Figure 8.

Thrombin-induced migration of Swiss 3T3 cells does not require the EGF receptor but potentiates EGF receptor action. (A) The effect of the EGF receptor kinase inhibitor (AG1478) on thrombin- and EGF-induced cell migration was examined in a transwell migration assay. Cells were labeled with the fluorescent indicator CFSE and placed in an 8-μm transwell insert in the presence or absence of AG1478 (0.5 μM). The insert was then placed in a 24-well plate with DME alone or in wells to which was added thrombin (2.5 U/ml) or EGF (25 nM). Fluorescence measurements to assess migration of CFSE-labeled cells through the transwell membrane were then carried out at the intervals shown. The results are means of duplicate assays from a single experiment, and are representative of the same effect seen in three separate preparations. (B) Cell migration in response to EGF and thrombin was assessed as described above, except that these agonists were added alone or in combination either in the upper transwell insert chamber or in the lower chamber of the 24-well plate. It can be seen that the presence of thrombin in the upper chamber potentiated the migratory response to EGF in the lower chamber. This was highly selective, as other combinations of agonist addition did not have this effect. The results are the mean ± SEM of three samples from a single experiment and are representative of the same qualitative effect seen in two such experiments.