c-Fos oncogene regulator Elk-1 interacts with BRCA1 splice variants BRCA1a/1b and enhances BRCA1a/1b-mediated growth suppression in breast cancer cells.
Elk-1, a c-Fos protooncogene regulator, which belongs to the ETS-domain family of transcriptional factors, plays an important role in the induction of immediate early gene expression in response to a variety of extracellular signals. In this study, we demonstrate for the first time the in vitro and in vivo interaction of Elk-1 with BRCA1 splice variants BRCA1a and BRCA1b using GST-pull down assays, co-imunoprecipitations/Western blot analysis of cell extracts from breast cancer cells and mammalian two-hybrid assays. We have localized the BRCA1 interaction domain of Elk-1 protein to the conserved ETS domain, a motif involved in DNA binding and protein-protein interactions. We also observed binding of BRCA1 proteins to other ETS-domain transcription factors SAP1, ETS-1, ERG-2 and Fli-1 but not to Elk-1 splice variant DeltaElk-1 and c-Fos protooncogene. Both BRCA1a and BRCA1b splice variants function as growth suppressors of human breast cancer cells. Interestingly, our studies reveal that although both Elk-1 and SAP-1 are highly homologous members of a subfamily of ETS domain proteins called ternary complex factors, it is only Elk-1 but not SAP-1 that can augment the growth suppressive function of BRCA1a/1b proteins in breast cancer cells. Thus Elk-1 could be a potential downstream target of BRCA1 in its growth control pathway. Furthermore, we have observed inhibition of c-Fos promoter activity in BRCA1a transfected stable breast cancer cells and over expression of BRCA1a/1b attenuates MEK-induced SRE activation in vivo. These results demonstrate for the first time a link between the growth suppressive function of BRCA1a/1b proteins and signal transduction pathway involving Elk-1 protein. All these results taken together suggest that one of the mechanisms by which BRCA1a/1b proteins function as growth/tumor suppressors is through inhibition of the expression of Elk-1 target genes like c-Fos.
Chai
Y
Y
Department of Medicine, Program of Cancer Genetics, Cancer Center, MCP Hahnemann University, 245 North 15th Street, New College Building, M.S. 481, Philadelphia, Pennsylvania 19102, USA.
Chipitsyna
G
G
Cui
J
J
Liao
B
B
Liu
S
S
Aysola
K
K
Yezdani
M
M
Reddy
E S
ES
Rao
V N
VN
D017398:Alternative Splicing; D000818:Animals; D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins; D005260:Female; D016147:Genes, Tumor Suppressor; D016762:Genes, fos / Q000235:genetics*; D006801:Humans; D015674:Mammary Neoplasms, Animal / Q000378:metabolism / Q000473:pathology; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009687:Nuclear Proteins; D011485:Protein Binding; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D020218:Response Elements; D026362:Serum Response Factor; D014157:Transcription Factors / Q000378:metabolism*; D050807:ets-Domain Protein Elk-1
D019313:BRCA1 Protein; D004268:DNA-Binding Proteins; C494112:ELK1 protein, human; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D026362:Serum Response Factor; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases