Growth control of A431 cells in protein-free medium: secretory products do not affect cell growth.

A431 cells grew at similar rates in protein-free Coon's modified Ham's F12 medium (PF-C-F12) with and without added bovine calf serum. The cells secreted a heparin-binding growth factor and a type-beta transforming growth factor, but their growth in PF-C-F12 was not affected by these factors, or by DNA synthesis factor from Rhodamine fibrosarcoma, basic fibroblast growth factor, insulin, human transferrin, bovine serum albumin, and their combinations. Growth of A431 cells in PF-C-F12 was not density dependent and was not affected by either addition of conditioned medium or replacement of conditioned medium by fresh medium. These results indicate that A431 cells have an intracellular mechanism for autonomous growth, and that their growth is not affected by factors that they secrete or by exogenous growth factors.