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J C Barrett

Publications and source records attributed to J C Barrett.

At least 289 records · Page 16Linked to original sources
PubMed1988

Cytogenetic changes in rat tracheal epithelial cells during early stages of carcinogen-induced neoplastic progression.

The cytogenetic changes in enhanced growth (EG) variants of rat tracheal epithelial cells in culture were examined. These variants which are detectable at 35 days after carcinogen exposure are the first phenotypic alteration in the multistep neoplastic process studied in this model system. Karyotypic analysis of N-methyl-N'-nitro-N-nitrosoguanidine-induced EG variants at Day 35 was made possible by the development of an in situ method of cytogenetic analysis on intact colonies containing too few cells for conventional chromosome preparation methods. Of the transformed EG variant colonies in both control and N-methyl-N'-nitro-N-nitrosoguanidine-treated groups, 62-78% had abnormal karyotypes which included numerical and structural changes. There were no specific chromosome changes, although aberrations of chromosomes 3 and 4 were recurrently observed. However, some colonies of even the most morphologically transformed EG variants were composed of only diploid cells. To confirm this finding 10 EG variant colonies were bisected and half of the clone was prepared for chromosome analysis and the other half was subcultured to measure the clonogenicity and karyotypes of the cells. Cells from 3 colonies plated very poorly on 3T3 feeders and therefore no karyotypic analysis of the colony-forming cells was possible; the cells of the 3 parental colonies were diploid. Three other parental colonies were predominantly diploid (80-90%) but upon replating the resultant daughter colonies had progressively smaller fractions of diploid cells indicating a selection for cells with abnormal karyotypes. When more selective conditions were used (i.e., growth after removal of the feeder cells), the percentage of abnormal cells increased even further. In one case the parental cells had a karyotypic alteration in the long arm of chromosome 4 and this karyotypic alteration was accentuated in the daughter colonies. Thus, selection of cells with increased growth ability upon subculturing or growth in the absence of feeder cells (properties associated with the acquisition of immortality) resulted in concomitant selection for cells with abnormal karyotypes. Since some of the carcinogen-induced rat tracheal epithelial cells expressing the EG variant phenotype were diploid, it is possible that the first step in this transformation process is an epigenetic change. However, most of the diploid cells became terminal. The aneuploid subpopulations present in these colonies have a selective growth advantage and comprise the cell compartment that expresses continued growth, immortality, and ultimately tumorigenicity.

Aneuploidy↗
PubMed1988

Monte Carlo simulation of the heterosexual selective spread of the human immunodeficiency virus.

The spread of human immunodeficiency virus (HIV) by heterosexual intercourse, during the first 2 years following the introduction of the virus among a sexually active and unprotected group of men and women, is modelled by Monte Carlo simulation. A beta distribution of the infectee's risks of infection per infected partner-month is assumed, with the same coefficient of variation as used in previous studies for risk of conception (natural fecundability), but with a mean of 0.04 per infected partner-month, after scaling the distribution. The number of sexual partners that one sex has (here, the women), is assumed to be more variable than for the other, with a mean of 2 partners each. The individual infection risks per infected partner-month are generated initially and do not change, but some random gains and losses of partners occur each month. Infections are updated each month. It is found in this simple model that women who become infected by 2 years had a mean risk of infection (not counting the original infector) only about 13% higher than the others. Some implications of the low selection are noted. Very great variability in the number of infections subsequently due to an index seropositive is found, which prevents easy discrimination in the characteristics of "at-risk" persons.

Acquired Immunodeficiency Syndrome↗
PubMed1988

Characterization of activated proto-oncogenes in chemically transformed Syrian hamster embryo cells.

The Syrian hamster embryo (SHE) cell transformation model has been used by many investigators to study the multistep process of neoplastic transformation induced by chemical carcinogens. In this study we have attempted to determine if activated proto-oncogenes are present in the transformed cells induced by a variety of chemical carcinogens. Twelve carcinogen-induced hamster cell lines, established by treatment of normal SHE cells with benzo[a]pyrene, diethylstilbestrol, or asbestos, were examined. One spontaneously transformed cell line (BHK-A) was also studied. Some of the cell lines were also tested for oncogene activation at the preneoplastic stage, before they acquired tumorigenic potential. DNAs from normal, preneoplastic, and neoplastic cells were tested by transfection into mouse NIH 3T3 cells, and morphologically transformed foci were scored on the contact-inhibited monolayer of 3T3 cells. The frequency of focus formation for normal SHE cell DNA was less than 0.0008 foci/microgram DNA, while approximately 40% (5 of 12) of the DNAs from carcinogen-induced, tumorigenic hamster cell lines induced foci at a frequency of greater than or equal to 0.012 foci/microgram DNA. The other seven carcinogen-induced cell lines and the BHK-A cells were negative (less than 0.002 foci/microgram DNA). When the DNAs from transformed foci induced by the five positive cell lines were retransfected into NIH 3T3 cells, the frequency of secondary foci of 3T3 cells was as much as 50-fold higher (1.34 foci/microgram DNA) than with the primary transfectants. DNAs from transformed foci or tumors derived from transformed foci were screened by Southern blot analyses with known oncogenes and with a hamster repetitive DNA probe for the presence of transfected hamster oncogenes.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Correlation of V-src gene amplification with the tumorigenic phenotype in a Syrian hamster embryo cell line.

A preneoplastic cell line (10W) isolated after treatment of Syrian hamster embryo cells with asbestos was cotransfected with pSV2-neo DNA and Rous sarcoma virus DNA. Six of these colonies contained v-src DNA; however, none of the six initially expressed v-src RNA. Five of the clones failed to grow in soft agar (frequency, less than 10(-6)). One clone (61) grew in soft agar, but with a low frequency. Three of the clones (41, 61, and 62) were tumorigenic in nude mice and three were nontumorigenic. Cells cloned from soft agar or established from tumor explants expressed the v-src gene. The gene copy number of v-src, which was three to 10 in the original neoR clones, was increased approximately 10-fold in the soft agar-derived cell clones and tumor-derived cell lines. Cytogenetic analyses indicated that cells with amplified v-src contained double minute chromosomes. The results suggest that gene amplification influences the expression of the transfected oncogene and is a mechanism which can overcome the initial suppression of transcription of the v-src oncogene in the 10W cell line.

Animals↗
PubMed1987

A National Institutes of Health Workshop Report. Cellular and molecular mechanisms for suppression and reversion of tumorigenicity. A Chemical Pathology Study Section workshop.

A workshop organized by the Chemical Pathology Study Section was convened to discuss recent findings on the suppression and/or reversal of neoplastic transformation. The existence of specific genes involved in suppressing tumorigenicity has been clearly demonstrated by molecular and cytogenetic analyses of tumor and normal cells from individuals predisposed to develop specific malignancies and by studies of hybrids between normal and neoplastic cells. The malignancy of tumor cells can be suppressed in hybrids with normal cells despite the continued expression of activated oncogenes. Reversal of the malignant state can also be affected by placing tumor cells in certain embryonic environments, such as the mouse blastocyst, or in response to differentiation inducing factors. The numerous examples of suppression and reversal of malignancy indicate that this is an important area for future study which may lead to new methods to control cancer.

Animals↗
PubMed1987

Expression of a fms-related oncogene in carcinogen-induced neoplastic epithelial cells.

Following carcinogen exposure in vitro, normal rat tracheal epithelial cells are transformed in a multistage process in which the cultured cells become immortal and, ultimately, neoplastic. Five cell lines derived from tumors produced by neoplastically transformed rat tracheal epithelial cells were examined for the expression of 11 cellular oncogenes previously implicated in pulmonary or epithelial carcinogenesis. RNA homologous to fms was expressed at a level 5-19 times higher than normal tracheal epithelial cells in three of five of the tumor-derived lines. All three lines expressing high levels of fms-related RNA gave rise to invasive tumors of epithelial origin when injected into nude mice. Increased expression of the fms-related mRNA was not due to gene amplification, and no gene rearrangement was detected by Southern analyses. RNA blot analysis using a 3' v-fms probe detected a 9.5-kilobase message in the three tumor-derived lines, whereas both normal rat alveolar macrophages and the human choriocarcinoma line BeWo expressed a fms transcript of approximately 4 kilobases. We conclude from these data that the gene expressed as a 9.5-kilobase transcript in these neoplastic epithelial cells is a member of a fms-related gene family but may be distinct from the gene that encodes the macrophage colony-stimulating factor (CSF-1) receptor.

Animals↗
PubMed1987

Chromosome aberrations in mouse bone marrow cells following in vivo exposure to 1,3-butadiene.

Chronic exposure to 1,3-butadiene (BD) results in a marked increase in the incidence of thymic lymphoma in male B6C3F1 relative to NIH Swiss mice whereas no demonstrable differences in bone marrow (target organ) toxicity exist. Repeated exposure to BD is known to produce a macrocytic anemia and an increase in the frequency of micronuclei in circulating erythrocytes in both strains. The present study was undertaken to determine if chromosomal breakage, aneuploidy or both reflect differences in BD leukemogenicity observed between B6C3F1 and NIH Swiss mice. Mice were exposed to a single concentration of BD (1250 p.p.m.) for 6 h. Bone marrow cell preparations were made at 24, 48, 72 and 96 h after cessation of exposure. In both strains comparable increases in the frequency of chromosomal aberrations (of the chromatid type) were observed following exposure to BD. Significant differences in the number of chromosomes were not observed, although a pattern of chromosomal loss in cells from treated animals was observed. These results indicate that BD-treatment in vivo produces significant increases in chromatid aberrations but not aneuploidy in both strains. Therefore it is concluded that bone marrow toxicity, including cytogenetic abnormalities, is not predictive of leukemogenicity in these mice.

Animals↗
PubMed1987

17beta-Estradiol-induced cell transformation and aneuploidy of Syrian hamster embryo cells in culture.

The ability of 17 beta-estradiol to induce morphological transformation of Syrian hamster embryo cells was examined and dose-dependent increases were observed over the concentration range of 1-10 micrograms/ml. However, treatment of the cells with 17 beta-estradiol failed to induce any detectable increases in gene mutations, chromosome aberrations, sister chromatid exchanges or unscheduled DNA synthesis. In contrast, over the dose range that was effective in inducing cell transformation, 17 beta-estradiol induced numerical chromosome changes (both chromosome gains and losses). These findings are similar to the reported observations with the synthetic estrogen, diethylstilbestrol, and support the hypothesis that aneuploidy induction is important in cell transformation and possibly carcinogenesis induced by estrogens.

Aneuploidy↗
PubMed1987

In vitro analysis of multistage carcinogenesis.

Several key events in the multistep process of neoplastic transformation of rat tracheal epithelium (RTE) are described. Whether tracheal epithelium is exposed in vivo to carcinogenic agents or whether primary tracheal epithelial cells are exposed in vitro to carcinogens, initiated stem cells can be detected soon after the exposure by their ability to grow under selective conditions in culture. These initiated stem cells differ fundamentally from normal stem cells in their response to factors normally constraining proliferation and self-renewal. Thus, disruption of inhibitory control mechanisms of stem cell replication appears to be the first event in RTE cell transformation. While the probability of self-renewal (PSR) is clearly increased in initiated stem cells, most of the descendants derived from such stem cells differentiate and become terminal and do not express transformed characteristics. Progression from the first to the second stage of RTE cell transformation, the stage of the immortal growth variant (IGV), is characterized by loss of responsiveness to the growth-restraining effects of retinoic acid. In the third stage of neoplastic transformation, the stage during which neoplastic growth variants (NGV) appear, a growth factor receptor gene is inappropriately expressed in some of the transformants. Thus, it appears that loss of growth-restraining mechanisms may be an early event, and activation of a growth stimulatory mechanism a late event, in neoplastic transformation of RTE cells.

Animals↗
PubMed1987

Cellular and molecular mechanisms of multistep carcinogenesis: relevance to carcinogen risk assessment.

Carcinogenesis is a multistep process involving alterations in at least two distinct classes of genes. Protooncogenes are activated qualitatively or quantitatively in certain tumors, and they appear to act as positive proliferative signals for neoplastic growth. In contrast, tumor suppressor genes are normal genes that must be inactivated or lost for tumor development. When active, tumor suppressor genes control neoplastic growth in a negative manner. Chemicals may influence the carcinogenic process by mutational activation of protooncogenes and/or inactivation of tumor suppressor genes. The types of genetic alterations involved in these mutational events are diverse, and their dose-response curves may be varied. In addition, chemical carcinogens may act on nonmutational processes such as the clonal expansion of premalignant cells. The carcinogenic risk of a specific chemical is a composite of its effects on multiple genetic and epigenetic processes.

Animals↗
PubMed1986

Chemically induced aneuploidy in mammalian cells: mechanisms and biological significance in cancer.

A growing body of evidence from human and animal cancer cytogenetics indicates that aneuploidy is an important chromosome change in carcinogenesis. Aneuploidy may be associated with a primary event of carcinogenesis in some cancers and a later change in other tumors. Evidence from in vitro cell transformation studies supports the idea that aneuploidy has a direct effect on the conversion of a normal cell to a preneoplastic or malignant cell. Induction of an aneuploid state in a preneoplastic or neoplastic cell could have any of the following four biological effects: a change in gene dosage, a change in gene balance, expression of a recessive mutation, or a change in genetic instability (which could secondarily lead to neoplasia). To understand the role of aneuploidy in carcinogenesis, cellular and molecular studies coupled with the cytogenetic studies will be required. There are a number of possible mechanisms by which chemicals might induce aneuploidy, including effects on microtubules, damage to essential elements for chromosome function (ie, centromeres, origins of replication, and telomeres), reduction in chromosome condensation or pairing, induction of chromosome interchanges, unresolved recombination structures, increased chromosome stickiness, damage to centrioles, impairment of chromosome alignment, ionic alterations during mitosis, damage to the nuclear membrane, and a physical disruption of chromosome segregation. Therefore, a number of different targets exist for chemically induced aneuploidy. Because the ability of certain chemicals to induce aneuploidy differs between mammalian cells and lower eukaryotic cells, it is important to study the mechanisms of aneuploidy induction in mammalian cells and to use mammalian cells in assays for potential aneuploidogens (chemicals that induce aneuploidy). Despite the wide use of mammalian cells for studying chemically induced mutagenesis and chromosome breakage, aneuploidy studies with mammalian cells are limited. The lack of a genetic assay with mammalian cells for aneuploidy is a serious limitation in these studies.

Aneuploidy↗
PubMed1986

An early, nonrandom karyotypic change in immortal Syrian hamster cell lines transformed by asbestos: trisomy of chromosome 11.

Cytogenetic studies were performed on eight early passage Syrian hamster embryo cell lines independently derived following asbestos exposure. The modal chromosome number of all the immortal cell lines was near-diploid. At the earliest passage examined, six of eight cell lines had only numerical chromosome changes. Cells in each of these six cell lines had an extra chromosome #11, either as a sole karyotypic change or with other numerical changes. The remaining two cell lines displayed both numerical and structural chromosome changes, but without involvement of chromosome #11. Common abnormalities were -X or -Y, +3, and 8p- in one cell line, and -13 and t(13;21) in the other cell line. A nonrandom gain of chromosome #8 was also found in four cell lines. In three of the four cell lines, trisomy of chromosome #8 seems to have occurred during karyotypic progression. The observation that nonrandom changes in chromosome number are an early karyotypic change after carcinogen treatment supports our hypothesis that induction of aneuploidy by asbestos is mechanistically important in the transformation of Syrian hamster embryo cells in culture and, further, suggests that trisomy 11 plays a major role in the early steps of immortalization and neoplastic progression.

Animals↗
PubMed1986

Loss of tumor-suppressive function during chemically induced neoplastic progression of Syrian hamster embryo cells.

Cell hybrids between normal, early-passage Syrian hamster embryo cells and a highly tumorigenic, chemically transformed hamster cell line, BP6T, were formed, selected, and analyzed. Tumorigenicity and anchorage-independent growth were suppressed in the hybrid cells compared to the tumorigenic BP6T cells. These two phenotypes segregated coordinately in these cells. To determine at what stage in the neoplastic process this tumor-suppressive function was lost, two chemically induced immortal cell lines were examined at different passages for the ability to suppress the tumorigenic phenotype of BP6T cells following hybridization. Hybrids of BP6T cells with the immortal, nontumorigenic cell lines at early passages were suppressed for tumorigenicity and anchorage-independent growth. This tumor-suppressive ability was reduced in the same cells at later passages and in some cases nearly completely lost, prior to the neoplastic transformation of the immortal cell lines. Subclones of the cell lines were heterogeneous in their ability to suppress tumorigenicity in cell hybrids; some clones retained the tumor-suppressive ability and others lost this function. The susceptibility to neoplastic transformation of these cells following DNA transfection with the viral ras oncogene or BP6T DNA inversely correlated with the tumor-suppressive ability of the cells. These results suggest that chemically induced neoplastic progression of Syrian hamster embryo cells involves at least three steps: induction of immortality, activation of a transforming oncogene, and loss of a tumor-suppressive function.

Animals↗
PubMed1986

Vincristine sulfate-induced cell transformation, mitotic inhibition and aneuploidy in cultured Syrian hamster embryo cells.

Vincristine, a naturally occurring Vinca alkaloid and widely used anti-neoplastic agent, was examined for its ability to induce cell transformation, inhibition of growth and mitosis, and genetic effects in Syrian hamster embryo cells in culture. Treatment of the cells with doses of less than or equal to 1 ng/ml vincristine sulfate (VCR) had no effect on cell growth, while exposure to greater than or equal to 3 ng/ml reduced the growth rate and treatment with 30 ng/ml resulted in no detectable increase in cell number. At this latter dose the mitotic index of the cells increased significantly suggesting that VCR delayed completion of mitosis. Exposure of the cells to VCR at doses of 1-10 ng/ml for 48 h resulted in morphological transformation of the cells in a doserelated fashion. The vincristine-treated transformed colonies were morphologically indistinguishable from colonies transformed by benzo[a]pyrene or other chemical carcinogens. Morphological transformation was induced by VCR at non-toxic and slightly toxic doses as measured by a reduction in colony-forming ability of the treated cells. Over the dose range which resulted in cell transformation, VCR failed to induce either detectable gene mutations at two genetic loci, unscheduled DNA synthesis, or chromosome aberrations in the Syrian hamster embryo cells. However, a significant dose-dependent increase in aneuploid cells with a near-diploid chromosome number was induced by VCR. Both chromosome losses and gains were induced which is consistent with a non-disjunctional mechanism. These results further support our hypothesis that aneuploidy is one possible mechanism for induction of this early step in the neoplastic transformation of Syrian hamster embryo cells. Furthermore, these findings indicate that VCR may have some carcinogenic potential if exposure to rapidly dividing cells occurs.

Aneuploidy↗
PubMed1986

Changing responsiveness to all-trans retinoic acid of rat tracheal epithelial cells at different stages of neoplastic transformation.

Retinoic acid (RA) treatment of rat tracheal epithelial (RTE) cells, pre-exposed to the direct-acting carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), inhibited transformation in a dose-dependent manner. Treatment with RA at concentrations ranging from 3-33 nM reduced the MNNG-induced transformation frequencies by 13-81% and in some experiments by greater than 90%. RA treatment for only 3 days caused 65-75% inhibition of transformation; treatments of longer duration resulted in greater inhibition of transformation. Delaying the onset of RA treatment reduced its effectiveness, but even when RA treatment was delayed for 3 weeks following MNNG exposure, 60% inhibition still occurred. The inhibition of transformation appeared to be irreversible. The colony forming efficiency of cells isolated from transformed colonies 5 weeks after MNNG exposure was drastically reduced when the replated cells were treated with RA either 1 day or 4 days after plating, indicating that RA blocked cell replication. However, cells isolated from transformed colonies at later times after MNNG exposure were increasingly resistant to the antiproliferative effects of RA. The RA concentration causing 50% inhibition (RA-IC50) of colony formation was 0.1-0.3 nM for cells isolated from 3-5 week-old transformed colonies; it increased greater than 100-fold for cells isolated from 12-week-old transformants. Five established RTE cell lines also showed a much increased resistance to the antiproliferative effects of RA; two of these cell lines were even slightly stimulated in their colony forming ability by RA. The RA-IC50 of colony forming efficiency of normal RTE cells was also determined and compared to that of cells isolated from 5-week-old transformed colonies. Since the normal RTE cells require 3T3 feeder layers for clonal growth, both cell types were grown on feeders. For both cell types, the RA-IC50 was similar (150-300 nM); the requirement for relatively high RA concentrations was attributed in part to the rapid RA metabolism by the feeder cells. These experiments show that early RTE cell transformants are growth-inhibited by RA; however, they increasingly lose their sensitivity to the growth controlling effects of RA as they progress to a more advanced stage of transformation. The inhibition of tracheal cell transformation by RA is probably due to the antiproliferative effects of the retinoid.

Animals↗
PubMed1986

Alteration in diethylstilbestrol-induced mutagenicity and cell transformation by exogenous metabolic activation.

It was shown previously that diethylstilbestrol (DES) can induce morphological and neoplastic transformation of Syrian hamster embryo cells in culture in the absence of detectable gene mutations or DNA damage. However, in the presence of exogenous metabolic activation with rat liver post-mitochondrial supernatant, DES can induce unscheduled DNA synthesis. In this report we have examined whether with exogenous metabolic activation DES can also induce biological effects possibly related to its carcinogenicity, i.e. specific locus mutations in Syrian hamster embryo cells and cell transformation. We observed that DES was mutagenic only in the presence of exogenous metabolic activation. DES induced morphological transformation both in the absence and presence of exogenous metabolic activation. Enhanced cell transformation was observed in the presence of exogenous metabolic activation. These results indicate that two pathways may exist for the induction of cell transformation by DES. One does not apparently involve direct DNA damage, and the other, which requires rat liver post-mitochondrial supernatant-mediated exogenous metabolic activation, is associated with DNA damage and mutagenicity. These results may provide an experimental model to elucidate the biological properties of DES metabolites.

Animals↗