Brefeldin A (BFA) inhibits proMMP-1 secretion. A: BFA (10 μg/ml) inhibits the increase in proMMP-1 in media of AGS-GR cells in response to hG17ns treatment for 16 h by arresting secretion and causing accumulation in the cells; when BFA is added to cells already treated with hG17ns for 16 h the pattern of bands in media after a further 8 h (i.e., at 24 h) is similar to that at 16 h suggesting a low capacity for proMMP-1 activation or degradation. B: enzyme activity of MMP-1 determined using a specific substrate [DNP-Pro-Cha-Abu-Cys(Me)-His-Ala-Lys(N-Me-Abz)-NH2 (Cha, β-cyclohexylalanyl; Abu, l-α-aminobutyryl; Abz, 2-aminobenzoyl)] is increased in hG17ns stimulated AGS-GR media (16 h) and is inhibited by treatment with BFA; no further increase in MMP-1 activity was detected in AGS-GR media, after treatment with hG17ns and addition of BFA for a further 8 h. Data are means ± SE, n = 3; horizontal arrows, P < 0.05.