ESCAPE OF AUTOCRINE LIGANDS INTO EXTRACELLULAR MEDIUM - EXPERIMENTAL TEST OF THEORETICAL-MODEL PREDICTIONS

We have developed an experimental system for testing mathematical mode l predictions concerning escape of autocrine ligands into the extracel lular bulk medium. This system employs anti-receptor blocking antibodi es against the epidermal growth factor receptor (EGFR)/transforming gr owth factor alpha (TGF alpha) receptor/ligand pair. TGF alpha was expr essed under the control of a tetracycline-repressed promoter, together with a constitutively expressed human EGFR in B82 mouse fibroblast ce lls. This expression system allowed us to vary TGF alpha synthesis rat es over a roughly 300-fold range by adjusting tetracycline concentrati on. TGF alpha accumulation in the extracellular bulk medium was then m easured as a function of cell density, TGF alpha synthesis rate, and a nti-EGFR blocking antibody concentration. Consistent with model predic tions, amounts of ligand in the medium on a per cell basis were found to diminish as cell density was increased but with reduced dependence on cell density at higher ligand synthesis rates. Similarly consistent with model predictions, higher ligand synthesis rates also decreased the effect of anti-receptor blocking antibodies. Our investigation has established that we can successfully analyze and understand autocrine ligand secretion behavior from the basis of our theoretical model. (C ) 1998 John Wiley & Sons, Inc.