In monolayer cultures human rheumatoid synovial fibroblasts (HRSF) secrete gelatinase A (MMP-2) and, unlike other human fibroblasts, to a minor extent also gelatinase B (MMP-9) as inactive proenzymes. In this regard HRSF resemble the fibrosarcoma cell line HT-1080. Unlike HT-1080, however, HRSF do not increase the secretion of MMP-9 in response to phorbol-12-myristate-13-acetate. This indicates that in HRSF the protein kinase C pathway for an enhanced MMP-9 secretion is inactive. None of the substances used in our study increased MMP-9 secretion, but some of them inhibited MMP-9 secretion.
The secretion of MMP-2 could not be enhanced either, not even by dbcAMP, which has been reported to be effective in Sertoli and peritubular cells.
Activation of MMP-2 in HRSF could be induced by treatment with concanavalin A (ConA) or cytochalasin D, as was shown for other cell types. This activation was not accompanied by a significant change in the amount of secreted TIMP-1 and TIMP-2. In contrast to reports on human skin fibroblasts, however, the activation of MMP-2 could not be induced in HRSF by treatment of the cells with monensin or sodium orthovanadate. Moreover, monensin was shown to act as an inhibitor of ConA or cytochalasin Dmediated activation. Additionally, and in contrast to a report on a rat fibroblast cell line, MMP-2 activation is not mediated via the MAP kinase pathway in HRSF: PD 98059, a specific inhibitor of MAP kinase kinase, did not inhibit the activation of MMP-2. Similarly ineffective were PD 169316, an inhibitor for p38 MAP kinase, other inhibitors for protein kinases as lavendustin A, Gö 6983, wortmannin, rapamycin, as well as the protein tyrosine kinase inhibitors herbimycin A and genistein. Only staurosporin, a broad spectrum inhibitor of protein kinases, and the ionophores monensin and A 23187 effectively inhibited MMP-2 activation in HRSF.
Our results demonstrate that MMP-2 can be activated by quite different pathways, and that different cells, even when belonging to the fibroblast family, do not necessarily use the same activating pathways.