The structurally distinct neuronal product of the gene, pp60c-srN, expressed during normal development in neuroblasts and neurons, was identified by immunoblotting technique together with the fibroblast form, pp60c-src. While pp60c-src was found in most tumors studied, the neuronal form was restricted to neuroblastomas (23 of 27) and retinoblastomas (3 of 3) and could not be detected in the other childhood tumors. A dominance of the neuronal form, pp60c-srcN, was exclusively found in the infant cases of neuroblastoma (9 of 12), estimated to have good prognosis. These results indicate that pp60c-srcN might be a diagnostic marker in primitive childhood tumors. When expressed in higher amounts than pp60c-src, pp60c-srcN may be a positive prognostic marker in neuroblastoma, especially useful in the evaluation of infants. In addition, lack of pp60c-srcN seems to be incompatible with low stage neuroblastoma.

Aging↗
PubMed1980

Restriction of the rat-specific RNS sequences of Ki-MSV to the nucleus of dibutyryl cyclic AMP-treated K-A31 cells.

The treatment of oncogenically transformed cells in culture, with dibutyryl cyclic AMP (cAMP) has, in many cases, resulted in a general phenotypic change towards the normal state. A virus-specific gene product(s) is responsible for the transformation of cells by sarcoma viruses and it has been suggested that the src gene product may act through the alteration of cAMP levels. With these premises we have studied the effects of dibutyryl cAMP on cell growth and virus genome expression in a Kirsten sarcoma virus-transformed mouse cell line. Our results suggest that certain virus-specific RNA sequences are restricted to the nucleus of these cells after several days of growth in medium containing dibutyryl cAMP and that these sequences appear to be those coding for the sarcoma information.

Animals↗
PubMed1992

Translocation of pp60c-src to the cytoskeleton during platelet aggregation.

The high amount of pp60c-src in platelets has led to speculation that this kinase is responsible for tyrosine-specific phosphorylation of cellular proteins during platelet activation by different agonists, and is, therefore, implicated in signal transduction of these cells. Unlike pp60v-src, the association of which with the cytoskeleton appears to be a prerequisite for transformation, pp60c-src is detergent-soluble in fibroblasts overexpressing the c-src gene, and its role in normal cellular function remains elusive. To gain a better understanding of the function of pp60c-src we have investigated the subcellular distribution of pp60c-src and its relationship to the cytoskeleton during platelet activation. Quantitative immunoblotting and immunoprecipitation have revealed that pp60c-src is detergent-soluble in resting platelets, while 40% of total platelet pp60c-src becomes associated with the cytoskeletal fraction upon platelet activation. We have also shown that a small pool of pp60c-src is associated with the membrane skeletal fraction which remains unchanged during the activation process. The interaction of pp60c-src with cytoskeletal proteins strongly correlates with aggregation and is mediated by GPIIb/IIIa receptor-fibrinogen binding. We suggest that the translocation of pp60c-src to the cytoskeleton and its association with cytoskeletal proteins may regulate tyrosine phosphorylation in platelets.

Biological Transport↗
PubMed1980

Characterization of Y73, an avian sarcoma virus: a unique transforming gene and its product, a phosphopolyprotein with protein kinase activity.

The Y73 strain of avian sarcoma virus recently isolated in Japan is defective in replication and is associated with subgroup A leukosis virus (YAV). The virus caused sarcoma but not acute leukosis when inoculated into chickens. Studies on the viral RNA showed that a 26S RNA, etimated to be 4.8 kilobases long, was Y73 viral RNA carrying a transforming gene. The 26S RNA has sequences in common with the RNA of an avian leukosis virus but no homology with the src gene sequence of avian sarcoma virus (ASV). Thus, Y73 has a unique sarcoma-inducing gene. A phosphorylated polyprotein of 90,000 daltons (p90) was immunoprecipitated from extracts of Y73-transformed chicken embryo cells by a variety of antisera reacting with gag gene products. When a bacteria-bound immunocomplex containing the p90 protein was incubated with [gamma-32P]ATP, the Y73-specific p90 and the IgG heavy chain were phosphorylated by a p90-associated protein kinase. The amino acid phosphorylated in vitro was exclusively tyrosine in both cases, whereas p90 phosphorylated in vivo contained phosphoserine as a major phospho amino acid with traces of phosphotyrosine and phosphothreoine.

Alpharetrovirus↗
PubMed1988

Immunological characterization of proteins detected by phosphotyrosine antibodies in cells transformed by Rous sarcoma virus.

Phosphotyrosine antibodies were used to identify tyrosine-phosphorylated proteins in Rous sarcoma virus (RSV)-transformed chicken embryo fibroblasts. A large number of tyrosine phosphoproteins were detected. A similar set of proteins was observed in RSV-transformed murine cells. An 85,000-dalton protein, however, was present in transformed avian cells but missing in transformed murine cells. Neither the 85,000-dalton protein nor any of the other tyrosine phosphoproteins appeared to be viral structural proteins. Use of RSV mutants encoding partially deleted src gene products enabled us to identify a 60,000-dalton cellular tyrosine phosphoprotein that comigrated with wild-type pp60v-src. With the exception of calpactin I, the major tyrosine phosphoproteins detected in immunoblots appeared to be different from several previously characterized substrates of pp60v-src with similar molecular masses (ezrin, vinculin, and the fibronectin receptor).

Annexins↗
PubMed1984

Structurally and functionally modified forms of pp60v-src in Rous sarcoma virus-transformed cell lysates.

When analyzed from transformed cell lysates, pp60v-src, the product of the Rous sarcoma virus src gene, typically appears as a single polypeptide of 60,000 molecular weight, phosphorylated at two major sites, an amino-terminal region serine residue and carboxy-terminal region tyrosine residue. We describe here the identification of variant forms of pp60v-src present in transformed cell lysates that exhibited an altered electrophoretic mobility in sodium dodecyl sulfate-polyacrylamide gels. This change in migration appeared to be the result of some alteration in the amino-terminal portion of the molecule and paralleled the appearance of extensive amino-terminal region tyrosine phosphorylation on the pp60v-src molecule. These structural modifications were further correlated with a dramatic increase in the protein kinase-specific activity of pp60v-src. The detection of these variant forms of pp60v-src depended on the prior treatment of the transformed cell cultures with vanadium ions or the inclusion in the cell disruption buffer of Mg2+ or ATP-Mg2+. The implications is that modified, highly active forms of the pp60v-src protein exist in transformed cells, but are transient and rapidly converted to stable forms, possibly by specific dephosphorylation. We suggest that amino-terminal region tyrosine phosphorylation of pp60v-src, presumably the result of autophosphorylation, serves to greatly enhance src protein enzymatic activity, but that much of the regulation of this transforming protein's function may involve a phosphotyrosyl protein phosphatase.

Animals↗
PubMed1987

Cell transformation by pp60c-src mutated in the carboxy-terminal regulatory domain.

We introduced two mutations into the carboxy-terminal regulatory region of chicken pp60c-src. One, F527, replaces tyrosine 527 with phenylalanine. The other, Am517, produces a truncated pp60c-src protein lacking the 17 carboxy-terminal amino acids. Both mutant proteins were phosphorylated at tyrosine 416 in vivo. The specific activity of the Am517 mutant protein kinase was similar to that of wild-type pp60c-src whereas that of the F527 mutant was 5- to 10-fold higher. Both mutant c-src genes induced focus formation on NIH 3T3 cells, but the foci appeared at lower frequency, and were smaller than foci induced by polyoma middle tumor antigen (mT). The wild-type or F527 pp60c-src formed a complex with mT, whereas the Am517 pp60c-src did not. The results suggest that one, inability to phosphorylate tyrosine 527 increases pp60c-src protein kinase activity and transforming ability; two, transformation by mT involves other events besides lack of phosphorylation at tyrosine 527 of pp60c-src; three, activation of the pp60c-src protein kinase may not be required for transformation by the Am517 mutant; and four, the carboxyl terminus of pp60c-src appears to be required for association with mT.

Animals↗
PubMed1989

Expression of v-src induces a myeloproliferative disease in bone-marrow-reconstituted mice.

A recombinant retrovirus, N-TK-src, was used to introduce the v-src oncogene into mouse hematopoietic cells. This vector efficiently expresses both the neo and v-src genes in different hematopoietic lineages in culture as well as in mice reconstituted with infected bone marrow cells. Expression of v-src had no dramatic effect on the proliferative and differentiative capacity of hematopoietic precursors when assayed in methyl cellulose cultures. However, in mice reconstituted with N-TK-src-infected bone marrow cells, expression of v-src leads to the rapid development of a severe myeloproliferative disease, characterized by splenomegaly, anemia, and a shift of hematopoiesis from the bone marrow to the spleen.

Animals↗
PubMed1990

Simultaneous overexpression of avian pp60c-src and polyomavirus middle T antigen in mammalian cells.

Recombinant adenoviruses bearing the avian c-src gene and polyomavirus middle-T-antigen gene were isolated and used to simultaneously overexpress both proteins in human 293 cells. Cells overexpressing both proteins had greater middle-T-antigen-associated tyrosine kinase activity than cells overexpressing only middle T antigen. By contrast, the intrinsic pp60c-src tyrosine kinase activity was not greater in cells overexpressing both proteins than in cells overexpressing only pp60c-src. This system of simultaneous overexpression provides a means of obtaining large quantities of pp60c-src, middle T antigen, and the complex between them.

Adenoviruses, Human↗
PubMed2003

Review of the in vivo functions of the p160 steroid receptor coactivator family.

The p160 steroid receptor coactivator (SRC) gene family contains three homologous members, which serve as transcriptional coactivators for nuclear receptors and certain other transcription factors. These coactivators interact with ligand-bound nuclear receptors to recruit histone acetyltransferases and methyltransferases to specific enhancer/promotor regions, which facilitates chromatin remodeling, assembly of general transcription factors, and transcription of target genes. This minireview summarizes our current knowledge about the molecular structures, molecular mechanisms, temporal and spatial expression patterns, and biological functions of the SRC family. In particular, this article highlights the roles of SRC-1 (NCoA-1), SRC-2 (GRIP1, TIF2, or NCoA-2) and SRC-3 (p/CIP, RAC3, ACTR, AIB1, or TRAM-1) in development, organ function, endocrine regulation, and nuclear receptor function, which are defined by characterization of the genetically manipulated animal models. Furthermore, this article also reviews our current understanding of the role of SRC-3 in breast cancer and discusses possible mechanisms for functional specificity and redundancy among SRC family members.

Acetyltransferases↗
PubMed1988

Transforming potential and growth stimulating activity of the v-fos and c-fos genes carried by avian retrovirus vectors.

To study transforming potential as well as growth stimulating activity of the fos genes on primary cells, we have developed avian retrovirus vectors by constructing derivatives of Rous sarcoma virus DNA in which the v-src gene was replaced by either the v-fos gene of FBJ-MuSV or the mouse c-fos gene. After each derivative was introduced into chicken embryo fibroblasts by transfection, replication-competent viruses that carry the v-fos gene (FJ2) or the c-fos gene (FM4) were recovered. FM4 and FJ2 introduced the fos genes into almost all chicken embryo fibroblasts within 3 days after infection, expressed their gene products, and induced morphological transformation and colony formation in soft agar. Results show that overproduction of the c-fos gene product is enough for cellular transformation not only of rat established fibroblasts as reported previously but also of avian primary fibroblasts. Using this vector system, we have further shown that the c-fos gene and the v-fos gene have biological activities that induce cellular proliferation of chicken neuroretinal cells, which normally stay in the resting stage of growth in monolayer culture.

Animals↗
PubMed1988

p60c-src is complexed with a cellular protein in subcellular compartments involved in exocytosis.

We found high levels of the c-src gene product in neuroendocrine tissues from adult animals. To understand the role of this proto-oncogene product, the subcellular localization of p60c-src was studied in neuroendocrine tissue from adrenal medulla. The results indicate that p60c-src was highly enriched in chromaffin granule membranes, in stable association with a protein of 38 kD. The complex with the 38-kD protein was also detected in brain, a tissue known to carry high levels of p60c-src. The 38-kD protein is not calpactin I, II, or synaptophysin. Comparison of its peptide map showed a high degree of conservation among the different species and tissues examined. The interaction between p60c-src and the 38-kD protein involves disulphide bonds that are stable even when the cell fractionation is performed in the presence of a reducing agent. Since the presence of disulphide bonds among cytoplasmic proteins is very unlikely, the possibility of a noncovalent association between p60c-src and the 38-kD protein in vivo is discussed. The 38-kD protein may be involved in a function of p60c-src related to secretory organelles.

Adrenal Medulla↗
PubMed1990

Sequence specificity of mRNA N6-adenosine methyltransferase.

The sequence specificity of chicken mRNA N6-adenosine methyltransferase has been investigated in vivo. Localization of six new N6-methyladenosine sites on Rous sarcoma virus (RSV) virion RNA has confirmed our extended consensus sequence for methylation: RGACU, where R is usually a G (7/12). We have also observed A (2/12) and U (3/12) at the -2 position (relative to m6A at +1) but never a C. At the +3 position, the U was observed 10/12 times; an A and a C were observed once each in weakly methylated sequences. The extent of methylation varied between the different sites up to a maximum of about 90%. To test the significance of this consensus sequence, it was altered by site-specific mutagenesis, and methylation was assayed after transfection of mutated RSV DNA into chicken embryo fibroblasts. We found that changing the G at -1 or the U at +3 to any other residue inhibited methylation. However, inhibition of methylation at all four of the major sites in the RSV src gene did not detectably alter the steady-state levels of the three viral RNA species or viral infectivity. Additional mutants that inactivated the src protein kinase activity produced less virus and exhibited relatively less src mRNA in infected cells.

Animals↗
PubMed1979

High-frequency recombination within the gag gene of Rous sarcoma virus.

We isolated 28 recombinants of Rous sarcoma virus at early (24 h) and late (7 days) times after infection. These recombinants were selected for wild type in the pol and src genes and analyzed for their env and gag phenotypes. We were unable to show strong linkage between any two markers, including two markers within a single gene (gag).

Animals↗
PubMed1983

Small deletion in src of Rous sarcoma virus modifying transformation phenotypes: identification of 207-nucleotide deletion and its smaller product with protein kinase activity.

Partial deletion in the src gene and the gene product were characterized in a deletion mutant, dl5, isolated from the Prague strain of Rous sarcoma virus. The mutant induced fusiform-like transformed cells, unlike the parental Prague strain, which induced round transformed cells. Determination of the total nucleotide sequences of src in dl5 and the Prague strain of Rous sarcoma virus demonstrated that in the former two deletions of 196 and 11 nucleotides had occurred at positions 403 and 696, respectively, from the 5' end of src. A protein with a molecular weight of 52,000 (p52src) was detected in cells infected with dl5, as predicted from the deletion size in src. From the nucleotide sequence, it was predicted that p52src had two deletions of 65 and 4 amino acids at positions 135 and 232, respectively, from the N-terminal methionine of p60src and also had 33 amino acid changes between these two deletion sites due to alteration of the reading frame. p52src, which contained deletions and alterations of amino acids near the N-terminus, showed protein kinase activity similar to that of p60src and functioned in the infected cells. These results strongly suggest that changes in the N-terminal region of p60src modified its transforming ability, causing induction of the fusiform-like transformation phenotype.

Avian Sarcoma Viruses↗
PubMed1980

Unifected avian cells contain structurally unrelated progenitors of viral sarcoma genes.

A single gene, src of Rous sarcoma virus (RSV) coding for a protein of pp60src, is responsible for the transformation of fibroblasts. DNA sequences homologous to src (the endogenous sarc) are presented in uninfected cells of chickens and other vertebrates. Endogenous nucleotide sequences have also been found in the putative transforming genes of MC29 (ref. 6) and avian erythroblastosis virus. These viruses, however, induce different spectra of tumours in animals. From analysis of a new avian sarcoma virus, Y73, we present here evidence suggesting that multiforms of viral sarcoma genes originated from cellular genetic sequences, and that these viral genes are structurally unrelated, but have similar pathogenicities.

Alpharetrovirus↗