BRMS1 contributes to the negative regulation of uPA gene expression through recruitment of HDAC1 to the NF-κB binding site of the uPA promoter

The BRMS1 metastasis suppressor was recently shown to negatively regulate NF-kappa B signaling and down regulate NF-kappa B-dependent uPA expression. Here we confirm that BRMS1 expression correlates with reduced NF-kappa B DNA binding activity in independently derived human melanoma C8161.9 cells stably expressing BRMS1. We show that knockdown of BRMS1 expression in these cells using small interfering RNA (siRNA) leads to the reactivation of NF-kappa B DNA binding activity and re-expression of uPA. Further, we confirm that BRMS1 expression does not alter IKK beta kinase activity suggesting that BRMS1-dependent uPA regulation does not occur through inhibition of the classical upstream activators of NF-kappa B. BRMS1 has been implicated as a corepressor of HDAC1 and consistent with this, we show that BRMS1 promotes HDAC1 recruitment to the NF-kappa B binding site of the uPA promoter and is associated with reduced H3 acetylation. We also confirm that BRMS1 expression stimulates disassociation of p65 from the NF-kappa B binding site of the uPA promoter consistent with its reduced DNA binding activity. These data suggest that BRMS1 recruits HDAC1 to the NF-kappa B binding site of the uPA promoter, modulates histone acetylation of p65 on the uPA promoter, leading to reduced NF-kappa B binding activity on its consensus sequence, and reduced transactivation of uPA expression.