Comparison of the cell cycle regulated synthesis and phosphorylation of stress proteins, actin isoforms and a novel actin-like protein following drug administration in cultured rat lymphocytes

Induction of stress proteins by electromagnetic fields in cultured HL-60 cells

HL-60 cells in culture were exposed for 2 h to a sinusoidal 0.1 or 1 mT (1 or 10 Gauss) magnetic field at 60 Hz and pulse labeled after exposure with radioactive isotopes by incubation by using either [(35)S]methionine, [(3)H]leucine, or [(33)P]phosphate. The radioactive labels were incorporated into cellular proteins through synthesis or phosphorylation. Proteins were extracted from electrostatically sorted nuclei, and the heat shock/stress proteins (sp) were analyzed for synthesis and phosphorylation by two-dimensional polyacrylamide gel electrophoresis. In the control cultures (no exposure to the magnetic field), sp 72c (cognate form) was faintly observed. A 0.1 mT exposure did not show sp metabolism to be different from that of the controls; however, after a 1 mT exposure of the HL-60 cells, sp 70i (inducible form) was synthesized ([(35)S]methionine incorporation). Sp 90 was not synthesized at either field level, but was phosphorylated ([(33)P]phosphate incorporation) in the 1 mT exposure. Sp 27 (isoforms a and b) was induced after a 1 mT exposure as reflected by labeling with [(3)H]leucine. These sps were not detected after a 0.1 mT exposure. After a 1 mT exposure and labeling with [(33)P], sp 27 isoforms b and c were phosphorylated whereas isoform 'a' was not observed. Sps 70i, 72c, and 90 were identified by commercial sp antibodies. Likewise, polypeptides a, b, and c were verified as sp 27 isoforms by Western blotting. Statistical evaluation of sp areas and densities, determined from fluorographs by Western-blot analysis, revealed a significant increase in sps 90 and 27a after a 1 mT magnetic field exposure. The 1 mT magnetic field interacts at the cellular level to induce a variety of sp species. Bioelectromagnetics 20:347-357, 1999. Published 1999 Wiley-Liss, Inc.

The relationship of p53 and stress proteins in response to bleomycin and retinoic acid in the p53 heterozygous mouse

A single, i.p. dose of bleomycin was administered simultaneously with [35S]methionine to 4-month-old p53 wild type (+/+) and p53 heterozygous (+/-) C57BL/6 mice. Following a period of 3.5 h from dosing, the bone marrow nuclei were examined by two-dimensional PAGE and fluorography for induction of stress proteins (sps). Eight sps ranging from 22000 to 100000 Mr were synthesized in p53+/- and p53+/+ mice following elicitation by bleomycin. No quantitative or qualitative differences were observed in sp expression in these two groups of animals. In a second experiment, three doses of retinoic acid were given i.p. to p53+/- and p53+/+ mice over a 36 h period. The p53 isoforms in bone marrow nuclei from these mice were analyzed by PAGE for incorporation of [35S]methionine following retinoic acid injections. Quantitative and qualitative alterations in p53 isotypes were substantially increased in p53+/+ as compared with p53+/- mice. The increased complexity in the synthesis patterns in both groups of dosed mice consisted of additional isoforms possessing more acidic isoelectric values. In an in vitro binding assay, individual p53 isoforms demonstrated varying degrees of association with sps 25a, 70i, 72c and 90 which was consistently greater in p53+/+ mice. Both the synthesis and binding of isoforms were greater in G1 than in S+G2 phase, in both groups of animals, reflecting a cell cycle regulated mechanism for these events. Collectively, these data implied that the synthesis and the binding characteristics of p53 isoforms with sps were enhanced in the p53+/+ mice relative to the p53+/- mouse; however, sp labeling was not affected by p53 genotype.

Development and utilization of the rat lymphocyte hprt mutation assay

Much of the recent progress in the field of genetic toxicology has come from an increased understanding of the molecular and cellular biology of the mammalian organism. Most prominent has been the ability to detect and quantify somatic mutation and relate the nature of the mutation to the specific type of chemical damage. Building upon the foundation of the human lymphocyte hypoxanthine guanine phosphoribosyl transferase (hprt) system, and later, the mouse hprt system, methods for the detection and quantification of hprt mutations in rat lymphocytes were developed. These methods are described in this report as is the ongoing validation of the assay. Additionally, the characterization of the recovered mutants and a comparison of the mutation spectrum in the rat lymphocyte system to the spectrum in cancer genes, such as H-ras and p53, and the spectrum in transgenic systems, such as lacI, are included. The development of the rat lymphocyte hprt system and validation of the assay at the molecular level, provide an effective and reliable measure of genetic damage in an in vivo system which is readily comparable to measurement of genetic damage in the human.