HGNC Approved Gene Symbol: LTC4S
Cytogenetic location: 5q35.3 Genomic coordinates (GRCh38): 5:179,793,986-179,796,647 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 5q35.3 | Leukotriene C4 synthase deficiency | 614037 | Autosomal recessive | 1 |
Leukotriene C4 synthetase (LTC4S) catalyzes the synthesis of leukotriene C4 (LTC4) through conjugation of LTA4 with reduced glutathione (GSH), which is synthesized by glutathione synthetase (GSS; 601002). Leukotriene C4 and its receptor-binding metabolites LTD4 and LTE4 are cysteinyl leukotrienes that are potent lipid mediators of tissue inflammation. In general, leukotrienes are potent proinflammatory mediators synthesized from membrane-derived arachidonic acid after activation of certain granulocytes (Kanaoka et al., 2001).
The cysteinyl leukotrienes have been implicated in bronchial asthma. CYSLTR1 (300201) and CYSLTR2 (605666) are receptors for LTC4 and its metabolites. CYSLTR-selective pharmacologic antagonists are important in the treatment of asthma (Martinez Molina et al., 2007).
Penrose et al. (1992) purified LTC4 synthase and characterized it as an 18-kD protein. Lam et al. (1994) cloned the LTC4S gene and showed that its open reading frame encodes a 150-residue protein with a molecular mass of 16.5-kD and a pI of 11.05. The deduced sequence contains 2 consensus protein kinase C phosphorylation sites and a potential N-linked glycosylation site as well as 3 putative membrane-spanning regions. The deduced amino acid sequence of LTC4S showed no significant homology to GSH S-transferases but shared 31% overall sequence identity with 5-lipoxygenase activating protein (FLAP; 603700). Peptide structural analysis of the deduced LTC4 synthase predicted the presence of 3 transmembrane domains nearly superimposable on those of FLAP. LTC4 synthase was inhibitable by a FLAP inhibitor, MK-886.
By genomic cloning from a P1 library, Penrose et al. (1996) found that the LTC4S gene is 2.52 kb long and contains 5 exons. The investigators noted that although the intron-exon junctions of LTC4S and the human FLAP gene are identical, the size of FLAP reported by Kennedy et al. (1991) is over 31 kb. Penrose et al. (1996) found multiple transcription initiation sites in the 5-prime flanking region of the LTC4S gene.
Using fluorescence in situ hybridization, Penrose et al. (1996) mapped the LTC4S gene to chromosome 5q35.
Crystal Structure
Ago et al. (2007) showed the atomic structure of human LTC4S in complex with glutathione at 3.3 angstrom resolution by x-ray crystallography and provided insights into the high substrate specificity for a glutathione and LTA4 that distinguishes LTC4S from other microsomal glutathione S-transferases. The LTC4S monomer has 4 transmembrane alpha-helices and forms a 3-fold symmetric trimer as a unit with functional domains across each interface. Glutathione resides in a U-shaped conformation within an interface between adjacent monomers, and this binding is stabilized by a loop structure at the top of the interface. LTA4 would fit into the interface so that arg104 of one monomer activates glutathione to provide the thiolate anion that attacks C6 of LTA4 to form a thioether bond, and arg31 in the neighboring monomer donates a proton to form a hydroxyl group at C5, resulting in 5(S)-hydroxy-6(R)-S-glutathionyl-7,9-trans-11,14-cis-eicosatetranoic acid (LTC4).
Martinez Molina et al. (2007) independently presented the crystal structure of human LTC4S in its apo and glutathione-complexed forms to 2.0 and 2.15 angstrom resolution, respectively. The structure revealed a homotrimer, where each monomer is composed of 4 transmembrane segments. The structure of the enzyme in complex with substrate revealed that the active site enforces a horseshoe-shaped conformation on glutathione and effectively positions the thiol group for activation by a nearby arginine at the membrane-enzyme interface. In addition, the structure provides a model for how the omega end of the lipophilic cosubstrate is pinned at one end of a hydrophobic cleft, providing a molecular 'ruler' to align the reactive epoxide at the thiol of glutathione.
Pace-Asciak et al. (1986) demonstrated that the leukotriene precursor, LTA4, is transformed by human platelets into LTC4 by a glutathione-dependent pathway.
Pace-Asciak et al. (1986) found that LTC4 synthesis was severely impaired in 2 sibs with glutathione synthetase deficiency (266130). Platelets from the patients had approximately 30% of normal glutathione levels, reflecting a decrease of glutathione synthetase activity. The findings in these patients suggested that cellular glutathione levels may regulate the production of LTC4 synthetase.
The formation of leukotriene C4 from membrane-derived arachidonic acid is catalyzed by 3 successive enzymatic steps after transmembrane activation of eosinophils, basophils, mast cells, and monocytes/macrophages. Arachidonic acid is released from cell membranes by the action of phospholipase A2 (see 600522). 5-Lipoxygenase is activated independently via a 5-lipoxygenase-associated protein and Ca(2+) and catalyzes 2 sequential enzymatic reactions to form LTA4. Leukotriene C4 synthase catalyzes the conjugation of LTA4 with reduced glutathione to form LTC4 (Penrose et al., 1992).
Asthma and Aspirin-Intolerant Asthma
Aspirin-intolerant asthma (AIA; 208550) is a distinct clinical syndrome characterized by adverse respiratory reactions to aspirin and other nonsteroidal antiinflammatory drugs (NSAIDs). Aspirin causes bronchoconstriction in AIA patients by triggering cysteinyl-leukotriene production, probably by removing PGE(2)-dependent inhibition. Sampson et al. (1997) and Cowburn et al. (1998) found increased LTC4S expression in bronchial biopsies from patients with AIA. The study by Cowburn et al. (1998) reported that LTC4S expression in AIA patients was increased 5-fold and 18-fold compared to aspirin-tolerant asthmatics and nonasthmatic controls, respectively. The authors postulated that AIA patients may have a polymorphism involved in the regulation of LTC4S expression that results in overproduction of cysteinyl-leukotrienes leading to bronchoconstriction.
Sanak et al. (1997) identified a promoter polymorphism in the LTC4S gene, -444A-C, that was overrepresented among patients with aspirin-intolerant asthma. Six of 11 AIA patients were homozygous for the -444C allele, compared to only 1 individual in the aspirin-tolerant asthmatic and control groups. The frequency of the -444C allele was nearly doubled in AIA (0.436) compared to aspirin-tolerant asthmatics (0.227) and nonasthmatic controls (0.226), yielding a relative risk of 3.89 for the -444C allele.
Sanak et al. (2000) found that peripheral blood eosinophils from patients with AIA had increased LTC4S mRNA. An inhaled aspirin provocation test led to increased urinary output of LTC4, which reached significance only in carriers of the -444C allele. Nuclear-protein interaction studies on HeLa cells showed that the -444C allele created an additional binding site for the transcriptional signal of histone H4 transcription factor-2 (H4FN; 142750), and in vitro studies demonstrated that the -444C allele resulted in increased reporter gene expression. Sanak et al. (2000) concluded that overexpression of LTC4S may predispose to AIA.
Using in vitro transfection of promoter-reporter constructs, Sayers et al. (2003) showed that dexamethasone increased transcription of LTC4S by more than 50% for the -1072G/-444A, A-C, and G-C haplotype constructs (p less than 0.02), but had no effect on the A-A haplotype (p = 0.27). Sayers et al. (2003) concluded that the 9% of the Caucasian asthmatic population with the A-A haplotype may have genetically predetermined lower cysteinyl-leukotriene levels in the presence of corticosteroids compared to other patients, which has potential implications in the evaluation of combined corticosteroid and antileukotriene therapy in asthma.
Kanaoka et al. (2001) found that Ltc4s-null mice developed normally and were fertile. Bone marrow-derived cells from these mice provided no Ltc4 in response to IgE-dependent activation. In addition, zymosan-induced peritoneal vascular permeability and IgE-mediated passive cutaneous anaphylaxis were significantly diminished in these mice. The findings indicated that Ltc4s is the major Ltc4-producing enzyme in tissues, and that Ltc4 plays a role in vascular permeability in innate and adaptive immune host inflammatory responses.
Ago, H., Kanaoka, Y., Irikura, D., Lam, B. K., Shimamura, T., Austen, K. F., Miyano, M. Crystal structure of a human membrane protein involved in cysteinyl leukotriene biosynthesis. Nature 448: 609-612, 2007. [PubMed: 17632548] [Full Text: https://doi.org/10.1038/nature05936]
Cowburn, A. S., Sladek, K., Soja, J., Adamek, L., Nizankowska, E., Szczeklik, A., Lam, B. K., Penrose, J. F., Austen, K. F., Holgate, S. T., Sampson, A. P. Overexpression of leukotriene C(4) synthase in bronchial biopsies from patients with aspirin-intolerant asthma. J. Clin. Invest. 101: 834-846, 1998. [PubMed: 9466979] [Full Text: https://doi.org/10.1172/JCI620]
Kanaoka, Y., Maekawa, A., Penrose, J. F., Austen, K. F., Lam, B. K. Attenuated zymosan-induced peritoneal vascular permeability and IgE-dependent passive cutaneous anaphylaxis in mice lacking leukotriene C4 synthase. J. Biol. Chem. 276: 22608-22613, 2001. [PubMed: 11319240] [Full Text: https://doi.org/10.1074/jbc.M103562200]
Kennedy, B. P., Diehl, R. E., Boie, Y., Adam, M., Dixon, R. A. Gene characterization and promoter analysis of the human 5-lipoxygenase-activating protein (FLAP). J. Biol. Chem. 266: 8511-8516, 1991. [PubMed: 1673682]
Lam, B. K., Penrose, J. F., Freeman, G. J., Austen, K. F. Expression cloning of a cDNA for human leukotriene C4 synthase, an integral membrane protein conjugating reduced glutathione to leukotriene A4. Proc. Nat. Acad. Sci. 91: 7663-7667, 1994. [PubMed: 8052639] [Full Text: https://doi.org/10.1073/pnas.91.16.7663]
Martinez Molina, D., Wetterholm, A., Kohl, A., McCarthy, A. A., Niegowski, D., Ohlson, E., Hammarberg, T., Eshaghi, S., Haeggstrom, J. Z., Nordlund, P. Structural basis for synthesis of inflammatory mediators by human leukotriene C4 synthase. Nature 448: 613-616, 2007. [PubMed: 17632546] [Full Text: https://doi.org/10.1038/nature06009]
Pace-Asciak, C. R., Klein, J., Spielberg, S. P. Human genetic defect in leukotriene C(4) synthesis. Biochem. Biophys. Res. Commun. 140: 857-860, 1986. [PubMed: 3022737] [Full Text: https://doi.org/10.1016/0006-291x(86)90713-8]
Pace-Asciak, C. R., Klein, J., Spielberg, S. P. Metabolism of leukotriene A4 into C4 by human platelets. Biochim. Biophys. Acta 877: 68-74, 1986. [PubMed: 2872925] [Full Text: https://doi.org/10.1016/0005-2760(86)90119-0]
Penrose, J. F., Gagnon, L., Goppelt-Struebe, M., Myers, P., Lam, B. K., Jack, R. M., Austen, K. F., Soberman, R. J. Purification of human leukotriene C(4) synthase: organization, nucleotide sequence, and chromosomal localization to 5q35. Proc. Nat. Acad. Sci. 89: 11603-11606, 1992. [PubMed: 1454853] [Full Text: https://doi.org/10.1073/pnas.89.23.11603]
Penrose, J. F., Spector, J., Baldasaro, M., Xu, K., Boyce, J., Arm, J. P., Austen, K. F., Lam, B. K. Molecular cloning of the gene for human leukotriene C(4) synthase. J. Biol. Chem. 271: 11356-11361, 1996. [PubMed: 8626689] [Full Text: https://doi.org/10.1074/jbc.271.19.11356]
Sampson, A. P., Cowburn, A. S., Sladek, K., Adamek, L., Nizankowska, E., Szczeklik, A., Lam, B. K., Penrose, J. F., Austen, K. F., Holgate, S. T. Profound overexpression of leukotriene C4 synthase in bronchial biopsies from aspirin-intolerant asthmatic patients. Int. Arch. Allergy Immun. 113: 355-357, 1997. [PubMed: 9130576] [Full Text: https://doi.org/10.1159/000237600]
Sanak, M., Pierzchalska, M., Bazan-Socha, S., Szczeklik, A. Enhanced expression of the leukotriene C4 synthase due to overactive transcription of an allelic variant associated with aspirin-intolerant asthma. Am. J. Resp. Cell Molec. Biol. 23: 290-296, 2000. [PubMed: 10970818] [Full Text: https://doi.org/10.1165/ajrcmb.23.3.4051]
Sanak, M., Simon, H.-U., Szczeklik, A. Leukotriene C4 synthase promoter polymorphism and risk of aspirin-induced asthma. Lancet 350: 1599-1600, 1997. [PubMed: 9393345] [Full Text: https://doi.org/10.1016/s0140-6736(05)64015-9]
Sayers, I., Sampson, A. P., Ye, S., Holgate, S. T. Promoter polymorphism influences the effect of dexamethasone on transcriptional activation of the LTC4 synthase gene. Europ. J. Hum. Genet. 11: 619-622, 2003. [PubMed: 12891383] [Full Text: https://doi.org/10.1038/sj.ejhg.5201015]