MMP1 and neoplasm: Since up-regulation of MMP1 might result from activating NF-κB signaling in many cell types like tumor cells and mesenchymal stem cells [18,19], we found that PMPs markedly increased the p-IκB and p-NF-κB, manifesting the positive effect of PMPs on activating NF-κB signaling in RA-FLSs.