Reversible transformation by urea of contact-inhibited fibroblasts.

200 mM urea elicits alterations of cell social behavior in vitro. In the presence of urea, contact inhibition of movement and growth is reduced compared to untreated fibroblastic cell populations. This reduction of contact inhibition is rapidly reversible, but reversal requires some cycloheximide-sensitive cellular process. Cells treated with urea are agglutinable by concanavalin A, suggesting that urea might remove some cell-surface component(s). A nondialyzable factor can, in fact, be detected in the supernatant medium of urea-treated cells. This active constituent appears to be heat-labile and trypsin-sensitive, and can itself restore normal contact-inhibitory behavior to cells maintained in the urea-transformed state by cycloheximide. This system may permit identification and characterization of surface components that are involved in regulating normal cell social behavior.