Submitted October 11, 2005
Accepted February 16, 2007
The adaptor protein Lad associates with the G protein
subunit and mediates chemokine-dependent T cell
migration
Dongsu Park, Inyoung Park, Deogwon Lee, Young Bong Choi, Hyunsook Lee, and Yungdae Yun*
Department of Life Science, Ewah Womans University, Seoul, Korea, Republic of
Department of Biological Science, Seoul National University, Seoul, Korea, Republic of
* Corresponding author; email: yunyung{at}ewha.ac.kr.
Lad/RIBP was previously identified as an adaptor protein involved in TCR-mediated T-cell activation. To elucidate the functions of Lad further, we here performed yeast two-hybrid screening using Lad as bait and discovered that the G protein 
subunit (G) is a Lad-binding partner. Since the most well-known G protein-coupled receptor in T cells is the chemokine receptor, we investigated whether Lad is involved in chemokine signaling. We found that, upon chemokine treatment, Lad associated with G in Jurkat T cells. Furthermore, ectopic expression of dominant negative Lad or the reduction of endogenous Lad expression by siRNA impaired the chemokine-induced migration of T cells, indicating that Lad is required for chemokine-induced T-cell migration. Subsequent investigation of the signaling pathways revealed that, in response to chemokine, Lad associated with the tyrosine kinases Lck and Zap-70 and that Lad was essential for the activation of Zap-70. Moreover, Lad was required for the chemokine-dependent tyrosine phosphorylation of focal adhesion molecules that included Pyk2 and paxillin. Taken together, these data show that, upon chemokine stimulation, Lad acts as an adaptor protein that links the G protein subunit to the tyrosine kinases Lck and Zap-70, thereby mediating T-cell migration.
