Macrophages Secrete Matrix Metalloproteinase 9 Covalently Linked to the Core Protein of Chondroitin Sulphate Proteoglycans
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文摘
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 medium as a monomer of 92kDa, and in dimeric forms, including a homodimer of approximately 225kDa. In addition, a new heterodimer complex is described, in which proMMP-9 is covalently linked to the core protein of chondroitin sulphate proteoglycan (CSPG) through one or more disulphide bridges. After SDS-PAGE electrophoresis, at least two forms of this complex were detected, a large form in the stacking gel and a smaller form with an estimated size of 300kDa. When the CS chains were removed by chondroitin ABC lyase treatment, heterodimers of proMMP-9/CSPG core protein of approximately 145, 127 and 109kDa were found, based on zymography and Western blots. Since as much as 10-15 % of the total proMMP-9 secreted from THP-1 cells was covalently linked to CSPG, this association may have important implications for transport, targetting and regulation of the enzyme activity.