Culture of a prostatic cell line in basement membrane gels results in an enhancement of malignant properties and constitutive alterations in gene expression.

Interaction of a transformed rat prostate epithelial cell (NbMC-2) with basement membrane gels (Matrigel) has been evaluated using a long-term matrix culture system. NbMC-2 cells, and single-cell clonal derivatives, formed spheroidal multicellular structures (aggregates) on Matrigel surfaces and were weakly invasive or noninvasive during a 1 week period. During subsequent 2-4 week periods, invasive cells originating from the aggregates and exhibiting a fusiform morphology became evident and increased in number in the matrix cultures. This biphasic pattern of behavior did not occur on laminin, type I or type IV collagen, or fibronectin substrates, but it did occur on Matrigel in serum-free medium. Characterization of sublines enriched in fusiform cells indicated that they maintained their distinct morphology with continuous culture. Further, they exhibited significantly greater invasive potential, saturation density, and random motility (chemokinesis) than the parent cell line. Steady-state levels of fibronectin mRNA were highly elevated in the fusiform variants, demonstrating a constitutive alteration in patterns of gene expression coinciding with the altered morphology. These results indicate that clonal NbMC-2 cells differentiate at a reproducible frequency into a more aggressive cell type in response to culture in the basement membrane-like matrix. The altered phenotypic properties appear to be stable since they can be inherited by daughter cells and because they are evident in the absence of matrix. These observations suggest a cell-specific mechanism for promotion of malignant growth by matrix-mediated induction of novel cell properties.