Identification and characterization of CKLiK, a novel granulocyte Ca⁺⁺/calmodulin-dependent kinase

Human granulocytes are characterized by a variety of specific effector functions involved in host defense. Several widely expressed protein kinases have been implicated in the regulation of these effector functions. A polymerase chain reaction-based strategy was used to identify novel granulocyte-specific kinases. A novel protein kinase complementary DNA with an open reading frame of 357 amino acids was identified with homology to calcium-calmodulin-dependent kinase I (CaMKI). This has been termed CaMKI-like kinase (CKLiK). Analysis of CKLiK messenger RNA (mRNA) expression in hematopoietic cells demonstrated an almost exclusive expression in human polymorpho-nuclear leukocytes (PMN). Up-regulation of CKLiK mRNA occurs during neutrophilic differentiation of CD34⁺ stem cells. CKLiK kinase activity was dependent on Ca⁺⁺ and calmodulin as analyzed by in vitro phosphorylation of cyclic adenosine monophosphate responsive element modulator (CREM). Furthermore, CKLiK-transfected cells treated with ionomycin demonstrated an induction of CRE-binding protein (CREB) transcriptional activity compared to control cells. Additionally, CaMK-kinaseα enhanced CKLiK activity. In vivo activation of CKLiK was shown by addition of interleukin (IL)-8 to a myeloid cell line stably expressing CKLiK. Furthermore inducible activation of CKLiK was sufficient to induce extracellular signal-related kinase (ERK) mitogen-activated protein (MAP) kinase activity. These data identify a novel Ca⁺⁺/calmodulin-dependent PMN-specific kinase that may play a role in Ca⁺⁺-mediated regulation of human granulocyte functions. (C) 2000 by The American Society of Hematology.