Expression of trypsin in human cancer cell lines and cancer tissues and its tight binding to soluble form of Alzheimer amyloid precursor protein in culture

It was recently found that overexpression of the trypsin gene in tumor cell s stimulates their growth in culture and in nude mice. In the present study , expression of trypsin in various human cancer cell lines and tissues was studied by gelatin zymography and immunoblotting before and after enterokin ase treatment and by immunohistochemistry. The analyses showed that many st omach, colon, and breast cancer cell lines secreted trypsinogens-1 and/or - 2, as well as an unidentified serine proteinase of about 70 kDa, into cultu re medium. Lung cancer cell lines secreted 18- and 19-kDa unidentified tryp sin-like proteins. Stomach cancer cell lines frequently secreted active try psin, suggesting that they produced an endogenous activator of trypsinogen, most likely enterokinase. Active trypsin formed a complex with a soluble f orm of Alzheimer amyloid precursor protein (sAPP), a Kunitz-type trypsin in hibitor, which was secreted by all cell lines tested. This indicated that s APP is a primary inhibitor of secreted trypsin, Immunohistochemical analysi s showed that trypsin(ogen) was frequently expressed at high levels in stom ach and colon cancers, but scarcely in breast cancers. In the stomach cance rs, the trypsin immunoreactivity was higher in the malignant, non-cohesive type than in the cohesive type. These results support the hypothesis that t umor-derived trypsin is involved in the malignant growth of tumor cells, es pecially stomach cancer cells.