SDF-1 activates Cdc42 and PAK in CEM cells.

(A) SDF-1 activates Cdc42. Cells deprived of serum were treated with 500 ng/mL SDF-1 for the indicated times, and Cdc42-GTP was pulled down using GST-CRIB. The top panel shows the kinetics of accumulated Cdc42 in the GTP-bound form that associates with GST-CRIB; the lower panel shows the total amount of Cdc42 in 4% of total cell extract. The bands corresponding to Cdc42-GTP were quantified by scanning densitometry, and the results shown are the mean ± SE of 3 independent experiments. (B) SDF-1 increases PAK-2 and PAK-4 kinase activity. Cells were stimulated as above and lysed. The lysates were immunoprecipitated with specific antibodies to PAK-2 or PAK-4. PAK activity was determined by in vitro kinase assay followed by SDS-PAGE and autoradiography. Quantitative analyses were performed by scanning densitometry, and the results shown are the mean ± SE of 5 (PAK-2) and 3 (PAK-4) independent experiments. (––), Pak-2; (––), Pak-4.