Effect of serine/threonine kinase inhibitors on motility of human lymphocytes and U937 cells.

Mononuclear cell migration across the endothelium and through connective tissue into inflammatory sites is a multi-step process. After adhesion to the endothelium, there is an initial change in shape from spherical to irregular, followed by the migratory phase itself in which the cells constantly change in shape. In this paper we have investigated the possibility that the shape-changing in this latter phase is controlled by serine/threonine phosphorylation. For this purpose, we used a spontaneously shape-changing variant of U937 monocytoid cells as well as human peripheral blood lymphocytes that had been previously activated by anti-CD3. To test the role of phosphorylation in shape-changing, a wide range of serine/threonine kinase inhibitors was tested, including ML-7, KT5720, KT823, H7, H8, staurosporine, calphostin C, sphingosine, bisindolylmaleimide, chelerythrine and KN-62. Only those compounds which inhibited protein kinase C prevented lymphocyte and U937 shape-change and transmigration across polycarbonate filters. However, one specific protein kinase C inhibitor, bisindolylmaleimide, stimulated lymphocyte shape-change. In conclusion, these studies show that activation of a serine/threonine kinase is necessary for the constant shape-changing required for motility of mononuclear cells. The kinase may be a protein kinase C isotype or a closely related enzyme.