CD38 increases Rap1 activity that is required for cell motility. (A) Representative blot (left) and quantification (right) of active Rap1-GTP levels, assessed by Rap1 pulldown assays, in MEC1-GFP and MEC1-CD38H cells untreated or treated with CCL21 (100 ng/mL) for the indicated times. Graph shows the mean of 3 independent experiments ± SEM. Relative active Rap1 levels were obtained by normalizing each value to the untreated MEC1-GFP control cells. *P < .05; **P < .01 determined by 2-tailed Student t test. (B-D) MEC1-GFP and MEC1-CD38H cells were transfected with siRNAs targeting Rap1a or Rap1b. (B) Representative blots of Rap1a and Rap1b expression levels in MEC1-GFP and MEC1-CD38H cells. (C-D) Migration of MEC1-GFP and MEC1-CD38H cells through transwell filters after Rap1a (C) or Rap1b depletion (D). The migration index was obtained by normalizing the values to the MEC1-GFP control cells. Data shown are the mean of 3 independent experiments ± SEM. *P < .05; **P < .01 determined by 2-tailed Student t test.