Elastase and metalloproteinase activities regulate soluble complement receptor 1 release

Abstract

Complement receptor 1 (CR1) is cleaved from the surface of polymorphonuclear cells (PMN) in the membrane-proximal region to yield a soluble fragment (sCR1) that contains the functional domains. The enzymes involved in this cleavage are produced by the PMN itself, since in vitro stimulation of purified PMN is followed by sCR1 release. Purified human neutrophil elastase (HNE) cleaved CR1 from erythrocytes and urinary vesicles originating from podocytes and enhanced tenfold the cleavage of CR1 from activated PMN. The largest fragment released from PMN by HNE was identical in size to CR1 shed spontaneously. The CR1 fragments cleaved from erythrocytes were functional. The shedding of sCR1 by activated PMN was inhibited by phenylmethylsulfonyl fluoride (80 ± 10%), α1-antiprotease (50 ± 5%) and elafin (60 ± 5%). Furthermore the cleavage was blocked by the metalloprotease inhibitor 1,10-phenanthroline (70 ± 6%) as well as by a monoclonal antibody against human neutrophil collagenase MMP8 (40 ± 10%). Maximal inhibition of sCR1 shedding was obtained by a combination of 1,10-phenanthroline with elafin (86 ± 6%). These inhibitors had no effect on L-selectin shedding, indicating that the cleavage of CR1 was specific. In conclusion, elastase or elastase-like activity may be responsible for the shedding of functional sCR1 in vivo, and this activity is controlled by the local release of PMN metalloproteases and α1-antiprotease.