Possible contribution of aminopeptidase N (APN/CD13) to invasive potentialenhanced by interleukin-6 and soluble interleukin-6 receptor in human osteosarcoma cell lines

This study aimed at clarifying the role of Aminopeptidase N (APN), a Zn2+-d ependent ectopeptidase localized on the cell surface of human osteosarcoma cell lines treated with proinflammatory cytokines. We investigated the proi nflammatory cytokines interleukin-1 beta (IL-1 beta), IL-6 and tumor necros is factor alpha (TNF-alpha) as well as the anti-inflammatory cytokine trans forming growth factor beta (TGF-beta) for their influence on APN regulation . Soluble IL-6 receptor (sIL-6R) was always used together with IL-6 to achi eve a stable effect. In addition, the invasive potential of the osteosarcom a cell lines MG63 and HOS was examined. Competitive RT-PCR and Ala-pNA acti vity assays revealed that IL-6 and sIL-6R significantly increased the mRNA expression and activity of APN in both osteosarcoma cell lines. Although IL -1 beta significantly stimulated APN mRNA expression in both cell lines, it influenced the enzyme activity only in MG63. TNF-alpha and TGF-beta, howev er, had an effect neither on mRNA expression nor on the enzyme activity of APN in both cell lines. In the Matrigel invasion assay, IL-6 and sIL-6R sig nificantly up-regulated the transmigration of these cell lines, whereas oth er cytokines did not. The up-regulated invasion was inhibited by bestatin, a specific inhibitor of APN. Cellular migration correlated highly with APN activity (r=0.79, P < 0.002). These findings suggest that APN contributes t o the invasive potential of human osteosarcomas enhanced by IL-6 and SIL-6R .