Matrix metalloproteinases (MMPs), especially MMP-2 and MMP-9, are expressed in most colonic, gastric, and ovarian carcinomas, and they play a key role in their invasiveness. Previous studies have shown the involvement of arachidonic acid (AA)-derived metabolites in the regulation of MMP expression and cancer dissemination, thus suggesting a role for phospholipase A₂, the AA producing enzymes, in these processes. The present study was undertaken to explore the role of phospholipases in MMP production and tumor cell invasiveness. Human fibrosarcoma cells were found to express and secrete type IB, IIA and V sPLA₂. The cells were found also to express the M-type sPLA₂ receptor. Treatment with an extracellular sPLA₂ inhibitor inhibited tumor cell's invasiveness concomitantly with MMP-2/9 production. Correspondingly, adding an exogenous sPLA₂-IB (but not IIA) resulted in significant elevation of MMP-2/9 secretion from the fibrosarcoma cells. Time-course determination of AA and oleic acid release by HT-1080 cells suggested that cPLA₂ is activated subsequently to sPLA₂ action. Accordingly, using Western blot analysis it was found that sPLA₂-IB induced cPLA₂ phosphorylation, a requirement for its activation, by a receptor-mediated activity, rather than its lipolytic activity. At the same time, sPLA₂-IIA did not induce either MMPs secretion or cPLA₂ phosphorylation. The results of this study show for the first time that MMP-2/9 production by human fibrosarcoma HT-1080 cells and their invasiveness is regulated by sPLA₂-IB acting as a receptor ligand to activate cPLA₂, which in turn provides the AA for production of eicosanoids required for MMP expression.