beta4 integrin and epidermal growth factor coordinately regulate electric field-mediated directional migration via Rac1.

Endogenous DC electric fields (EF) are present during embryogenesis and are generated in vivo upon wounding, providing guidance cues for directional cell migration (galvanotaxis) required in these processes. To understand the role of beta (beta)4 integrin in directional migration, the migratory paths of either primary human keratinocytes (NHK), beta 4 integrin-null human keratinocytes (134-), or those in which beta 4 integrin was reexpressed (beta 4+), were tracked during exposure to EFs of physiological magnitude (100 mV/mm). Although the expression of beta 4 integrin had no effect on the rate of cell movement, it was essential for directional (cathodal) migration in the absence of epidermal growth factor (EGF). The addition of EGF potentiated the directional response, suggesting that at least two distinct but synergistic signaling pathways coordinate galvanotaxis. Expression of either a ligand binding- defective 04 (beta 4+AD) or 64 with a truncated cytoplasmic tail (beta 4+CT) resulted in loss of directioriality in the absence of EGF, whereas inhibition of Racl blinded the cells to the EF even in the presence of EGF. In summary, both the beta 4 integrin ligand-binding and cytoplasmic domains together with EGF were required for the synergistic activation of a Rac-dependent signaling pathway that was essential for keratinocyte directional migration in response to a galvanotactic stimulus.