Novel 5-lipoxygenase isoforms affect the biosynthesis of 5-lipoxygenase products

5-Lipoxygenase (5-LO) is the essential enzyme for the biosynthesis of leukotrienes, important mediators of inflammation. This study investigated whether variants of 5-LO exist in human leukocytes. 5-LO mRNA isoforms that are consistent with alternative splicing were identified by RT-PCR in a cell line or cell type-specific pattern. All evaluated cells expressed mRNA containing all 14 exons of 5-LO with the expected splicing sites. Individual isoforms that retained intron 10 (alpha-10), lacked exon 13 (Delta-13), and lacked exons 10 and 13 (Delta-10,13) or that lacked the first 96 base pairs of exon 10 (Delta-p10) were identified. Immunoreactive bands coeluting with the cloned alpha-10 and Delta-13 isoforms were measured in primary neutrophils and in Raji cells. When expressed in HEK293 cells, alternative proteins were without catalytic activity. However, when coexpressed with the active full-length 5-LO, alternative isoforms significantly decreased the biosynthesis of 5-LO products by up to 44%, as assessed by reverse-phase HPLC analysis. Additionally, in stimulated neutrophils the full-length active 5-LO was detected by immunoblot in both nuclear and nonnuclear compartments, while the Delta-13 isoform was only detected in the nuclear fraction. These alternative 5-LO isoforms may represent a new mechanism for the regulation of the 5-LO pathway and lipid mediator biosynthesis.-Boudreau, L. H., Bertin, J., Robichaud, P. P., Laflamme, M., Ouellette, R. J., Flamand, N., Surette, M. E. Novel 5-lipoxygenase isoforms affect the biosynthesis of 5-lipoxygenase products. FASEB J. 25, 1097-1105 (2011). www.fasebj.org