T. Brock, E. Maydanski, R. McNish
Sep 14, 2001
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Journal
The Journal of Biological Chemistry
Abstract
The synthesis of leukotriene B4 from arachidonic acid requires the sequential action of two enzymes: 5-lipoxygenase and leukotriene A4hydrolase. 5-Lipoxygenase is known to be present in the cytoplasm of some leukocytes and able to accumulate in the nucleoplasm of others. In this study, we asked if leukotriene A4 hydrolase co-localizes with 5-lipoxygenase in different types of leukocytes. Examination of rat basophilic leukemia cells by both immunocytochemistry and immunofluorescence revealed that leukotriene A4 hydrolase, like 5-lipoxygenase, was most abundant in the nucleus, with only minor occurrences in the cytoplasm. The finding of abundant leukotriene A4 hydrolase in the soluble nuclear fraction was substantiated by two different cell fractionation techniques. Leukotriene A4 hydrolase was also found to accumulate together with 5-lipoxygenase in the nucleus of alveolar macrophages. This result was obtained using both in situand ex vivo techniques. In contrast to these results, peripheral blood neutrophils contained both leukotriene A4hydrolase and 5-lipoxygenase exclusively in the cytoplasm. After adherence of neutrophils, 5-lipoxygenase was rapidly imported into the nucleus, whereas leukotriene A4 hydrolase remained cytosolic. Similarly, 5-lipoxygenase was localized in the nucleus of neutrophils recruited into inflamed appendix tissue, whereas leukotriene A4 hydrolase remained cytosolic. These results demonstrate for the first time that leukotriene A4hydrolase can be accumulated in the nucleus, where it co-localizes with 5-lipoxygenase. As with 5-lipoxygenase, the subcellular distribution of leukotriene A4 hydrolase is cell-specific and dynamic, but differences in the mechanisms regulating nuclear import must exist. The degree to which these two enzymes are co-localized may influence their metabolic coupling in the conversion of arachidonic acid to leukotriene B4.