Breast cancer metastasis suppressor 1 inhibits gene expression by targeting nuclear factor-κB activity

Breast cancer metastasis suppressor I (BRMS1) functions as a metastasis suppressor gene in breast cancer and melanoma cell lines, but the mechanism of BRMS1 suppression remains unclear. We determined that BRMS1 expression was inversely correlated with that of urokinase-type plasminogen activator (uPA), a prometastatic gene that is regulated at least in part by nuclear factor-kappa B (NF-kappa B). To further investigate the role of NF-kappa B in BRMS1-regulated gene expression, we examined NF-kappa B binding activity and found an inverse correlation between BRMS1 expression and NF-kappa B binding activity in MDA-MB-231 breast cancer and C8161.9 melanoma cells stably expressing BRMS1. In contrast, BRMS1 expression had no effect on activation of the activator protein-1 transcription factor. Further, we showed that suppression of both constitutive and tumor necrosis factor-alpha-induced NF-kappa B activation by BRMS1 may he due to inhibition of I kappa B alpha. phosphorylation and degradation. To examine the relationship between BRMS1 and uPA expression in primary breast tumors, we screened a breast cancer dot blot array of normalized cDNA from 50 breast tumors and corresponding normal breast tissues. There was a significant reduction in BRMS1 mRNA expression in breast tumors compared with matched normal breast tissues (paired t test, P < 0.0001) and a general inverse correlation with uPA gene expression (P < 0.01). These results suggest that at least one of the underlying mechanisms of BRMS1-dependent suppression of tumor metastasis includes inhibition of NF-kappa B activity and subsequent suppression of uPA expression in breast cancer and melanoma cells.