EXPRESSION OF CATHEPSIN-B IN SMALL-CELL LUNG-CARCINOMA CELLS IN RELATION TO IN-VITRO INVASIVENESS

Cathepsin B expression and its relation to in vitro invasiveness were investigated in small cell lung carcinoma cells (OC-10 cells), A subcl one derived from OC-10 cells(10N) was similar to the parental cells bo th in growth pattern and morphology. However, the in vitro invasive ca pacity of OC-10 cells was 4 times higher than that of 10N cells. Cathe psin B activities in the plasma membrane fraction and spent medium of OC-10 cells were 2-fold higher than those of 10N cells, The invasivene ss of OC-10 cells was markedly blocked by the addition of cysteine pro teinase inhibitors, E-64C or leupeptin, while treatment of ION cells w ith 2% (v/v) DMSO resulted in a 2-fold increment both in invasive capa city and cathepsin B activity, Immunoblot analysis demonstrated that t he intensity of the cathepsin B band from OC-10 or 10N cells was not r emarkably different regardless of DMSO treatment, Although no signific ant correlation was observed between the biochemical activity and prot ein of cathepsin B, in vitro invasive capacity of OC-10 cells strongly correlated with cathepsin B activity. These results suggest that cath epsin B plays an important role in the invasiveness of human small cel l lung carcinoma cells.