We have shown previously that a 500-bp region of the human insulin receptor promoter (−0.3 to −1.8 kb) was able to stimulate transcription from a heterologous thymidine kinase promoter in HepG2 hepatoma cells but not in HeLa fibroblasts. Footprint analysis localized the transcription factor binding sites to a 36-bp region at −1420. In this paper, we analyze the factors that recognize this element and show that it contains binding sites for the CAAT/enhancer binding protein C/EBP and nuclear factor 1 (NF-1). In addition we show that both C/EBPα and the C/EBPβ can transactivate the human insulin receptor promoter in a dose-dependent manner.

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