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Biomedical subjects

N C Popescu

Publications and source records attributed to N C Popescu.

At least 127 records · Page 7Linked to original sources
PubMed1987

Integration sites of human papillomavirus 18 DNA sequences on HeLa cell chromosomes.

Human papillomaviruses (HPV) 16 and 18 are closely linked with human genital cancer. In most cervical carcinomas, viral sequences are integrated into the host genome. HeLa, a cervical carcinoma cell line, has multiple copies of integrated HPV 18 DNA. In this study, in situ chromosome hybridization was used to assign the integration sites of HPV 18 DNA sequences on HeLa cell chromosomes. Four sites of hybridization were identified at 8q23----q24, 9q31----q34, p11----p13 on an abnormal chromosome 5, and q12----q13 on an abnormal 22. Three of these sites correspond with the locations of MYC, ABL, and SIS protooncogenes, and are at or in close proximity to fragile sites. The chromosomal localization of HPV 18 DNA may be useful in assessing the role of viral integration in the development of this malignancy.

Chromosome Banding↗
PubMed1986

A novel human gene closely related to the abl proto-oncogene.

A DNA sequence related to the abl proto-oncogene was identified in human placenta. Molecular cloning and nucleotide sequence analysis revealed two putative exons whose predicted amino acid sequence was most homologous to the corresponding sequences of c-abl and v-abl but was related to other tyrosine kinase genes as well. The new sequence was localized by in situ hybridization and somatic cell genetic analysis to human chromosome 1q24-25, which differs from the location of any previously identified tyrosine kinase gene. The detection of a novel 12-kb transcript by this gene in human normal and tumor cells establishes it as a new member of the tyrosine kinase family that is closely related to but distinct from c-abl.

Amino Acid Sequence↗
PubMed1986

Chromosome distribution of intracisternal A-particle sequences in the Syrian hamster and mouse.

Metaphase chromosomes of Syrian hamster and BALB/c mice were hybridized in situ with radiolabeled probes derived from cloned intracisternal A-particle (IAP) genes of the corresponding species. The DNAs of these species are known to contain about 900 and 1,000 copies, respectively, of the retrovirus-like IAP sequence elements per haploid genome. Multiple IAP sequences were found on all chromosomes of both hamster and mouse. In the hamster, more than half of the IAP sequences were located in regions of non-centromeric constitutive heterochromatin, at an average concentration per unit chromosome length 5 times greater than in the euchromatic regions. The other dispersed sequences showed marked local variations in concentration along the chromosome lengths; both discrete foci and large grain clusters were observed as well as regions apparently lacking IAP sequences. Within the resolution of the techniques, IAP sequences appeared to be more evenly distributed over the mouse chromosomes; however, some prominent variations in concentration were seen. The number of potentially active IAP genes in the Syrian hamster, and by extension in the mouse, may be restricted by the preferential location of IAP sequences in genetically inert regions of the genome.

Animals↗
PubMed1986

In vitro models for studying the molecular biology of carcinogenesis.

Although carcinogens cause various similar deleterious effects on rodent and human cells, only rodent cells can convert to malignancy in a quantitative, predictable fashion. Therefore, the control mechanisms involving indefinite proliferation and tumorigenicity are different. Human cell lines may exhibit normal or aneuploid chromosome constitutions with numerical or structural alterations frequently involving proto-oncogene loci, but fail to produce progressively growing tumors in nude mice. A new approach for obtaining human cells susceptible to malignant transformation by chemical or physical carcinogens is to use DNA from a cancer associated virus. Transfection of human papilloma virus (HPV) DNA associated with genital cancer can extend life-span of human cells; post-X-irradiated cells grow in agar suspension. Southern blot analysis of extracted DNA indicates that HPV sequences persist. Similar results are obtained with human fibroblast and epithelial cells.

Animals↗
PubMed1986

Expression and chromosomal localization of the cytochrome P1-450 gene in human mitogen-stimulated lymphocytes.

Genetic differences in aryl hydrocarbon hydroxylase (AHH) (flavoprotein-linked monoxygenase EC 1.14.14.1) activity in cultured lymphocytes have been linked with individual risk for certain environmentally caused cancers. Cytochrome P1-450 is the form of cytochrome P-450 most closely associated with AHH activity. In this study the chromosomal localization and the expression of human cytochrome P1-450 gene were determined in phytohemagglutinin-stimulated lymphocytes. In situ hybridization analysis provides assignment of the structural gene for human cytochrome P1-450 to chromosome 15q22-q24. Treatment of lymphocytes with benzanthracene increased the amount of mRNA hybridized to the cloned cytochrome P1-450 gene. The level of cytochrome P1-450 mRNA in these lymphocytes correlates well with the induced AHH activity indicating that non-cytochrome P1-450 enzymes contribute little to the individual differences in the level of AHH activity in the lymphocytes. Southern analyses of genomic DNA from individuals with high and low induced AHH activity demonstrated no detectable differences in the pattern or intensity of restriction fragments after treatment with benzanthracene from either individual. This finding together with the excellent correlation between the induced cytochrome P1-450 and AHH activity, suggests that transcriptional control rather than gene amplification or gross form of gene rearrangement accounts for cytochrome P1-450 induction in man. Measurements of cytochrome P1-450 mRNA content in cultured lymphocytes provide an alternative approach to the assay of AHH activity in assessing AHH phenotype and predicting different susceptibilities to deleterious environmental agents.

Aryl Hydrocarbon Hydroxylases↗
PubMed1986

Chromosome alterations associated with in vitro exposure of human fibroblasts to chemical or physical carcinogens.

Normal human foreskin fibroblasts treated in vitro with a chemical carcinogen or irradiated with ultraviolet light subsequently acquired anchorage independent growth and an extended but finite capacity for exponential growth. All cell lines were derived from cells recovered from colonies that had grown in semisolid medium; cell lines originally treated with a chemical carcinogen produced nodules after s.c. inoculation into nude mice. G-banding analysis of 10 cell lines (including one ultraviolet light line) revealed that seven were chromosomally abnormal with structural and numerical chromosome alterations, one was characterized by a consistent trisomy, and the other two were normal diploid. Structural alterations consisted of chromosome deletions, translocations, and partial chromosome duplications. Although no common structural or numerical abnormality was detected, several structural alterations were observed involving chromosomes 1, 7, 11, and 22, where fgr, erb-B, H-ras-1, and sis protooncogenes, respectively, are located. In one cell line trisomy 17 was a unique chromosome alteration. The induction of chromosome changes may have influenced the proliferative capacity of the treated cells relative to nontreated cells. However, the two cell lines without detectable chromosome changes also had an increased proliferative life span, suggesting that other submicroscopic genetic alterations may have affected cell multiplication. Although carcinogen induced chromosome abnormalities may represent a step in the process of neoplastic development, additional genetic and/or epigenetic changes, are required for indefinite growth and the expression of malignancy.

Carcinogens↗
PubMed1985

Chromosomal localization of three human ras genes by in situ molecular hybridization.

Three human ras family protooncogenes, c-Ki-ras-1, and c-Ki-ras-2, and N-ras, have been mapped to chromosome bands 6p11-12, 12p11.1-12.1, and 1p11-13, respectively by in situ molecular hybridization. Certain human cancers display consistent and specific alterations involving chromosomes 1, 6, and 12. The precise chromosomal localization of ras genes will permit evaluation of the possible effect of these chromosome changes on the structure and activities of ras protooncogenes in human neoplasia.

Chromosome Mapping↗
PubMed1985

Isolation and chromosomal localization of the human fgr protooncogene, a distinct member of the tyrosine kinase gene family.

The cell-derived domain of Gardner-Rasheed feline sarcoma virus (GR-FeSV) consists of a gamma-actin- and a tyrosine-specific protein kinase-encoding sequence designated v-fgr. By utilizing a v-fgr probe, it was possible to detect related sequences present at low copy number in DNAs of a variety of mammalian species and to isolate a human fgr homologue. Comparative studies revealed that this human DNA clone represented all but 200 base pairs of v-fgr. Analysis of human genomic DNA demonstrated that the fgr protooncogene was distinct from the cellular homologues of other retrovirus onc genes. In addition, the fgr protooncogene was localized to the distal portion of the short arm of human chromosome 1 at p36.1-36.2 by in situ hybridization. Taken together, our findings establish that the fgr protooncogene is a unique member of the tyrosine kinase gene family.

Actins↗
PubMed1985

Persistence of sister chromatid exchanges and in vitro morphological transformation of Syrian hamster fetal cells by chemical and physical carcinogens.

The induction of neoplastic cell transformation is closely associated with DNA alterations which occur shortly after carcinogen exposure. Sister chromatid exchange (SCE) formation is a sensitive indicator of carcinogen-DNA interaction and correlates with the induction of morphological cell transformation. The persistence of lesions generating SCE produced by chemical and physical carcinogens and its relevance to the induction of morphologic transformation was evaluated in coordinated experiments with cultured Syrian hamster fetal cells (HFC). Exponentially growing HFC were exposed for 1 h to benzo[a]pyrene (BP), methyl-methanesulfonate (MMS), cis-platinum (II) diaminedichloride (cis Pt II), N-methyl-N'-nitrosourea (MNU), mitomycin C (MMC), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), N-acetoxy-2-fluorenyl-acetamide (AcAAF) or u.v. light irradiated. Cells were incubated for 24 h with 5-bromodeoxyuridine (BrdUrd) required for SCE visualization at 1, 24 and 48 h after carcinogen exposure. The induction of morphological transformation was determined on the quantitative colony assay at 6 days after carcinogen treatment. SCE analysis demonstrates that for a period of 48 h after carcinogen exposure, during which time the cells undergo at least four replicative cycles, DNA damage generating SCE induced by all chemical carcinogens either persisted or was partially removed, whereas u.v.-induced lesions were completely removed. An elevated SCE frequency persisted after two additional cell cycles after treatment with BP, AcAAF or MMC without increased cell lethality as compared to other carcinogens whose lesions were completely eliminated during the same period. Although a correlation between the persistence of SCE and the induction of transformation was not observed for all carcinogens, this study illustrates that DNA damage generating SCE can persist over several replicative cycles, thus raising the possibility that lasting DNA alterations are important for the induction of neoplastic cell transformation.

Animals↗
PubMed1985

Induction of chromosome banding by trypsin/EDTA for gene mapping by in situ hybridization.

We describe an easy and reproducible procedure that utilizes trypsin/EDTA for the induction of chromosome banding in conjunction with in situ hybridization. The high quality banding resolution required for grain localization is obtained on both elongated and contracted chromosomes derived from synchronized or nonsynchronized human lymphocytes or fibroblasts. This procedure can also be useful for gene localization on chromosomes from cancer cells.

Cells, Cultured↗
PubMed1985

Enhancement and inhibition of transformation of Syrian hamster embryo cells.

Diploid Syrian hamster embryo cells are particularly appropriate for the study of the transformation phenomenon in target cells. In vitro morphologic transformation occurs in a dose-dependent manner and is characterized by random crisscrossing and piling of cells; it correlates with tumorigenicity because individually transformed cell colonies can be isolated, cell lines can be developed, and the formation of tumors can be demonstrated after the injection of the transformed cells into either Syrian hamsters or athymic nude mice. HEC can also be used to investigate stages of carcinogenesis, initiation, and promotion. The susceptibility of normal HEC to transformation by environmental carcinogens including asbestos, bisulfite, nitrated non-carcinogenic polycyclic hydrocarbons, and X- or ultraviolet irradiation has made possible the determination of a variety of cell responses as they proceed to the neoplastic state. The initiation is usually a hereditary process involving single-hit kinetics and the transformation data indicate there is no measurable threshold response to carcinogens. The promotional aspects of transformation are readily modulated by environmental factors and have a threshold, as well as a maximal effect. The results of transformation studies using hamster cells indicate that in vitro studies are relevant to carcinogenesis and indicate that the various steps involved can be identified. Therefore, it should be possible to intervene with the various stages or steps leading to neoplasia so that cancer can be prevented.

Animals↗
PubMed1984

Modulation of radiation induced transformation by combinations of a phorbol diester and a lymphotoxin.

The susceptibility of normal Syrian hamster embryo cells to transformation by environmental carcinogens has made possible the determination of a variety of responses as cells proceed to the neoplastic state. Expression of the initiated and promoted stages of irradiation carcinogenesis, for example, can be modified by cell surface alterations. Phytohemagglutin (PHA) or its isolectins decrease 12-O-tetradecanolphorbal-13-acetate (TPA) promoted transformation whereas PHA does not affect carcinogen only induced transformation. In contrast, both initiated and promoted transformation are sensitive to hamster lymphotoxin, a hormone-like, non-antibody lymphocyte glycoprotein. A 48 hr lymphotoxin treatment before or immediately after X-irradiation, or during TPA exposure causes a persistent inhibition independent of when carcinogen was added. A 6 hr lymphotoxin pulse before irradiation and TPA causes a persistent but nonpermanent effect unless followed by the carcinogen treatment; lymphotoxin becomes more potent as the interval between the lymphotoxin pulse and carcinogen insult or TPA addition is reduced. PHA and lymphotoxin affect the biological activity of TPA by diverse mechanisms. PHA may alter either the binding of TPA to a critical cellular receptor for promotion or alter a later step in promotion. Lymphotoxin can prevent the initiation of transformation and modulate carcinogenesis as well at both initiated and promoted stages in the transition to the neoplastic state.

Animals↗
PubMed1984

Correlation of morphological transformation to sister chromatid exchanges induced by split doses of chemical or physical carcinogens on cultured Syrian hamster cells.

The relationship between the induction of DNA damage as reflected by sister chromatid exchange (SCE) formation and morphological transformation in exponentially growing Syrian hamster embryo cells was determined quantitatively after split doses of chemical or physical carcinogens. With split doses of carcinogen separated by 2 to 24 hr, only N-acetoxy-2-fluorenyl-acetamide (0.50 microgram/ml) enhanced both SCE induction and transformation when compared to single exposure. Split doses of N-methyl-N'-nitro-N- nitrosoguanidine (0.20 microgram/ml), mitomycin C (50 ng/ml), or ultraviolet light (3.0 J/sq m) were less effective than single exposures, while split doses of methyl methanesulfonate (40 micrograms/ml) caused transformation frequencies similar to a single treatment and decreased SCE frequencies with time intervals greater than 4 hr. Split or single exposures of X-irradiation (200 R) resulted in similar low frequencies of transformation and SCE. Contrasting with these results, a significant potentiation of SCE occurred after split doses of N-methyl-N'-nitro-N-nitrosoguanidine in cultures arrested in G1 with arginine-glutamine-deficient medium or by contact inhibition compared to a single treatment. This response was attributed to the interaction of carcinogen with DNA containing unrepaired damage and demonstrates the importance of the cell cycle phase of the target cell during carcinogen exposure for the induction of SCE by split doses of N-methyl-N'-nitro-N-nitrosoguanidine. The similarity of responses for transformation and SCE induction with split doses of carcinogens suggests that DNA lesions involved in SCE are essential for the initiation of neoplastic development.

Animals↗
PubMed1983

Transformation of Bloom's syndrome fibroblasts by DNA transfection.

Nonmalignant diploid human fibroblast cells (GM3498B) derived from a skin biopsy of a patient with Bloom's syndrome have been transformed by transfection with DNA from a tumorigenic mouse cell line (Ha-8) carrying a single copy of the Harvey murine sarcoma virus (Ha-MuSV) genome. The transformed cell lines have an extended life-span, form colonies in agarose, and proliferate in nude mice--characteristics of neoplastic transformation. Like the parental cells, they also exhibit a high spontaneous level of sister chromatid exchanges. Finally, the transformed cells contain most, if not all, of the Ha-MuSV genome as well as the human rasH sequence. These experiments show that these diploid nonmalignant human cells can be used as recipients in transfection experiments for studying the genetic control of neoplastic transformation.

Bloom Syndrome↗
PubMed1983

Human and rodent transformed cells are more sensitive to in vitro induction of SCE by N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) than normal cells.

The sensitivity to sister chromatid exchange (SCE) induction by N-methyl-nitro-N'-nitrosoguanidine (MNNG) in human, mouse, Chinese hamster, and Syrian hamster normal cell strains and in permanent transformed cell lines of the same species was compared. Exponentially growing or growth-inhibited cultures of permanent cell lines transformed spontaneously or by chemical carcinogen or oncogenic virus responded with a higher SCE frequency after MNNG treatment than did normal diploid cell strains. Compared with the normals, exponentially growing Simian virus 40 transformed human fibroblast GM637 had the highest SCE frequency, followed by mouse cell line alpha L929 and Chinese hamster V79-4; the least sensitive were two Syrian hamster cell lines, OBP, derived from transformation of embryo cells with benzo(a)pyrene, and BHK, a spontaneously transformed baby hamster kidney line. Similar results were obtained with cultures arrested in G1 with glutamine-arginine deficient medium. The SCE response observed with transformed cells to carcinogen probably reflects cellular changes associated with the transformed state, such as shortening of the cell cycle, excision repair deficiency, or an increase in DNA replicon size. The current results demonstrating a difference in SCE induction between normal and malignant cells are important since normal or transformed cultured cells are utilized to assess potentially deleterious environmental agents, particularly carcinogens. In general, SCE induction by a specific direct acting carcinogen may be a useful approach for identifying transformed cells with the ability to produce tumors.

Animals↗