Disease relevance of LTA4H

• High levels of biologically active LTA4H were expressed in cultured Spodoptera frugiperda insect cells infected with a baculovirus expression vector containing the LTA4H cDNA [1].
• The cDNA for LTA4H was cloned using oligonucleotide-directed amplification of the cDNA sequence by polymerase chain reaction and by oligonucleotide-based screening of a bacteriophage lambda gt11 cDNA library derived from human placental tissue [1].
• In a chronic inflammation-associated animal model of esophageal adenocarcinoma, we have shown that LTA4H was overexpressed in tumor as compared to normal tissues [2].
• The human gene encoding the bifunctional aminopeptidase and epoxide hydrolase enzyme, leukotriene A4 hydrolase (LTA4 hydrolase) has been cloned from a placental lambda phage genomic library [3].
• A variant of the gene encoding leukotriene A4 hydrolase confers ethnicity-specific risk of myocardial infarction [4].

High impact information on LTA4H

• Here we show that a haplotype (HapK) spanning the LTA4H gene encoding leukotriene A4 hydrolase, a protein in the same biochemical pathway as ALOX5AP, confers modest risk of myocardial infarction in an Icelandic cohort [4].
• These results also unveil a dual role for red blood cells in upregulating LTB4 biosynthesis, namely, the removal of endogenous Ado and the conversion of LTA4 released by activated PMNs [5].
• This effect of red blood cells on LTB4 biosynthesis was blocked by dipyridamole, an inhibitor of Ado transport, or captopril, an inhibitor of LTA4 hydrolase [5].
• Addition of red blood cells to suspensions of PMNs in plasma mimicked the effect of adding Ado deaminase and LTA4 hydrolase in enhancing LTB4 biosynthesis upon ligand stimulation [5].
• However, when free AA was additionally provided, a strong activation of the 5-lipoxygenase pathway was demasked, with the appearance of excessive quantities of leukotriene (LT)B4, LTA4, and 5-hydroxyeicosatetraenoic acid [6].

Chemical compound and disease context of LTA4H

• Leukotriene C4 (LTC4) synthase catalyzes the conjugation of LTA4 with reduced GSH to form LTC4, the parent of the receptor active cysteinyl leukotrienes implicated in the pathobiology of bronchial asthma [7].
• 5-Lipoxygenase is the first committed enzyme in the leukotriene biosynthetic pathway and is known to catalyze not only the first oxygenation of arachidonate to form 5(S)-hydroperoxyeicosatetraenoic acid (5(S)-HPETE), but also dehydration of this intermediate into leukotriene A4 (LTA4) by an activity termed leukotriene A4 synthase [8].
• The first step consists of the oxidation of arachidonic acid to the unstable intermediate 5-hydroperoxyeicosatetraenoic acid (5-HPETE), and the second step is the dehydration of 5-HPETE to form LTA4 [9].
• These results suggest that LTA4 hydrolase, which synthesizes LTB4, plays a significant role in the pathogenesis and development of atopic dermatitis [10].
• The novel amino acid 8(S)-amino-2(R)-methyl-7-oxononanoic acid (1) was isolated from the soil-borne microorganism Streptomyces diastaticus during our screening for inhibitors of leukotriene-A4 hydrolase (LTA4H), a requisite enzyme in the biosynthesis of the potent inflammatory mediator leukotriene-B4 (LTB4) [11].

Biological context of LTA4H

• Up-regulation of LTA4H was investigated at the transcriptional level [12].
• The relative potency of 1 (LTA4H IC50 = 0.6 microM) warranted further biological studies [11].
• As an epoxide hydrolase, LTA4H catalyzes the hydrolysis of the epoxide LTA4 to the diol, leukotriene B4 (LTB4), which mainly functions as a chemoattractant and an activator of inflammatory cells [2].
• Molecular cloning and amino acid sequence of leukotriene A4 hydrolase [13].
• Regulation of leukotriene A4 hydrolase activity in endothelial cells by phosphorylation [14].

Anatomical context of LTA4H

• Immunohistochemical staining revealed abundant expression of 5-LO, FLAP, and LTA4H protein, colocalizing in macrophages of intimal lesions [15].
• Upon activation of inflammatory cells 5-LO is translocated to the nuclear envelope (NE) where it converts arachidonic acid to the unstable epoxide LTA4 [16].
• LTA4 is further converted to LTC4 by conjugation with glutathione, a reaction catalyzed by the integral membrane protein LTC4 synthase (LTC4S), which is localized on the NE and endoplasmic reticulum (ER) [16].
• Coculture of ionophore-stimulated primary neutrophils with BCBL-1 cells leads to an increased production of LTB4 compared with coculture with BJAB and L-428 cells as measured by enzyme immunoassay, demonstrating the functional significance of LTA4H up-regulation [12].
• Leukotriene A4 hydrolase in human leukocytes. Purification and properties [17].

Associations of LTA4H with chemical compounds

• Leukotriene (LT) A(4) hydrolase/aminopeptidase (LTA4H) is a bifunctional zinc enzyme that catalyzes the biosynthesis of LTB4, a potent lipid chemoattractant involved in inflammation, immune responses, host defense against infection, and PAF-induced shock [18].
• The high resolution crystal structure of LTA4H in complex with the competitive inhibitor bestatin reveals a protein folded into three domains that together create a deep cleft harboring the catalytic Zn(2+) site [18].
• Furthermore, expression of 5-LO and LTA4H, but not FLAP, is increased in patients with recent or ongoing symptoms of plaque instability, and medication with warfarin correlates with increased levels of FLAP mRNA [15].
• To further examine the role of LTB4 in oral carcinogenesis, two LTA4H inhibitors, bestatin and SA6541, were evaluated in a long-term chemoprevention experiment [19].
• From the crystal structure of LTA4H, a hydrophilic patch composed of Gln-134, Tyr-267, and Asp-375 was identified in a narrow and otherwise hydrophobic pocket, believed to bind LTA4 [20].

Regulatory relationships of LTA4H

• Reverse transcriptase (RT)-PCR analysis demonstrated the expression of 5-lipoxygenase, 5-lipoxygenase-activating protein (FLAP) and LTA4 hydrolase mRNA in B-CLL cells [21].

Other interactions of LTA4H

• In summary, our studies have demonstrated that 5-Lox/LTA4H pathway is one of the major AA-metabolizing pathways involved in DMBA-induced oral carcinogenesis in hamsters, and may be targeted for chemoprevention [19].
• In the present report we used site-directed mutagenesis and x-ray crystallography to show that Asp-375, but none of the other candidate residues, is specifically required for the epoxide hydrolase activity of LTA4H [20].
• Based on our present knowledge, inhibitors of LTA4H or antagonists of LTB4 receptors may be used alone or in combination with other agents (e.g., cyclooxygenase 2 inhibitors) in cancer prevention and treatment trials to test their effectiveness [2].
• This novel technique, termed ARC-PCR, allowed us to characterize the proximal promoters of the human LTA4 hydrolase and SPARC genes, each within 1 day [22].
• These cells were found to express 5- and 15-lipoxygenase, leukotriene A4 hydrolase and cyclooxygenase-1 and -2 mRNAs [23].

Analytical, diagnostic and therapeutic context of LTA4H

• LTA4H was recovered from the medium and purified to > 95% purity by ion-exchange and gel-filtration chromatography, with an overall yield of 76% [1].
• METHODS: LTA4H expression was examined by western blotting and immunohistochemistry [24].
• Bestatin, an LTA4H inhibitor, suppresses tumorigenesis in this animal model [2].
• We identified a novel short (s-) mRNA of the human leukotriene-A4 (LTA4) hydrolase using sequential reverse transcriptase PCR mapping [25].
• To purify leukotriene A4 hydrolase from human epidermis a new non-specific affinity chromatography column, with the leukotriene A4 hydrolase inhibitor bestatin coupled to AH-Sepharose, was introduced [26].

References