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U R Rapp

Publications and source records attributed to U R Rapp.

At least 181 records · Page 10Linked to original sources
PubMed1988

Negative regulation of c-myc transcription involves myc family proteins.

Expression of the c-myc gene is suppressed in NIH 3T3 mouse fibroblast cells infected with recombinant retroviruses expressing high levels of v-myc (10-fold greater than those of c-myc). Suppression of steady state levels of c-myc mRNA occurred at least in part at the level of transcription from c-myc promoters P1 and P2, and involved v-myc protein since cells infected with constructs containing frameshifts and deletions in v-myc had normal levels of c-myc mRNA and protein. Suppression of c-myc expression was also observed in fibroblasts transfected with a N-myc expression vector and in fibroblasts infected with a c-myc retrovirus. These findings establish that v-myc protein is involved either directly or indirectly in a regulatory circuit which represses c-myc proto-oncogene transcription. Feedback regulation of c-myc transcription may be relevant in establishing the lineage specific expression of myc family proto-oncogenes. Reduced steady state levels of c-myc mRNA were also observed in NIH 3T3 cells infected with 12S and 13S EIA recombinant retroviruses suggesting that the exogenous oncogene of adenovirus, EIA, can alleviate the requirement of myc for cell growth and may also share transcriptional target genes.

Adenovirus Early Proteins↗
PubMed1988

Identification and characterization of c-raf phosphoproteins in transformed murine cells.

Protein products of the c-raf gene were detected and characterized in two transformed murine cells lines by immunoprecipitation analysis with raf-specific sera. Both proteins reacted with an antiserum directed to the carboxyl terminus of the c-raf coding region. The p48raf (Mr48,000) phosphoprotein was found in a cell line transformed by an LTR-activated c-raf gene (Mueller & Mueller, 1984). It was found to be phosphorylated on serine and threonine residues and became phosphorylated in immunoprecipitates when supplied with [gamma-32]ATP. In contrast, P74raf, which was detected into a spontaneously transformed 3T3 (R+/Cl 3) cell line and may represent the full-length gene product of c-raf, appeared to incorporate [32P]PO4 less efficiently in vivo and exhibited a barely detectable associated kinase activity in only half of the experiments. The p48raf is a transforming protein which, like P75gag-raf, lacks the amino-terminal region of the c-raf coding region. P74raf, which retains the amino-terminal region, differs from p48raf in its phosphorylation characteristics and may not be a transforming protein. These data are consistent with a model in which lack of amino-terminal sequences in the c-raf gene product p48raf may, in and of itself, suffice to make it a transforming protein.

Animals↗
PubMed1988

Histogenesis and clonality of pancreatic tumors induced by v-myc and v-raf oncogenes in NFS/N mice.

Newborn NFS/N mice were inoculated with pseudotypes of murine retroviruses containing murine v-raf, avian v-myc, or both v-raf and v-myc within a single construct. Foci of dysplastic acinar cells, similar to those observed in rats given chemical carcinogens, were induced in 77% of mice inoculated with the raf/myc construct with a latency as short as 15 days. However, all animals given this construct also developed fibrosarcomas, erythroblastosis, and lymphomas and died within 70 days of infection, before pancreatic acinar carcinomas developed. Dysplastic foci were also observed in mice infected with viruses containing v-raf or v-myc alone with latencies of 3-4 weeks, and carcinomas were seen after an average latency of 150 days in 31% of mice infected with either of two viruses expressing v-myc alone. Two primary carcinomas were transplanted in mice, and in vitro cell lines were developed from one of the transplants. DNA prepared from seven primary carcinomas, the two transplanted tumors, and the in vitro cell lines was hybridized with a v-myc probe. Each tumor had a unique pattern of proviral integrations that was retained, with the gain or loss of single sites, in the transplants and derivative cell lines. The clonal nature of the advanced pancreatic acinar carcinomas is discussed in relation to their histogenesis and the transforming potentials of the raf and myc oncogenes.

Animals↗
PubMed1987

Effects of anti-proliferative cyclic AMP on interleukin 2-stimulated gene expression.

Elevation of intracellular cyclic adenosine 3':5' monophosphate (cAMP) inhibits interleukin 2 (IL-2)-stimulated proliferation of a murine cytotoxic cell clone, CT6. The effects of antiproliferative dosages of stable cAMP-derivative, 8-bromoadenosine 3':5'-monophosphate (8-Br-cAMP), on steady state mRNA expression stimulated by IL-2 was examined. IL-2 stimulated mRNA accumulation of three nuclear proto-oncogenes c-fos, c-myc, and c-myb. 8-Br-cAMP alone stimulated c-fos, c-myb, and IL-2 receptor mRNA accumulation as determined by Northern blot analysis. 8-Br-cAMP, however, markedly inhibited c-myc expression stimulated by IL-2. Furthermore, although c-fos and IL-2 receptor mRNA expression was potentiated by 8-Br-cAMP, suppression of protein synthesis was seen. We show that antiproliferative cAMP stimulates similar mRNA expression as does IL-2, with the exception of c-myc. Although a comparative stimulation of steady state mRNA accumulation of some genes occurs, cAMP may profoundly effect protein synthesis. cAMP, therefore, acts on multiple targets involved in the macromolecular events stimulated by IL-2.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1987

Role of c-myc and other genes in interleukin 2 regulated CT6 T lymphocytes and their malignant variants.

The cloned murine cytotoxic T cell line CT6 solely requires interleukin 2 (IL 2) for viability and cell cycle progression. Treatment of G arrested cultures of CT6 cells with recombinant IL 2 induces the rapid sequential expression of the nuclear proto-oncogenes c-fos, c-myc, and c-myb but does not affect the expression of several cytosolic or membrane-associated proto-oncogenes. A comparison of early genes induced by growth factor treatment of quiescent NIH/3T3 fibroblasts and CT6 cells demonstrated that only c-fos and c-myc induction is shared in the two different lineages. Factor-independent lines derived from CT6 cells show no mitogenic response to IL 2, yet binding of IL 2 with its receptor in the cells was capable of inducing the expression of c-fos and c-myc. In factor-independent cell lines, c-myc was uniformly expressed at high constitutive levels, suggesting that c-myc abrogates growth factor requirements of these cells. The levels of c-myc expression in the factor-independent lines was not due to an autocrine production of IL 2 but may be a consequence of constitutively activated IL 2 receptors.

Animals↗
PubMed1987

Avian v-myc replaces chromosomal translocation in murine plasmacytomagenesis.

Deregulation of c-myc expression in association with chromosomal translocations occurs in over 95% of murine plasmacytomas, rat immunocytomas, and human Burkitt lymphomas. Infection with a murine retrovirus (J-3) containing an avian v-myc rapidly induced plasmacytomas in pristane-primed BALB/cAn mice. Only 17% of the induced plasmacytomas that were karyotyped showed the characteristic chromosomal translocations involving the c-myc locus. Instead, all of the translocation-negative tumors demonstrated characteristic J-3 virus integration sites that were actively transcribed. Thus, the high levels of v-myc expression have replaced the requirement for chromosomal translocation in plasmacytomagenesis and accelerated the process of transformation.

Animals↗
PubMed1987

The complete coding sequence of the human A-raf-1 oncogene and transforming activity of a human A-raf carrying retrovirus.

The complete 606 amino acid sequence of the human A-raf oncogene has been deduced from the 2453 nucleotide sequence of a human T cell cDNA. A cysteine-rich region located near the amino terminus, which is highly conserved in A-raf and c-raf, shows significant homology with protein kinase C. A 5' deleted fragment of the cDNA has been incorporated into a murine retrovirus which endows the virus with the ability to transform cells in vivo and in vitro. Functionally, human A-raf is similar to v-raf and v-mos in that transformation is independent of ras gene function.

Amino Acid Sequence↗
PubMed1987

Insertion and truncation of c-myb by murine leukemia virus in a myeloid cell line derived from cultures of normal hematopoietic cells.

A retroviral insertion into the c-myb gene, which resulted in a 3' truncation, was found in an in vitro-derived myeloid cell line. The retroviral insertion occurred at precisely the same nucleotide at which another murine leukemia virus insertion occurred in an in vivo-induced myeloid leukemia. These findings suggest that comparable events may be required for the derivation of myeloid cell lines in vitro and for induction of myeloid leukemia in vivo.

Base Sequence↗
PubMed1987

Role of myc in the abrogation of IL3 dependence of myeloid FDC-P1 cells.

We have constructed a recombinant retrovirus containing the murine c-myc and the neo gene and introduced the virus into the interleukin-3 (IL3) dependent myeloid cell line FDC-P1. Unregulated expression of the introduced c-myc gene is associated with both an increased viability and constitutive ornithine decarboxylase mRNA levels in FDC-P1 cells grown in the absence of IL3. FDC-P1 cells infected with the c-myc virus gave rise to IL3 independent lines. Three out of four independent lines have an activated endogenous c-myc or N-myc gene. We have also shown that c-myc mRNA levels are tightly regulated by IL3 in FDC-P1 cells. Taken together these results indicate that myc plays a critical role in the signal transduction pathway of IL3. Furthermore, activation of the N-myc gene may be one mechanism for myeloid cells to progress to complete IL3 independence.

Animals↗
PubMed1986

Interaction between Raf and Myc oncogenes in transformation in vivo and in vitro.

3611 MSV, a raf-oncogene-transducing murine retrovirus, induces fibrosarcomas and erythroid hyperplasia in newborn mice after a latency of 4-8 wk. In contrast, new recombinant murine retroviruses carrying the myc oncogene (J-3, J-5 construct viruses) do not induce tumors before greater than 9 wk. A combination of both oncogenes in an infectious murine retrovirus (J-2) induces hematopoietic neoplasms in addition to less prominent fibrosarcomas and pancreatic adenocarcinoma 1-3 wk after inoculation. The hematologic neoplasms consist of immunoblastic lymphomas of T and B cell lineage and erythroblastosis. If animals were inoculated with a variant of the J-3 virus, which induces altered foci in cultures of NIH 3T3 cells, carcinoma developed in the pancreas with a 2-6 mo latency. In parallel to the synergistic action of both oncogenes on hematopoietic cells in vivo, we find that raf-oncogene-induced transformation of bone marrow cells in culture is enhanced by the addition of myc, which by itself does not transform these cells when grown in standard media. We conclude that concomitant expression of raf and myc oncogenes in hematopoietic and epithelial cells alters their respective transforming activities. The contribution of v-myc in this synergism was examined by use of a series of recombinant murine retroviruses capable of expressing the avian v-myc to study the effect of altered myc expression on hematopoietic/lymphoid cells. With either interleukin 3- or interleukin 2-dependent cell lines, introduction of the recombinant viruses abrogated the requirement for IL 3 or IL 2 for growth, and associated with this was the suppression of c-myc expression. The findings suggest that myc is a component in the signal transduction pathway for IL 3 and IL 2 and support an autoregulatory mechanism of c-myc expression. In contrast to v-myc, expression of v-raf in primary lymphoid/hematopoietic cells has an immortalizing function without abrogating the requirement for IL 3 for growth. This suggests that v-raf and v-myc affect different components of growth regulation, as, for example, commitment (v-myc) and cell cycle progression (v-raf).

Animals↗
PubMed1986

Recombinant murine retroviruses containing avian v-myc induce a wide spectrum of neoplasms in newborn mice.

NFS/N mice were infected within 48 hr of birth with pseudotypes of recombinant murine leukemia viruses containing avian v-myc developed T-cell, pre-B-cell, and B-cell lymphomas and epithelial tumors including pancreatic and mammary adenocarcinomas. Primary hematopoietic and epithelial tumors and continuous in vitro cell lines derived from some of these tumors, established in the absence of added growth factors, exhibited clonal integrations of v-myc and expressed v-myc RNA. These results show that deregulated expression of the myc oncogene in mammalian cells can initiate a wide variety of neoplasms.

Adenocarcinoma↗
PubMed1986

Characterization of murine A-raf, a new oncogene related to the v-raf oncogene.

A 1.6-kilobase cDNA (A-raf) has been isolated from a murine spleen cDNA library which encodes part of a protein related to the raf oncogene. Its amino acid sequence has 85% homology to raf in a central portion of 100 amino acids. In contrast to raf, A-raf shows a highly restricted tissue distribution of expression, with highest levels observed in epididymis, followed by intestine. When incorporated into a retrovirus, the resulting gag-A-raf fusion gene causes transformation in vitro and induces tumors in newborn mice. Thus, A-raf represents a new proto-oncogene. Transformation by A-raf is independent of ras gene function, as is the case for raf and mos but not other oncogenes.

Amino Acid Sequence↗
PubMed1986

Transformation by raf and myc oncogenes.

raf oncogenes were shown to act synergistically with myc in transformation. The contribution of myc was identified as that of a "second messenger" in signal transduction of at least some, competence inducing, growth factors. The role of raf appears to be that of a cytosolic ser/thr specific protein kinase which was placed downstream of ras in the signal transduction of serum growth factors by ras and raf antibody microinjection experiments. Because of the inability of raf to abrogate a cells need for myc inducing competence factors, as well as its synergistic effect with myc, raf was placed downstream of ras in the progression pathway of cellular growth control. We speculate that the basis for synergism with myc might be the ability of raf to activate competence factor induced myc protein or a myc induced protein by phosphorylation. The role of raf in lung tumors was examined by the development of a high incidence mouse model system using ethylnitrosourea as carcinogen and butylated hydroxytoluene as promoter. raf proteins of normal size were expressed at high levels, raf protein vaccination was apparently effective in eliminating the promoted phase of tumor induction.

Amino Acid Sequence↗