Characterization of the role of CaMKI-like kinase (CKLiK) in human granulocyte function

Activation of granulocyte effector functions, such as induction of the respiratory burst and migration, are regulated by a variety of relatively ill-defined signaling pathways. Recently, we identified a novel Ca 2 /calmodulin-dependent kinase I-like kinase, CKLiK, which exhibits restricted mRNA expression to human granulocytes. Using a novel antibody generated against the C-terminus of CKLiK, CKLiK was detected in CD34-derived neutrophils and eosinophils, as well as in mature peripheral blood granulocytes. Activation of human granulocytes by N-formyl-methionyl-leucyl-phenylalanine (fMLP) and platelet-activating factor (PAF), but not the phorbol ester PMA (phorbol 12-myristate-13-acetate), resulted in induction of CKLiK activity, in parallel with a rise of intracellular Ca 2 [Ca 2 ]i .T o study the functionality of CKLiK in human granulocytes, a cell-permeable CKLiK peptide inhibitor (CKLiK 297-321 ) was generated which was able to inhibit kinase activity in a dose-dependent manner. The effect of this peptide was studied on specific granulocyte effector functions such as phagocytosis, respiratory burst, migration, and adhesion. Phagocytosis of Aspergillus fumigatus particles was reduced in the presence of CKLiK 297-321 and fMLP-induced reactive oxygen species (ROS) production was potently inhibited by CKLiK 297-321 in a dosedependent manner. Furthermore, fMLPinduced neutrophil migration on albumin-coated surfaces was perturbed, as well as 2-integrin‐mediated adhesion. These findings suggest a critical role for CKLiK in modulating chemoattractantinduced functional responses in human granulocytes. (Blood. 2005;106:1076-1083)