title: AG490, a Jak2-specific inhibitor, induces osteoclast survival by activating the Akt and ERK signaling pathways.
abstract: Osteoclasts are multinucleated cells with the unique ability to resorb bone. Elevated activity of these cells under pathologic conditions leads to the progression of bone erosion that occurs in osteoporosis, periodontal disease, and rheumatoid arthritis. Thus, the regulation of osteoclast apoptosis is important for bone homeostasis. In this study, we examined the effects of the Janus tyrosine kinase 2 specific inhibitor AG490 on osteoclast apoptosis. We found that AG490 greatly inhibited osteoclast apoptosis. AG490 stimulated the phosphorylation of Akt and ERK. Adenovirus-mediated expression of dominant negative (DN)-Akt and DN-Ras in osteoclasts inhibited the survival of osteoclasts despite the presence of AG490. Cytochrome c release during osteoclast apoptosis was inhibited by AG490 treatment, but this effect was inhibited in the presence of LY294002 or U0126. AG490 suppressed the proapoptotic proteins Bad and Bim, which was inhibited in osteoclasts infected with DN-Akt and DN-Ras adenovirus. In addition, constitutively active MEK and myristoylated-Akt adenovirus suppressed the cleavage of pro-caspase-9 and -3 and inhibited osteoclast apoptosis induced by etoposide. Taken together, our results suggest that AG490 inhibited cytochrome c release into the cytosol at least partly by inhibiting the pro-apoptotic proteins Bad and Bim, which in turn suppressed caspase-9 and -3 activation, thereby inhibiting osteoclast apoptosis.
authors.affiliation: Department of Anatomy, School of Medicine, Wonkwang University, Iksan 570-749, Korea.
authors.forename: Han Bok
authors.initials: HB
authors.lastname: Kwak
authors.forename: Hyun Min
authors.initials: HM
authors.lastname: Sun
authors.forename: Hyunil
authors.initials: H
authors.lastname: Ha
authors.forename: Jong Ho
authors.initials: JH
authors.lastname: Lee
authors.forename: Ha Neui
authors.initials: HN
authors.lastname: Kim
authors.forename: Zang Hee
authors.initials: ZH
authors.lastname: Lee
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D045304:Cytochromes c / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D053614:Janus Kinase 2 / Q000037:antagonists & inhibitors*; D020935:MAP Kinase Signaling System / Q000187:drug effects*; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D010010:Osteoclasts / Q000166:cytology* / Q000187:drug effects / Q000201:enzymology*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D020032:Tyrphostins / Q000494:pharmacology*; D051025:bcl-Associated Death Protein / Q000378:metabolism
chemical_list: D051017:Apoptosis Regulatory Proteins; D000072224:Bcl-2-Like Protein 11; C000606776:Bcl2l11 protein, mouse; D008565:Membrane Proteins; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D020032:Tyrphostins; C095512:alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamide; D051025:bcl-Associated Death Protein; D045304:Cytochromes c; D053614:Janus Kinase 2; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases; D020169:Caspases