REGULATION OF MMP-9 (92 KDA TYPE-IV COLLAGENASE GELATINASE-B) EXPRESSION IN STROMAL CELLS OF HUMAN GIANT-CELL TUMOR OF BONE/

Matrix metalloproteinases (MMPs) play an important regulatory role in tissue morphogenesis, cell differentiation, tumor invasion and metasta sis. Several authors have reported a direct correlation between the pr oduction of 72 kDa (MMP-2) and 92 kDa (MMP-9) type IV collagenases/gel atinases and the metastatic potential of cancer cells, Recently, we ha ve identified the expression of both MMP-2 and MMP-9 in primary cultur es of human giant cell tumor (GCT) of bone in vitro, and in tissue ext racts in vivo, Interestingly, MMP-9 is not secreted by late-passaged G CT cells, It is possible that the production of MMP-9 is regulated by certain factor(s) secreted by the multinucleated giant cells in the pr imary culture, In order to test this hypothesis, the effect of primary -culture-conditioned medium on the expression of MMP-9 by late-passage d mononuclear stromal cells was examined, Adding conditioned medium fr om the primary GCT culture to the late-passaged stromal cells induced MMP-9, as evidenced by the presence of lytic bands at M-r 92 000 and 7 2 000 on a gelatin zymogram, These enzyme activities were inhibited by EDTA, a well-known inhibitor of the MMPs. We confirmed these results by Western blotting using specific antibodies and RT-PCR for MMP-2 and MMP-9, Immunofluorescence studies with specific antibodies to MMP-9 f urther confirmed its expression by the passaged stromal cells cultured in the primary-culture-conditioned medium. The data indicate that MMP -2 and MMP-9 are produced by the mononuclear stromal cells when cultur ed in GCT primary-culture-conditioned medium, This suggests that multi nucleated giant cells in primary cultures secrete a factor(s) that sti mulates stromal cells to produce MMP-9, which, in turn, may contribute to the aggressive behavior of GCT.