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Breast Cancer Metastasis Suppressor 1 (BRMS1), a recently discovered metastasis suppressor, inhibits metastasis without blocking tumorigenesis in multiple human and murine cancer cells. BRMS1 is part of multi-protein complexes (>1 MDa total mass) that include mSin3 and HDAC-1/2, which function in transcriptional regulation. However, all of the proteins involved in these complexes are incompletely known. The goal of these studies was to identify BRMS1 interacting proteins (BIPs). Yeast two-hybrid, affinity chromatography, and bi-directional co-immunoprecipitation (co-IP) experiments identified the chaperone proteins Hsp40, Hsp70, and Hsp90 as BIPs. To further characterize the functional interaction of these BIPs with BRMS1, cells were treated with the Hsp90 inhibitor geldanamycin (GA). BRMS1 was degraded in a dose-dependent manner in GA treated cells that was rescued by treatment with the proteasome inhibitor MG-132. The degradation pathway is most likely ubiquitin-independent because immunoprecipitation of BRMS1 showed no detectable levels of ubiquitin. The acetylation state of Hsp90 affects chaperone function and has been recently demonstrated to be regulated by HDAC-6. Co-IP also identified HDAC-6 and two other class II HDACs, HDAC-4 and -5 as BIPs. These data demonstrate that BRMS1 is dynamically regulated by the Hsp90 chaperone complex which may be important in maintaining the functional role of BRMS1 in metastasis suppression. Support: CA87728, F32CA113037, and National Foundation for Cancer Research

[Proc Amer Assoc Cancer Res, Volume 47, 2006]