Co-localization of leukotriene A(4) hydrolase with 5-lipoxygenase in nuclei of alveolar macrophages and rat basophilic leukemia cells but not neutrophils

The synthesis of leukotriene B-4 from arachidonic acid requires the sequent ial action of two enzymes: 5-lipoxygenase and leukotriene A(4) hydrolase. 5 -Lipoxygenase is known to be present in the cytoplasm of some leukocytes an d able to accumulate in the nucleoplasm of others. In this study, we asked if leukotriene A(4) 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 A(4) h ydrolase, like 5-lipoxygenase, was most abundant in the nucleus, with only minor occurrences in the cytoplasm. The finding of abundant leukotriene A(4 ) hydrolase in the soluble nuclear fraction was substantiated by two differ ent cell fractionation techniques. Leukotriene A(4) hydrolase was also foun d to accumulate together with 5-lipoxygenase in the nucleus of alveolar mac rophages. This result was obtained using both in situ and ex vivo technique s. In contrast to these results, peripheral blood neutrophils contained bot h leukotriene A(4) hydrolase and 5-lipoxygenase exclusively in the cytoplas m. After adherence of neutrophils, 5-lipoxygenase was rapidly imported into the nucleus, whereas leukotriene A(4) hydrolase remained cytosolic. Simila rly, 5-lipoxygenase was localized in the nucleus of neutrophils recruited i nto inflamed appendix tissue, whereas leukotriene A(4) hydrolase remained c ytosolic. These results demonstrate for the first time that leukotriene A(4 ) hydrolase can be accumulated in the nucleus, where it co-localizes with 5 -lipoxygenase. As with 5-lipoxygenase, the subcellular distribution of leuk otriene A(4) 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 B-4.