Epidermal growth factor receptor distribution during chemotactic responses

To determine the distribution bf the epidermal growth factor (EGF) receptor (EGFR) on the surface of cells responding to EGF as a chemoattractant, an EGFR-green fluorescent protein chimera was expressed in the MTLn3 mammary c arcinoma cell line. The chimera was functional and easily visualized on the cell surface. In contrast to other studies indicating that the EGFR might be localized to certain regions of the plasma membrane, we found that the c himera is homogeneously distributed on the plasma membrane and becomes most concentrated in vesicles after endocytosis. In spatial gradients of EGF, e ndocytosed receptor accumulates on the upgradient side of the cell. Visuali zation of the binding of fluorescent EGF to cells reveals that the affinity properties of the receptor, together with its expression level on cells, c an provide an initial amplification step in spatial gradient sensing.