Academic journal article Environmental Health Perspectives

Power-Line Frequency Electromagnetic Fields Do Not Induce Changes in Phosphorylation, Localization, or Expression of the 27-Kilodalton Heat Shock Protein in Human Keratinocytes. (Research)

Academic journal article Environmental Health Perspectives

Power-Line Frequency Electromagnetic Fields Do Not Induce Changes in Phosphorylation, Localization, or Expression of the 27-Kilodalton Heat Shock Protein in Human Keratinocytes. (Research)

Article excerpt

The linkage of the exposure to the power-line frequency (50-60 Hz) electromagnetic fields (EMF) with human cancers remains controversial after more than 10 years of study. The in vitro studies on the adverse effects of EMF on human cells have not yielded a clear conclusion. In this study, we investigated whether power-line frequency EMF could act as an environmental insult to invoke stress responses in human keratinocytes using the 27-kDa heat shock protein (HSP27) as a stress marker. After exposure to 1 gauss (100 [micro] T) EMF from 20 min to 24 hr, the isoform pattern of HSP27 in keratinocytes remained unchanged, suggesting that EMF did not induce the phosphorylation of this stress protein. EMF exposure also failed to induce the translocation of HSP27 from the cytoplasm to the nucleus. Moreover, EMF exposure did not increase the abundance of HSP27 in keratinocytes. In addition, we found no evidence that EMF exposure enhanced the level of the 70-kDa heat shock protein (HSP70) in breast or leukemia cells as reported previously. Therefore, in this study we did not detect any of a number of stress responses in human keratinocytes exposed to power-line frequency EMF. Key words: electromagnetic fields, heat shock proteins, HSP70, HSP27 phosphorylation, HSP27 translocation, keratinocytes, signal transduction, stress.

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The health risks posed by power-line frequency electromagnetic fields (EMF) are controversial. Almost 50 epidemiologic studies have been published on the topic of residential and occupational exposure to power-frequency fields and cancer risk. The majority of these reports indicate a weak association between exposure to 50-60 Hz fields and the incidence of cancer; however, numerous methodologic flaws reduce their credibility (1). Recent studies by the National Cancer Institute indicate that children living near high-voltage power lines do not have an increased risk of lymphoblastic leukemia (2). In contrast, other recent reviews of the issue have concluded that it is premature to dismiss concerns about residential EMF and childhood leukemia (3). Also controversial are the early epidemiologic data suggesting a connection between EMF and breast cancer (4,5); this connection has not been verified by recent studies using animal models (6). Although there have been no specific reports regarding the incidence of skin tumors in populations exposed to 60-Hz fields, one study notes that 60 Hz (2 mT) EMF may act as a tumor co-promoter in murine skin previously initiated by the application of chemical carcinogens (7). Again, adding to the controversy, using essentially the same protocols, other investigators found no co-promoting activity of EMF (8). These uncertainties have led investigators to study the possible effects of power-line frequency EMF on human and mammalian cells in culture where the mechanisms that mediate cellular responses can be dissected. Of note, most of the studies over the past decade have failed to detect any significant cellular responses to EMF exposure (9,10).

There are no general models or biomarkers for the assessment of cellular effects of EMF exposure (11). It is generally agreed that the low energy EMF, of power-line frequency, is insufficient to cause direct damage to DNA. Therefore, it is unlikely that EMF exposure is able to initiate tumor formation through DNA mutation (11,12). An alternative hypothesis is that EMF exposure alters the biochemical signaling pathways that regulate cell proliferation, differentiation, and apoptosis (12,13). A number of gene products involved in signal transduction, including tyrosine kinases, phospholipase C, protein kinase C, and protein kinase A, have been linked to effects of EMF exposure (13-15), but the results have not been consistent (12,16,17). A highly cited study by Lin and Goodman (18) reported that EMF exposure induced expression of c-myc, an oncogene implicated in a host of cancers including breast cancer. …

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