To investigate the possible mechanism of gene transcription changes induced by magnetic field (MF), we examined the DNA binding behavior of the transcription factor cyclic-AMP responsive element binding protein (CREB) in HL60 cells after exposure to a 0.1 mT 50-Hz extremely low frequency (ELF) sinusoidal MF by a gel shift assay. Magnetic field induced a time-dependent activation of CREB binding. The complex formation increased shortly after MF exposure for 10 min, reaching a peak level after 1 h, and then recovered to basal level at 4 It after exposure. A novel MF-induced ATF2/ATF2 homodimer formation was observed after MF exposure for 30 min, 1, and 2 h. Furthermore, We found that the MF-induced increase of CREB DNA binding in HL60 cells was dependent on both extracellular and intracellular Ca2+ but not PKA, PKC, ERK, or p38 MAPK by using various pathway inhibitors. These data indicate that MF exposure activates CREB DNA binding through calcium-related signal transduction pathways under our experimental conditions. (C) 2002 Elsevier Science (USA). All rights reserved.