A schematic model of role of MafB in osteoclastogenesis. MafB, which is abundantly expressed in BMMs, associates with c-Fos and Mitf, thereby suppressing NFATc1 and OSCAR expression. RANKL stimulation down-regulates MafB expression via JNK and p38 MAPK and also up-regulates c-Fos expression; therefore, NFATc1 expression is induced by c-Fos and NFATc1 autoamplification. Lower levels of MafB enable Mitf and NFATc1 to bind to the OSCAR promoter region, subsequently leading to the up-regulation of OSCAR during osteoclastogenesis. A positive feedback loop between NFATc1 and OSCAR appears to be important for efficient differentiation of osteoclasts.