A FOS-JUN ELEMENT IN THE 1ST INTRON OF AN ALPHA(2U)-GLOBULIN GENE

The hepatic expression of the alpha-2u-globulin gene family is control led by a variety of hormones including steroids, growth hormone and in sulin. The mechanisms by which these hormones affect alpha2u-globulin expression are only partially understood. Recently we isolated and cha racterized clone RAP 01, an alpha2u-globulin gene expressed in the liv er. In preliminary experiments we noted that partial hepatectomy, a pr ocedure which results in a sharp rise in the level of the oncoproteins c-Fos and c-Jun, also causes a transient induction of the messenger R NA corresponding to clone RAP 01. Using the DNAseI footprinting techni que we were able to show that this clone contains a TPA (phorbol 12-my ristate 13-acetate)-responsive element (TRE) in its first intron. This element (denoted as element X) is identical to the consensus AP-1 bin ding site (TGACTCAG) and is protected by rat liver nuclear extracts as well as by purified c-Jun. Gel retardation experiments show that an o ligonucleotide containing the TRE consensus sequence competes for bind ing of liver nuclear proteins to element X and that antibodies directe d against the M2 peptide of the mouse Fos protein or the PEP-2 peptide of Jun prevent the formation of specific complexes With the same elem ent. Moreover, element X functions as a TRE in transfected BWTG3 hepat oma cells treated with TPA. Co-transfection with fos and jun expressio n vectors mimics the effects of TPA suggesting that AP-1 is in fact th e mediator of the observed response. It is concluded that the first in tron of RAP 01 contains a functional Fos-Jun element.