Biomedical subjects

W Dahlberg

Publications and source records attributed to W Dahlberg.

8 recordsLinked to original sources

PubMed2003

Differing effects of breast cancer 1, early onset (BRCA1) and ataxia-telangiectasia mutated (ATM) mutations on cellular responses to ionizing radiation.

PURPOSE: The ataxia-telangiectasia mutated (ATM) gene encodes a protein kinase, the activation of which is an early event in the cellular response to ionizing radiation. One of the many substrates of ATM is BRCA1 (breast cancer 1, early onset gene), which has been associated with susceptibility to breast and ovarian cancer, and has been implicated in DNA repair processes. Various cellular responses to radiation were analysed in cells with mutations in ATM or BRCA1 in an attempt to clarify which effects of ATM can be mediated through BRCA1. MATERIALS AND METHODS: The response to radiation of cells with mutations in ATM or BRCA1 was examined, as were BRCA1-mutant tumour cells transfected with an exogenous wild-type BRCA1 allele. Assays included cell-survival curves, studies of potentially lethal damage repair, measurement of chromosomal aberrations and of G1 arrest, and Western blot analysis of lysates of irradiated cells to determine the phosphorylation of the product of the human Mdm2 gene (HDM2). RESULTS: Both ATM and BRCA1 mutations were associated with sensitivity to ionizing radiation, deficient repair of potentially lethal damage and markedly increased chromosomal aberrations. A BRCA1-mutated tumour cell line HCC1937, like ATM mutant cells, did not exhibit a normal G1 arrest but, unlike ATM mutant cells, did exhibit phosphorylation of HDM2. Expression of wild-type BRCA1 in HCC1937 cells partially restored radioresistance, restored repair of potentially lethal damage and markedly reduced radiation-induced chromosomal aberrations. G1 arrest, however, was not restored by expression of BRCA1. CONCLUSIONS: The results are consistent with a model in which ATM phosphorylation of BRCA1 regulates DNA repair functions, particularly those involved in potentially lethal damage repair and chromosomal integrity, but not other aspects of the cellular response to radiation such as G1 cell cycle arrest. To the authors' knowledge, this is the first demonstration of the ability of exogenously expressed BRCA1 to restore the ability to perform potentially lethal damage repair and maintain chromosomal integrity in irradiated cells.

Ataxia Telangiectasia Mutated Proteins↗

PubMed1998

Differential p53, p21, mdm2 and Rb regulation in glioma cell lines that overexpress wild-type p53.

Gliomas are part of a subset of tumors in which overexpression of p53 protein in the absence of p53 gene mutation has been described. We have utilized a series of glioma cell lines to study the effects of ionizing radiation on the regulation of p53, p21, mdm2 and Rb proteins. The induction of p53 protein in glioma cell lines that overexpress wild-type p53 differs from normal control cells and glioma cell lines containing mutant p53. Alterations in the accumulation of p53 and p21 proteins are associated with diminished Rb hypophosphorylation. Gliomas that overexpress wild-type p53 also express high levels of mdm2 protein and exhibit a radiosensitivity that is intermediate between normal cells and cells with mutant p53. These findings suggest that, at least in certain glioma cell lines that over-express p53 which is wild-type in sequence, the function of p53 protein is abnormal.

Astrocytes↗

PubMed1994

Relationship between gamma-ray-induced G2/M delay and cellular radiosensitivity.

Seven human and rodent cell lines with markedly differing cellular radiosensitivities were examined by the anti-Br-dUrd antibody and flow cytometric method in order to measure the progression of S phase cells and their accumulation in the G2 phase of the cell cycle after gamma-irradiation. Exponentially growing cells were labelled with 10 microM BrdUrd for 2 h, gamma-irradiated, then washed and cultured at 37 degrees C. At 2-h intervals postirradiation, the cells were harvested and fixed for flow cytometric analysis. Two parameter distributions of BrdUrd content and DNA content were analysed. The time intervals for unirradiated labelled cells to progress from S to G2/M phase were about 450 min for the human squamous cell carcinoma cell lines SCC-12B.2 (D0 = 2.66 Gy), SQ-20B (D0 = 2.39 Gy) and SCC-61 (D0 = 1.07 Gy) as well as for wild-type CHO cells (D0 = 2.62 Gy). After irradiation with 2 Gy, SCC-12B.2, SQ-20B, CHO and human diploid AG1521 cells showed similar small G2/M delays (about 1 h), whereas, a G2/M delay of about 2.2 h occurred in radiosensitive SCC-61 cells and delays of 5.0-7.7 h were observed in two extremely radiosensitive mutant cell strains (human AT homozygote and CHO xrs-5 respectively). When the cells were irradiated with doses yielding similar levels of survival (about 10%), however, the duration of the G2/M delay was generally similar (2-4 h) in all seven cell lines indicating a parallel relationship between radiation-induced G2/M delay and cellular radiosensitivity. These results suggest that the delay time may be related to the level of unrepaired damage present in the cell as it approaches mitosis.

Animals↗

PubMed1988

Heterogeneity of radiation response of a parent human epidermoid carcinoma cell line and four clones.

We examined the radiobiological parameters of a parent tumor cell line and four tumor clones of a human skin squamous cell carcinoma. The parent line and all clones have a tumor morphology, aneuploid karyotype, and the ability to passage infinitely in vitro. The parent cell line and three of four clones formed tumors in nude mice. The parent line, SCC-12, has a D0 of 1.59 Gy and an n of 7.5. In the four clones, D0 ranges from 1.31 Gy to 2.66 Gy and n ranges from 2.1 to 22.8. Potentially lethal damage repair (PLDR) following 11 Gy ranges from 1.7 to 13.1, at 24 hours, however PLDR following equitoxic doses of radiation is similar. The mean inactivation dose value (D) in the parent tumor cell line is 3.48 and ranges from 3.31 to 4.17 in the tumor clones. Radiobiological interpretation of heterogeneity may complicate predictive assays for clinical radiotherapy.

Carcinoma, Squamous Cell↗

PubMed1986

Radiation-resistant and repair-proficient human tumor cells may be associated with radiotherapy failure in head- and neck-cancer patients.

Inherent cellular radioresistance and repair of x-ray damage was studied in 19 early-passage squamous cell carcinoma lines derived from head- and neck-cancer patients with known clinical results following radiotherapy. Human tumor cells that were radioresistant and/or proficient in accumulation/repair of x-ray damage were cultured from patients unsuccessfully treated with radiotherapy. Thus, the presence of radiation-resistant and repair-proficient tumor cells was associated with clinical radiation failure, suggesting the possibility of a predictive assay based on in vitro radiobiological parameters.

Carcinoma, Squamous Cell↗

PubMed1985

Inherently radioresistant cells exist in some human tumors.

We investigated the survival of 29 human tumor cell lines after treatment with ionizing radiation during exponential growth. The radiosensitivity of 20 tumor cell lines was within the range of normal fibroblasts. However, 9 cell lines derived from radio-incurable tumors appeared inherently radioresistant. When the ability to repair potentially lethal x-ray damage was studied in plateau phase cultures, some tumor cell lines derived from radio-incurable tumors were more efficient in this process. These results indicate that the presence of radioresistant and/or repair-proficient cells, which exist in some human tumors, may be responsible for failure to obtain local control following therapeutic x-ray treatment.

Cell Line↗

PubMed1984

Cellular X-ray repair parameters of early passage squamous cell carcinoma lines derived from patients with known responses to radiotherapy.

We have investigated X-ray survival parameters and repair of potentially lethal damage ( PLDR ) in ten early passage squamous cell carcinoma cell lines derived from patients who were biopsied before initiation of radiotherapy or after radiation therapy failure. Radiosensitivity (D0) ranged from 1.07 to 1.93 (Gy), extrapolation numbers (-n) from 1.17 to 2.14 and PLD recovery at 24 h from 1.4 to 20.3. Despite significant differences in these parameters amongst the cell lines, a firm correlation between radiocurability and any individual radiobiological parameter could not be established. Our data suggest that the mechanisms associated with radioresistance are complex and that any single radiobiological parameter may not predict clinical success or failure.

Carcinoma, Squamous Cell↗

PubMed1984

Lethal effects of 1-beta-D-arabinofuranosylcytosine incorporation into deoxyribonucleic acid during ultraviolet repair.

We have previously demonstrated that 1-beta-D-arabinofuranosylcytosine (ara-C) incorporates into leukemic cell DNA and that the extent of this incorporation correlates significantly with loss of clonogenic survival. These studies have now been extended by monitoring the incorporation of ara-C in DNA undergoing repair of UV-induced damage. The present studies have been performed using human foreskin diploid fibroblasts that undergo density-dependent growth arrest. The results demonstrate that ara-C incorporates specifically into DNA undergoing repair of damage by UV light. The extent of ara-C incorporation in AG1522 DNA during UV repair correlates significantly (p less than 0.0006) with cell lethality. These findings confirm that incorporation of ara-C into DNA undergoing either semiconservative or unscheduled DNA synthesis results in lethal cellular events. The present findings may provide the experimental basis for the development of new therapeutic approaches using ara-C in combination with agents that damage DNA.

Cell Survival↗