Neutrophil serine proteinases inactivate surfactant protein D by cleaving within a conserved subregion of the carbohydrate recognition domain.
Surfactant protein D (SP-D) plays important roles in innate immunity including the defense against bacteria, fungi, and respiratory viruses. Because SP-D specifically interacts with neutrophils that infiltrate the lung in response to acute inflammation and infection, we examined the hypothesis that the neutrophil-derived serine proteinases (NSPs): neutrophil elastase, proteinase-3, and cathepsin G degrade SP-D. All three human NSPs specifically cleaved recombinant rat and natural human SP-D dodecamers in a time- and dose-dependent manner, which was reciprocally dependent on calcium concentration. The NSPs generated similar, relatively stable, disulfide cross-linked immunoreactive fragments of approximately 35 kDa (reduced), and sequencing of a major catheptic fragment definitively localized the major sites of cleavage to a highly conserved subregion of the carbohydrate recognition domain. Cleavage markedly reduced the ability of SP-D to promote bacterial aggregation and to bind to yeast mannan in vitro. Incubation of SP-D with isolated murine neutrophils led to the generation of similar fragments, and cleavage was inhibited with synthetic and natural serine proteinase inhibitors. In addition, neutrophils genetically deficient in neutrophil elastase and/or cathepsin G were impaired in their ability to degrade SP-D. Using a mouse model of acute bacterial pneumonia, we observed the accumulation of SP-D at sites of neutrophil infiltration coinciding with the appearance of approximately 35-kDa SP-D fragments in bronchoalveolar lavage fluids. Together, our data suggest that neutrophil-derived serine proteinases cleave SP-D at sites of inflammation with potential deleterious effects on its biological functions.
Hirche
Tim O
TO
Department of Medicine, Washington University School of Medicine, Saint Louis, Missouri 63110, USA.
Crouch
Erika C
EC
Espinola
Marcia
M
Brokelman
Thomas J
TJ
Mecham
Robert P
RP
DeSilva
Nihal
N
Cooley
Jessica
J
Remold-O'Donnell
Eileen
E
Belaaouaj
Abderrazzaq
A
D000595:Amino Acid Sequence; D000818:Animals; D002118:Calcium / Q000737:chemistry / Q000378:metabolism; D002403:Cathepsins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D017124:Conserved Sequence; D006801:Humans; D007710:Klebsiella Infections / Q000378:metabolism; D007711:Klebsiella pneumoniae / Q000378:metabolism / Q000472:pathogenicity; D037102:Lectins / Q000235:genetics*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008969:Molecular Sequence Data; D009504:Neutrophils / Q000201:enzymology*; D017434:Protein Structure, Tertiary; D011649:Pulmonary Alveolar Proteinosis / Q000378:metabolism / Q000382:microbiology; D037663:Pulmonary Surfactant-Associated Protein D / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012697:Serine Endopeptidases / Q000378:metabolism* / Q000502:physiology; D015842:Serine Proteinase Inhibitors / Q000494:pharmacology; D013696:Temperature
D037102:Lectins; D037663:Pulmonary Surfactant-Associated Protein D; D011994:Recombinant Proteins; D015842:Serine Proteinase Inhibitors; D002403:Cathepsins; D012697:Serine Endopeptidases; D002118:Calcium