JNK/c‐Jun Signaling Mediates an Anti‐Apoptotic Effect of RANKL in Osteoclasts |
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Authors: | Fumiyo Ikeda Takuma Matsubara Taro Tsurukai Kenji Hata Riko Nishimura PhD Toshiyuki Yoneda |
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Affiliation: | 1. Department of Biochemistry, Osaka University Graduate School of Dentistry, Osaka, Japan;2. Institute of Biochemistry II, Goethe University Medical School, Frankfurt, Germany;3. Kaken Pharmaceutical Co., Drug Discovery Research Department, Kyoto, Japan;4. Dr Tsurukai is an employee of Kaken Pharmaceutical Co. All other authors state that they have no conflicts of interest. |
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Abstract: | Introduction: RANKL is known to be important not only for differentiation and activation of osteoclasts but also for their survival. Experimentally, apoptosis of osteoclasts is rapidly induced by the deprivation of RANKL. RANKL activates Elk‐related tyrosine kinase (ERK), p38, c‐Jun N‐terminal kinase (JNK), and NF‐κB pathways through TRAF6 in osteoclasts and the precursor cells. It has been shown that ERK is critical for regulation of osteoclast survival. However, an involvement of other RANKL signaling pathways such as JNK signaling in survival of osteoclasts has not been fully understood yet. Materials and Methods: Osteoclasts derived from primary mouse bone marrow cells by soluble RANKL (sRANKL) were treated with a JNK inhibitor, SP600125, or infected with adenovirus carrying dominant‐negative (DN)‐c‐jun, DN‐c‐fos, mitogen‐activated protein kinase kinase 1 (MEKK1), I‐κBα mutant, or NF‐κB components, p50 and p65. Osteoclasts were cultured with or without sRANKL, and apoptotic phenotype was determined by TUNEL assay, DAPI staining, and expression of cleaved caspase 3 followed by TRACP staining. Results: Overexpression of TRAF6 activated JNK and NF‐κB signaling pathways and clearly prevented osteoclasts from apoptosis caused by abrogation of sRANKL. An anti‐apoptotic effect of RANKL/RANK/TRAF6 signaling on osteoclast was inhibited by JNK‐specific inhibitor SP600125 and by overexpression of dominant‐negative JNK1, c‐jun, and c‐fos. Also, overexpression of MEKK1 inhibited apoptosis of osteoclasts even in the absence of sRANKL along with activation of JNK/c‐jun signaling. On the other hand, blockade of NF‐κB signaling by I‐κBα mutant or overexpression of NF‐κB components showed a marginal effect on apoptosis of osteoclasts. Conclusions: An important role of RANKL‐induced activation of MEKK1/JNK/c‐jun signaling in the regulation of apoptosis in osteoclasts was shown. Our study suggests that c‐fos plays a role as a partner of activator protein‐1 factor, c‐jun, during the regulation of apoptosis in osteoclasts. |
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Keywords: | osteoclast apoptosis RANKL c‐Jun N‐terminal kinase c‐Jun |
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