Identification of two distinct nuclear factors with DNA binding activity within the glucocorticoid regulatory region of the rat alpha-1-acid glycoprotein promoter

Abstract

Efficient glucocorticoid induction of alpha-1-acid glycoprotein (AGP) mRNA in rat hepatoma cells HTC (JZ-1) requires the activity of one or more preexisting and labile proteins acting cooperatively with the glucocorticoid receptor. Inhibiting protein synthesis markedly diminishes the glucocorticoid induction of rat AGP mRNA without affecting the inducibility of other glucocorticoid inducible genes such as the mouse mammary tumor virus (MMTV) or tyrosine amino transferase (TAT). The sequences responsible for conferring glucocorticoid inducibility to the rat AGP gene have localized on the AGP promoter between nucleotides −121 and −42. A typical glucocorticoid regulatory element (GRE) is found between residues −121 and −105 and downstream of this are the sequences (−90 to −42) responsible for the cycloheximide inhibition of the hormonal induction (10). Using mobility shift assays we have characterized the binding of two proteins or complexes of proteins to this promoter region (−90 to −64). Our data show that the binding of these factors (called ANF-1 and ANF-2) to the DNA is highly specific, and is not directly affected by cycloheximide. Furthermore a second binding site for ANF-2 has been localized in the AGP regulatory region to a sequence that overlaps the GRE.