Interplay of the liver-enriched trans-acting factors, DBP and HNF1, in the transactivation of human IGFBP-1 promoter.

In the liver, expression of insulin-like growth factor binding protein-1 (IGFBP-1) is regulated essentially at the transcriptional level, at least in part by HNF1. In this study, the functional role of DBP and C/EBP (which have several potential binding sites on the IGFBP-1 proximal promoter) have been investigated. Transient co-transfection of the reporter plasmid, pBP-1341 and eukaryotic expression vectors which code for DBP and C/EBP in human cell lines Hep3B, HepG2 and C33 showed that IGFBP-1 promoter activity was unchanged by C/EBP, but increased between 2 and 7 times by DBP (depending on the cell line). In addition, DBP and HNF1 were capable of functional co-operation in activating the IGFBP-1 promoter. Our results support the notion of DBP being involved in limited tissue specificity of IGFBP-1 expression.