SFL production by carcinoma cells induces the aggressive properties of nonproducing cells in vivo via a community effect.

A metastatic rat bladder carcinoma cell line, M-NBT-II, produces and secretes a dissociating factor called SFL, whereas the tumorigenic parental cell line from which it originated (E-NBT-II) does not. In this work, we report that SFL production is correlated with an invasive phenotype in three-dimensional collagen gels or organotypic cocultures. This invasiveness may be related to the production of gelatinolytic activity. We have also investigated the behavior of SFL-producing cells within an NBT-II solid tumor. Here we report that the presence of 14% of SFL-factor-producing cells are sufficient to increase the tumorigenicity, and subsequently the metastatic behavior, of the entire cell population, indicating that there is no clonal dominance of the SFL-producing cells for tumorigenicity and metastatic spreading, but rather a community effect. SFL factor may contribute to cell-cell cooperativity by paracrine or other indirect mechanisms.