[Cysteine proteinases at various stages of neoplastic transformation of rat fibroblasts].

Cysteine-dependent proteinases were studied in a model system of rat embryonal fibroblasts which enabled to evaluate two discrete steps of malignant transformation in vitro: immortalization and tumoral transformation. Dynamics of intracellular and secreted activities of cysteine proteinases was estimated in relation to the stage of transformation and duration of cells cultivation. Activation of cysteine proteinases cathepsins L and B correlated with developed transformation of fibroblasts; each step of the process was characterized. Intracellular and secreted activities of the proteinases were distinctly increased in immortalized cells as compared with primary fibroblasts. The highest activity of the enzymes was detected both in intra- and extracellular fractions at the stage of complete fibroblast transformation. Cysteine-dependent cathepsin L-like proteinase was mainly responsible for intracellular and secreted activities of the fibroblast cultures studied. This proteinase was found to be produced in the form of precursor in all the cell strains studied and/or main part of the enzyme developed complexes with an inhibitor.