The human haptoglobin gene promoter: interleukin-6-responsive elements interact with a DNA-binding protein induced by interleukin-6.

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Abstract
Transcription of the human haptoglobin (Hp) gene is induced by interleukin‐6 (IL‐6) in the human hepatoma cell line Hep3B. Cis‐acting elements responsible for this response are localized within the first 186 bp of the 5′‐flanking region. Site‐specific mutants of the Hp promoter fused to the chloramphenicol acetyl transferase (CAT) gene were analysed by transient transfection into uninduced and IL‐6‐treated Hep3B cells. We identified three regions, A, B and C, defined by mutation, which are important for the IL‐6 response. Band shift experiments using nuclear extracts from untreated or IL‐6‐treated cells revealed the presence of IL‐6‐inducible DNA binding activities when DNA fragments containing the A or the C sequences were used. Competition experiments showed that both sequences bind to the same nuclear factors. Polymers of oligonucleotides containing either the A or the C regions confer IL‐6 responsiveness to a truncated SV40 promoter. The B region forms several complexes with specific DNA‐binding proteins different from those which bind to the A and C region. The B region complexes are identical in nuclear extracts from IL‐6‐treated and untreated cells. While important for IL‐6 induction in the context of the haptoglobin promoter, the B site does not confer IL‐6 inducibility to the SV40 promoter. Our results indicate that the IL‐6 response of the haptoglobin promoter is dependent on the presence of multiple, partly redundant, cis‐acting elements.