Role of MRP8 and MRP14 in cytoskeletal organization during transmigration of phagocytes. In resting phagocytes, MRP8/MRP14 complexes promote formation and stabilization of MTs. Isolated activation of the p38 MAPK signaling pathway (signal 1) has no effect because complex formation with MRP8 does not allow phosphorylation of MRP14. Concomitant calcium signaling (signal 2), however, induces conformational changes of the MRP8/MRP14 complex, which then permits phosphorylation of MRP14. The MT-stabilizing effect of MRP8/MRP14 complexes is thereby abrogated. After dissociation from depolymerizing MTs, small GTPases Rac1 and Cdc42 are activated and transmigration of granulocytes is facilitated.