15-Lipoxygenase products affect protein phosphorylation in Friend erythroleukemia cells

Mammalian arachidonate 15-lipoxygenases structure, function, and biological implications

Lipoxygenases (LOXs) constitute a heterogeneous family of lipid peroxidizing enzymes capable of oxygenating polyunsaturated fatty acids to their corresponding hydroperoxy derivatives. In mammals, LOXs are classified with respect to their positional specificity of arachidonic acid oxygenation into 5-, 8-, 12-, and 15-LOXs. Arachidonate 15-LOXs may be sub-classified into a reticulocyte-type (type-1) and an epidermis-type (type-2) enzyme. Since the leukocyte-type 12-LOXs are very similar to the reticulocyte-type 15-LOXs, these enzymes are designated 12/15-LOXs. Several LOX isoforms, in particular the reticulocyte-type 15-LOX and the human 5-LOX, are well characterized with respect to their structural and functional properties On the other hand, the biological role of most LOX-isozymes including the reticulocyte-type 15-LOC is far from clear. This review is intended to summarize the recent developments in 15-LOX research with particular emphasis to molecular enzymology and regulation of gene expression. In addition, the major hypotheses on the physiological and patho-physiological roles of 15-LOXs will be discussed briefly.

NO synthase and guanylate cyclase inhibitors block modulation of the plasticity of common snail cholinoreceptors by 15-hydroxy-eicosatetraenoic acid

The probable role of two second messengers, nitrogen oxide (NO) and cyclic guanosine monophosphate (cGMP) in the short- and long-latency effects of the acyclic eicosanoid 15(S)-hydroxy-5Z,8Z,11Z,13E-eicosatetraenoic acid (15-HETE) on the plasticity of somatic cholinoreceptors of identified RPa3 and LPa3 neurons of Helix lucorum, was investigated using the two-electrode voltage clamp technique on the membrane. It was demonstrated that N omega-methyl-L-arginine (an inhibitor of NO synthase), LY-83,583 [sic], and the dye methylene blue (inhibitors of soluble guanylate cyclase), when applied extracellularly, disrupt the short- and long-latency modulatory influences of 15-HETE on the depression of the inward current induced by acetylcholine during its rhythmic application to the soma. The participation of NO and cGMP in the modulatory effects of 15-HETE on the plasticity of cholinoreceptors is hypothesized.

Differential effect of growth- and differentiation-inducing factors on the release of eicosanoids and phospholipids from ML-1 human myeloblastic leukemia cells

In the absence of serum, growth of ML-1 human myeloblastic leukemia cells is induced by the insulin-like growth factor-1 (IGF1) together with transferrin (Tf), whereas monocytic differentiation is initiated by the transforming growth factor-beta (TGF-beta) in combination with Tf. Initiation of growth was followed by the rapid release of arachidonic acid (AA), hydroxyeicosatetraenoic acids (HETEs) and phospholipids into the culture medium. In contrast, induction of differentiation occurred without the release of these lipids beyond the level present in control. Inhibitors of enzymes involved in the formation of AA and of HETEs, including phospholipase A2 and lipoxygenases, caused interference with growth but not with differentiation, and an inhibitor of the cyclooxygenase path affected neither growth nor differentiation. These results indicate that the initiation of ML-1 cell growth but not of cell differentiation is dependent upon the increased formation of AA and its derivatives formed primarily via the lipoxygenase path.