Ann S. Henderson

Exposure of human cells to low-frequency electromagnetic fields results in quantitative changes in transcripts

The exposure of human cultured cells to electromagnetic signals with extremely low repetition rates resulted in an increased level of selected RNA transcripts. RNA with homology to beta-actin, histone H2B, and v-myc DNA was monitored by dot blot hybridization following 20 min exposures of HL60 cells to five different electromagnetic signals. The experiments used three asymmetric electromagnetic signals with different repetition rates, and two symmetric sinusoidal signals, delivered at 60 and 72 Hz. The degree of increase in homologous transcripts was dependent on the signal characteristics.

Increased levels of hsp70 transcripts induced when cells are exposed to low frequency electromagnetic fields

Abstract Previous experiments have shown that the steady state levels of some RNA transcripts are increased when cells are exposed to extremely low frequency electric or magnetic fields. Experiments have exposed a variety of cell types, including dipteran salivary gland cells, yeast and human HL-60 cells. The range of responsive transcripts includes oncogenes such as c-myc, as well as transcripts associated with growth and development. One hypothesized mechanism of how cells respond to electromagnetic (EM) fields assumes that the response represents or mimics a generalized physiological stress response. RNA from exposed HL-60 cells, previously shown to have increased transcript levels for c-myc, was analyzed for hsp70 transcripts levels. The hsp70 transcripts were found to be elevated in all cases, even though the cells were exposed to various fields at normal growth temperatures. The conditions of maximum induction for hsp70 were coordinate with those of c-myc. In yeast cells, the SSA1 gene (homologous to hsp70) was found to be elevated in cells exposed to EM fields at 0.8−80 μT. In the case of yeast, conditions for maximum induction of SSA1 were coordinate with those for URA3, the gene for uracil metabolism. Thus the model of cell interaction with electric and/or magnetic fields appears to be related to the stress response model for heat shock.

Calcium is necessary in the cell response to EM fields

Previous research showed that exposure of human HL‐60 cells to extremely low frequency electromagnetic fields increases the steady‐state levels of some mRNAs. Modifications in calcium flux have been suggested as a means of amplifying electromagnetic signals, and induced changes in calcium influx could hypothetically lead to gene activation. The present experiments tested the role of calcium in the response of cells to electromagnetic fields. Steady state transcript levels for c‐fos and c‐myc were determined under conditions of low extracellular calcium. The present study confirms that calcium plays a role in the response of cells to electromagnetic fields.

Changes in transcription in HL-60 cells following exposure to alternating currents from electric fields

Abstract The effect of varying field strength and exposure time on histone H2B and c- myc transcript levels in HL-60 cells exposed to 60 Hz electric fields (sine waves) is reported here. An increase in the basal levels of these normally expressed transcripts was observed, which was dependent on both field strength and time of exposure. β2-microglobulin, a transcript known to be uninducible, was unaffected by cellular exposure to the field strengths used in these experiments.

REGULATION OF C-FOS IS AFFECTED BY ELECTROMAGNETIC FIELDS

The goal of the present study was to determine if regulatory regions of the c‐fos gene were responsive to electromagnetic field exposure. The research design used transfected cells to increase the sensitivity of assays designed to identify changes following exposure. HeLa cells were transiently transfected with plasmids containing upstream regulating regions of c‐fos up to ‐700 base pairs, coupled with the prokaryotic reporter gene CAT. Cells were exposed to an environmentally relevant EMF of 60 Hz at 60 mGrms. CAT expression above control levels in transfected cells (region +42 to ‐700 bp) was observed following 5 min exposure to the electromagnetic field, with a peak at 20 min. The expression was at basal levels following 40 min exposure. Deletion analysis of upstream DNA narrowed the responsive region to 138 base pairs from ‐363 to ‐225, which contains the SRE/AP‐1 sites.

MAP kinase activation in cells exposed to a 60 Hz electromagnetic field

This research provides evidence that mitogen‐activated protein kinase or extracellular signal‐regulated kinase (MAPK/ERK) is activated in HL‐60 human leukemia cells, MCF‐7 human breast cancer cells, and rat fibroblast 3Y1 cells exposed to a 60 Hertz (Hz), 1 Gauss (G) electromagnetic field (EMF). The effects of EMF exposure were compared to those observed using 12‐O‐tetradecanoylphorbal‐13‐acetate (TPA) treatment. The level of MAPK activation in cells exposed to EMF was approximately equivalent to that in cells treated with 0.1–0.5 ng/ml of TPA. A role for protein kinase C (PKC) in the process leading to MAPK activation in EMF exposed cells is also suggested by the results. MAPK activation is negated by an inhibitor to PKCα, but not PKCδ inhibitors, in cells subjected to EMF exposure or TPA treatment. Thus, similarities between the effects of EMF exposure and TPA treatment are supported by this investigation. This provides a possible method for revealing other participants in EMF–cell interaction, since the TPA induction pathway is well documented.

EMF induces differentiation in HL‐60 cells

This investigation provides evidence that a 60‐Hz electromagnetic field (EMF) at 1 gauss (G) can drive differentiation of cultured hematopoietic progenitor cells. HL‐60 cells are known to differentiate from a nonphagocytic suspension culture to an attached fibroblast‐like culture with high phagocytic activity in the presence of the tumor‐promoting phorbol ester 12–0‐tetradecanoylphorbal‐13‐acetate (TPA). The effect of 60‐Hz EMF at 1 G on differentiation is approximately equivalent to treatment of the cells with 250–500 pg/ml TPA. Furthermore, the effect of both EMF and TPA treatment on differentiation is additive at low TPA concentrations. The results strongly suggest similarities between the effects of TPA treatment and EMF exposure and thus provide an approach for tracing the origins of the molecular effects of EMF exposure, as many transduction pathways in the differentiative process are defined. J. Cell. Biochem. 73:212–217, 1999.

Some biological effects of electromagnetic fields

Abstract It has been known for some time that specific asymmetric electromagnetic fields can induce union in non-healing bones. Despite the clinical effectiveness of low frequency electromagnetic (e.m.) signals, virtually nothing is known concerning basic mechanisms in cells involved in bone healing, or other cells in soft tissue, which can also be affected by e.m. signals. It has thus become increasingly important to understand the molecular basis of e.m. field stimulation in order to evaluate the clinical effectiveness and the results of inadvertent environmental exposure. We have developed a test system to examine a fundamental cellular function, that of transcription, in Sciara polytene chromosomes. Since RNA synthesis is a basic cellular event, alterations arising from exogenous stimulation of cells by e.m. fields should be reflected in transcriptional patterns. Our results show this to be the case. e.m. signals in the 72 Hz frequency range, both quasi-rectangular and sinusoidal, induce new RNA transcription in the 6–10S size class and augment a RNA size class in the 20–25S range. e.m. signals in the 1.5 to 15 Hz frequency range result in either a similar response as that seen in 72 Hz signals, or one which is indistinguishable from non-stimulated control cells. Since translational effects would be expected to be reflected as a result of alterations in transcription, we examined protein biosynthesis following e.m. field stimulation. Changes in the form of augmentation, deletion, and appearance of new polypeptides are observed. Finally, we found that e.m. signals, even at some distance from the non-stimulated control samples, emit an undefined signal that is detected by the non-stimulated control cells. For this reason, we have shielded non-stimulated cells. Our ultimate goal is to correlate a specific parameter of the e.m. signal waveform with cellular induction of particular classes of RNA and/or molecular weight ranges of protein. To date, the data suggest that the 72 Hz range is an important frequency component and that waveshape may not be as crucial to clinical usefulness as previously supposed.

Oncogene mobility in a human leukemia line HL-60☆

HL-60, a cell line derived from a human promyelocytic leukemia, shows amplification of the oncogene c-myc. Chromosome aberrations reported in HL-60 include double minutes (DMs) and an abnormally banded region (ABR) on chromosome #8. A relationship between these chromosomal aberrations and amplification of c-myc DNA has been suggested. We report the localization by cytologic hybridization of amplified c-myc DNA to a marker chromosome, M3q+, in an early passage of HL-60. The localization of c-myc to an ABR on an 8q+ chromosome was confirmed in later passage clones. The most probable derivation of the M3q+ chromosome is t(5p;17q) with additional material associated with c-myc amplification inserted into 17q. This localization is of interest in light of the association between t(15:17) and promyelocytic leukemia. The results indicate that amplification and chromosome integration can occur at a site other than the native gene locus and at different integration sites in different lineages of the same tumor.

Transcription in Drosophila melanogaster salivary gland cells is altered following exposure to low frequency electromagnetic fields: Analysis of chromosomes 3L and X

The use of the transcription autoradiographic method permits identification of nascent RNA chains directly on identifiable regions of Drosophila salivary gland chromosomes. Changes in transcriptional activity at 13 defined regions of the right arm of chromosome 3 (3R) were observed following 20-min exposures of salivary glands to five different extremely low frequency (ELF) electromagnetic (EM) fields. Changes in translational patterns were also induced by the ELF EM fields in exposed cells. Differences included an increase in over-all polypeptide synthesis as well as in the number of polypeptides resolved in cells exposed to EM fields.