Angiotensinogen Gene-Inducible Enhancer-Binding Protein 1, a Member of a New Family of Large Nuclear Proteins That Recognize Nuclear Factor κB-Binding Sites through a Zinc Finger Motif

Transcriptional activation of the rat angiotensinogen gene during the acute-phase response is dependent on a previously characterized acute-phase response element (APRE) that binds at least two types of nuclear proteins: a cytokine-inducible activity indistinguishable from nuclear factor κ-B (NFκB) and a family of C/EBP-like proteins. We screened a rat liver cDNA expression library with a labeled APRE DNA probe and isolated a single clone that encodes a sequence-specific APRE-binding protein. This new protein, the angiotensinogen gene-inducible enhancer-binding protein 1 (AGIE-BP1), is encoded by a large continuous open reading frame and contains a zinc finger motif virtually identical to the DNA-binding domain of a recently described human protein, MBP-1/PRDII-BF1, and a homologous mouse protein, αA-CRYBP1. Outside the binding domain, the sequences diverged considerably. Southern blot analysis indicated that AGIE-BP1 and αA-CRYBP1 are encoded by separate genes, thus defining a new family of DNA-binding proteins. Electrophoretic mobility shift assays, methylation interference, and DNase I footprint protection assays with the bacterially expressed DNA-binding domain of AGIE-BP1 demonstrated a binding specificity indistinguishable from that of purified NFKB. Antiserum raised against the bacterially expressed DNA-binding domain of AGIE-BP1 detected on immunoblots of cellular proteins a large (>250-kDa) nuclear protein. Northern (RNA) blot analysis of RNAs from different rat tissues and cell lines indicated different levels of expression of the large (>10-kb) AGIE-BP1 transcript in different tissues. The potential role of AGIE-BP1 in the regulation of gene expression is discussed.