Differential localization of 5-and 15-lipoxygenases to the nuclear envelope in RAW macrophages

Leukotriene formation is initiated in myeloid cells by an increase in intracellular calcium and translocation of B-lipoxygenase from the cytoplasm to the nuclear envelope where it can utilize arachidonic acid. Monocyte-macrophages and eosinophils also express 15-lipoxygenase, which converts arachidonic acid to 15(S)-hydroxyeicosatetraenoic acid. Enhanced green fluorescent B-lipoxygenase (5-LO) and 15-lipoxygenase (15-LO) fusion proteins were expressed in the cytoplasm of RAW 264.7 macrophages, Only B-lipoxygenase translocated 60 the nuclear envelope after cell stimulation, suggesting that differential subcellular compartmentalization can regulate the generation of leukotrienes versus 15(S)-hydroxyeicosatetraenoic acid in cells that possess both lipoxygenases, A series of truncation mutants of 5-LO were created to identify putative targeting domains; none of these mutants localized to the nuclear envelope. The lack of targeting of 15-LO was then exploited to search for specific targeting motifs in 5-LO, by creating 5-LO/15-LO chimeric molecules. The only chimera that could sustain nuclear envelope translocation was one which involved replacement of the N-terminal 237 amino acids with the corresponding segment of 15-LO, Significantly, no discrete targeting domain could be identified in 5-LO, suggesting that sequences throughout the molecule are required for nuclear envelope localization.