Characterization of proADAMTS5 processing by proprotein convertases.
ADAMTS5 (aggrecanase-2), a key metalloprotease mediating cartilage destruction in arthritis, is synthesized as a zymogen, proADAMTS5. We report a detailed characterization of the propeptide excision mechanism and demonstrate that it is a major regulatory step with unusual characteristics. Using furin-deficient cells and a furin inhibitor, we found that proADAMTS5 was processed by proprotein convertases, specifically furin and PC7, but not PC6B. Mutagenesis of three sites containing basic residues within the ADAMTS5 propeptide (RRR(46), RRR(69) and RRRRR(261)) suggested that proADAMTS5 processing occurs after Arg(261). That furin processing was essential for ADAMTS5 activity was illustrated using the known ADAMTS5 substrate aggrecan, as well as a new substrate, versican, an important regulatory proteoglycan during mammalian development. When compared to other ADAMTS proteases, proADAMTS5 processing has several distinct features. In contrast to ADAMTS1, whose furin processing products were clearly present intracellularly, cleaved ADAMTS5 propeptide and mature ADAMTS5 were found exclusively in the conditioned medium. Despite attempts to enhance detection of intracellular proADAMTS5 processing, such as by immunoprecipitation of total ADAMTS5, overexpression of furin, and secretion blockade by monensin, neither processed ADAMTS5 propeptide nor the mature enzyme were found intracellularly, which was strongly suggestive of extracellular processing. Extracellular ADAMTS5 processing was further supported by activation of proADAMTS5 added exogenously to HEK293 cells stably expressing furin. Unlike proADAMTS9, which is processed by furin at the cell-surface, to which it is bound, ADAMTS5 does not bind the cell-surface. Thus, the propeptide processing mechanism of ADAMTS5 has several points of distinction from those of other ADAMTS proteases, which may have considerable significance in the context of osteoarthritis.
Longpré
Jean-Michel
JM
Department of Pharmacology, Faculty of Medicine and Health Sciences, Université de Sherbrooke, Sherbrooke, Que. J1H 5N4, Canada.
McCulloch
Daniel R
DR
Koo
Bon-Hun
BH
Alexander
J Preston
JP
Apte
Suneel S
SS
Leduc
Richard
R
D051722:ADAM Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D000071116:ADAMTS5 Protein; D002460:Cell Line; D002462:Cell Membrane / Q000201:enzymology / Q000235:genetics; D004792:Enzyme Precursors / Q000378:metabolism*; D045683:Furin / Q000378:metabolism; D006031:Glycosylation; D006367:HeLa Cells; D006801:Humans; D043484:Proprotein Convertases / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D004792:Enzyme Precursors; D043484:Proprotein Convertases; C468731:FURIN protein, human; D045683:Furin; D051722:ADAM Proteins; D000071116:ADAMTS5 Protein; C121532:ADAMTS5 protein, human