Nuclear translocation and DNA-binding activity of NFKB (NF-κB) after exposure of human monocytes to pulsed ultra-wideband electromagnetic fields (1 kV/cm) fails to transactivate κB-dependent gene expression

The objective of this study was to investigate whether exposure of human monocytes to a pulsed ultra-wideband electromagnetic field (EMF) of 1 kV/cm average peak power triggers a signaling pathway responsible for the transcriptional regulation of NFKB (NF-κB)-dependent gene expression. Human Mono Mac 6 (MM6) cells were exposed intermittently to EMF pulses for a total of 90 min. The pulse width was 0.79 ± 0.01 us and the pulse repetition rate was 250 pps. The temperature of the medium was maintained at 37°C in both sham- and EMF-exposed flasks. Total NFKB DNA-binding activity was measured in the nuclear extracts by the electrophoretic mobility shift assay. Cells exposed to the EMFs and incubated for 24 h postexposure showed a 3.5 ± 0.2-fold increase in the NFKB DNA-binding activity. Since activation of NFKB was observed, the possibility of κB-dependent gene expression in response to exposure to the EMFs was investigated using NFKB signal-specific gene arrays. The results revealed no difference in the NFKB-dependent gene expression profiles at 8 or 24 h postexposure, indicating that activated NFKB does not lead to the differential expression of κB-dependent target genes. To determine whether the absence of the κB-dependent gene expression was due to compromised transcriptional regulation of NFKB, the functional activity of NFKB was examined in cells transiently transfected with Mercury Pathway® constructs containing 4× NFKB binding sites associated either with the luciferase reporter system or a control vector. Pulsed EMF exposure did not induce NFKB-driven laciferase activity in these cells, indicating that the activation of NFKB at 24 h after the 1 kV/cm EMF exposure is functionally inactive. From these results, it is clear that the EMF-induced NFKB activation is only a transient response, with minimal or no downstream effect.