Calcium-induced activation and truncation of promatrix metalloproteinase-9 linked to the core protein of chondroitin sulfate proteoglycans

In the leukemic macrophage cell-line THP-1, a fraction of the secreted matrix metalloproteinase 9 (MMP-9) is linked to the core protein of chondroitin sulfate proteoglycans (CSPG). Unlike the monomeric and homodimeric forms of MMP-9, the addition of exogenous CaCl2 to the proMMP-9/CSPG complex resulted in an active gelatinase due to the induction of an autocatalytic removal of the N-terminal prodomain. In addition, the MMP-9 was released from the CSPG through a process that appeared to be a stepwise truncation of both the CSPG core protein and a part of the C-terminal domain of the gelatinase. The calcium-induced activation and truncation of the MMP-9/CSPG complex was independent of the concentration of the complex, inhibited by the MMP inhibitors EDTA, 1,10-phenanthroline and TIMP-1, but not by general inhibitors of serine, thiol and acid proteinases. This indicated that the activation and truncation process was not due to a bimolecular reaction, but more likely an intramolecular reaction. The negatively charged chondroitin sulfate chains in the proteoglycan were not involved in this process. Other metal-containing compounds like aminophenylmercuric acetate (APMA), NaCl, ZnCl2 and MgCl2 were not able to induce activation and truncation of the proMMP-9 in this heterodimer. On the contrary, APMA inhibited the calcium-induced process, whereas high concentrations of either MgCl2 or NaCl had no effect. Our results indicate that the interaction between the MMP-9 and the core protein of the CSPG was the causal factor in the calcium-induced activation and truncation of the gelatinase, and that this process was not due to a general electrostatic effect.