SUDS3 regulates BRMS1-mediated phenotypes by affecting SIN3-HDAC complex composition

2484 The involvement of Breast Cancer Metastasis Suppressor 1 (BRMS1) in SIN3-HDAC chromatin remodeling complexes has been implicated as a mechanism by which BRMS1 can suppress metastasis. This involvement is thought to be mediated by the direct interaction of BRMS1 with the SIN3-HDAC complex components SUDS3 and ARID4A. In yeast, SUDS3 acts as a scaffolding protein that stabilizes SIN3-HDAC complexes. We hypothesized that direct interaction of SUDS3 and BRMS1 regulates the composition of these complexes and, thus, regulates the transcription of genes required for metastasis. Mutational analysis showed that deletion of the first coiled-coil domain results in a BRMS1 mutant, BRMS1ΔCC1, that does not interact with SUDS3 in yeast two hybrid genetic screens. While BRMS1ΔCC1 still directly interacts with ARID4A in yeast, it was unable to co-immunoprecipitate ARID4A in MDA-MB-435 cells. These data suggest that the interaction of SUDS3 with BRMS1 is necessary for the formation of a BRMS1-protein complex containing ARID4A and, moreover, suggests that SUDS3 influences the composition of BRMS1-SIN3-HDAC protein complexes. Unlike wild-type BRMS1, BRMS1ΔCC1 did not decrease levels of PtdIns(4,5)P2. However, like wild-type, BRMS1ΔCC1 completely down-regulated expression of Epidermal Growth Factor Receptor in MDA-MB-435 cells. Through more refined mutational analysis, the site of BRMS1:SUDS3 interaction is being mapped to confirm that these and other results are a direct effect of disrupting this interaction. Taken together these data indicate that the interaction of SUDS3 and BRMS1, at least partially, dictates the composition of BRMS1-SIN3-HDAC complexes to alter specific (i.e., not all) BRMS1-mediated phenotypes. These insights into the formation of BRMS1-SIN3-HDAC complexes can lead to a better understanding of how BRMS1 regulates transcriptional events to suppress metastasis.
 Support: CA87728, F32CA113037, Natl. Fndn Cancer Res