Breast cancer metastasis suppressor 1(BRMS1) was originally identified as a metastasis suppressor gene in breast cancer and melanoma cell lines. The role of metastases suppressors, including BRMS1, in non-small cell lung cancer (NSCLC) is unknown. NF-κB is constitutively activated in many cancers, including NSCLC, and plays a critical role in the regulation of apoptosis, cell growth, and metastatic movement of tumors. The ability of BRMS1 to modulate NF-κB signal transduction pathways is poorly understood. In this study, we used quantitative RT-PCR and western blot to screen BRMS1 expression in NSCLC cell lines and in surgically excised tumors from lung cancer patients. Both the expression levels of mRNA and protein were dramatically decreased in NSCLC cells and tumor tissues compared with normal lung epithelial cells and matched adjacent tissues. To determine the relationship between BRMS1 and NF-κB signaling, BRMS1 levels were modulated by overexpression or via siRNA BRMS1 to determine NF-κB-dependent gene expression in NSCLC and HEK 293T cells. We found that BRMS1 expression was inversely correlated with endogenous NF-κB-dependent gene expression, including anti-apoptotic genes (cIAP-2, Bfl1/A1) and prometastatic genes (IL-8). BRMS1 repressed both constitutive and TNF-induced NF-κB-dependent gene expression. GST-pull down and Gal4-luciferase activity assays indicated that the ability of BRMS1 to inhibit NF-κB transcriptional activity was associated with significant decreases in the transactivation potential of the RelA/p65 subunit of NF-κB. We also showed that BRMS1 abolished p300 induced RelA/p65 acetylation by binding with HDAC1 in a series of acetylation assays. Chromatin immunoprecipitation assays revealed that suppression of NF-κB activation by BRMS1 was associated with the recruitment of the mSin3A-HDAC1 transcriptional co-repressors complex and the dismissal of the p300 transcriptional co-activator to promoters which contain -κB binding site(s). Furthermore, overexpression of BRMS1 dramatically sensitized NSCLC cells to apoptosis following of the addition of TNF. In conclusion, these findings support a role for BRMS1-mediated regulated control of NF-κB in NSCLC cells through deacetylation of RelA/p65; and suggest that tumor cell loss of BRMS1 provides another mechanism through which the anti-apoptotic and pro-metastatic functions of NF-κB are unchecked in lung cancer.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]