E1A + cHa-ras Transformed Rat Embryo Fibroblast Cells Are Characterized by High and Constitutive DNA Binding Activities of AP-1 Dimers With Significantly Altered Composition

• Published in: Gene expression 1999-01, Vol.8 (1), p.19-32
• Main Authors: POSPELOVA, TATIANA V., MEDVEDEV, ALEXANDER V., KUKUSHKIN, ALEXANDER N., SVETLIKOVA, SVETLANA B., VAN DER EB, ALEX J., DORSMAN, JOSEPHINE C., POSPELOV, VALERY A.
• Format: Article
• Language: English
• Subjects: Adenovirus E1A Proteins - metabolism; Animals; Ap-1 Transcription Factors; Blotting, Western; Cell Line; Cell Line, Transformed; Chloramphenicol O-Acetyltransferase - metabolism; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; E1a And Cha-Ras Oncogenes; Fibroblasts; Fos And Jun Expression; Gene Expression Regulation; Genes, ras; Promoter Regions, Genetic; Proto-Oncogene Proteins c-fos - genetics; Proto-Oncogene Proteins c-fos - metabolism; Proto-Oncogene Proteins c-jun - genetics; Proto-Oncogene Proteins c-jun - metabolism; Rats; Response Elements; Transcription Factor AP-1 - genetics; Transcription Factor AP-1 - metabolism
• ISSN: 1052-2166; 1555-3884

Transcription factors of the AP-1/ATF family, including c-Fos, c-Jun, and ATF-2, play an important role in the regulation of cell proliferation and differentiation, and changes in their levels and/or activities may contribute to oncogenesis. We analyzed the alterations of AP-1/ATF transcription factors upon immortalization and transformation in a panel of cell lines derived from rat embryo fibroblast (REF) cells. The tumorigenic E1A + cHa-ras cells are characterized by high and constitutive DNA binding activities of AP-1, in contrast to nontransformed cells and the E1A cells. The expression of c-fos and c-jun genes was affected differently by the oncogenic transformation. By using antibodies to c-Jun and c-Fos proteins in electrophoretic mobility shift assays (EMSA), we showed that E1A + ras-ras transformants did not contain c-Fos under any condition of cell cultivation and growth factor stimulation, whereas c-Jun was constitutively upregulated. In the absence of c-fos gene expression, c-Fos protein appears to be replaced by proteins of Fos family (Fra-1) and ATF family (ATF-2 and ATFa). To determine the possible mechanisms of c-fos downregulation in E1A + cHa-ras transformants we have obtained populations of geneticin-resistant clones containing integrated reporter construct -711fos-CAT and its mutants in serum-responsive element (SRE) and cAMP-responsive element (CRE). Data obtained show that the mutations within the SRE lead to a manifold activation of fos-CAT expression. This allows to suggest that c-fos downregulation in E1A + cHa-ras transformants is provided by a negative control mediated through the SRE regulatory region. The profound differences in regulation and composition of transcription factors of the AP-1 family probably play a pivotal role in the transformation of REF cells by E1A and cHa-ras oncogenes.