Study On The Effects Of Extremely Low Frequency Magnetic Field On Cytokine Receptor Gene Expression And Transcription Factor Activation

The potential involvement in carcinogenesis of extremely-low-frequency (ELF) electromagnetic field (EMF) suggested by the data of several epidemiologic studies have prompted a large number of laboratory experiments to investigate the effects of exposure to 50 or 60 Hz EMF at cellular and molecular levels. However, so far no clear and unequivocal biophysical mechanisms are available to explain the variety of biological effects elicited by EMF exposure. The cell membrane plays an essential role in mediating signal transduction events and it has been suggested to be the primary interaction site of magnetic field (MF) signals. A variety of MF-induced changes in membrane and cell surface receptor expression have been described. To our knowledge, no information is available regarding the effects of ELF MF on the cell surface cytokine receptors: tumor necrosis factor receptor (TNFR), interlukine-6 receptor (IL-6R), and transforming growth factor-p receptor (TGFpR). Tumor necrosis factor alpha (TNF-ct) exerts a wide range of biological functions and plays a critical role in the defense againstpathogens. Like other cytokines, TNF-a acts by activating cell surface receptors. Two distinct receptors have been identified: 55 kDa (TNFRp55) and 75 kDa (TNFRp75). Both TNFRs are implicated in the mediation of apoptosis and activation of nuclear factor kappa B (NF-icB), as well as immune reactions to infectious organisms. Interlukine 6 receptor a (IL-6Ra) and transforming growth factor P receptors (TGF-(3Rs) involve in the regulation of cell differentiation and proliferation. A balance of expression of these receptors is important in immunological functions. HL60 cells, a promyelocytic leukemia cell line, are frequently being used to study the immuno-physiologic effects of EMF as a model linking EMF with leukemia, since the cell line is sensitive to various stimuli and easy to culture. The Ribonuclease Protection Assay (RPA) was used in our experiments to analyse mRNA level. It is a highly sensitive and reliable method for simultaneous detection and semi-quantitation of multiple mRNA species in a single sample of total RNA, allowing the detection of target cytokine receptor mRNAs down to at least 0.01 microgram of poly(A)-RNA. In the present study, we investigated the effects on expression of genes relating to these cytokine receptors in HL60 cells exposed to MF at flux density of 0.1 or 0.8 mT for durations up to 72 h by employing RPA method.In addition, there have been many studies reporting that cellular signal transduction pathways are affected by EMF. Many transcription factors are the final targets of specific transduction pathways. As an environmental physical factor, seveval reports suggested that EMF can influence DNA binding activity of multiple transcription factors, including AP-1, SP-1, and HSF. CREB and NF-kB are two of important transcrition factors. CREB was originally identified as an activator that responds to the cyclic-AMP (cAMP)-dependent signaling pathwayand phosphorylated by cAMP-dependent protein kinase (PKA). Studies on the biological functions of CREB have shown that CREB is critical for a variety of cellular processes, including proliferation, differentiation, and adaptive responses. CREB activates transcription of target genes in a homodimer or heterodimer form in response to a diverse array of stimuli that activate a variety of protein kinases including PKA, PKC, mitogen-activated protein kinases (MAPKs), and Ca2+/calmodulin-dependent protein kinases (CaMKs). Another transcrotion factor, NF-icB is a protein heterodimer-complex for DNA binding that acts as an ubiquitous transcription activator. It binds to a 10-bp consensus sequence that is found in a variety of promoter/enhancer regions of cellular and viral genes to regulate acute-phage response. NF-icB is maintained in an inactive form in the cytoplasm because it is bound to the inhibitory protein 1KB, which is rapidly phosphorylated, ubiquitinylated, and degraded after exposure of cells to appropriate stimuli. Inferred from the...