The anti-proliferative properties of Bowman-Birk proteins from legumes on colon cancer cells are related to their ability to inhibit trypsin- and chymotrypsin-like proteases

Abstract

Bowman-Birk inhibitors (BBI) from legumes, such as soybean, pea, lentil and chickpea, are naturally-occurring protease inhibitors with potential health-promoting properties within the gastrointestinal tract. Recently, we have demonstrated that BBI proteins are structurally and functionally resistant to the harsh environment of the gastrointestinal tract in vivo. BBI proteins from chickpea seeds can resist both acidic conditions and the action of proteolytic enzymes, and transit through the pig stomach and small intestine without major degradation, permitting significant amounts to reach the large intestine in active form. Further studies have demonstrated that the protease (trypsin- and chymotrypsin-like) inhibitory activities of soybean BBI are unaffected by the metabolic/proteolytic activity of faecal microbiota. We demonstrated that soybean BBI, consisting of multiple isoinhibitors, inhibited the in vitro cell growth of HT29 human colorectal adenocarcinoma cells as a consequence of their intrinsic ability to inhibit the proteolytic activities of serine proteases, where chemically inactive BBI showed no such effect. In contrast, the growth of non-malignant colonic fibroblast CCD-18Co cells was unaffected by soybean BBI. In our studies, sequence variation within the inhibitory domains suggested to be of biological relevance. Two major soybean isoinhibitors, IBB1 and IBBD2, showing considerable amino acid sequence divergence within and between their inhibitory domains, were purified in order to evaluate their individual effects on the proliferation of HT29 colon cancer cells. The anti-proliferative properties of individual isoinhibitors from soybean reveal that both trypsin- and chymotrypsin-like proteases involved in carcinogenesis should be considered as potential targets of BBI-like proteins.