A previous study showed that the exposure to non-thermal microwave electromagnetic field at 1.95 GHz, a frequency used in mobile communication, affects the refolding kinetics of eukaryotic proteins (see publication 11255).
On these basis the authors have evaluated the in vivo non-thermal effect of microwave electromagnetic field on the apoptosis of human epidermoid cancer cells.
Modulation of the expression, activity, and proteasome-dependent degradation of the components of Ras --> Erk- and Akt-dependent survival signaling induced by electromagnetic field were studied. Ras --> extracellular signal regulated kinase (Erk)-dependent signal transduction pathway: involved in regulation of both proliferation and apoptosis. Akt: another important anti-apoptotic pathway (Akt can be activated concomitantly or independently from Ras --> Erk-1/-2 signaling.
Finally the role of HSP90/multi-chaperone-dependent multi-chaperone complex in the regulation of expression and activity of anti-apoptotic signaling Ras and Raf-1 and of their relative survival signaling induced by microwave electromagnetic fields were investigated.
Many HSPs form complexes that act as chaperones and bind other proteins (so called client proteins). These complexes play a regulatory role in the fate of proteins. HSP90 acts in concert with other chaperones to provide maturation and folding, as well as trafficking and function of their client proteins (e.g. c-Raf, Ras, Mek) through the formation of the HSP90/multi-chaperone complex. Several protein kinases (including Raf-1) depend upon the HSP90/multi-chaperone for function and stability. This is likely the way by which HSP90/multi-chaperone is involved in the regulation of apoptotic processes. The HSP90 client proteins Raf-1 and Mek are components of the Ras --> Erk-dependent signal transduction pathway.
Exposure duration: continuous for 1, 2 and 3 h or for 48 h
|Exposure duration||continuous for 1, 2 and 3 h or for 48 h|
|Chamber||thermostated at 37°C|
|Setup||A flask containing KB cells was positioned along the principle axis of the waveguide.|
|Additional info||A transverse electric (TE) field was generated, i.e. the electric field component of the wave was orthogonal to the travelling direction.|
|SAR||3.6 mW/g||average over mass||-||-||± 0.2 mW/g|
The authors revealed that exposure 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 decreased, its activity was unchanged likely as a consequence of the increased expression of its upstream activator PI3K.
An about 2.5-fold increase of the ubiquitination of Ras and Raf-1 was also revealed. The addition of proteasome inhibitor lactacystin caused an accumulation of the ubiquitinated isoforms of Ras and Raf-1 and counteracted the effects of exposure on Ras and Raf-1 expression suggesting an increased proteasome-dependent degradation induced by the irradiation.
The irradiation induced a differential activation of stress-dependent pathway with an increase of JNK-1 activity and HSP70 and HSP27 expression and with a reduction of p38 kinase activity and HSP90 expression.
The overexpression of HSP90 (induced by transfection of the cells) completely antagonized the apoptosis and the inactivation of the Ras --> Erk-dependent survival signal induced by electromagnetic field. Conversely, the inhibition of Erk activity induced by 12 h exposure to Mek-1 inhibitor U0126 antagonized the effects induced by HSP90 transfection on apoptosis caused by irradiation.
In conclusion, these data demonstrate for the first time that microwave electromagnetic fields induce 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).