The 4B12 preosteoclast cells differentiate into osteoclasts upon the stimulation of M-CSF and sRANKL. We found that Erk5 is activated by M-CSF. Inhibition of MEK5 by BIX02189 or inhibition of Erk5 by XMP 8-92 blocked the osteoclast differentiation. MEK5 siRNA inhibited differentiation of 4B12 cells, confirming these results. Raw264.7D clone cells, which are monocytic cells, differentiate into osteoclasts after stimulation with sRANKL. Erk5 was activated without any stimulation in these cells. Inhibition of the Erk5 pathway by the inhibitors also blocked differentiation of these cells into osteoclasts. Moreover, induction of c-Fos was inhibited. Therefore, activation of ERK5 is required for induction of c-Fos. Taken together, activation of the Erk5 pathway is required for differentiation of preosteoclasts into osteoclasts through induction of c-Fos.
Disclosure: The authors declared no competing interests. This work was supported by grants-in-aid from the Ministry of Education, Science, Sports, and Culture of Japan to S.A. and This paper is supported by a grant from the National Health Research Institute: 01A1-CSPP04-014 and from the National Science Council Taiwan: 101-2300-B-400-015 to Y. F.