MYC-MEDIATED TRANSACTIVATION OF HSP70 EXPRESSION FOLLOWING EXPOSURE TO MAGNETIC-FIELDS

We investigated c-myc protein-binding sites on the HSP70 promoter as m odulators of the induction of HSP70 gene expression in response to mag netic field stimulation (8 mu T at 60Hz) and whether the presence of c -myc protein potentiates transactivation of HSP70 expression. A 320 ba se pair region in the HSP70 promoter (+1 to -320) was analyzed. This r egion contains two c-myc-protein binding sites with consensus sequence s located at -230 and -160 nucleotide positions (relative to the trans cription initiation site) and overlapping with the region reported for the regulation of HSP70 gene expression by c-myc protein. This promot er region is upstream of other regulatory sequences, including the hea t shock element (HSE), AP-2, and serum response element (SRE). Transfe ctants containing both c-myc protein-binding sites, HSP-MYC A and HSP- MYC B, and exposed to magnetic fields showed a 3.0-fold increase in ex pression of CAT activity as compared with sham-exposed control transfe ctants. Transfectants containing one c-myc binding site, HSP-MYC A, an d exposed to magnetic fields showed a 2.3-fold increase in CAT express ion. Transfectants in which both HSP-MYC A and HSP-MYC B binding sites were deleted showed no magnetic field sensitivity; values were virtua lly identical with sham-exposed controls. If the c-myc expression vect or was not co-transfected with the constructs containing myc-binding s ites, there was no difference in the expression of CAT activity betwee n magnetically stimulated and sham-exposed controls, although both res ponded to heat shock. These data suggest that endogenous elevated leve ls of myc protein contribute to the induction of HSP70 in response to magnetic field stimulation. (C) 1998 Wiley-Liss, Inc.