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J L Roti

Publications and source records attributed to J L Roti.

12 recordsLinked to original sources
PubMed2001

Delaying S-phase progression rescues cells from heat-induced S-phase hypertoxicity.

The mechanism by which a cell protects itself from the lethal effects of heat shock and other stress-inducing agents is the subject of much research. We have investigated the relationship between heat-induced damage to DNA replication machinery and the lethal effects of heat shock, in S-phase cells, which are more sensitive to heat shock than either G1 or G2. We found that maintaining cells in aphidicolin, which prevents the passage of cells through S-phase, can rescue S-phase HeLa cells from the lethal effects of heat shock. When S-phase, HeLa cells were held for 5-6 h in 3 microM aphidicolin the measured clonogenic survival was similar to that for exponentially growing cells. It is known, that heat shock induces denaturation or unfolding of proteins, rendering them less soluble and more likely to co-isolate with the nuclear matrix. Here, we show that enhanced binding of proteins involved in DNA replication (PCNA, RPA, and cyclin A), with the nuclear matrix, correlates with lethality of S-phase cells following heat shock under four different experimental conditions. Specifically, the amounts of RPA, PCNA, and cyclin A associated with the nuclear matrix when cells resumed progression through S-phase correlated with cell killing. Heat-induced enhanced binding of nuclear proteins involved with other aspects of DNA metabolism, (Mrell, PDI), do not show this correlation. These results support the hypothesis that heat-induced changes in the binding of proteins associated with DNA replication factories are the potentially lethal lesions, which become fixed to lethal lesions by S-phase progression but are repairable if S-phase progression is delayed.

Aphidicolin↗
PubMed2001

Cytometric methods to analyze ionizing-radiation effects.

Four cytometric assays for the assessment of radiation-induced DNA damage in individual cells are presented. Two of these, the alkaline and neutral comet assays, are useful for the detection of DNA damage due to very low radiation doses and promise to be useful for the quantitation of genomic damage after clinically or environmentally relevant exposures. The other two, the halo and halo-comet assays, reveal aspects of chromatin structure in the presence of DNA damage that reflect differences in intrinsic cellular radiosensitivity. Further development of these assays used alone, or in combination, should eventually lead to the definition of readily measurable cytometric parameters that will be useful as predictive markers for cellular responses to DNA damaging agents.

Animals↗
PubMed1999

Radiofrequency electromagnetic fields have no effect on the in vivo proliferation of the 9L brain tumor.

The intracranial 9L tumor model was used to determine if exposure to a radiofrequency (RF) electromagnetic field similar to those used in cellular telephone has any effects on the growth of a central nervous system tumor. Fischer 344 rats implanted with different numbers of 9L gliosarcoma cells were exposed to 835.62 MHz frequency-modulated continuous wave (FMCW) or 847.74 MHz code division multiple access (CDMA) RF field with nominal slot-average specific absorption rates in the brain of 0.75 +/- 0.25 W/kg. The animals were exposed to the RF field for 4 h a day, 5 days a week starting 4 weeks prior to and up to 150 days after the implantation of tumor cells. Among sham-exposed animals injected with 2 to 10 viable cells (group 1), the median survival was 70 days, with 27% of the animals surviving at 150 days. The median survival length and final survival fraction for animals injected with 11 to 36 viable cells (group 2) were 52 days and 14%, respectively, while the values for those injected with 37 to 100 cells (group 3) were 45 days and 0%. The animals exposed to CDMA or FMCW had similar survival parameters, and the statistical comparison of the survival curves for each of the groups 1, 2 and 3 showed no significant differences compared to sham-exposed controls.

Animals↗
PubMed1996

Detection of single-base mutations by a competitive mobility shift assay.

We have developed an assay for the rapid screening of point mutations in specific genes. Our assay is based upon competitive hybridization of differentially labeled wild-type and mutant oligonucleotide probes to a PCR-generated DNA template and a subsequent analysis of the mobility of the probe-template hybrids. The assay is referred to as a competitive mobility shift assay. Generation of a hybridization stringency gradient allows perfect-matched hybrids to be formed to a greater extent at a slightly higher stringency than the corresponding mismatched hybrids. The stringency gradient is achieved by carrying out the hybridizations at a steadily decreasing temperature (from 95 to 20 degrees C) in a thermal cycler. This step allows the assay to be competitive while avoiding the need to establish precise hybridization conditions for each gene-specific probe, a major disadvantage associated with reverse oligonucleotide hybridization. The assay is rapid and sensitive and can selectively detect mutant DNA in the presence of a large (up to one million-fold) excess of wild-type DNA.

DNA Mutational Analysis↗
PubMed1978

Kinetic models of C3H mouse mammary tumor growth: implications regarding tumor cell loss.

Three models of tumor cell loss are described. The effects of cell loss on other cellular kinetic parameters are evaluated, and experiments which may distinguish among the models are discussed. Each model is based on a different cell-loss mechanism, and equations for the cell-cycle, cell-frequency distribution, the growth of both the proliferating and non-proliferating cell population, the growth fraction (GF), and the relative rate of volumetric growth, (dV/dt)/V, are derived. The following types of data are simulated for each model: the pulse labelling index, the mitotic index, and the labeling index as a function of time after a single or a series of 3H-TdR injections. The relative volumetric growth rate has the same mathematical form for each model. The PLM curves predicted by each model for the tumor lines studied (S102F and Slow) are not appreciably different. The predicted initial labeling index and mitotic index may differ significantly among the models depending upon the tumor line. The most striking difference among the models lies in the predictions regarding the labeling index as a function of time after a single or after a series of 3H-TdR injections. These types of labeling experiments should be valuable for distinguishing the different cell-loss mechanisms in solid tumors.

Animals↗
PubMedDate not supplied

Chronic thermotolerance with continued cell proliferation.

The human colon adenocarcinoma cell line, NSY42129, is capable of proliferation at 41.1 degrees C. This ability appears to be due to a type of chronic thermotolerance, as opposed to selection or adaptation, that allows these cells to traverse S phase at elevated temperatures. Four other human cell lines were studied for their ability to proliferate at 41.1 degrees C. Of those only one, also a colon adenocarcinoma, showed the ability to sustain proliferation at 41.1 degrees C. While all the cell lines examined showed increased levels of the major heat shock proteins at 41.1 degrees C, the cellular amounts of these proteins did not correlate with their ability to proliferate at 41.1 degrees C. However, the ability of the cells to proliferate at 41.1 degrees C did correlate with their ability to sustain elevated rates of synthesis of hsp70 and hsp90. These results could have implications in the clinical application of hyperthermia, particularly the use of long duration moderate hyperthermia.

Bromodeoxyuridine↗