Protocatechuic acid inhibits cancer cell metastasis involving the down-regulation of Ras/Akt/NF-κB pathway and MMP-2 production by targeting RhoB activation

BACKGROUND AND PURPOSE Protocatechuic acid (PCA) is plentiful in edible fruits and vegetables and is thus one anti-oxidative component of normal human diets. However, the molecular mechanisms involved in the chemopreventive activity of PCA are poorly understood. Here, we investigated the mechanism(s) underlying the anti-metastatic potential of PCA. EXPERIMENTAL APPROACH We used AGS cells in a wound healing model and Boyden chamber assays in vitro and injection of B16/F10 melanoma cells in mice (metastasis model in vivo) to analyse the effect of PCA on cancer cell invasion and metastasis. The activities and expression of molecular proteins were measured by zymographic assay, real-time RT-PCR and Western blotting. KEY RESULTS PCA inhibited cell migration and invasion at non-cytotoxic concentrations. Decreased expression of matrix metalloproteinase (MMP)-2 and a coincident increase in tissue inhibitor of MMP followed treatment with PCA. The PCA-inhibited MMP-2 activity and expression was accompanied by inactivation of NF-kappa B. All these effects of PCA could be mediated via the RhoB/ protein kinase C epsilon (PKC epsilon) and Ras/Akt cascade pathways, as demonstrated by inhibition of PKC epsilon and transfection of PKC epsilon siRNA and ras overexpression vector. Finally, PCA inhibited metastasis of B16/F10 melanoma cells to the liver in mice. CONCLUSION AND IMPLICATIONS Our data imply that PCA down-regulated the Ras/Akt/NF-kappa B pathway by targeting RhoB activation, which in turn led to a reduction of MMP-mediated cellular events in cancer cells and provides a new mechanism for the anti-cancer activity of PCA.