Mouse leukotriene A4 hydrolase is expressed at high levels in intestinal crypt cells and splenic lymphocytes.

LTA4 hydrolase (EC 3.3.2.6) is a dual-function enzyme that is essential for the conversion of leukotriene A4 (LTA4) to leukotriene B4 (LTB4) and also possesses an aminopeptidase activity. To characterize the expression of this unusual enzyme, we have cloned the mouse LTA4 hydrolase cDNA. The deduced amino acid sequence revealed 92% identity with the human sequence. Cloning and analysis of genomic sequences of mouse LTA4 hydrolase indicated that it is a single-copy gene spanning over 40kb and containing 20 exons. LTA4 hydrolase is widely expressed, with the highest levels of expression occurring in the small intestine, followed by the spleen. In situ hybridization revealed that LTA4 hydrolase is localized in the crypt cells of the small intestine, white pulp of the spleen, bronchiolar epithelium of the lung, myocardium, adrenal cortex, epithelium of the seminal vesicles, proximal tubules and the collecting ducts of the kidney, and occasional hepatocytes. Thus the widespread distribution of LTA4 hydrolase in various cell types in the tissues suggests that LTB4 may possess biological activities other than those known at present. It is also plausible that the widespread occurrence of LTA4 hydrolase in various tissues may correspond more with its function as an aminopeptidase than its function as an LTA4 hydrolase.