AbstractMetal‐responsive transcription factor‐1 (MTF‐1), which is involved in sensing heavy metal load, induces the transcription of several protective genes. The mouse Mtf‐1 gene is essential, and Mtf‐1−/− embryos die from liver degeneration. We showed that DNA synthesis induced in hepatocytes by epidermal growth factor (EGF) was delayed by inhibition of MTF‐1. To inhibit MTF‐1 activity, MTFΔC, a C‐terminal deletion mutant of MTF‐1, was expressed by infection with the virus Ad5MTFΔC. Lactate dehydrogenase (LDH) release and/or caspase‐3/7 activation was not observed under our experimental conditions. The inhibitory effect of MTFΔC on EGF‐dependent DNA synthesis in hepatocytes was not eliminated by zinc addition. EGF‐dependent extracellular signal‐related kinase (ERK) phosphorylation, an essential reaction for EGF‐dependent DNA synthesis, was decreased in MTF‐1‐inhibited hepatocytes. Moreover, decrease of ERK phosphorylation was observed by using siRNA in MTF‐1‐downregulated hepatocytes. These results indicate that MTF‐1 is particularly important for proper hepatocyte proliferation. This is the first report to suggest the function of MTF‐1 in the ERK pathway. J. Cell. Biochem. 99: 485–494, 2006. © 2006 Wiley‐Liss, Inc.