ALPHA(1)-ANTITRYPSIN-INDEPENDENT AND ANCHORAGE-INDEPENDENT GROWTH OF MCF-7 BREAST-CANCER CELLS

Alpha1-Antitrypsin (alpha1-AT) and alpha1-antichymotrypsin (alpha1-ACHY) are closely related protease inhibitors, synthesized primarily by the liver, which play major roles in modulation of the inflammatory response. Previously, we had shown that MCF-7 human breast cancer cells were able to synthesize active alpha1-AT and alpha1-ACHY and that the synthesis of both inhibitors varied among different MCF-7 sublines. We now show that when MCF-7(ML) cells (a subline synthesizing low levels of al-AT) are grown in soft agar in medium depleted of its trypsin inhibitory capacity (ie. alpha1-AT-free), addition of alpha1-AT (50 mug/ml) significantly reduces colony formation in both the presence and absence of estradiol (34% and 44%, respectively). Under these conditions, incubation with 10(-7) M estradiol alone increased colony formation 2- to 3-fold. Colony formation was also significantly reduced by serum leukocyte protease inhibitor, which, like alpha1-AT, is a potent inhibitor of elastase-like enzymes. We also found that a variety of inflammatory mediators, cytokines, and steroid hormones are able to stimulate synthesis of alpha1-AT and alpha1-ACHY by MCF-7 cells. Stimulation by interleukin-6 (IL-6; 200 U/ml), epidermal growth factor (4 nM), and estradiol (10(-7) M) was 2- to 3-fold, whereas stimulations by tetradecanoylphorbol-13-acetate (TPA; 80 nm) and IL-1 (10 U/ml) were 2- to 5-fold and 5- to 10-fold, respectively. In each instance, protein synthesis, monitored by immunoprecipitation of S-35-labeled proteins followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and steady state mRNA levels, monitored by Northern blot analysis with specific cDNA probes, increased to the same extent. Consistent with their ability to stimulate alpha1-AT synthesis, TPA and IL-1 reduced colony formation in the absence of estradiol by 65% and 63%, respectively. In addition, the effects of both TPA and IL-1 could be reversed by antibody to alpha1-AT. These results suggest that local synthesis of alpha1-AT and possibly other protease inhibitors may be important in regulating the tumorigenic potential of MCF-7 breast cancer cells.