The Experts below are selected from a list of 210 Experts worldwide ranked by ideXlab platform
Paul B Fisher - One of the best experts on this subject based on the ideXlab platform.
-
coopeRation between ap1 and pea3 sites within the progression elevated gene 3 peg 3 promoter regulate basal and differential expression of peg 3 during progression of the oncogenic phenotype in transformed Rat Embryo cells
Oncogene, 2000Co-Authors: Yijie Shi, Paul B FisherAbstract:Cancer is a progressive disease in which a tumor cell temporally develops qualitatively new transformation related phenotypes or a further elaboRation of existing transformation associated properties. Subtraction hybridization identified a novel gene associated with transformation progression in mutant adenovirus type 5, H5ts125, transformed Rat Embryo cells, progression elevated gene-3 (PEG-3). To define the mechanism by which expression of PEG-3 is enhanced as a function of cancer progression a 5'-flanking promoter region of approximately 2.0-kb, PEG-Prom, was isolated, cloned and characterized. The full-length and various mutated regions of the PEG-Prom were linked to a luciferase reporter construct and evaluated for promoter activity during cancer progression. These assays demonstRate a requirement for AP1 and PEA3 sites adjacent to the TATA box region of PEG-3 in mediating basal promoter activity and the enhanced expression of PEG-3 in progressed H5ts125-transformed Rat Embryo cells. An involvement of AP1 and PEA3 in PEG-3 regulation was also confirmed by electrophoretic mobility shift assays (EMSA) and transfection studies with cJun and PEA3 expression vectors. Our findings document the importance of both AP1 and PEA3 transcription factors in mediating basal and elevated expression of PEG-3 in H5ts125-transformed Rat Embryo cells displaying an aggressive and progressed cancer phenotype.
-
apoptosis mediates the selective toxicity of caffeic acid phenethyl ester cape toward oncogene transformed Rat Embryo fibroblast cells
Anticancer Research, 1995Co-Authors: Jiao Jiao Lin, Marie Prewett, N I Goldstein, Paul B FisherAbstract:The active component of the folk medicine propolis, caffeic acid phenethyl ester (CAPE), displays selective toxicity toward cloned Rat Embryo fibroblast (CREF) cells transformed by a spectrum of diverse acting oncogenes. Identification of the mode of action of CAPE should provide useful information for possible applications of this compound for cancer therapy. The present study uses a series of oncogene transformed, oncogene-reverted and CAPE-resistant oncogene transformed CREF cells to investigate the mechanism underlying the increased sensitivity of transformed cells to CAPE. A direct relationship exists between the cytotoxic effects of CAPE and the induction of DNA fragmentation and apoptosis. DNA degradation into nucleosomal fragments and apoptotic shifts in DNA cell cycle profiles occur in CAPE-treated CREF cells transformed by wild-type 5 adenovirus (Ad5), a mutant Ad5 (H5hr1), the wild-type Ad5 E1A transforming gene, v-src, Ha-ras and the human papilloma virus type 18 transforming genes (HPV-18). In contrast, untransformed CREF cells, human fibroblast expression library-induced morphological revertants of Ad5- and v-src-transformed CREF cells, and Krev-1 expressing revertant Ha-ras-transformed CREF cells are resistant to CAPE-induced toxicity and apoptosis. Similarly, mutant Ad5-transformed CREF cells selected by step-wise growth in increasing concentRations of CAPE are resistant to growth inhibition and apoptosis induced by CAPE. These findings indicate that expression of the transformed phenotype by rodent cells evokes sensitivity to CAPE induced toxicity through apoptosis. The acquisition of CAPE sensitivity in rodent cells is independent of the mode of action of the oncogenic agent. CAPE may prove useful as an antiprolifeRative agent in cancer cells transformed by mechanistically diverse acting oncogenes.
-
growth suppression and toxicity induced by caffeic acid phenethyl ester cape in type 5 adenovirus transformed Rat Embryo cells correlate directly with transformation progression
Cancer Research, 1994Co-Authors: Jian Lin, Dezider Grunberger, Paul B FisherAbstract:The active component of the honeybee hive product propolis, caffeic acid phenthyl ester (CAPE), induces a selective growth suppressive and toxic effect toward cloned Rat Embryo fibroblast cells transformed by adenovirus type 5 (Ad5) or the Ad5 E1A transforming gene versus untransformed cloned Rat Embryo fibroblast cells (Z-z. Su et al. , Mol. Carcinog., 4: 231–242, 1991). The present study was conducted to determine whether CAPE-induced growth suppression/toxicity was a direct result of expression of the Ad5 E1A and E1B transforming genes or a consequence of the action of these genes resulting in the transformed state. For this investigation we used somatic cell hybrids and 5-azacytidine-treated Ad5-transformed Rat Embryo cells that display different stages of expression of the transformed phenotype. This series of cell lines has permitted us to determine whether expression of the transformed state and the stage of transformation progression regulates CAPE sensitivity. Evidence is presented indicating that sensitivity to CAPE is directly determined by the state of expression of the transformed progression phenotype, as opposed to simply the expression of the Ad5 E1A and E1B transforming genes. These results provide further evidence that CAPE may represent a unique compound that can specifically target progressed transformed cells for growth suppression and toxicity. An understanding of the mechanism underlying this selective effect of CAPE could result in the identification of important biochemical pathways mediating cellular transformation and progression of the transformed state.
Pui Yu Chiu - One of the best experts on this subject based on the ideXlab platform.
-
An in‐vitro study of ginsenoside Rb1‐induced teRatogenicity using a whole Rat Embryo culture model
Human reproduction (Oxford England), 2003Co-Authors: Louis Yiksi Chan, Pui Yu Chiu, Tze-kin LauAbstract:BACKGROUND Ginseng is a commonly used herbal medicine worldwide. However, there is limited information regarding its effects on the developing Embryo. METHODS The effect of ginsenoside on the developing Embryo during the critical period of organogenesis was investigated using a whole Rat Embryo culture model. Embryos were exposed to various concentRations of ginsenoside Rb(1) and scored for growth and differentiation at the end of the culture period. RESULTS Median total morphological scores in Embryos exposed to 30 micro g/ml of ginsenoside Rb(1) was significantly lower (P < 0.05) than that in control Embryos (35 versus 45). Morphological scores for flexion, forelimb and hindlimb were also significantly reduced. The median total morphological scores further decreased to 28 when the concentRation of ginsenoside Rb(1) was increased to 50 micro g/ml. At this concentRation, the Embryonic crown-rump length and somite number were also significantly reduced compared with control Embryos (2.8 versus 3.0 mm and 16.0 versus 21.0, respectively). CONCLUSIONS Our study has demonstRated that ginsenoside exerts direct teRatogenic effects on Rat Embryos. Until more is known about the effects of ginsenoside in women of reproductive age, we suggest its use should be treated with caution.
-
an in vitro study of ginsenoside rb1 induced teRatogenicity using a whole Rat Embryo culture model
Human Reproduction, 2003Co-Authors: Louis Yiksi Chan, Pui Yu ChiuAbstract:BACKGROUND: Ginseng is a commonly used herbal medicine worldwide. However, there is limited information regarding its effects on the developing Embryo. METHODS: The effect of ginsenoside on the developing Embryo during the critical period of organogenesis was investigated using a whole Rat Embryo culture model. Embryos were exposed to various concentRations of ginsenoside Rb(1) and scored for growth and differentiation at the end of the culture period. RESULTS: Median total morphological scores in Embryos exposed to 30 micro g/ml of ginsenoside Rb(1) was significantly lower (P < 0.05) than that in control Embryos (35 versus 45). Morphological scores for flexion, forelimb and hindlimb were also significantly reduced. The median total morphological scores further decreased to 28 when the concentRation of ginsenoside Rb(1) was increased to 50 micro g/ml. At this concentRation, the Embryonic crown-rump length and somite number were also significantly reduced compared with control Embryos (2.8 versus 3.0 mm and 16.0 versus 21.0, respectively). CONCLUSIONS: Our study has demonstRated that ginsenoside exerts direct teRatogenic effects on Rat Embryos. Until more is known about the effects of ginsenoside in women of reproductive age, we suggest its use should be treated with caution.
-
an in vitro study of ginsenoside rb1 induced teRatogenicity using a whole Rat Embryo culture model
Human Reproduction, 2003Co-Authors: Louis Yiksi Chan, Pui Yu Chiu, Tze-kin LauAbstract:BACKGROUND Ginseng is a commonly used herbal medicine worldwide. However, there is limited information regarding its effects on the developing Embryo. METHODS The effect of ginsenoside on the developing Embryo during the critical period of organogenesis was investigated using a whole Rat Embryo culture model. Embryos were exposed to various concentRations of ginsenoside Rb(1) and scored for growth and differentiation at the end of the culture period. RESULTS Median total morphological scores in Embryos exposed to 30 micro g/ml of ginsenoside Rb(1) was significantly lower (P < 0.05) than that in control Embryos (35 versus 45). Morphological scores for flexion, forelimb and hindlimb were also significantly reduced. The median total morphological scores further decreased to 28 when the concentRation of ginsenoside Rb(1) was increased to 50 micro g/ml. At this concentRation, the Embryonic crown-rump length and somite number were also significantly reduced compared with control Embryos (2.8 versus 3.0 mm and 16.0 versus 21.0, respectively). CONCLUSIONS Our study has demonstRated that ginsenoside exerts direct teRatogenic effects on Rat Embryos. Until more is known about the effects of ginsenoside in women of reproductive age, we suggest its use should be treated with caution.
-
a study of diclofenac induced teRatogenicity during organogenesis using a whole Rat Embryo culture model
Human Reproduction, 2001Co-Authors: Louis Yiksi Chan, Pui Yu ChiuAbstract:BACKGROUND: Diclofenac is a non-steroidal anti-inflammatory drug, commonly used by reproductive age women for the treatment of a variety of conditions. However, there is limited information regarding the teRatogenic effects of this drug. METHODS: The effect of diclofenac on the developing Embryo during the critical period of organogenesis was investigated by using a whole Rat Embryo culture model. Embryos were exposed to various concentRations of diclofenac and scored for growth and differentiation at the end of the culture period. RESULTS: Total developmental score and score for caudal neural tube, flexion and hindlimb were significantly lower in Embryos exposed to high concentRations of diclofenac (7.5 and 15.0 microg/ml), but no difference in these parameters was observed when Embryos were exposed to low concentRation of diclofenac (1.5, 2.5 and 5.0 microg/ml). No significant differences in yolk sac diameter, crown-rump length and number of somites was found between Embryos in the experimental and the control group. CONCLUSIONS: Our study has demonstRated that diclofenac exerts direct teRatogenic effects on Rat Embryos. Until more is known about the effects of diclofenac (especially in modeRate to high doses) in women of reproductive age, we suggest its use should be treated with caution.
Ruth J. Muschel - One of the best experts on this subject based on the ideXlab platform.
-
transcriptional activation of the matrix metalloproteinase 9 gene in an h ras and v myc transformed Rat Embryo cell line
Oncogene, 1997Co-Authors: Bruce P Himelstein, Edward J Lee, Hiroshi Sato, Motoharu Seiki, Ruth J. MuschelAbstract:The 92 kd type IV collagenase/gelatinase (MMP-9) is important in mediating basement membrane and extracellular matrix degradation in metastasis. Because MMP-9 is made in tumor cells, but not in quiescent normal cells, we wished to identify the transcriptional elements responsible for its synthesis in tumor cells. We chose to characterize transcriptional regulation of the MMP-9 gene in a highly metastatic H-ras and v-myc transformed Rat Embryo cell line which overexpresses MMP-9. Using transient transfection of reporter gene constructs containing either 5′-deleted or mutated MMP-9 promoter fragments, as well as electrophoretic mobility shift assays, we have demonstRated that multiple transcription factor consensus binding motifs in the promoter, including those for NFκB, SP-1, Ets, AP-1, and a retinoblastoma binding element, participate in transcriptional regulation of MMP-9 expression in this cell line. Also, deletion of an alternating purine-pyrimidine tract in the downstream promoter was found to decrease transcriptional activity, suggesting that promoter conformation may be important in MMP-9 regulation. Thus multiple pathways leading to activation of NFκB, SP-1, Ets, AP-1, and retinoblastoma binding factors in tumor cells all may contribute to MMP-9 transcription and hence to metastasis.
-
the farnesyltransferase inhibitor fti 277 radiosensitizes h ras transformed Rat Embryo fibroblasts
Cancer Research, 1996Co-Authors: Eric J. Bernhard, Adrienne D Cox, Ruth J. Muschel, Gary D Kao, Said M Sebti, Andrew D Hamilton, Gillies W MckennaAbstract:Many tumor cells have a greater resistance to ionizing radiation than their normal counterparts, suggesting that the development of drugs that can reduce that radioresistance would potentiate the efficacy of radiation therapy. Because activated H-ras expression has been shown to markedly increase radiation resistance in some transformed cells, the inactivation of H-ras would then be predicted to radiosensitize these tumor cells, while leaving normal cells unaffected. H-ras depends for activity upon farnesylation, which can be blocked by farnesylation inhibitors, including the compound FTI-277. In keeping with this prediction, inhibition of H-ras processing using FTI-277 resulted in higher levels of apoptosis after irradiation and increased radiosensitivity in H-ras-transformed Rat Embryo cells but did not affect control cells. These experiments suggest that farnesylation inhibitors may prove clinically useful as radiosensitizers of tumors that depend on ras function.
-
direct evidence linking expression of matrix metalloproteinase 9 92 kda gelatinase collagenase to the metastatic phenotype in transformed Rat Embryo cells
Proceedings of the National Academy of Sciences of the United States of America, 1994Co-Authors: Eric J. Bernhard, Stephen B Gruber, Ruth J. MuschelAbstract:Abstract Members of the matrix metalloproteinase (MMP) family have been implicated in the metastasis of tumor cells, but no direct evidence linking any given member of the MMP family to metastatic behavior has been presented. Rat Embryo cells transformed by the Ha-ras and v-myc oncogenes or by Ha-ras alone are metastatic in nude mice and release the 92-kDa gelatinase/collagenase (MMP-9), whereas those transformed by Ha-ras plus the adenovirus E1A gene are not metastatic and do not release MMP-9. Here we demonstRate that MMP-9 expression can be induced in these tumorigenic but nonmetastatic Rat cells by transfection with an MMP-9 expression vector. Transfection of a MMP-9 expression vector, but not control DNAs, conferred metastatic capacity on the nonmetastatic cells. The majority of colonies isolated after continued passage either in vivo or in vitro had lost the MMP-9 expression vector. However, occasional cells were isolated from metastases which retained MMP-9 expression after passage. These cells retained metastatic capacity. In contrast, cells isolated after losing MMP-9 expression also lost the ability to metastasize. These results provide direct evidence that MMP-9 has a role in tumor metastasis.
-
Cysteine endopeptidases and their inhibitors in malignant progression of Rat Embryo fibroblasts.
Biological chemistry Hoppe-Seyler, 1992Co-Authors: Bonnie F. Sloane, Jurij Rozhin, Kamiar Moin, Grace Ziegler, Dunne Fong, Ruth J. MuschelAbstract:Cathepsins B and L and their endogenous inhibitors were evaluated in Rat Embryo fibroblast lines which have been developed as a model system for the study of malignant progression and metastatic capability. Three groups of lines were analyzed: 1) immortalized/non-tumorigenic, 2) tumorigenic/metastatic lines transfected with c-Ha-ras, and 3) metastatic revertants transfected with c-Ha-ras+the E1A region of adenovirus type 2. The metastatic revertants are tumorigenic, but non-metastatic. No correlation was seen between tumorigenicity and metastatic potential and the level of expression of cathepsin B or the subcellular distribution of cathepsins B and L. However, cathepsin L activity was increased 2-fold in the 4R metastatic line. Although transfection of aneuploid 3T3 fibroblasts with ras has been shown to increase the expression of cathepsin L and cathepsin B, transfection of the diploid Rat Embryo fibroblasts with ras did not correlate with increased expression of cathepsin L or cathepsin B. However, ras transfection of the Rat Embryo fibroblasts was associated with a significant (4-15-fold) decrease in the activity of heat-stable cysteine endopeptidase inhibitors. Thus, in tumorigenic Rat Embryo fibroblast lines, regulation of the activities of cysteine endopeptidases by their endogenous inhibitors may be compromised, resulting in increased effective activities of the cysteine endopeptidases.
Louis Yiksi Chan - One of the best experts on this subject based on the ideXlab platform.
-
An in‐vitro study of ginsenoside Rb1‐induced teRatogenicity using a whole Rat Embryo culture model
Human reproduction (Oxford England), 2003Co-Authors: Louis Yiksi Chan, Pui Yu Chiu, Tze-kin LauAbstract:BACKGROUND Ginseng is a commonly used herbal medicine worldwide. However, there is limited information regarding its effects on the developing Embryo. METHODS The effect of ginsenoside on the developing Embryo during the critical period of organogenesis was investigated using a whole Rat Embryo culture model. Embryos were exposed to various concentRations of ginsenoside Rb(1) and scored for growth and differentiation at the end of the culture period. RESULTS Median total morphological scores in Embryos exposed to 30 micro g/ml of ginsenoside Rb(1) was significantly lower (P < 0.05) than that in control Embryos (35 versus 45). Morphological scores for flexion, forelimb and hindlimb were also significantly reduced. The median total morphological scores further decreased to 28 when the concentRation of ginsenoside Rb(1) was increased to 50 micro g/ml. At this concentRation, the Embryonic crown-rump length and somite number were also significantly reduced compared with control Embryos (2.8 versus 3.0 mm and 16.0 versus 21.0, respectively). CONCLUSIONS Our study has demonstRated that ginsenoside exerts direct teRatogenic effects on Rat Embryos. Until more is known about the effects of ginsenoside in women of reproductive age, we suggest its use should be treated with caution.
-
an in vitro study of ginsenoside rb1 induced teRatogenicity using a whole Rat Embryo culture model
Human Reproduction, 2003Co-Authors: Louis Yiksi Chan, Pui Yu ChiuAbstract:BACKGROUND: Ginseng is a commonly used herbal medicine worldwide. However, there is limited information regarding its effects on the developing Embryo. METHODS: The effect of ginsenoside on the developing Embryo during the critical period of organogenesis was investigated using a whole Rat Embryo culture model. Embryos were exposed to various concentRations of ginsenoside Rb(1) and scored for growth and differentiation at the end of the culture period. RESULTS: Median total morphological scores in Embryos exposed to 30 micro g/ml of ginsenoside Rb(1) was significantly lower (P < 0.05) than that in control Embryos (35 versus 45). Morphological scores for flexion, forelimb and hindlimb were also significantly reduced. The median total morphological scores further decreased to 28 when the concentRation of ginsenoside Rb(1) was increased to 50 micro g/ml. At this concentRation, the Embryonic crown-rump length and somite number were also significantly reduced compared with control Embryos (2.8 versus 3.0 mm and 16.0 versus 21.0, respectively). CONCLUSIONS: Our study has demonstRated that ginsenoside exerts direct teRatogenic effects on Rat Embryos. Until more is known about the effects of ginsenoside in women of reproductive age, we suggest its use should be treated with caution.
-
an in vitro study of ginsenoside rb1 induced teRatogenicity using a whole Rat Embryo culture model
Human Reproduction, 2003Co-Authors: Louis Yiksi Chan, Pui Yu Chiu, Tze-kin LauAbstract:BACKGROUND Ginseng is a commonly used herbal medicine worldwide. However, there is limited information regarding its effects on the developing Embryo. METHODS The effect of ginsenoside on the developing Embryo during the critical period of organogenesis was investigated using a whole Rat Embryo culture model. Embryos were exposed to various concentRations of ginsenoside Rb(1) and scored for growth and differentiation at the end of the culture period. RESULTS Median total morphological scores in Embryos exposed to 30 micro g/ml of ginsenoside Rb(1) was significantly lower (P < 0.05) than that in control Embryos (35 versus 45). Morphological scores for flexion, forelimb and hindlimb were also significantly reduced. The median total morphological scores further decreased to 28 when the concentRation of ginsenoside Rb(1) was increased to 50 micro g/ml. At this concentRation, the Embryonic crown-rump length and somite number were also significantly reduced compared with control Embryos (2.8 versus 3.0 mm and 16.0 versus 21.0, respectively). CONCLUSIONS Our study has demonstRated that ginsenoside exerts direct teRatogenic effects on Rat Embryos. Until more is known about the effects of ginsenoside in women of reproductive age, we suggest its use should be treated with caution.
-
a study of diclofenac induced teRatogenicity during organogenesis using a whole Rat Embryo culture model
Human Reproduction, 2001Co-Authors: Louis Yiksi Chan, Pui Yu ChiuAbstract:BACKGROUND: Diclofenac is a non-steroidal anti-inflammatory drug, commonly used by reproductive age women for the treatment of a variety of conditions. However, there is limited information regarding the teRatogenic effects of this drug. METHODS: The effect of diclofenac on the developing Embryo during the critical period of organogenesis was investigated by using a whole Rat Embryo culture model. Embryos were exposed to various concentRations of diclofenac and scored for growth and differentiation at the end of the culture period. RESULTS: Total developmental score and score for caudal neural tube, flexion and hindlimb were significantly lower in Embryos exposed to high concentRations of diclofenac (7.5 and 15.0 microg/ml), but no difference in these parameters was observed when Embryos were exposed to low concentRation of diclofenac (1.5, 2.5 and 5.0 microg/ml). No significant differences in yolk sac diameter, crown-rump length and number of somites was found between Embryos in the experimental and the control group. CONCLUSIONS: Our study has demonstRated that diclofenac exerts direct teRatogenic effects on Rat Embryos. Until more is known about the effects of diclofenac (especially in modeRate to high doses) in women of reproductive age, we suggest its use should be treated with caution.
George Iliakis - One of the best experts on this subject based on the ideXlab platform.
-
Persistent Inhibition of DNA Synthesis in Irradiated Rat Embryo Fibroblasts Expressing the Oncogenes H-ras plus v-myc Derives from Inhibition of Replicon Initiation and Is Mitigated by Staurosporine
Cancer research, 1993Co-Authors: Ya Wang, Nge Cheong, George IliakisAbstract:We have previously shown that Rat Embryo fibroblasts expressing the oncogenes H- ras plus v- myc experience a prolonged inhibition of DNA replication after exposure to ionizing radiation as compared to normal Rat Embryo fibroblasts, or Rat Embryo fibroblasts expressing H- ras or v- myc alone. Here we show that this enhanced inhibition of DNA replication in cells expressing H- ras plus v- myc is due to inhibition of the main controlling event of DNA replication, i.e. , replicon initiation, that this inhibition is reversible, and that the expression of this phenotype is reverted by staurosporine, a protein kinase inhibitor. These findings implicate genetic influences in the processes that control DNA replication in irradiated cells and identify events in the regulation of DNA replication that become apparent several hours after irradiation. The products of the oncogenes H- ras and v- myc appear to be members of, or exert influence on, this controlling pathway.
-
Radioresistance induced in Rat Embryo cells by transfection with the oncogenes H-ras plus v-myc is cell cycle dependent and maximal during S and G2
International journal of radiation biology, 1993Co-Authors: Cheong N, Y. Wang, George IliakisAbstract:Rat Embryo cells (REC) transformed by the H-ras oncogene plus the coopeRating oncogene v-myc are highly resistant to ionizing radiation as compared with the non-transformed parent cells, REC, or immortalized REC. We inquired whether the phenotype of increased radioresistance is maximally expressed in certain phases of the cell cycle. We addressed this question by studying the fluctuations in radiosensitivity throughout the cycle in an H-ras plus v-myc transformed cell line (3·7), and an immortalized Rat Embryo cell line (MR). Cells synchronized in various phases of the cell cycle were produced using a combination of elutriation and chemical resynchronization with aphidicolin. The relative radioresistance of 3·7 cells, as compared with MR cells, varied throughout the cell cycle. The two cell lines had similar radiosensitivity when irradiated in G1, or at the G1/S border. However, 3·7 cells progressively developed radioresistance as they progressed into S and remained significantly more radioresistant durin...
-
Persistent Inhibition of DNA Synthesis after Radiation Exposure in Four Clones Obtained from Rat Embryo Fibroblasts by Transfection with the Oncogenes H-ras Plus V-myc
International journal of radiation biology, 1993Co-Authors: X. Wang, George IliakisAbstract:We have previously shown that two cell lines, 2.8 and 3.7, obtained from Rat Embryo fibroblasts (REF) by transfection with the oncogenes, H-ras plus v-myc, experience a prolonged inhibition of DNA replication after exposure to ionizing radiation as compared with normal REF, or REF expressing, H-ras or v-myc alone. We report here that four additional cell lines geneRated in our laboRatory by cotransfection of REF with the same oncogenes also show prolonged inhibition of DNA replication after radiation exposure. These results indicate a regulatory mechanism for DNA replication in irradiated REF in which the products of the oncogenes H-ras and v-myc have a central role.
-
Prolonged inhibition by X-rays of DNA synthesis in cells obtained by transformation of primary Rat Embryo fibroblasts with oncogenes H-ras and v-myc.
Cancer research, 1992Co-Authors: Ya Wang, George IliakisAbstract:Transfection of primary Rat Embryo fibroblasts with the H- ras oncogene plus the coopeRating oncogene v- myc results in the development of foci of morphologically altered tumorigenic cells. We examined radiation (X-rays) induced inhibition of DNA synthesis in cell lines derived from such transformed clones and compared the results to those obtained with the nontransformed parental cells, Rat Embryo fibroblasts, as well as with cells immortalized either spontaneously, or after transfection with nuclear oncogenes (v- myc , E1A ). Inhibition by X-rays of DNA synthesis was higher and persisted for longer periods of time in the H- ras - plus v- myc -transformed cell lines as compared to their nontransformed counterparts. When the Rate of DNA synthesis was measured as a function of dose 3 h after irradiation, biphasic curves were observed in all cell lines tested with a radiation sensitive and a radiation resistant component, known to correspond to inhibition of replicon initiation and chain elongation, respectively. A substantially larger inhibition of DNA synthesis was observed between 0 and 30 Gy in H- ras - plus v- myc -transformed cell lines, as compared to their nontransformed counterparts, presumably caused by sustained inhibition of replicon initiation. Hypersensitive DNA synthesis to X-rays was also observed in a transformed cell line obtained by transfection of Rat Embryo fibroblasts with H- ras in coopeRation with the oncogene E1A , but normosensitive DNA synthesis in a rare transformant obtained by transfection with H- ras alone. These results suggest a direct or indirect involvement of the oncogene H- ras in coopeRation with the oncogene v- myc (or other nuclear oncogenes such as E1A ) in the control of DNA synthesis in irradiated cells. This control of DNA synthesis may be mediated via a trans -acting mechanism that involves the production of a diffusible factor in response to the radiation insult, or, by a cis -acting mechanism that directly affects the replication machinery. Circumstantial evidence for possible involvement of oncogenes of the ras and myc families in DNA synthesis support this hypothesis. There was an inverse correlation between sensitivity to radiation-induced killing and prolonged inhibition by radiation of DNA synthesis, with radioresistant cell lines displaying longer inhibition of DNA synthesis. However, inhibition by radiation of DNA synthesis was similar in normal human fibroblasts (W138) and cells derived from a radiation-resistant human carcinoma cell line (SQ-20B) suspected to carry an abnormal c- raf -1 oncogene. In addition, inhibition of DNA synthesis in SQ20B cells was similar to that of SCC61 cells, a radiation-sensitive cell line derived from a carcinoma of the tongue.
