Adenylate cyclase and calmodulin-dependent kinase have opposite effects on osteoclastogenesis by regulating the PKA-NFATc1 pathway.

Nuclear factor of activated T cells c1 (NFATc1) is a transcription factor crucial for the differentiation of osteoclasts. In this study we discovered new signaling pathways involving cAMP regulators that modulate NFATc1 during osteoclastogenesis. The osteoclast differentiation factor receptor activator of NF-κB ligand (RANKL) increased the expression of adenylate cyclase 3 (AC3), accompanied by a rise in the intracellular cAMP level in osteoclasts. The knockdown of AC3 enhanced in vitro osteoclastogenesis and in vivo bone resorption, whereas cAMP-elevating agents showed opposite effects. The antiosteoclastogenic effect of the AC3-cAMP pathway was mediated by the inhibition of NFATc1 nuclear translocation and its autoamplification via a protein kinase A (PKA)-dependent mechanism. RANKL has been shown to activate Ca(2+) /calmodulin-dependent protein kinases (CaMKs). Knockdown or catalytic inhibition of CaMKs elevated intracellular cAMP levels in RANKL-treated osteoclast precursors and suppressed the activation of NFATc1. Taken together, our results demonstrate a pivotal role for the cAMP-PKA-NFATc1 signaling pathway during osteoclast differentiation, suggesting a mechanism by which osteoclastogenesis is fine-tuned by a balance between AC3 and CaMKs activities.