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J Samarut

Publications and source records attributed to J Samarut.

At least 91 records · Page 5Linked to original sources
PubMed1990

The carbonic anhydrase II gene, a gene regulated by thyroid hormone and erythropoietin, is repressed by the v-erbA oncogene in erythrocytic cells.

The v-erbA oncogene encodes an altered form of the nuclear receptor of the thyroid hormone triiodothyronine (T3). This altered receptor is unable to bind T3, and blocks the differentiation of chicken erythrocyte progenitor cells. To identify the cellular target genes of v-ErbA in the transformed cells, we analysed the expression of several genes in normal erythrocytic cells exposed to T3, and found that the gene encoding carbonic anhydrase II is transcriptionally activated by the hormone. In contrast, this gene is repressed in erythroleukemic cells transformed by the v-erbA product. To investigate in more details the effects of v-ErbA, we constructed a mutant of v-ErbA in which we restored the ability to bind T3. This mutant developed its oncogenicity only in the absence of T3. Upon binding of T3, the transformed cells differentiated and immediately expressed the carbonic anhydrase II gene. These data show that v-ErbA directly inhibits the transcription of the carbonic anhydrase II gene, presumably by competing with normal T3 receptors. The carbonic anhydrase II gene is the first identified target gene of the v-ErbA oncoprotein in erythroleukemic cells.

Animals↗
PubMed1990

[Oncogene cooperation in cellular transformation].

Oncogenic cell transformation induces major changes in the structure and physiology of the cells: modifications of morphology, differentiation block, disorganisation of cytoskeleton and extracellular matrix, alterations in growth control. The identification of oncogenes relies upon transfer into host normal cells of DNA isolated from cancer cells. The recent development of DNA transfer into germinal cells has provided new insights into the genetic control of tumorogenesis in vivo. In most cases, full transformation into leukemic or tumor cell requires the cooperation of several oncogenes. These observations support the hypothesis of cancer as a multistep process. However, many of the cooperative oncogenes have not yet been identified, especially in human cancers. The recent discovery of genes acting as repressors of cell growth in normal cells has brought to light a new class of potential recessive oncogenes that might have a contributory function in cancer development.

Animals↗
PubMed1989

Expression of the v-erbA product, an altered nuclear hormone receptor, is sufficient to transform erythrocytic cells in vitro.

We investigated the effect of the v-erbA oncogene product, an altered thyroid hormone receptor, in chicken erythrocyte progenitor cells. Bone marrow cells were infected with a retrovirus vector (XJ12) carrying the v-erbA gene in association with the neoR gene. XJ12-infected erythrocyte progenitor cells gave rise to G418-resistant clones. Some were composed of blast cells identified as transformed CFU-Es blocked in their differentiation. These cells could be grown in culture for at least 25 generations and required anemic chicken serum as a source of erythropoietic growth factors. XJ12 can infect erythrocyte progenitor cells in vivo but is not sufficient to induce erythroleukemia. These data suggest that the activation of a nuclear hormone receptor might represent one step toward the development of neoplasms.

Animals↗
PubMed1989

Avian retroviral vectors derived from avian defective leukemia virus: role of the translational context of the inserted gene on efficiency of the vectors.

We have constructed retroviral vectors derived from the genome of avian erythroblastosis virus ES4 (AEV ES4). The neo selectable gene was substituted for the original v-erbA or v-erbB oncogenes of AEV, either in the same or in a different reading frames. Recombinant retrovirus were rescued and used to infect chicken embryo fibroblasts or quail QT6 cells. When the neo gene was inserted in the same reading frame as the original oncogene, we obtained (1) a high level of expression of the neo gene, (2) a balanced ration of both genomic and subgenomic RNAs, and (3) high titer recombinant viruses. Conversely, when the neo gene was inserted in a reading frame different from that of the original oncogene, we observed (1) a very low level of expression of the neo protein, (2) a predominance of the viral transcript used as translational template for the neo protein synthesis, and (3) low titer recombinant viruses. One of the vectors was used to transfer a human delta-globin gene into avian cells in culture without detectable rearrangement of this gene, but exhibited a deletion within the conserved noncoding region located between the two original oncogenes. Our data provide information for further construction of double expression vectors. Furthermore, three of the vectors would provide helpful tools to identify genetic elements of the virus genome involved in splicing regulation.

Alpharetrovirus↗
PubMed1989

A translocation involving a specific breakpoint (q35) on chromosome 5 is characteristic of anaplastic large cell lymphoma ('Ki-1 lymphoma').

Two cases of non-Hodgkin's lymphoma are reported in which a chromosomal translocation was observed involving the same site (q35) on the long arm of chromosome 5. The other breakpoint involved in the translocation was chromosome 2 (p23) in one case and chromosome 3 (q12) in the other. Both cases were large cell lymphomas expressing CD30 antigen ('Ki-1 lymphoma'). One was clearly of T lymphoid origin, the other probably B cell derived. One other case of a Ki-1 lymphoma with 2;5 translocation (involving the same breakpoint on chromosome 5) has been reported previously, and it is suggested that this cytogenetic abnormality may be specifically associated with Ki-1 lymphoma. The literature contains a further eight cases of lymphoid neoplasms with a translocation involving a breakpoint at q35 on chromosome 5. They have all been described as cases of 'malignant histiocytosis', but the present findings make it likely that these cases were in reality also examples of Ki-1 lymphoma. The breakpoint at the q35 region on chromosome 5 is close to the position of the fms proto-oncogene, suggesting that an abnormality affecting this gene might possibly play a causal role in 'Ki-1 lymphoma'. However, DNA restriction fragment analysis of the present cases showed no evidence that the breakpoint on chromosome 5 involves the fms gene or its immediate vicinity.

Adolescent↗
PubMed1989

Increase in ribosomal protein S6 phosphorylation is due to v-erbB-transforming activity and not to v-erbA mitogenic activity in avian erythroblastosis virus-infected chicken embryo fibroblasts.

Avian erythroblastosis virus (AEV-ES4), a transforming avian retrovirus, transforms chicken embryo fibroblasts (CEFs) in culture and induces the maintenance of ribosomal protein S6 phosphorylation in the absence of serum. This effect is less pronounced after AEV-ES4 transformation than after transformation by Rous sarcoma virus (PR-RSV A). However, our results indicate that the two viruses induce an activation of the same S6 phosphokinase, as evidenced by the identity of S6 phosphopeptides and phosphoaminoacids in the two cases. Moreover this activation is performed through a protein kinase C-independent pathway. Expression of the v-erbA oncogene alone, which enhances the growth potential of CEFs, is not able to maintain S6 phosphorylation either in the absence of serum or in the presence of low serum concentration (0.5%). Expression of the v-erbB oncogene alone is responsible for all these AEV-ES4-induced effects. Furthermore, the maintenance of S6 phosphorylation in the absence of serum might be correlated with the degree of transformation of AEV-ES4-infected CEFs. These results show that S6 phosphorylation is one of the biochemical mechanisms deregulated by v-erbB expression and is involved in the transformation process.

Alpharetrovirus↗
PubMed1987

Expression of the v-erbA oncogene in chicken embryo fibroblasts stimulates their proliferation in vitro and enhances tumor growth in vivo.

In contrast to uninfected chicken embryo fibroblasts (CEFs), CEFs infected with a retroviral vector that carries the v-erbA gene of avian erythroblastosis virus displayed new properties. These included limited anchorage-independent growth in soft agar, growth without latency in serum-supplemented medium, ability to overcome quiescence induced by serum deprivation, growth at low cell density, and an extended life span in vitro. Furthermore, when explanted in vivo onto the chorioallantoic membrane of chicken embryo, the transformed CEFs expressing v-erbA in addition to v-erbB exhibited a high proliferative rate, giving rise to fibrosarcoma tumors that were ten times larger than those developed from transformed CEFs expressing v-erbB alone. All these data show that CEFs expressing the v-erbA oncogene display activated growth and suggest that the v-erbA product interferes with the mechanisms regulating the growth and/or differentiation of primary CEFs.

Alpharetrovirus↗
PubMed1987

AEV-transformed erythroleukemia cell induced differentiation: expression of specific cell membrane antigenic molecules.

A simultaneous decay of the expression of Im 140 kDa, Im 150 kDa and Im 160 kDa high MW membrane antigens, concomitant with the cell proliferation arrest, was observed during erythropoietin induced differentiation of ts 34 AEV-transformed erythroid cells cultivated at the restrictive temperature. Expression of embryo-immature antigens was maintained during induced differentiation of erythroleukemia cells, but their MW shifted from 50 to 48 kDa, which corresponds to the MW of embryo-immature antigens detected on normal erythroid cells. In the absence of erythropoietin at the restrictive temperature, conditions under which the ts 34 AEV-transformed erythroid cells fail to differentiate and maintain their capacity to proliferate, the expression of high MW antigens as well as the expression of embryo-immature antigens remained unaffected. Therefore, it is shown that the expression of specific membrane antigens is modulated under conditions rendering the erythroleukemia cell differentiation process possible.

Alpharetrovirus↗
PubMed1987

Transforming and mitogenic effects of avian leukemia virus E26 on chicken hematopoietic cells and fibroblasts, respectively, correlate with level of expression of the provirus.

We have investigated the effect of E26, an avian leukemia retrovirus, on the growth properties of chicken embryo fibroblasts (CEFs). E26-infected CEFs were not transformed, according to several transformation parameters, but exhibited an activated growth in vitro. They started to grow without latency in serum-supplemented medium, maintained long-term growth in regular or low-serum medium, and could grow when seeded at low cell density in low-serum medium. We compared the integration and the level of expression of the proviral DNA in E26-infected CEFs and E26-transformed hematopoietic cells. An average of two provirus copies were found in each kind of cells. However, whereas high contents of both viral mRNA and E26-specific protein products were found in transformed hematopoietic cells, we detected only low amounts of viral mRNA and no E26 protein in infected CEFs. These data show that the level of expression of the E26 provirus is lower in CEFs than in hematopoietic cells. They suggest that transformation efficiency of the virus depends on its level of expression.

Animals↗
PubMed1987

The chicken c-erbA proto-oncogene is preferentially expressed in erythrocytic cells during late stages of differentiation.

We analyzed the expression of the c-erbA proto-oncogene in different tissues of chicken embryos. c-erbA transcripts were found at low levels in the lung, kidney, liver, and heart and in high amounts in embryonic blood cells. Nuclease mapping assays proved that these transcripts were true c-erbA transcripts. In situ hybridization on fractionated embryonic blood cells showed that c-erbA transcripts were predominantly found in erythroblasts, particularly during the final step of differentiation. Life span analysis of c-erbA mRNAs revealed their relative instability, demonstrating that the high level of c-erbA transcripts in embryonic erythroblasts was not the result of passive accumulation. These results suggest that the c-erbA genes play some role in erythrocyte differentiation.

Animals↗
PubMed1986

Chicken myeloid stem cells infected by retroviruses carrying the v-fps oncogene do not require exogenous growth factors to differentiate in vitro.

To determine the function of c-fps in chicken macrophages and granulocytic cells we have infected chicken bone marrow cells with retroviruses containing the v-fps oncogene. Normal chicken macrophage progenitors, M-CFCs, give rise to macrophage colonies in semisolid cultures when macrophage colony stimulating factor (M-CSF) is added into the culture medium. Upon infection with v-fps bearing retroviruses, we observed that M-CFCs were induced to develop macrophage colonies in vitro without exogenous M-CSF. This activation results from a direct effect of v-fps on the M-CFCs. No leukemic transformation was observed in the infected colonies. By comparing the effects of several retroviruses, we showed that the induction of M-CFC development is specific to v-fps containing viruses and mediated by the v-fps protein. These observations support the hypothesis that the c-fps gene is involved in the control of proliferation and/or differentiation of myeloid cells.

Animals↗
PubMed1985

Preferential expression of the c-fps protein in chicken macrophages and granulocytic cells.

We have studied the expression of the protein kinase activity of NCP98, the c-fps gene product, in several hemopoietic tissues of chickens as a function of the developmental stage of these organs. We found that in bone marrow, spleen, and bursa, maximum NCP98 kinase activity on a per-cell basis correlates with the peak of granulopoiesis in these organs. Furthermore, in a bovine serum albumin density gradient fractionation of bone marrow cells, granulocytic cells appeared to account for most of the NCP98 kinase activity. No correlation was found between the distribution of erythrocytic, lymphocytic, or thrombocytic cells and the distribution of the expression of NCP98 kinase activity. However, NCP98 protein and kinase activity were 10-fold higher in macrophages than in bone marrow. In addition, depletion by complement-mediated lysis of erythrocytic cells in bone marrow did not significantly reduce the total recovery of NCP98 kinase activity. These results argue for the specific expression of the c-fps gene product in granulocytic cells and macrophages.

Animals↗
PubMed1984

Revertants and partial transformants of rat fibroblasts infected with Fujinami sarcoma virus.

Fifteen revertants were isolated from three independent clones of rat fibroblasts transformed by Fujinami sarcoma virus (FSV). Three revertant clones resulted from the deletion of the one copy of the FSV provirus, and one encoded an enzymatically inactive, transformation-defective protein. The remaining revertant clones were characterized by a transcriptional block of the provirus. Digestion of chromosomal DNA with MspI and HpaII revealed that the FSV provirus was hypermethylated in these revertants, whereas proviral DNA of their spontaneous retransformants was hypomethylated. Furthermore, the revertants had lost DNase I-hypersensitive sites in and around the FSV provirus. The effect of transcriptional regulation of the FSV provirus was further analyzed in clones showing various degrees of phenotypic transformation. We quantitated v-fps mRNA levels in these cells by liquid hybridization and found that increasing levels of viral RNA correlated with a more pronounced transformed phenotype. These results suggest that transcription of FSV proviral DNA is under both viral and cellular control and that transformation by FSV is a function of the dosage of v-fps mRNA.

Animals↗
PubMed1984

A factor present in normal mouse serum stimulates late erythroid precursor proliferation.

A factor present in normal mouse serum stimulates proliferation of late erythroid precursors grown in cultures in vitro. This factor was shown not to have a corrective effect on culture conditions by the following criteria: (a) CFU-E frequency in the absence of NMS was at least as great as published data for various mouse strains, (b) an inhibitory effect of endotoxin was ruled out, (c) sensitivity of erythroid precursors to erythropoietin was similar in the presence or absence of NMS, and (d) the number of colonies was linearly related to the cell dose. The enhancing effect of NMS was independent of hemin, transferrin, or dexamethasone, products all known to be stimulators of erythropoiesis. It was shown to be specific for CFU-E. We propose that this material be termed erythropoietic stimulating cofactor (ESCF).

Animals↗
PubMed1983

Transforming ability of avian defective leukemia viruses in early embryogenesis.

The response to infection of chicken hemopoietic cells derived from the early stages of embryogenesis by avian myeloblastosis virus (AMV) and avian erythroblastosis virus (AEV) was investigated. It was found that erythroid progenitor cells were present in the blastoderm at a higher frequency than that of myeloid progenitor cells. These results correlate with the observation that target cells for AEV were found to be more numerous than those for AMV. Therefore, blastoderm cells are of potential value in understanding the mechanisms of oncogenesis at the level of the target cells.

Alpharetrovirus↗