Macrophages secrete matrix metalloproteinase 9 covalently linked to the core protein of chondroitin sulphate proteoglycans

Matrix metalloproteinases (MMPs) secreted from the leukemic macrophage cell -line THP-1 have been investigated. Under serum-free conditions, this cell- line synthesizes and secretes proMMP-9, which was detected in the culture m edium as a monomer of 92 kDa, and in dimeric forms, including a homodimer o f approximately 225 kDa. In addition, a new heterodimer complex is describe d, in which proMMP-9 is covalently linked to the core protein of chondroiti n sulphate proteoglycan (CSPG) through one or more disulphide bridges. Afte r SDS-PAGE electrophoresis, at least two forms of this complex were detecte d, a large form in the stacking gel and a smaller form with an estimated si ze of 300 kDa. When the CS chains were removed by chondroitin ABC lyase tre atment, heterodimers of proMMP-9/CSPG core protein of approximately 145, 12 7 and 109 kDa were found, based on zymography and Western blots. Since as m uch as 10-15% of the total proMMP-9 secreted from THP-1 cells was covalentl y linked to CSPG, this association may have important implications for tran sport, targetting and regulation of the enzyme activity. (C) 2000 Academic Press.