Production of Leukotriene C4 in Different Human Tissues Is Attributable to Distinct Membrane Bound Biosynthetic Enzymes

Abstract

Microsomal glutathione S-transferase-II (GST-II) has recently been discovered and characterized as a member of the 5-lipoxygenase-activating protein (FLAP)/5(S)-hydroxy-6(R)-S-glutathionyl-7,9-trans-11,14-cis-eicosatetraenoic acid (LTC 4 ) synthase gene family, which also includes microsomal glutathione S-transferase-I (GST-I) as a distant member of this gene family. This new enzyme is unique as it is the only member of this family capable of efficiently conjugating reduced glutathione to both 5,6-oxido-7,9,11,14-eicosatetraenoic acid (LTA 4 ) and 1-chloro-2,4-dinitrobenzene. Although microsomal GST-II has been demonstrated to display both general glutathione S-transferase (GST) and specific LTC 4 synthase activities, its biological function remains unknown. In this study, we investigated the physiological location of microsomal GST-II as well as the relative importance of this enzyme versus LTC 4 synthase for the production of LTC 4 in various human tissues and cells that have been previously demonstrated to possess LTC 4 synthase activity. As determined by Western blot, microsomal GST-II was predominantly expressed in human liver microsomes, human endothelial cell membranes, and sparsely detected in human lung membranes. In contrast, LTC 4 synthase was prevalent in human lung membranes, human platelet homogenates, and human kidney tissue. Concomitant to the formation of LTC 4 , microsomal GST-II also produces a new metabolite of LTA 4 , a postulated LTC 4 isomer. This isomer was used to distinguish between microsomal GST-II and LTC 4 synthase activities involved in the biosynthesis of LTC 4 . Based on the relative production of LTC 4 to the LTC 4 isomer, microsomal GST-II was demonstrated to be the principal enzyme responsible for LTC 4 production in human liver microsomes and human endothelial cells and played a minor role in the formation of LTC 4 in human lung membranes. In comparison, LTC 4 synthase was the main enzyme capable of catalyzing the conjugation of reduced glutathione to LTA 4 in human lung membranes and human platelet homogenates. Therefore, microsomal GST-II appears to be an integral component in the detoxification of biological systems due to its marked presence in human liver, in accordance with its known GST activity. Microsomal GST-II, however, may also be pivotal for cysteinyl leukotriene formation in endothelial cells, and this could change our current understanding of the regulation of leukotriene biosynthesis in inflammatory disorders such as asthma.

Transcellular biosynthesis of cysteinyl leukotrienes in vivo during mouse peritoneal inflammation

“…It is interesting to note that physical interaction between 5LO, FLAP, and LTC 4 S has been reported (12), and the absence of one of these enzymes during cell differentiation may affect the stability of the others. As an additional conclusion, the fact that LTC 4 S Ϫ/Ϫ bone marrow cells were unable to synthesize LTC 4 upon A23187 stimulation, indicates that LTC 4 S was the predominant enzyme able to convert LTA 4 into LTC 4 in this model, suggesting that microsomal GSTs (38,39) are not involved.…”

Thematic Review Series: Proteomics. An integrated omics analysis of eicosanoid biology

“…The enzyme mainly responsible for LTC 4 production is LTCS, identified as a transmembrane protein from the MAPAG superfamily that includes FLAP and mPGES-1 (87,88). Other MAPEG enzymes, mGST-2 and mGST-3, also exhibit LTC 4 synthase activity and appear to play a role in LTC 4 biosynthesis in epithelial cells and the testis (89,90). However, LTCS knockout mice demonstrate its role as the primary contributor to LTC 4 biosynthesis in vivo.…”

Sickle Erythrocytes and Platelets Augment Lung Leukotriene Synthesis with Downregulation of Anti‐Inflammatory Proteins: Relevance in the Pathology of the Acute Chest Syndrome

“…[4][5][6][7] synthase has been measured in human lung membranes and human platelet homogenates. 8,9 Sickle cell disease (SCD) chronic lung disease and the acute chest syndrome are two of the notable causes of death in adult patients with sickle cell disease. [10][11][12] Some lung complications in SCD result from direct or indirect effects of pulmonary microvascular occlusion by sickled erythrocytes and their adhesion to the vascular endothelium, 13,14 leading to release of potent vasoactive molecules, including prostacyclin, thromboxane A 2 , and LTC 4 .…”