V. A. Pospelov1, T. V. Pospelova1, S. B. Svetlikova1, A. N. Kukushkin1, and A. van der Eb2
1 Institute of Cytology, Russian Academy of Sciences, St. Petersburg, 194064 Russia
2 Silvius Laboratory of Leiden University, the Netherlands
Received February 27, 1998
Abstract—The composition of transcription factor AP-1 in rat embryo fibroblasts transformed with E1A + Ha-
Ras oncogenes was analyzed with antibodies causing formation of high-molecular weight complexes (super-
shift) in the oligonucleotide gel retardation assay (EMSA). The AP-1 oligonucleotides AP-1coll (coll-TRE) and
jun2-TRE characterized by different binding of Fos/Jun and Jun/ATF dimers, respectively, were used as probes.
The composition of the AP-1 complex in E1A + Ha-Ras transformants undergoes significant alterations. In the
absence of c-fos gene expression, the c-Fos protein is replaced in the transformants by Fra-1 and ATF family
factors ATF-2 and ATFa. To analyze the possible mechanisms of the fos promoter suppression in the E1A + Ha-
Ras cells, populations of geneticin-resistant clones were obtained, which contained the reporter plasmid 711fos-
CAT and its mutants in the serum-dependent (SRE) and cAMP-dependent (CRE) elements of the fos promoter.
Since only mutation in SRE resulted in a marked increase in the activity of the 711fos-CAT integrated plasmid,
we have supposed that the SRE region is involved in negative regulation leading to inhibition of c-fos transcrip-
tion upon transformation with E1A + Ha-Ras oncogenes.
Key words: transformation with E1A + Ha-Ras oncogenes, transcription factor AP-1, fos promoter, Fos family
factors
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