Breast cancer metastasis suppressor 1 (BRMS1) is a member of the msin3-HDAC transcription co-repressor complex. However, the proteins associated with BRMS1 have not been fully identified. Yeast two-hybrid screen, immuno-affinity chromatography, and co-immunoprecipitation experiments were performed to identify BRMS1 interacting proteins (BIPs). In addition to known core mSin3 transcriptional complex components RBBP1 and mSDS3, BRMS1 interacted with other proteins including three chaperones: DNAJB6 (MRJ), Hsp90, and Hsp70. Hsp90 is a known target of HDAC6 and reversible acetylation is one of the mechanisms that is implicated in regulation of Hsp90 chaperone complex activity. BRMS1 interacted with class II HDACs, HDAC 4, 5, and 6. We further found that BRMS1 is stabilized by Hsp90, and its turnover is proteasome dependent. The stability of BRMS1 protein may be important in maintaining the functional role of BRMS1 in metastasis suppression. (c) 2006 Elsevier Inc. All rights reserved.