The cells respond to the growth factors from the environment and migrate toward the growth factors.  Such directional migration of the cells are extremely important in angiogenesis, newly forming vessels from pre-existing blood vessels.

      Then, how do the cells know which direction to migrate?

The cells sense the gradient of the growth factors and accumulate the receptors of the growth factors at the area facing the growth factors. 

      We are studying the mechanism of the trafficking of the receptors and signaling molecules in mammalian cells.