Effects of CXCL12 and CXCL13 stimulation on p44/p42 MAPK activation. SP-53 cells were stimulated with 250 ng/mL CXCL12 or 1 μg/mL CXCL13 for different times. To block CXCR4-derived signaling, cells were preincubated for 1 hour with 100 μg/mL Plerixafor and then stimulated with CXCL12. MCL cell lysates were probed with antiphospho p44/p42, antiβ-actin mAbs, and (on separate gels) with anti-p44/p42 mAbs. As indicated, maximum p44/p42 activation occurs within 2 minutes of stimulation with a subsequent decline in signal intensity. Pretreatment with Plerixafor effectively inhibits CXCL12-mediated p44/p42 MAPK activation. Results shown are representative of 3 experiments.