Biomedical subjects

J Jackman

Publications and source records attributed to J Jackman.

36 records · Page 2Linked to original sources

PubMed1994

WAF1/CIP1 is induced in p53-mediated G1 arrest and apoptosis.

The tumor growth suppressor WAF1/CIP1 was recently shown to be induced by p53 and to be a potent inhibitor of cyclin-dependent kinases. In the present studies, we sought to determine the relationship between the expression of WAF1/CIP1 and endogenous regulation of p53 function. WAF1/CIP1 protein was first localized to the nucleus of cells containing wild-type p53 and undergoing G1 arrest. WAF1/CIP1 was induced in wild-type p53-containing cells by exposure to DNA damaging agents, but not in mutant p53-containing cells. The induction of WAF1/CIP1 protein occurred in cells undergoing either p53-associated G1 arrest or apoptosis but not in cells induced to arrest in G1 or to undergo apoptosis through p53-independent mechanisms. DNA damage led to increased levels of WAF1/CIP1 in cyclin E-containing complexes and to an associated decrease in cyclin-dependent kinase activity. These results support the idea that WAF1/CIP1 is a critical downstream effector in the p53-specific pathway of growth control in mammalian cells.

Alleles↗

PubMed1994

Cell cycle control and cancer chemotherapy.

As detailed information accumulates about how cell cycle events are regulated, we can expect new opportunities for application to cancer therapy. The altered expression of oncogenes and tumor suppressor genes that commonly occurs in human cancers may impair the ability of the cells to respond to metabolic perturbations of stress. Impaired cell cycle regulation would make cells vulnerable to pharmacologic intervention by drug regimens tailored to the defects existing in particular tumors. Recent findings that may become applicable to therapy are reviewed, and the possible form of new therapeutic stratagems is considered.

Cell Cycle↗

PubMed1994

Transcription-independent repair of nitrogen mustard-induced N-alkylpurines in the c-myc gene in Burkitt's lymphoma CA46 cells.

Recently, it has been demonstrated that N-alkylpurines produced by nitrogen mustard are excised more rapidly from actively transcribing genes compared to non-coding regions of the overall genome. Such studies have suggested that transcriptional activity is a determinant of the rate of removal of these DNA lesions. We have examined the removal of nitrogen mustard-induced N-alkylpurines in the actively transcribed/translocated and transcriptionally repressed native alleles of the c-myc gene in Burkitt's lymphoma, CA46 cells. Burkitt's lymphoma cells, exhibiting a c-myc translocation that can be distinguished from the native allele by Southern blotting, provide a useful model system in which to explore regulatory elements that govern DNA repair in transcriptionally active genes. Northern analysis verified the selective allelic expression of the translocated c-myc gene in CA46 cells. At the drug exposure examined, nitrogen mustard produced a similar level of N-alkylpurines in the two alleles of c-myc. Also, the kinetics of lesion repair from both c-myc alleles over a 24 h repair incubation period was of the same order of magnitude: approximately 34% and approximately 25% of nitrogen mustard-induced N-alkylpurines were removed by 8 h; approximately 72% and approximately 66% of nitrogen mustard lesions were removed by 24 h from the untranslocated and translocated alleles respectively. The untranslocated allele did not become transcriptionally activated upon drug treatment and nitrogen mustard produced a suppression of c-myc message levels from the translocated allele. Therefore, our results suggest that the rate of repair of nitrogen mustard-induced N-alkylpurines is independent of transcriptional activity of the c-myc gene in Burkitt's lymphoma. These findings are discussed in terms of the current views about the mechanisms of gene-specific repair.

Alkylation↗

PubMed1993

Analysis of the mammalian gadd45 gene and its response to DNA damage.

The gadd45 gene is transcriptionally activated through at least two different mechanisms; one following treatment with base-damaging agents such as methylmethane sulfonate and UV radiation and the other following ionizing radiation. To investigate the sequences involved in induction of gadd45 by agents producing high levels of base damage, the hamster, human, and mouse genes were sequenced. Comparison of these sequences revealed a high level of conservation between species of 1500 base pairs of the proximal promoter and 700 base pairs within the third intron. However, in the promoter regions, there was no conservation between species of any transcription factor binding sites known to confer DNA damage responsiveness. The promoter of the hamster gene was inducible by base-damaging agents in both rodent and human cell lines and the human gene was inducible in a rodent cell line. This indicates that both sequence elements in the gadd45 promoter and factors binding to these sites are conserved in mammalian cells. Deletion analysis of the hamster promoter did not reveal any specific sequence which conferred damage inducibility and the maximal response required a large portion of the promoter. The hamster promoter was not inducible by ionizing radiation, suggesting that sequences outside the promoter region used, such as a p53 binding site in the third intron, are necessary. The human GADD45 gene was mapped to chromosome 1p31.1-31.2.

Animals↗

PubMed1993

Role of the p53 tumor suppressor gene in cell cycle arrest and radiosensitivity of Burkitt's lymphoma cell lines.

We have assessed the role of the p53 tumor suppressor gene in cell cycle arrest and cytotoxicity of ionizing radiation in 17 Burkitt's lymphoma and lymphoblastoid cell lines. Cell cycle arrest was assessed by flow cytometry of cells 16 h following irradiation. In addition to the usual G2 arrest, the cell lines exhibited three types of responses in G1: Class I, strong arrest in G1 following radiation; Class II, minimal arrest; and Class III, an intermediate response. All Class I cells contained normal p53 genes. Of the ten lines that showed minimal G1 arrest, eight had mutant p53 alleles, and two lines were heterozygous for p53 mutations. Both of the lines showing an intermediate response contained wild-type p53. Our results are consistent with the view that mutations abrogate the ability of p53 to induce G1 arrest following radiation. Studies with the heterozygotes showed that the mutant protein can have a dominant negative influence upon wild-type p53, and the reduced ability of two normal p53 lines to arrest in G1 indicated that p53 function can be impaired by other mechanisms. The radiosensitivity of most of the lines appeared to depend on the ability of p53 to induce a G1 arrest. The mean radiation dose that inhibited proliferation of the Class I lines by 50% was 0.98 Gy. Of the eight p53 mutant cell lines tested, five lines required approximately 2.9 Gy to cause a 50% inhibition of cell proliferation. The two heterozygotes were also more resistant to radiation than the Class I cells (50% inhibitory dose, 2.1 and 2.9 Gy). Our results suggest that radioresistance is afforded by a loss of function of wild-type p53, which would normally induce a G1 arrest and promote cell death in the presence of DNA damage.

Burkitt Lymphoma↗

PubMed1992

Genotoxic-stress-response genes and growth-arrest genes. gadd, MyD, and other genes induced by treatments eliciting growth arrest.

As discussed throughout this paper, many mammalian DDI genes are associated with growth responses, including both positive responses to growth stimulation and negative responses involving transient growth arrest and terminal differentiation. It is interesting that several immediate-early genes encoding transcription factors, the jun genes, are DDI, are induced by terminal differentiation, and also are associated with positive growth responses. In negative growth-response genes, their control is complex and almost certainly involves multiple regulatory mechanisms. The role of growth-arrest genes after exposure to DNA-damaging agents is currently not known, but as growth arrest can have a protective effect on cells exposed to DNA-damaging agents in both bacteria and eukaryotes, some protective role(s) for the gadd genes may exist. Whatever the roles are for the individual gadd genes, the response of the gadd genes to DNA-damaging agents and other growth-arrest signals has been highly conserved during mammalian evolution, and it is likely that this stress response, as reflected by induction of one or more gadd genes, is present in most or perhaps all mammalian cells. Our findings that the gadd group overlaps with another group of growth-arrest genes, the MyD, indicate that these two groups combined define a new class of genes whose protein products are likely to play a role in cell growth cessation.

Aging↗

PubMed1990

Clinical case definition for AIDS in Africa.

Explore the source record for details and available documents.

Acquired Immunodeficiency Syndrome↗

PubMed1988

ATP secretion and extracellular protein phosphorylation by CNS neurons in primary culture.

The significant role of secreted ATP in the regulation of neuronal function and the activity of ecto-protein kinases which utilize extracellular ATP to phosphorylate proteins localized at the cell surface have been previously studied in peripheral neurons and in cloned neural cell lines. In the present study we have utilized neostriatal neurons differentiated in primary culture to demonstrate vesicular secretion of ATP and phosphorylation of proteins by extracellular ATP in neurons derived from the central nervous system (CNS). Neostriatal neurons from embryonic mice were maintained in a chemically defined medium for 15-18 days. Functional differentiation was determined by measuring evoked GABA-release. ATP-secretion was measured by luciferin-luciferase assays, and protein phosphorylation by adding gamma-32P-ATP to the extracellular medium. Depolarization by 50 mM KCl induced a Ca++-dependent ATP release, and stimulation by 100 microM veratridine resulted in secretion of ATP that could be blocked by tetrodotoxin. Phosphorylation of specific protein components with apparent molecular mass of 110 Kd, 80 Kd, 55 Kd, 30 Kd and 20 Kd was detected in striatal neurons incubated for 15 min with gamma-32P-ATP added to the medium, but not by labeling intracellular ATP pools with equivalent amounts of radioactivity presented as inorganic 32Pi. These results open for investigation the role of extracellular protein phosphorylation systems in processes underlying the responsiveness of CNS neurons to secreted ATP.

Adenosine Triphosphate↗

PubMed1987

Commercial hickory-smoke flavouring is a human lymphoblast mutagen but does not induce lung adenomas in newborn mice.

Commercial aqueous wood-smoke flavouring induced significant increases in the 6-thioguanine resistance mutation frequency of TK6 human lymphoblasts at 0.1 microliter flavouring/ml of cell suspension. This corresponds to 6 micrograms/ml of dissolved 'solids' as determined by fully drying the aqueous flavouring in a vacuum desiccator. In AHH-1 human lymphoblasts, which contain a cytochrome P-450 monooxygenase system, mutations were induced at 0.3 microliter/ml, corresponding to 18 microliters/ml of dissolved 'solids'. The flavouring did not induce 8-azaguanine resistant mutations in Salmonella typhimurium at concentrations up to 1.5 microliter/ml. At higher concentrations the flavouring was toxic to bacteria. The flavouring did not induce lung adenomas or other tumours in newborn mice when injected ip with total doses of up to 26 microliters over a 3-wk period. Toxicity to the kidney, colon and rectum was observed in some mice at 15 wk of age.

Adenoma↗

PubMed1986