Aggrecanase-1 (ADAMTS-4) interacts with α1-antitrypsin

In degradative articular diseases such as rheumatoid arthritis and osteoarthritis, loss of the extracellular matrix occurs, resulting in the destruction of joint cartilage. Proteolysis of aggrecan is one of the early events that leads to breakdown of the extracellular matrix. Aggrecanase-1 (ADAMTS-4) is considered to play a pivotal role in the abrasion of cartilage aggrecan in rheumatoid arthritis and osteoarthritis. To identify an endogenous inhibitor of aggrecanase-1, we performed a yeast two-hybrid screen using the catalytic domain of human aggrecanase-1 as a bait and transformed an EGY48 yeast strain carrying the bait plasmid with a human liver cDNA library plasmid. This screen identified α1-antitrypsin, a member of the family of plasma serine proteinase inhibitors, as a prey. Recombinant aggrecanase-1 and α1-antitrypsin were expressed in mammalian cells and used in coimmunoprecipitation experiments, which showed that full-length aggrecanase-1 and α1-antitrypsin are also associated in vivo. However, aggrecanase-1 did not interfere with the inhibitory activity of α1-antitrypsin against elastase, and α1-antitrypsin had no effect on the proteolytic activity of aggrecanase-1. Taken together, these data suggest that aggrecanase-1 and α1-antitrypsin bind in vivo, although the physiological significance of the interaction between aggrecanase-1 and α1-antitrypsin remains unclear.