We have recently reported that osteopontin (OPN) stimulates tumor growth and activation of promatrix metalloproteinase-2 (pro-MMP-2) through nuclear factor kappa B (NF kappa B)-mediated induction of membrane type 1 matrix metalloproteinase (MT1-MMP) in murine melanoma cells (Philip, S., Bulbule, A., and Kundu, G. C. (2001) J. Biol. Chem. 276, 44926-44935). However, the molecular mechanism by which OPN activates NF kappa B and regulates pro-MMP-2 activation in murine melanoma (B16F10) cells is not well defined. We also investigated the mechanism of action of curcumin (diferulolylmethane) on OPN-induced NF kappa B-mediated activation of pro-MMP-2 in B16F10 cells. Here we report that OPN induces phosphorylation and degradation of the inhibitor of nuclear factor kappa B (I kappa B alpha) by inducing the activity of I kappa B kinase (IKK) in these cells. OPN also induces the nuclear accumulation of NF kappa B p65, NF kappa B-DNA binding, and transactivation. However, curcumin a known anti-inflammatory and anticarcinogenic agent suppressed OPN-induced I kappa B alpha phosphorylation and degradation by inhibiting the IKK activity. Moreover, our data revealed that curcumin inhibited the OPN-induced translocation of p65, NF kappa B-DNA binding, and NF kappa B transcriptional activity. The OPN-induced pro-MMP-2 activation and MT1-MMP expression were also drastically reduced by curcumin. Curcumin also inhibited OPN-induced cell proliferation, cell migration, extracellular matrix invasion, and synergistically induced apoptotic morphology with OPN in these cells. Most importantly, curcumin suppressed the OPN-induced tumor growth in nude mice, and the levels of pro-MMP-2 expression and activation in OPN-induced tumor were inhibited by curcumin. To our knowledge, this is the first report that OPN induces NF kappa B activity through phosphorylation and degradation of I kappa B alpha by activating IKK that ultimately triggers the activation of pro-MMP-2 and further demonstrates that curcumin potently suppresses OPN-induced cell migration, tumor growth, and NF kappa B-mediated pro-MMP-2 activation by blocking the IKK/I kappa B alpha signaling pathways.