Adhesion Regulation of Stromal Cell-derived Factor-1 Activation of ERK in Lymphocytes by Phosphatases

We have investigated whether chemokine signaling to the extracellular-signal-regulated kinase (ERK) was regulated by β1-integrin-mediated adhesion in B- and T-cell lines. Activation of ERK by the chemokine SDF-1 can be regulated by adhesion to β1-integrin substrates in the T-cell lines MOLT-3, Jurkat, and H9 and in the Daudi B-cell line. In Jurkat T-cells, adhesion to the immobilized α4β1-integrin ligand VCAM-1 or to the α5β1-integrin ligand fibronectin regulated stromal-cell derived factor-1 (SDF-1) activation of ERK. Adhesion control of SDF-1 signaling was a rapid event, occurring as early as 10 min after adhesion, and loss of signaling occurred within 10 min of deadhesion. In contrast, SDF-1 activation of the ERK kinase MEK was independent of adhesion. Partial restoration of signaling to ERK in suspension was accomplished by pretreatment with pharmacological inhibitors of serine/threonine or protein-tyrosine phosphatases. In addition, we used a non-radioactive phosphatase assay using phosphorylated ERK as the substrate to determine relative ERK dephosphorylation in whole cell extracts. These results showed greater relative ERK dephosphorylation in extracts from Jurkat cells treated in suspension, as compared with adherent cells. Therefore, these data suggest that adhesion influences SDF-1 activation of ERK by regulating the activity of ERK phosphatases. This identifies a novel locus of adhesion regulation of the ERK cascade.