Lack of Timp-1 mRNA expression and presence of gelatinase activity in conditioned media of ESbL-lacZ cells. (A) Total RNA isolated from ESbL-lacZ or H59.NA3 (Lewis lung carcinoma used as positive control) cells was analyzed by Northern blotting. Lower panel shows the loading control, 18S rRNA. (B) Zymographic analysis was performed using 5 μg protein from mammary tissue or freshly collected ESbL-lacZ–conditioned media. Mouse mammary tissue served as a positive control for enzymatic activity. 92-kD gelatinase A (MMP-9) and 72-kD gelatinase B (MMP-2) are indicated.