C/EBP beta and Elk-1 synergistically transactivate the c-fos serum response element.
BACKGROUND
The serum response element (SRE) in the c-fos promoter is a convergence point for several signaling pathways that regulate induction of the c-fos gene. Many transcription factors regulate the SRE, including serum response factor (SRF), ternary complex factor (TCF), and CCAAT/enhancer binding protein-beta (C/EBPbeta). Independently, the TCFs and C/EBPbeta have been shown to interact with SRF and to respond to Ras-dependent signaling pathways that result in transactivation of the SRE. Due to these common observations, we addressed the possibility that C/EBPbeta and Elk-1 could both be necessary for Ras-stimulated transactivation of the SRE.


RESULTS
In this report, we demonstrate that Elk-1 and C/EBPbeta functionally synergize in transactivation of both a Gal4 reporter plasmid in concert with Gal4-SRF and in transactivation of the SRE. Interestingly, this synergy is only observed upon activation of Ras-dependent signaling pathways. Furthermore, we show that Elk-1 and C/EBPbeta could interact both in an in vitro GST-pulldown assay and in an in vivo co-immunoprecipitation assay. The in vivo interaction between the two proteins is dependent on the presence of activated Ras. We have also shown that the C-terminal domain of C/EBPbeta and the N-terminal domain of Elk-1 are necessary for the proteins to interact.


CONCLUSIONS
These data show that C/EBPbeta and Elk-1 synergize in SRF dependent transcription of both a Gal-4 reporter and the SRE. This suggests that SRF, TCF, and C/EBPbeta are all necessary for maximal induction of the c-fos SRE in response to mitogenic signaling by Ras.
Hanlon
M
M
Department of Molecular Physiology and Biophysics Vanderbilt University School of Medicine, Nashville, Tennessee USA. marry.hanlon@mcmail.vanderbilt.edu
Bundy
L M
LM
Sealy
L
L
D016475:3T3 Cells / Q000737:chemistry; D000818:Animals; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000378:metabolism / Q000502:physiology*; D019556:COS Cells / Q000737:chemistry; D002460:Cell Line; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins; D051379:Mice; D010455:Peptides / Q000378:metabolism; D025941:Protein Interaction Mapping; D011518:Proto-Oncogene Proteins / Q000378:metabolism / Q000502:physiology*; D016760:Proto-Oncogene Proteins c-fos / Q000502:physiology*; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology; D027602:Serum Response Element / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1
D022782:CCAAT-Enhancer-Binding Protein-beta; D004268:DNA-Binding Proteins; C494113:Elk1 protein, mouse; D010455:Peptides; D011518:Proto-Oncogene Proteins; D016760:Proto-Oncogene Proteins c-fos; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D016283:Proto-Oncogene Proteins p21(ras)