Long-Lasting Activity of ERK Kinase Depends on NFATc1 Induction and Is Involved in Cell Migration-Fusion in Murine Macrophages RAW264.7

Macrophages are mononuclear cells that become osteoclasts (OCs) in the presence of twocytokines, macrophage colony-stimulating factor (M-CSF), and receptor activator of NF-?B ligand(RANKL). RANKL binding to its specific receptor RANK leads to OCs differentiation mainly bynuclear factor of activated T-cells cytoplasmic 1 (NFATc1). In our previous study, the analysis of theprotein network in NFATc1-knockdown cells, using the Ingenuity Pathway Analysis (IPA), showed alink between NFATc1 and Mitogen-activated protein kinase kinase (MEK)-extracellular receptor kinase(ERK) signaling pathway. Therefore, this study aimed to extend our knowledge of the relationshipbetween NFATc1 and the ERK. Here, we demonstrate that delayed ERK1/2 phosphorylation inpre-OC RANKL-induced depends on NFATc1. Indeed, the knockdown of NFATc1 reduced thephosphorylation of ERK1/2 (60%) and the pharmacological inhibition of the ERK1/2 kinase activityimpairs the expression of NFATc1 without preventing its translocation into the nucleus. Furthermore,silencing of NFATc1 significantly reduced RANKL-induced migration (p < 0.01), and most pre-OCsare still mononuclear after 48 h (80 ± 5%), despite the presence of actin rings. On the otherhand, the inhibitors FR180204 and PD98059 significantly reduced RANKL-induced cell migration(p < 0.01), leading to a reduction in the number of multinucleated cells. Finally, we suggest thatlong-lasting ERK activity depends on NFATc1 induction and is likely linked to cell migration, fusion,and OC differentiation