Calyculin A increases basal cpERM phosphorylation and inhibits SDF-1α–induced dephosphorylation. (A) Pharmacologic perturbation of basal kinase/phosphatase balance. Western blotting was performed for cpERM and total ERM on PBT cells treated with 50 nM calyculin A or 500 nM staurosporine for the indicated times. (B) ERM dephosphorylation following 1 minute of SDF-1α stimulation can be inhibited by costimulation (50 nM) or by brief pretreatment (10 nM, 2 minutes) with calyculin A. Western blots of duplicate membranes detecting cpERM versus total ERM versus phospho-p44/42 MAPK.