Induction of fibroblast 92 kDa gelatinase/type IV collagenase expression by direct contact with metastatic tumor cells

Abstract

Previous studies have correlated release of the 92 kDa type IV collagenase/gelatinase by tumor cells in culture with metastatic potential. We have now demonstrated that the ability of tumor cells that do not express the 92 kDa gelatinase to induce release of this metalloproteinase from normal fibroblasts may also be associated with the metastatic phenotype. A transformed rat embryo cell line, 2.8, failed to release the 92 kDa gelatinase alone in culture, but gave rise to metastatic tumors whose explants contained the 92 kDa gelatinase. In contrast, a non-metastatic transformed cell line, RA3, did not express the 92 kDa gelatinase alone in culture or in tumor explants. To explore the mechanisms that might govern host-tumor cell interactions in this system, we have studied the effects of co-culture of these transformed cell lines with rat embryo fibroblasts (REF) in culture. 92 kDa gelatinase expression was induced by co-culture of 2.8 with REF, but co-culture of the non-metastatic line RA3 with REF did not result in induction of the 92 kDa gelatinase. The 92 kDa gelatinase in these co-cultures was released by the fibroblasts; methanol-fixed 2.8 cells induced 92 kDa gelatinase expression in REF, but fixed REF cells did not induce enzyme expression in 2.8 cells. This suggested that cell contact was required for induction, which was confirmed by showing that 92 kDa gelatinase induction in co-culture was abolished by separating REF from 2.8 by solute-permissive membranes. In addition, REF could not be stimulated to produce the 92 kDa gelatinase by 2.8-derived conditioned medium, by 2.8-derived extracellular matrix, or by isolated matrix components. These data indicate that metastatic tumor cells can induce 92 kDa gelatinase expression in fibroblasts through a mechanism dependent upon cell contact. In situ hybridization of nude mouse tumors derived from these transformed cell lines revealed 92 kDa gelatinase expression in the stroma of tumors from 2.8, but not in tumors from RA3. Therefore, the experiments based on in vitro co-culture of tumor cells and fibroblasts, together with the in situ localization of mRNA to host cells, suggest that host production of the 92 kDa gelatinase may occur in response to direct contact with metastatic tumor cells.