Essential Role of p38 Mitogen-activated Protein Kinase in Cathepsin K Gene Expression during Osteoclastogenesis through Association of NFATc1 and PU.1

Abstract

The receptor activator of NF-B ligand (RANKL) induces various osteoclast-specific marker genes during osteoclast differentiation mediated by mitogen-activated protein (MAP) kinase cascades. However, the results of transcriptional programming of an osteoclastspecific cathepsin K gene are inconclusive. Here we report the regulatory mechanisms of RANKL-induced cathepsin K gene expression during osteoclastogenesis in a p38 MAP kinase-dependent manner. The reporter gene analysis with sequential 5-deletion constructs of the cathepsin K gene promoter indicates that limited sets of the transcription factors such as NFATc1, PU.1, and microphthalmia transcription factor indeed enhance synergistically the gene expression when overexpressed in RAW264 cells. In addition, the activation of p38 MAP kinase is required for the maximum enhancement of the gene expression. RANKL-induced NFATc1 forms a complex with PU.1 in nuclei of osteoclasts following the nuclear accumulation of NFATc1 phosphorylated by the activated p38 MAP kinase. These results suggest that the RANKL-induced cathepsin K gene expression is cooperatively regulated by the combination of the transcription factors and p38 MAP kinase in a gradual manner.

Inhibitory effect of luteolin on osteoclast differentiation and function

“…It was shown that the expression of dominant-negative forms of p38 MAPK and MKK6 in RAW264.7 cells inhibited RANKL-induced differentiation of RAW264.7 cells into osteoclasts (Matsumoto et al 2000). Moreover, addition of luteolin to osteoclast cultures strongly inhibited the expression of NFATc1, which is a key transcription factor for the expressions of TRAP and other osteoclastogenesis-associated genes (Ikeda et al 2004;Matsumoto et al 2004;Sharma et al 2007). Therefore, the effects of luteolin on osteoclastogenesis are probably mediated by ATF2, downstream of p38 MAPK pathway.…”

Molecular Understanding of Osteoclast Differentiation and Physiology

“…The release of Ca 2+ activates the calmodulin-regulated phosphatase calcineurin, which binds the N-terminal domain of NFAT2 and dephosphorylates it [51,52]. NFAT2 undergoes nuclear translocation and regulates the expression of many osteoclast-specific genes, such as cathepsin K, TRAP, calcitonin receptor as well as NFAT2 it-self, in cooperation with other transcription factors, although the components of the transcriptional complex are not always the same [53][54][55][56]. The C-terminal domain of NFAT2 binds DNA sequence specifically and cooperates with AP-1 in vitro [52].…”

Focus on the p38 MAPK signaling pathway in bone development and maintenance

“…45 Once again, first evidence highlighting the role of p38a in osteoclastogenesis has come from in vitro experiments employing the RAW264 cell line and primary bone marrow cells with selective p38 inhibitors and dominant negative forms of p38 signaling components. [46][47][48] In those cells, p38a functions downstream of RANK after stimulation by RANKL (the proresorptive cytokine that is necessary and sufficient for osteoclastogenesis) to stimulate osteoclast formation, maturation and bone resorption 46,47 (Figure 3). Inhibition of p38 MAPK completely blocks osteoclastogenesis induced by RANKL.…”

“…Inhibition of p38 MAPK completely blocks osteoclastogenesis induced by RANKL. 46,47 In osteoclast precursors, p38a functions downstream of tumor necrosis factor (TNF) receptor after stimulation by TNF-a to stimulate early osteoclast differentiation 48 (Figure 3). Furthermore, p38a has been shown to be a major regulator of nuclear factor for activated T cells 1 expression (Nfatc1, encoding a master transcription factor regulating osteoclastogenesis).…”