The BRMS1 metastasis suppressor is part of SIN3:histone deacetylase chromatin remodeling complexes through direct interaction with the protein AT rich interactive domain 4A (ARID4A, retinoblastoma-binding protein 1, RBBP1). These transcriptional co-repressors regulate diverse cell phenotypes depending on the composition of the complex. To define BRMS1 complexes and their roles in metastasis suppression, we generated BRMS1 mutants (BRMS1mut) and mapped ARID4A interactions. A point mutant (BRMS1L174D) disrupted direct interaction with ARID4A in yeast two-hybrid genetic screens (Y2H) but retained an indirect association with ARID4A in MDA-MB-231 and -435 breast cancer cell lines by co-immunoprecipitation (co-IP). Deletion of the first coiled-coil domain (BRMS1ΔCC1) did not disrupt direct (Y2H) interaction, but did prevent their association by co-IP. These results suggest altered complex composition with BRMS1mut. Basal transcription repression was impaired and the pro-metastatic gene osteopontin (OPN) was differentially down-regulated by BRMS1L174D and BRMS1ΔCC1, however, both down-regulated epidermal growth factor receptor (EGFR) and suppressed metastasis in MDA-MB-231 and -435 breast cancer xenograft models. We conclude that BRMS1mut that modify the composition of a SIN3:HDAC chromatin remodeling complex leads to altered gene expression profiles. Because metastasis requires the coordinate expression of multiple genes, down-regulation of at least one important gene, such as EGFR, had the ability to suppress metastasis. Understanding which interactions are necessary for particular biochemical/cellular functions may prove important for future strategies targeting metastasis.

99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA