Suppression of ruffling by the EGF receptor in chemotactic cells

To clarify the relationship between ruffling and lamellipod extension in growth factor-stimulated chemotactic responses, we utilized cell lines derived from the rat 13762 NF mammary adenocarcinoma. Non-metastatic MTC cells expressing the human EGF receptor (termed MTC HER cells) demonstrated chemotactic responses to TGF-α, an EGF receptor ligand typically present in mammary tissue. In microchemotaxis chambers, peak chemotactic responses occurred in response to 5 nM TGF-α. MTC HER cells showed dramatic ruffling edges in the absence of external stimuli, and addition of 5 nM TGF-α led to a transient reduction in ruffling concomitant with lamellipod extension. Lamellipod extension correlated with an overall increase in actin polymerization. These responses were blocked by the PI 3 kinase inhibitor wortmannin but not by the MAP kinase inhibitors PD98059 and SB203580. We conclude that the initial chemotactic response to TGF-α involves lamellipod extension and that ruffling reflects a dynamic turnover of lamellipodia that is arrested during lamellipod extension. By regulating the dissolution of ruffles and extension of lamellipods, a chemotactic response can be achieved, which may contribute to the metastatic process.