title: Tyrosine kinase activity modulates catalysis and translocation of cellular 5-lipoxygenase.
abstract: Tyrosine kinase activity, a determinant of Src homology domain interactions, has a prominent effect on cellular localization and catalysis by 5-lipoxygenase. Six separate inhibitors of tyrosine kinase each inhibited 5(S)-hydroxyeicosatetraenoic acid formation by HL-60 cells stimulated with calcium ionophore, in the presence or absence of exogenous arachidonic acid substrate, indicating that they modulated cellular 5-lipoxygenase activity. The tyrosine kinase inhibitors also blocked the translocation of 5-lipoxygenase from cytosol to membranes during cellular activation, consistent with their effects on its catalytic activity. These results fit a model which postulates that Src homology domain interactions are a molecular determinant of the processes which coordinate the subcellular localization and functions of 5-lipoxygenase. In addition, we demonstrate that activated leukocytes contain two molecularly distinct forms of 5-lipoxygenase: a phosphorylated form and a nonphosphorylated form. In activated HL-60 cells the pool of phosphorylated 5-lipoxygenase accumulates in the nuclear fraction, not with the membrane or cytosolic fractions. The amount of phosphorylated 5-lipoxygenase is a small fraction of the total. Overall, equilibrium reactions involving the nuclear localizing sequence, the proline-rich SH3 binding motif, and the phosphorylation state of 5-lipoxygenase may each influence its partnership with other cellular proteins and any novel functions derived from such partnerships.
authors.affiliation: Department of Pharmacology, University of Colorado Health Science Center, Denver 80262, USA.
authors.forename: R A
authors.initials: RA
authors.lastname: Lepley
authors.forename: D T
authors.initials: DT
authors.lastname: Muskardin
authors.forename: F A
authors.initials: FA
authors.lastname: Fitzpatrick
mesh_terms: D058927:5-Lipoxygenase-Activating Proteins; D000368:Aged; D001094:Arachidonate 5-Lipoxygenase / Q000737:chemistry / Q000378:metabolism*; D001693:Biological Transport, Active / Q000187:drug effects; D002352:Carrier Proteins / Q000378:metabolism; D002384:Catalysis; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology; D003600:Cytosol / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D066298:In Vitro Techniques; D007962:Leukocytes / Q000187:drug effects / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018909:src Homology Domains
chemical_list: D058927:5-Lipoxygenase-Activating Proteins; C548592:ALOX5AP protein, human; D002352:Carrier Proteins; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D001094:Arachidonate 5-Lipoxygenase; D011505:Protein-Tyrosine Kinases