The tyrosine kinase ACK1 associates with clathrin-coated vesicles through a binding motif shared by arrestin and other adaptors

One target for the small GTPase Cdc42 is the nonreceptor tyrosine kinase activated Cdc42-associated kinase (Ack), which binds selectively to Cdc42.GTP. We report that Ack1 can associate directly with the heavy chain of Clathrin. A central region in Ack1 containing a conserved motif behaves as a Clathrin adaptor and competes with beta-arrestin for a common binding site on the Clathrin N-terminal head domain. Overexpressed Ack1 perturbs Clathrin distribution, an activity dependent on the presence of C-terminal "adaptor" sequences that are also present in the related nonkinase gene 33. Ack1 interacts with the adaptor Nck via SH3 interactions but does not form a trimeric complex with p21-activated serine/threonine kinase, which also binds Nck. Stable low level expression of green fluorescent protein-ACK1 in NIH 3T3 cells has been used to localize Ack1 to clathrin-containing vesicles. The co-localization of Ack1 in vivo with Clathrin and AP-2 indicates that it participates in trafficking, underlying an ability to increase receptor-mediated transferrin uptake.