NF-κB signaling pathways and the future perspectives of bone disease therapy using selective inhibitors of NF-κB

The transcriptional factor nuclear factor κB(NF-κB)regulates the expression of a wide variety of genes that are involved in immune and inflammatory responses, proliferation, and tumorigenesis. NF-κB consists of five members, such as p65(RelA), RelB, c-Rel, p50/p105(NF-κB1), and p52/p100(NF-κB2). There are two distinct NF-κB activation pathways, termed the classical and alternative NF-κB signaling pathways. Since mice lacking both p50 and p52 subunits developed typical osteopetrosis, due to total lack of osteoclasts, NF-κB is also important osteoclast differentiation. A selective NF-κB inhibitor blocked receptor activator of NF-κB ligand(RANKL)-induced osteoclastogenesis both in vitro and in vivo. Recent findings have shown that inactivation of NF-κB enhances osteoblast differentiation in vitro and bone formation in vivo. NF-κB is constitutively activated in many cancers including oral squamous cell carcinoma(OSCC), and is involved in the invasive characteristics of OSCC. A selective NF-κB inhibitor also prevented jaw bone destruction by OSCC by reduced osteoclast numbers in animal model. Thus the inhibition of NF-κB might useful for the treatment of bone diseases, such as arthritis, osteoporosis, periodontitis, and bone invasion by OSCC by inhibiting bone resorption and by stimulating bone formation.