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Biomedical subjects

J C Barrett

Publications and source records attributed to J C Barrett.

At least 217 records · Page 12Linked to original sources
PubMed1994

Isolation of a diverged homeobox gene, MOX1, from the BRCA1 region on 17q21 by solution hybrid capture.

Using the technique of solution hybridization coupled with magnetic bead capture, we have isolated a novel homeobox-containing gene from the BRCA1 region of 17q21. This gene is the human homologue of the mouse Mox1 gene previously localized to a syntenic region of mouse chromosome 11. Multiple overlapping cDNAs of human MOX1 were identified using both a cosmid and a P1 genomic clone containing the microsatellite markers D17S750 and D17S858 which map within the BRCA1 region defined by D17S776 and D17S78. MOX1 expression was observed in a variety of normal tissues examined, including breast and ovary. Given that the gene contains a homeobox domain and has the potential to regulate growth and differentiation, MOX1 represents an attractive candidate for the BRCA1 gene. This possibility was investigated in a series of BRCA1 kindreds and primary sporadic breast tumors. No evidence for mutation was found in the coding sequence, making it unlikely that MOX1 is the BRCA1 gene. However, the widespread expression of MOX1 in non-embryonal tissues suggests a role in normal cell biology which warrants further study.

Amino Acid Sequence↗
PubMed1994

Apoptosis and chemical carcinogenesis.

Long recognized as a normal component of organogenesis during development, apoptosis (programmed cell death) has recently been implicated in alterations of cell growth and differentiation. Tissue homeostasis is normally maintained by a balance between cell division and cell death, with apoptosis often functioning in complement to cell growth. Thus, antithetical parallels in chemical carcinogenesis can be drawn between apoptosis and the proliferative events more commonly addressed. While enhanced cell replication may contribute to an increased frequency of mutation, apoptosis within a tissue may counteract chemical carcinogenesis through loss of mutated cells. Many strong carcinogens act as tumor promoters, selectively expanding an initiated cell population advantageously over surrounding cells. Similarly, chemicals with a selective inhibition of apoptosis within an initiated population would offer a growth advantage. In contrast, chemicals causing selective apoptosis of initiated cells would be expected to have an anticarcinogenic effect. Selective apoptosis, in concert with cell-specific replication, may explain the unique promoting effects of different carcinogens such as the peroxisome-proliferating chemicals, phenobarbital, and 2, 3, 7, 8-tetrachloro-dibenzo-p-dioxin (TCDD). Cell turnover, both cell growth and cell death, is central to the process of chemically induced carcinogenesis in animals and understanding its impact is a critical determinant of the relevance of chemically induced effects to man.

Animals↗
PubMed1994

A gene involved in control of human cellular senescence on human chromosome 1q.

Normal cells in culture exhibit limited division potential and have been used as a model for cellular senescence. In contrast, tumor-derived or carcinogen- or virus-transformed cells are capable of indefinite division. Fusion of normal human diploid fibroblasts with immortal human cells yielded hybrids having limited life spans, indicating that cellular senescence was dominant. Fusions of various immortal human cell lines with each other led to the identification of four complementation groups for indefinite division. The purpose of this study was to determine whether human chromosome 1 could complement the recessive immortal defect of human cell lines assigned to one of the four complementation groups. Using microcell fusion, we introduced a single normal human chromosome 1 into immortal human cell lines representing the complementation groups and determined that it caused loss of proliferative potential of an osteosarcoma-derived cell line (TE85), a cytomegalovirus-transformed lung fibroblast cell line (CMV-Mj-HEL-1), and a Ki-ras(+)-transformed derivative of TE85 (143B TK-), all of which were assigned to complementation group C. This chromosome 1 caused no change in proliferative potential of cell lines representing the other complementation groups. A derivative of human chromosome 1 that had lost most of the q arm by spontaneous deletion was unable to induce senescence in any of the immortal cell lines. This finding indicates that the q arm of human chromosome 1 carries a gene or set of genes which is altered in the cell lines assigned to complementation group C and is involved in the control of cellular senescence.

Bone Neoplasms↗
PubMed1994

The RB gene locates on chromosome 15 at band 15q13 in the Syrian hamster.

The retinoblastoma susceptibility gene, which encodes a nuclear phosphoprotein (Rb), plays an important role in cell-cycle progression in both normal development and tumorigenesis. Using a Syrian hamster cDNA probe homologous to the human retinoblastoma gene (RB), we have localized the gene to chromosome band 15q13 by conventional in situ hybridization.

Animals↗
PubMed1994

Cellular and molecular mechanisms of asbestos carcinogenicity: implications for biopersistence.

Carcinogenic agents can influence the carcinogenic process either by mutating critical target genes or by increasing the number of cells at risk for mutations. Cytogenetic and molecular studies of asbestos-related cancers indicate that inactivation or loss of multiple tumor suppressor genes occurs during lung cancer development. Aneuploidy and other chromosomal changes induced by asbestos fibers may be involved in genetic alterations in asbestos-related cancers. Furthermore, asbestos fibers may influence the carcinogenic process by inducing cell proliferation, free radicals, or other promotional mechanisms. Therefore, asbestos fibers may act at multiple stages of the carcinogenic process by both genetic and epigenetic mechanisms. Biopersistence is undoubtedly important in fiber carcinogenicity. However, the time required for a fiber to remain in the lung to exert a cancer-related effect is difficult to specify.

Asbestos↗
PubMed1994

Transfer of human chromosome 3 to an ovarian carcinoma cell line identifies three regions on 3p involved in ovarian cancer.

The molecular pathogenesis of ovarian carcinoma involves altered expression of growth factors, activation of oncogenes and loss of tumor suppressor genes. Loss of heterozygosity on chromosomes 3p, 6q, 11p, 17 and 18q was reported as a significant alteration in ovarian cancer. However, no functional proof has been provided of tumor suppressor activity located in these chromosomal regions. We therefore introduced normal human chromosomes 3 and 11 into an ovarian carcinoma cell line by microcell mediated chromosome transfer. Transfer of chromosome 3 induced senescence and growth arrest as well as suppression of tumorigenicity. Tumors induced by chromosome 3 monochromosomic hybrids consistently lost three small regions on 3p, two of which located in 3p23-24.2 and one located in 3p21.1-21.2, suggesting that these chromosomal regions are important for suppression of tumorigenicity of ovarian carcinoma cells. Transfer of chromosome 11 reduced the in vitro growth properties of ovarian cancer cells but did not significantly affect tumorigenicity. These results provide functional evidence for chromosome 3 tumor suppressor activity in ovarian cancer and define the chromosomal regions on 3p involved in the pathogenesis of this tumor. This experimental system, based on functional effects, may be useful for further delimitation and isolation of critical regions on 3p involved in tumor suppression.

Animals↗
PubMed1994

Inhibition of tumorigenicity of a murine squamous cell carcinoma (SCC) cell line by a putative tumor suppressor gene on human chromosome 7.

Alterations in oncogenes and tumor suppressor genes (TSG) are considered to be critical steps in oncogenesis. However information on putative TSG involved in the development of squamous cell carcinomas (SCC) is very limited. In this study we confirmed the existence of a tumor suppressor gene (TSG) on human chromosome 7 (hchr 7) that suppresses the tumorigenicity of squamous cell carcinomas (SCCs). We injected seven clones of CH72 cells (a murine SCC-derived cell line) bearing a hchr 7 (CH72/hchr 7) introduced by microcell fusion, two clones bearing human chromosome 12 (CH72/hchr 12) and parental CH72 cells into athymic Balb/c nude mice. The sizes of the tumors were determined twice a week until tumors reached 12 mm diameter. In situ hybridization for centromeric repetitive sequences of the transferred chromosomes were performed on the cell lines injected and the tumors arising after the injection. Southern blots and polymerase chain reaction (PCR) amplifications of near terminal sequences and (CA) microsatellite repeats were done to test the integrity of the introduced chromosomes. Five out of seven CH72/hchr 7 clones had a twofold and threefold longer latency periods than CH72 cells. The remaining CH72/hchr 7 clones (MF 6 and 13 no. 4) had latency periods similar to that of parental CH72; MF 6 had a deletion in the introduced chromosome 7 involving q31.3-q31.3, whereas the other hybrid (MF 13 no. 4) seemed to have an intact hchr 7. Tumor-derived cells from CH72/hchr 7 hybrids with a delayed latency had lost centromeric and telomeric sequences of Chr 7. In contrast, tumors derived from the MF 6 and MF 13 no. 4 as well as the CH72/hchr 12 clones retained the introduced human chromosome as shown by chromosome 7 or 12 centromeric and telomeric sequences. These results indicate that the tumorigenicity of CH72 murine SCC cells was suppressed by hchr 7 and that the CH72/hchr 7 regain the tumorigenic phenotype after loss of the introduced chromosome, suggesting the presence of a TSG on hchr 7.

Animals↗
PubMed1993

Gap junction function and cancer.

Gap junctions (GJs) provide cell-to-cell communication of essential metabolites and ions. GJs allow tissues to average responses, clear waste products, and minimize the effects of xenobiotics by dilution and allowing steady-state catabolism. Many chemicals can adversely affect the membrane GJ assembly causing reversible alterations in GJ intercellular communication. During toxicity essential metabolites, ions, and regulators are not shared homeostatically throughout a tissue community. Alterations in metabolic circuits are thought to interrupt organ integration. Persistent GJ perturbation can cause chronic effects (e.g., cancer), and many tumor promoters inhibit GJ intercellular communication. Liver precancerous foci intracommunicate (but at a reduced level) and intercommunicate improperly (or not at all) across the foci boundary to normal cells. In time, foci can become less regulated and more isolated within the tissue. GJs remain reduced quantitatively in the tumor progression stage and may be qualitatively altered in metastasis since connections are made between the primary tumor cells and foreign host cells at the secondary metastatic site. Cell sorting and binding mechanisms by the cell adhesion molecules and integrins may also be altered at secondary sites. This may allow the relocation of primary tumor cells and nurturance via GJs at the secondary site.

Animals↗
PubMed1993

Amplification potential in preneoplastic and neoplastic Syrian hamster embryo fibroblasts transformed by various carcinogens.

Using a well-defined in vitro model system for neoplastic progression, we have examined two basic characteristics in the acquisition of amplification potential. Since Syrian hamster embryo fibroblasts can be transformed by a variety of methods (spontaneously, chemically, virally, or by transfection with oncogenes), we determined whether the method of transformation affects the capability of a cell to amplify. In addition, since variants can be isolated from cell populations as they progress toward tumorigenicity, we can monitor changes in amplification potential during this multistep process. We find that the capability to amplify is independent of the method of transformation and that the acquisition of this ability occurs in a defined step in the transformation process. In this model system, acquisition of amplification ability occurred concomitantly with the loss of tumor suppression function.

Animals↗
PubMed1993

Induction of neoplastic progression in Syrian hamster embryo cells treated with protein phosphatase inhibitors.

In these studies, Syrian hamster embryo cells (SHE), which were isolated at different stages of neoplastic progression, were used to test the ability of the protein phosphatase inhibitors, okadaic acid and sodium orthovanadate (Na3VO4) to induce neoplastic progression. We observed that these chemicals can induce transition of the cells from one stage to the other at different points in the multistep process of neoplastic transformation. Three steps in this multistep process were studied: escape from cellular senescence, loss of a tumor suppressor gene function in immortal cells, and aquisition of anchorage-independent growth. Treatment of normal, primary SHE cells with okadaic acid or Na3VO4 allowed the cells to escape senescence and become immortal at a low frequency. The induction of immortality was associated with nonrandom chromosome changes, including trisomy 8 and 11 and monosomy 13 and Xq. The transition of preneoplastic cells to more advanced stages was also studied in immortal, nontumorigenic cells that either have retained (supB+) or have lost (supB-) the ability to suppress tumorigenicity of a transformed cell line in cell hybrids. SupB+ and supB- cells do not normally grow in agar, but supB- cells will grow in agar if additional growth factors are added. However, upon addition of protein phosphatase inhibitors, supB+ cells exhibited the supB- phenotype; for example, colony formation of supB+ cells was observed in agar supplemented with growth factors and protein phosphatase inhibitors. Following treatment, selection of these colonies showed that 89% of these cells heritably acquired the phenotype of cells that have lost the suppressor gene function (supB-). SupB- cells were also treated with protein phosphatase inhibitors in soft agar in the presence of additional growth factors. While the frequency of colonies in agar supplemented with growth factors in agar was not greatly enhanced, approximately 50% of the colonies acquired the ability to grow in agar autonomously without the supplemented growth factors, similar to tumorigenic cells. These studies suggest that Na3VO4 and okadaic acid induce progression of cells through various stages in this multistep system.

Animals↗
PubMed1993

Suppression of tumorigenicity of A549 lung adenocarcinoma cells by human chromosomes 3 and 11 introduced via microcell-mediated chromosome transfer.

To map tumor suppressor genes for lung adenocarcinomas, we introduced normal human chromosomes 3, 7, and 11 into the A549 tumor cell line by microcell-mediated chromosome transfer to test which chromosomes had the ability to suppress tumorigenicity. These human chromosomes, which contain the neomycin gene as a selectable marker, were transferred into A549 lung adenocarcinoma cells at frequencies of 0.3-1.8 x 10(-6). Two microcell hybrid clones with an introduced chromosome 3, two with an introduced chromosome 7, and six with an introduced chromosome 11 were isolated and examined for their growth properties and tumorigenicity in nude mice. Whereas parental A549 cells formed tumors with an average latency of 68 d, both microcell hybrids with an introduced chromosome 3 failed to form tumors for over 360 d. Similar tumorigenicity results were obtained when the clones were implanted into denuded tracheas, a more orthotopic transplantation site. The two clones with an introduced chromosome 7 were still tumorigenic; they formed tumors within 100-123 d after injection and grew progressively, although the tumors grew slightly slower than the parental cells did. Among the six clones with an introduced chromosome 11, one clone was still highly tumorigenic but did not contain an extra copy of an intact introduced chromosome 11. Three clones with a single intact copy of introduced chromosome 11 formed tumors with latency periods significantly longer than those of the parental cells. Two clones had two copies of the introduced chromosome 11, and both failed to form tumors within 1 yr of injection. These results indicate that chromosomes 3 and 11 can suppress the tumorigenicity of A549 lung adenocarcinoma cells.

Adenocarcinoma↗
PubMed1993

Negative regulation of mitogen-stimulated, anchorage-independent cell growth by a tumor-suppressor gene function.

Immortal, nontumorigenic cell lines of Syrian hamster embryo (SHE) cells with different tumor-suppressing activity were isolated. Subclones from the parental cells were isolated that either had retained (supB+) or lost (supB-) the ability to suppress tumorigenicity after hybridization with tumor cells. The growth properties of these cells were studied to determine how this tumor-suppressor gene function influences cell growth. When the cells were grown on plastic, their growth properties were similar, and neither cell type grew in soft agar containing 10% serum, which supported the growth of tumorigenic cells. However, in agar supplemented with growth factors and 10% serum, supB- cells formed colonies whereas supB+ cells did not. Efficient growth (colony-forming efficiencies greater than 20%) of supB- cells was obtained in agar supplemented with serum and a combination of epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and insulin (EPI) or with serum and basic fibroblast growth factor (bFGF). The effect of EPI and bFGF together was additive. supB+ cells failed to grow under any of these conditions, suggesting that the suppressor gene function blocked the growth response of the cells to multiple growth factors when the cells were suspended in agar. In SupB- cells, transforming growth factor-beta 1 and retinoic acid inhibited anchorage-independent growth response to EPI but not the growth response to bFGF. These observations are consistent with the hypothesis that bFGF stimulates the growth of supB- cells by a signal transduction pathway that differs from the pathway stimulated by EGF or PDGF. Thus, this suppressor gene function may regulate anchorage-independent growth at some common point in signal transduction for multiple mitogens.

Animals↗
PubMed1993

Timing of replication of differentially transcribed genes in Syrian hamster embryo fibroblasts.

Syrian hamster embryo cell lines have been used as models of neoplastic progression in vitro. Changes in phenotype and biological properties have been observed in these cell lines in association with modulation of gene transcription. We explored this natural evolution of cells in culture to investigate the reported relationship between transcriptional activity and replication in early S phase. In this study we used two nontumorigenic cell lines that had either retained (supB+) or lost (supB-) the ability to suppress tumorigenicity of malignantly transformed hamster fibroblasts (BP6T). In association with the loss of suppressor gene function, supB- cells have downregulated the expression of the H19 and tropomyosin-I (TM-I) genes, which are actively transcribed in supB+ cells. Synchronous populations of supB+ and supB- cells were pulse-labeled with [3H]thymidine and bromodeoxyuridine at 1-h intervals during S phase; the replicating DNA was isolated by centrifugation in cesium chloride gradients and hybridized to 32P-labeled gene probes. No correlation was found between the timing of gene replication and the status of expression of these two genes. TM-I replicated during the first hour and H19 replicated between the second and third hours of the S phase in the expressing and nonexpressing cell lines. Immunoglobulin gene sequences, known to be late-replicating in fibroblasts, replicated at the end of the S phase. These results suggest that downregulation of transcription is not always accompanied by a concomitant change in time of gene replication from early to late S phase.

Animals↗