The transcription factor HNF1 acts with C/EBP alpha to synergistically activate the human albumin promoter through a novel domain.

HNF1 and C/EBP alpha are transcription factors that bind to and trans-activate the human albumin gene proximal promoter. Various 5' deletions of the human albumin promoter were coupled to a luciferase reporter gene (alb-luc constructs) and co-electroporated with HNF1 and/or C/EBP alpha expression vectors into HeLa cells. Luciferase activities from co-electroporation of the HNF1 and C/EBP alpha expression vectors with the alb-luc constructs were approximately 10-fold greater than the sum of the activities achieved with HNF1 and C/EBP alpha alone. Analysis of COOH-terminal or internal deletions of the HNF1 expression vector revealed that the domain important for collaborative interaction with C/EBP alpha could be localized to a 157 amino acid region not previously described. This domain is proline and glutamine-rich and is highly homologous (66%) to a portion of vHNF1, an evolutionarily related gene first identified in dedifferentiated hepatoma cells. A construct linking the negatively charged activation domain of herpes simplex virus protein VP16 to the DNA-binding domain of HNF1 showed that it could also synergize with C/EBP alpha to trans-activate the human albumin gene promoter. Our studies delineate a domain in HNF1 important for synergistic activation with C/EBP alpha.