Differential Production of Proteolytic Enzymes by Normal (KMS-6), Immortally Transformed (KMST-6), and Tumorigenetically Transformed (Ha-KMST-6) Human Fibroblasts
Production of proteolytic enzymes by human fibroblasts in the process of transformation was investigated in order to learn which step, the immortalizing or tumorigenic step, is more important for malignant transformation of human cells. The cells used were normal human fibroblasts (KMS-6), fibroblasts immortally transformed by treatment with Co-60 gamma rays (KMST-6), and KMST-6 cells further tumorigenetically transformed KMST-6 cells by infection with Harvey murine sarcoma viruses (Ha-KMST-6). Proteolytic enzymes in culture medium or cells were assayed using synthetic substrates, N-a-(p-tosyl)-L-arginine [3H]methyl ester hydrochloride and H-D-val-leu-lys-p-nitroaniline. Our results showed that the immortally transformed KMST-6 cells produced a larger amount of the enzymes than the normal and the tumorigenetically transformed cells. Since elevated production of proteolytic enzymes has been reported to correlate well with malignant transformation of cultured rodent or avian cells by many other investigators, our present results indicate that our immortalized human fibroblasts have already acquired properties characteristic to cancer cells.