Rapid inactivation of alpha-1-proteinase inhibitor by neutrophil specific leukolysin/membrane-type matrix metalloproteinase 6.

Leukolysin/MT6-MMP is a GPI-anchored matrix metalloproteinase (MMP) primarily expressed by neutrophils. It is stored in intracellular granules at resting state, but rapidly discharged upon stimulations into the extracellular milieu, presumably to promote tissue remodeling or destruction. The proteolytic targets for leukolysin at the inflammatory sites remain unknown. Here, we show that alpha-1-proteinase inhibitor, or alpha1-PI, a known protective shield against destructive serine proteinases, is a physiological target for leukolysin. We show that alpha1-PI failed to accumulate in media conditioned by cells co-expressing alpha1-PI and leukolysin. Purified leukolysin cleaves alpha1-PI efficiently at the Phe376Leu and Pro381Met bonds and the cleaved alpha1-PI lost its anti-proteolytic activity against human neutrophil elastase, cathepsin G (CatG) and proteinase 3 (PR3). In fact, leukolysin preferentially cleaves alpha1-PI when co-incubated with other extracellular molecules such as laminin and gelatin. Kinetically, leukolysin is more active than two known neutrophil MMPs, MMP8 and MMP9, in cleaving and inactivating alpha1-PI. Taken together, these results suggest that neutrophils may mediate tissue destruction by deploying leukolysin to weaken the alpha1-PI protective shield at inflammatory sites.