c-Fos oncogene regulator Elk-1 interacts with BRCA1 splice variants BRCA1a/1b and enhances BRCA1a/1b-mediated growth suppression in breast cancer cells

Abstract

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 ®rst 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 DElk-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 ®rst 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.

BRCA1a has antitumor activity in TN breast, ovarian and prostate cancers

“…Others have found BRCA1 to inhibit the growth of a number of cell lines with an Rb-positive and p53-negative background (Aprelikova et al, 1999;Randrianarison et al, 2001). Our earlier results demonstrate that inhibition of expression of endogenous BRCA1 in mouse fibroblast results in transformation and highlevel expression of BRCA1a in breast cancer cells decreases proliferation (Chai et al, 2001) and induces apoptosis . In an attempt to understand whether BRCA1a can function as a growth suppressor similar to BRCA1, we have transfected BRCA1a (pcDNA3-BRCA1a) into a number of cell lines with known status of tumor suppressor genes, such as p53 and pRb.…”

BRCA1 Suppresses Osteopontin-mediated Breast Cancer

“…Mut. BRCA1 and Trunc.BRCA1, fail to bind to and repress the activity of any of the three transcription factors suggests that the mutated/deleted region contains elements of the binding site(s) for all three transcription factors (32)(33)(34)60).…”

“…High level OPN expression may have adverse prognostic significance (6) and may be associated with up-regulation of ER ␣ , AP-1, or Ets factors in sporadic human breast cancers (30). Because BRCA1 protein may bind ER ␣ (12,32), AP-1 (33), and Ets-transcription factors (34), we now investigate the effects of wild type (WT. ), mutated (Mut.…”

BRCA1 gene in breast cancer

“…The BRCA1 splice variants BRCA1a and BRCA1b-which suppress the growth of breast cancer cellsinteract with Elk-1, an Ets-domain transcription factor that participates in the induction of immediate early gene expression (Chai et al, 2001). Over-expression of BRCA1a/b inhibited the expression of Elk-1 target genes, such as c-Fos, suggesting a mechanism of growth inhibition.…”