title: GTP-dependent secretion from neutrophils is regulated by Cdk5.
abstract: We have previously shown evidence for the existence of a calcium-independent, GTP-regulated mechanism of secretion from neutrophils, but this secretory mechanism remains to be fully elucidated. Cyclin-dependent kinase 5 (Cdk5), the various substrates of which include Munc18 and synapsin 1, has been implicated in neuronal secretion. Although the Cdk5 activator, p35, and Cdk5-p35 activity are primarily associated with neurons, we report here that p35 also exists in neutrophils and that an active Cdk5-p35 complex is present in these cells. Cdk5-p35 activity in human neutrophils is mostly localized in secretory granules, which show an increase in Cdk5-p35 level and activity upon GTP stimulation. The potent Cdk5 inhibitor, roscovitine, completely blocks GTP-stimulated granule Cdk5 activity, which accompanies lactoferrin secretion from neutrophil-specific granules. Roscovitine also inhibits GTP-induced lactoferrin secretion and surface localization of the secretion markers, CD63 and CD66b, to a certain extent. Furthermore, neutrophils from wild-type mice treated with roscovitine and neutrophils from p35(-/-) mice exhibit comparable surface expression levels of both CD63 and CD66b upon GTP stimulation. Although our data suggest that other molecules control GTP-induced secretion from neutrophils, it is clear that Cdk5-p35 is required to elicit the maximum GTP-induced secretory response. Our observation that multiple proteins in neutrophil granules serve as specific substrates of Cdk5 further supports the premise that the kinase is a key component of the GTP-regulated secretory apparatus in neutrophils.
authors.affiliation: Department of Cell Biology and Anatomy, Cancer Biology and Neuroscience Research Groups, The University of Calgary, Calgary, Alberta T2N 4N1, Canada. rosales@ucalgary.ca
authors.forename: Jesusa L
authors.initials: JL
authors.lastname: Rosales
authors.forename: Joel D
authors.initials: JD
authors.lastname: Ernst
authors.forename: Janice
authors.initials: J
authors.lastname: Hallows
authors.forename: Ki-Young
authors.initials: KY
authors.lastname: Lee
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D000951:Antigens, Neoplasm / Q000032:analysis; D015815:Cell Adhesion Molecules / Q000032:analysis; D051360:Cyclin-Dependent Kinase 5; D018844:Cyclin-Dependent Kinases; D004791:Enzyme Inhibitors / Q000494:pharmacology; D058851:GPI-Linked Proteins; D006160:Guanosine Triphosphate / Q000494:pharmacology*; D006801:Humans; D007781:Lactoferrin / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000172:deficiency / Q000502:physiology; D009504:Neutrophils / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D010980:Platelet Membrane Glycoproteins / Q000032:analysis; D011687:Purines / Q000494:pharmacology; D000077546:Roscovitine; D022142:Secretory Vesicles / Q000201:enzymology; D060149:Tetraspanin 30
chemical_list: D015703:Antigens, CD; D000951:Antigens, Neoplasm; C554586:CD63 protein, human; C504120:CEACAM8 protein, human; C554587:Cd63 protein, mouse; D015815:Cell Adhesion Molecules; D004791:Enzyme Inhibitors; D058851:GPI-Linked Proteins; D009419:Nerve Tissue Proteins; D010980:Platelet Membrane Glycoproteins; D011687:Purines; D060149:Tetraspanin 30; C089495:neuronal Cdk5 activator (p25-p35); D000077546:Roscovitine; D006160:Guanosine Triphosphate; D051360:Cyclin-Dependent Kinase 5; C495905:CDK5 protein, human; C495906:Cdk5 protein, mouse; D018844:Cyclin-Dependent Kinases; D007781:Lactoferrin