Heavy metals induce transcription of human genes including those coding for metallothionein and heat shock protein 70 (HSP70). It has been suggested that these processes are mediated by metal-activated transcription factors, MTF-1 and HSF1, respectively, and are independent of each other. We raised an antibody against human MTF-1 which efficiently supershifts the protein-DNA complex formed by MTF-1 and its cognate binding sequence, MRE. We discovered that this antibody could also supershift complexes formed by HSF1 and its recognition sequence HSE, which suggested the involvement of MTF-1 in these complexes. This supershift was observed for HSF1/HSE complexes induced by Zn, Cd, Ag, and heat shock. Furthermore, overexpression of MTF-1 in HeLa cells markedly reduced metal-induced transcription from the hsp70-I gene promoter which depends on HSF1. These data indicate that MTF-1 represses HSF1-mediated transcription probably through a direct protein-protein interaction, suggesting a cross talk of two lines of stress-responsive regulatory pathways. (c) 2006 Elsevier Inc. All rights reserved.