The soybean-derived Bowman Birk inhibitor (BBI) has been shown to inhibit carcinogenesis in both in vitro and in vivo model systems. In the present study, we have utilized a BBI affinity column to determine whether cellular enzymes, present in C3H/10T½ cells, specifically interact with this inhibitor. Using this technique, we have identified three proteins with masses of about 70, 60, and 50 kilodaltons. Cell fractionation experiments demonstrate that the 60- and 50-kilodalton proteins are present in the 10,000 × g pellet (lysosomal/golgi fraction) of C3H/10T½ cell homogenates. We have also identified two proteins with masses of 60 and 50 kilodaltons which bind to the BBI affinity column in fibroblasts from patients having Bloom syndrome. BBI as well as several other protease inhibitors has been shown previously to reduce the frequency of spontaneous chromosomal aberrations in these cells. Our results indicate that the 50- and 60-kilodalton proteins we have identified by affinity chromatography are present in both mouse and human cells and further suggest that these proteins are potential intracellular targets of the BBI in these cells.
Supported by NIH Grants CA45734, CA40214, CA22704, and ES00002.