ALOXE3

5934423801ENSG00000179148ENSMUSG00000020892Q9BYJ1Q9WV07NM_021628NM_001165960NM_001369446NM_011786NP_001159432NP_067641NP_001356375NP_035916Epidermis-type lipoxygenase 3 (ALOXE3 or eLOX3) is a member of the lipoxygenase family of enzymes; in humans, it is encoded by the ALOXE3 gene. This gene is located on chromosome 17 at position 13.1 where it forms a cluster with two other lipoxygenases, ALOX12B and ALOX15B. Among the human lipoxygenases, ALOXE3 is most closely (54% identity) related in amino acid sequence to ALOX12B. ALOXE3, ALOX12B, and ALOX15B are often classified as epidermal lipoxygenases, in distinction to the other three human lipoxygenases (ALOX5, ALOX12, and ALOX15), because they were initially defined as being highly or even exclusively expressed and functioning in skin. The epidermis-type lipoxygenases are now regarded as a distinct subclass within the multigene family of mammalian lipoxygenases with mouse Aloxe3 (also termed e-Lox-3) being the ortholog to human ALOXE3, mouse Alox12b being the ortholog to human ALOX12B (MIM 603741), and mouse Alox8 being the ortholog to human ALOX15B (MIM 603697). ALOX12B and ALOXE3 in humans, Alox12b and Aloxe3 in mice, and comparable orthologs in other in other species are proposed to act sequentially in a multistep metabolic pathway that forms products that are structurally critical for creating and maintaining the skin's water barrier function.arachidonic acid + O2 ⇌ {displaystyle ightleftharpoons } 12R-HpETELA + O2 ⇌ {displaystyle ightleftharpoons } 9R-HpODE. Epidermis-type lipoxygenase 3 (ALOXE3 or eLOX3) is a member of the lipoxygenase family of enzymes; in humans, it is encoded by the ALOXE3 gene. This gene is located on chromosome 17 at position 13.1 where it forms a cluster with two other lipoxygenases, ALOX12B and ALOX15B. Among the human lipoxygenases, ALOXE3 is most closely (54% identity) related in amino acid sequence to ALOX12B. ALOXE3, ALOX12B, and ALOX15B are often classified as epidermal lipoxygenases, in distinction to the other three human lipoxygenases (ALOX5, ALOX12, and ALOX15), because they were initially defined as being highly or even exclusively expressed and functioning in skin. The epidermis-type lipoxygenases are now regarded as a distinct subclass within the multigene family of mammalian lipoxygenases with mouse Aloxe3 (also termed e-Lox-3) being the ortholog to human ALOXE3, mouse Alox12b being the ortholog to human ALOX12B (MIM 603741), and mouse Alox8 being the ortholog to human ALOX15B (MIM 603697). ALOX12B and ALOXE3 in humans, Alox12b and Aloxe3 in mice, and comparable orthologs in other in other species are proposed to act sequentially in a multistep metabolic pathway that forms products that are structurally critical for creating and maintaining the skin's water barrier function. Immunologically detected ALOXE3 and ALOX12B in humans and Aloxe3 and Alox12b in mice have a similar tissue distribution in being highly expressed in the outer, differentiated layers of the epidermis; they co-localize at the surface of keratinocytes in the stratum granulosum of mouse skin and during mouse embryogenesis appear concurrently at the onset of skin development at day 15.5. ALOXE3 mRNA in humans was also detected at low levels in the pancreas, ovary, brain, testis, placenta, and some secretory epithelia. Aloxe3 and Alox12b mRNA was detected in the tongue, forestomach, trachea, brain, testis, and adipose tissue of mice and in the spinal cord of rats. ALOX12B, like most of the other lipoxygenases, possesses dioxygenase (EC 1.13.11) activity: it catalyzes the incorporate dioxygen (i.e. molecular oxygen ) into a single substrate. Owing to this activity, the enzyme adds (O2) in the form of a hydroperoxyl (HO2) residue to arachidonic acid at its 12th carbon thereby forming 12(R)-hydroperoxy-5Z,8Z,10E,14Z-icosatetraenoic acid (also termed 12(R)-HpETE or 12R-HpETE). Hydroperoxy-containing polyunsaturated fatty acids (PUFAs) such as 12R-HETE readily breakdown through non-enzymatic transformations in which the two oxygen atoms of the hydroperoxy residue rearrange to form PUFAs containing one hydroxyl (also termed alcohol) residue and one epoxide residue. This transformation may occur in tissues or during tissue preparations with 12-HpETE to form Hepoxilins, i.e. epoxyalcohols of 12-HpETE that are of the A type (i.e. hepoxilin As, which contain an epoxy and alcohol residue separated from each other by a double (i.e. alkene) bond or, alternatively, B type (i.e. hepoxilin Bs, which contain epoxy and alcohol residues on adjacent carbons); these non-enxymatically formed products are a mixture of hydroxy and epoxy R,S stereoisomers and diastereomers. In addition to arachidonic acid, ALOX12B metabolizes linoleic acid (LA) to 9(R)-hydroperoxy-10(E),12(Z)-octadecadienoic acid (9R-HpODE): ALOXE3 is an atypical lipoxygenase in that under most but not all experimental conditions, it lacks the dioxygenase activity that converts PUFA to hydroperoxide metabolites; rather, it possess hepoxilin synthase (i.e. hydroperoxy isomerase) activity; that is, it converts hydroperoxy-containing PUFAs to hepoxilin-like epoxyalcohol products; these products, unlike those formed by non-enzymatic transformations, are specific isomers with just one form of the chiral hydroxy and epoxy residues. ALOX3E metabolizes 12R-HpETE to 8R-hydroxy-11R,12R-epoxy-eicosatrienoic acid and metabolizes 9R-HpODE to products that contain either an epoxyalcohol or a ketone residue. It exhibits relatively weak activity in conducting this conversion on free 9R-HODE but stronger activity when 9R-HpODE is presented as its methyl ester. ALOXE3's primary function in epidermal tissue appears to be to metabolize the 9R-HpODE moiety that is not free but rather esterified to certain ceramide lipids. LA is the most abundant fatty acid in the skin epidermis, being present mainly esterified to the omega-hydroxyl residue of amide-linked omega-hydroxylated very long chain fatty acids (VLCFAs) in a unique class of ceramides termed esterified omega-hydroxyacyl-sphingosine (EOS). EOS is an intermediate component in a proposed multi-step metabolic pathway which delivers VLCFAs to the cornified lipid envelop in the skin's Stratum corneum; the presence of these wax-like, hydrophobic VLCFAs is needed to maintain the skin's integrity and functionality as a water barrier (see Lung microbiome#Role of the epithelial barrier). ALOX12B metabolizes the LA in EOS to its 9R-hydroperoxy derivative which ALOXE3 then converts to three ceramide-esterified products: a) 9R,10R-trans-epoxide,13R-hydroxy-10E-octadecenoic acid, b) 9-keto-10E,12Z-octadecadienoic acid, and c) 9R,10R-trans-epoxy-13-keto-11E-octadecenoic acid. The ALOX12B/ALOE3-oxidized products, it is proposed, signal for their hydrolysis (i.e. removal) from EOS; this allows the multi-step metabolic pathway to proceed in delivering the VLCFAs to the cornified lipid envelop in the skin's Stratum corneum. AloxE3 appears responsible for forming hepoxilins A and/or B from 12R-HpETE in the spinal fluids of rats and ALOXE3 is proposed to be responsible for the formation of these hepoxilins in various human tissues although the presence and activity of ALOXE3 in many of these hepoxilin-forming tissues has not yet been demonstrated. Spinal Aloxe3, apparently through its ability to make hepoxilins, appears responsible for the hyperalgesia which accompanies inflammation in rats. Aloxe3 appears necessary and sufficient for the differentiation of mouse 3T3-L1 fibroblast cells into adipocytes (i.e. fat cells); the function of Aloxe3 in this differentiation appears to be to its metabolism 12R-HpETE into hepoxilins A3 or B3 which directly activate(s) Peroxisome proliferator-activated receptor gamma which in turn initiates the expression of adipocyte-differentiation genes.