Tumor-host interactions in the rabbit V2 carcinoma: stimulation of cathepsin B in host fibroblasts by a tumor-derived cytokine.

Organ cultures of explanted V2 carcinoma specimens as well as cultured V2 carcinoma cells produced a cytokine which stimulated rabbit skin fibroblasts to synthesize increased amounts of cathepsin B. The cytokine was released by the tumor cells as a heterogeneous family of polypeptides: two inactive forms (Mr = 55,000 and 68,000) which could be activated by limited proteolysis with trypsin and three active forms with Mr values of 12,000, 16,000 and 18,000. The treatment of inactive cytokine-containing tumor-conditioned media with trypsin, followed by chromatographic separation of the products, suggested that the high-Mr inactive components may represent precursors of the active forms. Cathepsin B was immunolocalized in the tumor-host interzone in co-cultures of tumor and host tissues. Some other possible activities of the tumor cytokine which emerged from previous studies, such as the induction of host cells to produce increased levels of collagenase and extracellular matrix, as well as the stimulation of host cell proliferation, are discussed in the light of the new findings and are proposed as an important mechanism in tumor invasion.