Changes in U937 cell viability induced by stress factors - possible role of calmodulin

Current studies were aimed to elucidate influence of magnetic field (MF) stimulation on cell viability and its effect on expression of calmodulin (CaM) and Hsp70 protein which plays a role of cell stress indicator and is a Ca²⁺-dependent CaM-binding protein. For the experimental model we have chosen U937 cell line exposed to chemical- and/or physical stress factors. Puromycin (PMC) was used as a chemical apoptosis inducer. Alternating (AC) (6.5_rms mT, 35 Hz) magnetic field combined with 6 mT static (DC) component, or pulsed electromagnetic field (45 ± 5)mT, 50 Hz (PEMF) acted as physical stressors. Cell viability was assessed by flow cytometry, and the Western blot analysis was carried out for CaM and Hsp70 levels in cytosolic extracts of U937 cells. Cell viability in samples exposed to MF alone did not differ from sham sample, for both types of MF exposure systems. Simultaneous action of MF and PMC influenced cell viability in type of MF stimulation-dependent manner. In contrast to PEMF + PMC stimulated samples, combination of ACDCMF with PMC enhanced cell death compared to PMC control. The observed changes in cell viability were correlated with changes in level of CaM and Hsp70 proteins. Immunoblots have shown, that cytosolic content of both CaM and Hsp70 proteins was enhanced in PMC-treated sample, and further elevated for ACDCMF + PMC. For PEMF + PMC stimulated samples, level of CaM was reduced compared to PMC-treated sample. The results suggest that the changes in expression of CaM and CaM-dependent proteins might modulate effectiveness of cell death under stimulation with MF and/or cytotoxic agents.