Lad is required for the chemokine-induced activation of ERK. (A) Jurkat T cells transfected with empty pSUPER or pSUPER plasmids expressing SiA or SiB were treated with SDF-1α (S) or RANTES (R) for 10 minutes, and the cell lysates were analyzed by Western blotting with anti–phospho p42/44 ERK antibody (upper panel). The same blot was reprobed with anti–p42/44 ERK antibody to control for the level of ERK (middle panel). The same lysates were also analyzed for the level of endogenous Lad by Western blotting with antiLad antibody (bottom panel). (B) Jurkat T-cell clones that stably expressed Lad or the SH2 domain of Lad were activated and processed as described in panel A.