The liver is a major target organ of insulin and is important for glucose homeostasis. We analyzed the tissue specific regulation of the insulin receptor gene in the liver by studying the cis-acting element and trans-acting factor of the human insulin receptor gene in human hepatoma cell line, HepG2 cells. In the chloramphenicol acetyl transferase (CAT) assay with chimeric plasmids containing various deletions and insertions of the human insulin receptor promoter/CAT gene, a HepG2 cell specific cis-acting element was identified between nt -592 to -577 of the promoter. In electrophoretic mobility shift assay and UV cross-link analysis, a 35-kDa nuclear protein that bound to 5'-TCCCTCCC-3' (nt -588 to -581) sequence was identified in HepG2 cells as well as in rat hepatocytes. This nuclear protein, designated as hepatocyte-specific transcription factor of the insulin receptor gene (HT-FIR), might play an important role in tissue-specific expression of the insulin receptor gene in the liver.