Subcellular distribution and cytokine- and chemokine-regulated secretion of leukolysin/MT6-MMP/MMP-25 in neutrophils

Leukolysin, originally isolated from human leukocytes, is the sixth member of the membrane-type matrix metalloproteinase (MT-MMP) subfamily with a pot ential glycosylphosphatidylinositol (GPI) anchor. To understand its biologi cal functions, we screened subpopulations of leukocytes and localized the e xpression of leukolysin at the mRNA level to neutrophils. Polyclonal and mo no-specific antisera raised against a synthetic peptide from its hinge regi on recognized a major protein species at 56 kDa and several minor forms bet ween 38 and 45 kDa in neutrophil lysates, In resting neutrophils, leukolysi n is distributed among specific granules (similar to 10%), gelatinase granu les (similar to 40%), secretory vesicles (similar to 30%), and the plasma m embrane (similar to 20%), a pattern distinct from that of neutrophil MMP-8 and MMP-9. Consistent with its membrane localization and its reported GPI a nchor, leukolysin partitions into the detergent phase of Triton X-114 and c an be released from intact resting neutrophils by glycosylphosphatidylinosi tol-specific phospholipase C. Phorbol myristate acetate stimulates neutroph ils to discharge 100% of leukolysin from specific and gelatinase granules a nd similar to 50% from the secretory vesicles and plasma membrane, suggesti ng that leukolysin can be mobilized by physiological signals to the extrace llular milieu as a soluble enzyme. Indeed, interleukin 8, a neutrophil chem oattractant, triggered a release of similar to 85% of cellular leukolysins by a process resistant to a mixture of proteinase inhibitors, including apr otinin, BB-94, pepstatin, and E64. Finally, purified recombinant leukolysin can degrade components of the extracellular matrix. These results not only establish leukolysin as the first neutrophil-specific MT-MMP but also impl icate it as a cytokine/chemokine-regulated effector during innate immune re sponses or tissue injury.