Augmented excretion of procathepsin L of a fos-transferred highly metastatic rat cell line.

We previously reported that v-fos transfer to a src-transformed rat 3Y1 cell line (SR-3Y1-2) enhanced lung metastasis accompanied with an increase in invasiveness. When analyzing factors relating to the high invasiveness, with special reference to typical lysosomal proteases (cathepsins), involving degradation of stroma, we found that the excretion of procathepsin L was significantly larger in the fos-transferred highly metastatic cell line (fos-SR-3Y1-202) than that in the recipient cell lines. The cathepsin D-induced enzyme activity of the excreted procathepsin L in fos-SR-3Y1-202 was about 4 and 13 fold that of SR-3Y1-2 and 3Y1, respectively. The increase in the excretion of procathepsin L from fos-SR-3Y1-202 may play a role in the high invasiveness induced by transfer with the v-fos oncogene.