Electromagnetic fields at mobile phone frequency induce apoptosis and inactivation of the multi-chaperone complex in human epidermoid cancer cells.
The exposure to non-thermal microwave electromagnetic field (MW-EMF) at 1.95 MHz, a frequency used in mobile communication, affects the refolding kinetics of eukaryotic proteins (Mancinelli et al., 2004). On these basis we have evaluated the in vivo effect of MW-EMF in human epidermoid cancer KB cells. We have found that MW-EMF induces time-dependent apoptosis (45% after 3 h) that is paralleled by an about 2.5-fold decrease of the expression of ras and Raf-1 and of the activity of ras and Erk-1/2. Although also the expression of Akt was reduced its activity was unchanged likely as a consequence of the increased expression of its upstream activator PI3K. In the same experimental conditions an about 2.5-fold increase of the ubiquitination of ras and Raf-1 was also found and the addition for 12 h of proteasome inhibitor lactacystin at 10 microM caused an accumulation of the ubiquitinated isoforms of ras and Raf-1 and counteracted the effects of MW-EMF on ras and Raf-1 expression suggesting an increased proteasome-dependent degradation induced by MW-EMF. The exposure of KB cells to MW-EMF induced a differential activation of stress-dependent pathway with an increase of JNK-1 activity and HSP70 and 27 expression and with a reduction of p38 kinase activity and HSP90 expression. The overexpression of HSP90 induced by transfection of KB cells with a plasmid encoding for the factor completely antagonized the apoptosis and the inactivation of the ras --> Erk-dependent survival signal induced by MW-EMF. Conversely, the inhibition of Erk activity induced by 12 h exposure to 10 mM Mek-1 inhibitor U0126 antagonized the effects induced by HSP90 transfection on apoptosis caused by MW-EMF. In conclusion, these results demonstrate for the first time that MW-EMF induces apoptosis through the inactivation of the ras --> Erk survival signaling due to enhanced degradation of ras and Raf-1 determined by decreased expression of HSP90 and the consequent increase of proteasome dependent degradation.
Caraglia
Michele
M
Department of Biochemistry and Biophysics, Second University of Naples, Italy.
Marra
Monica
M
Mancinelli
Fabrizio
F
D'Ambrosio
Guglielmo
G
Massa
Rita
R
Giordano
Antonio
A
Budillon
Alfredo
A
Abbruzzese
Alberto
A
Bismuto
Ettore
E
D017209:Apoptosis / Q000528:radiation effects*; D002294:Carcinoma, Squamous Cell / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D045744:Cell Line, Tumor; D040421:Cell Phone; D002470:Cell Survival; D004574:Electromagnetic Fields; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D018832:Molecular Chaperones / Q000037:antagonists & inhibitors*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D015398:Signal Transduction / Q000528:radiation effects; D025801:Ubiquitin / Q000378:metabolism; D018631:ras Proteins / Q000378:metabolism
D018841:HSP90 Heat-Shock Proteins; D018832:Molecular Chaperones; D025801:Ubiquitin; D019908:Proto-Oncogene Proteins c-raf; D048049:Extracellular Signal-Regulated MAP Kinases; D046988:Proteasome Endopeptidase Complex; D018631:ras Proteins