Inhibition of osteoclasts differentiation by CDC2-induced NFATc1 phosphorylation

Bone homeostasis is regulated by a balance of bone formation and bone resorption; dysregulation of bone homeostasis may cause bone-related diseases (e.g., osteoporosis, osteopetrosis, bone fracture). Members of the nuclear factor of activated T cells (NFAT) family of transcription factors play crucial roles in the regulation of immune system, inflammatory responses, cardiac formation, skeletal muscle development, and bone homeostasis. Of these, NFATc1 is a key transcription factor mediating osteoclast differentiation, which is regulated by phosphorylation by distinct NFAT kinases including casein kinase 1 (CK1), glycogen synthase kinase 3 (GSK3), and dual-specificity tyrosine-phosphorylation-regulated kinases (DYRKs). In this study, we report that cell division control protein 2 homolog (cdc2) is a novel NFAT protein kinase that inhibits NFATc1 activation by direct phosphorylation of the NFATc1 S263 residue. Cdc2 inhibitors such as Roscovitine and BMI-1026 induce reduction of phosphorylation of NFATc1, and this process leads to the inhibition of NFATc1 translocation from the nucleus to the cytoplasm, consequently increasing the nuclear pool of NFATc1. Additionally, the inhibition of cdc2-mediated NFATc1 phosphorylation causes an elevation of osteoclast differentiation or TRAP-positive staining in zebrafish scales. Our results suggest that cdc2 is a novel NFAT protein kinase that negatively regulates osteoclast differentiation. •Mitotic kinase cdc2 has a close causality with NFATc1 cellular location during RANKL-induced osteoclast differentiation.•After treatment of cdc2 inhibitors such as Roscovitine and BMI-1026, cytoplasmic NFATc1 level was elevated in the cells.•NFATc1 is a novel substrate of Cdc2, which induced phosphorylation at serine 263 residues on NFATc1 and relocating NFATc1 from the nucleus to the cytoplasm.•Cdc2 phosphorylates NFATc1 directly, thereby regulating the intracellular location of NFATc1, which negatively affects osteoclast differentiation using mouse bone marrow induced macrophages (BMMs) and zebrafish scales.