Analysis of mechanisms underlying BRMS1 suppression of metastasis

Introduction of normal, neomycin-tagged human chromosome 11 (neo11) reduces the metastatic capacity of MDA-MB-435 human breast carcinoma cells by 70-9 0% without affecting tumorigenicity. Differential display comparing MDA-MB- 435 and neo11/435 led to the discovery of a human breast carcinoma metastas is suppressor gene, BRMS1, which maps to chromosome 11q13.1-q13.2. Stable t ransfectants of MDA-MB-435 and MDA-MB-231 breast carcinoma cells with BRMS1 cDNA still form progressively growing, locally invasive tumors when inject ed in mammary fat pads of athymic mice but exhibit significantly lower meta static potential (50-90% inhibition) to lungs and regional lymph nodes. To begin elucidating the mechanism(s) of action, we measured the ability of BR MS1 to perturb individual steps of the metastatic cascade modeled in vitro. Consistent differences were not observed for adhesion to extracellular mat rix components (laminin, fibronectin, type IV collagen, type I collagen, Ma trigel); growth rates in vitro or in vivo; expression of matrix metalloprot einases, heparanase, or invasion. Likewise, BRMS1 expression did not up reg ulate expression of other metastasis suppressors, such as NM23, Kai1, KiSS1 or E-cadherin. Motility of BRMS1 transfectants was modestly inhibited (30- 60%) compared to parental and vector-only transfectants. Ability to grow in soft agar was also decreased in MDA-MB-435 cells by 80-89%, but the decrea se for MDA-MB-231 was less (13-15% reduction). Also, transfection and re-ex pression of BRMS1 restored the ability of human breast carcinoma cells to f orm functional homotypic gap junctions. Collectively, these data suggest th at BRMS1 suppresses metastasis of human breast carcinoma by complex, atypic al mechanisms.