Activation of the Cdc42-associated tyrosine kinase-2 (ACK-2) by cell adhesion via integrin beta1.

Activated Cdc42-associated kinase-2 (ACK-2) is a non-receptor tyrosine kinase that appears to be a highly specific target for the Rho-related GTP-binding protein Cdc42. In order to understand better how ACK-2 activity is regulated in cells, we have expressed epitope-tagged forms of this tyrosine kinase in COS-7 and NIH3T3 cells. We find that ACK-2 can be activated by cell adhesion in a Cdc42-dependent manner. However, unlike the focal adhesion kinase, which also is activated by cell adhesion, the activation of ACK-2 is F-actin-independent and does not require cell spreading. In addition, overexpression of ACK-2 in COS-7 cells did not result in the stimulation of extracellular signal-regulated kinase activity but rather activated the c-Jun kinase. Both anti-integrin beta1 antibody and RGD peptides inhibited the activation of ACK-2 by cell adhesion. In addition, ACK-2 was co-immunoprecipitated with integrin beta1. Overall, these findings suggest that ACK-2 interacts with integrin complexes and mediates cell adhesion signals in a Cdc42-dependent manner.