title: HSP90 inhibitors enhance differentiation and MITF (microphthalmia transcription factor) activity in osteoclast progenitors.
abstract: The HSP90 (heat-shock protein 90) inhibitor 17-AAG (17-allylamino-demethoxygeldanamycin) increases osteoclast formation both in vitro and in vivo, an action that can enhance cancer invasion and growth in the bone microenvironment. The cellular mechanisms through which 17-AAG exerts this action are not understood. Thus we sought to clarify the actions of 17-AAG on osteoclasts and determine whether other HSP90 inhibitors had similar properties. We determined that 17-AAG and the structurally unrelated HSP90 inhibitors CCT018159 and NVP-AUY922 dose-dependently increased RANKL [receptor activator of NF-κB (nuclear factor κB) ligand]-stimulated osteoclastogenesis in mouse bone marrow and pre-osteoclastic RAW264.7 cell cultures. Moreover, 17-AAG also enhanced RANKL- and TNF (tumour necrosis factor)-elicited osteoclastogenesis, but did not affect RANKL-induced osteoclast survival, suggesting that only differentiation mechanisms are targeted. 17-AAG affected the later stages of progenitor maturation (after 3 days of incubation), whereas the osteoclast formation enhancer TGFβ (transforming growth factor β) acted prior to this, suggesting different mechanisms of action. In studies of RANKL-elicited intracellular signalling, 17-AAG treatment did not increase c-Fos or NFAT (nuclear factor of activated T-cells) c1 protein levels nor did 17-AAG increase activity in luciferase-based NF-κB- and NFAT-response assays. In contrast, 17-AAG treatment (and RANKL treatment) increased both MITF (microphthalmia-associated transcription factor) protein levels and MITF-dependent vATPase-d2 (V-type proton ATPase subunit d2) gene promoter activity. These results indicate that HSP90 inhibitors enhance osteoclast differentiation in an NFATc1-independent manner that involves elevated MITF levels and activity.
authors: Prince Henry's Institute, Monash Medical Centre, Clayton, VIC 3168, Australia.
authors: A Gabrielle J
authors: AG
authors: van der Kraan
authors: Ryan C C
authors: RC
authors: Chai
authors: Preetinder P
authors: PP
authors: Singh
authors: Benjamin J
authors: BJ
authors: Lang
authors: Jiake
authors: J
authors: Xu
authors: Matthew T
authors: MT
authors: Gillespie
authors: John T
authors: JT
authors: Price
authors: Julian M W
authors: JM
authors: Quinn
mesh_terms: D000818:Animals; D016227:Benzoquinones / Q000494:pharmacology*; D001854:Bone Marrow Cells / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects*; D002478:Cells, Cultured; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006574:Heterocyclic Compounds, 2-Ring / Q000494:pharmacology; D007555:Isoxazoles / Q000494:pharmacology; D047029:Lactams, Macrocyclic / Q000494:pharmacology*; D051379:Mice; D008810:Mice, Inbred C57BL; D051739:Microphthalmia-Associated Transcription Factor / Q000378:metabolism*; D016328:NF-kappa B / Q000378:metabolism; D050778:NFATC Transcription Factors / Q000378:metabolism; D010010:Osteoclasts / Q000166:cytology* / Q000187:drug effects* / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000187:drug effects; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D011720:Pyrazoles / Q000494:pharmacology; D012118:Resorcinols / Q000494:pharmacology; D013234:Stem Cells / Q000166:cytology / Q000187:drug effects*; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D025262:Vacuolar Proton-Translocating ATPases / Q000235:genetics / Q000378:metabolism
chemical_list: C528044:5-(2,4-dihydroxy-5-isopropylphenyl)-4-(4-morpholin-4-ylmethylphenyl)isoxazole-3-carboxylic acid ethylamide; D016227:Benzoquinones; C506244:CCT018159; D018841:HSP90 Heat-Shock Proteins; D006574:Heterocyclic Compounds, 2-Ring; D007555:Isoxazoles; D047029:Lactams, Macrocyclic; D051739:Microphthalmia-Associated Transcription Factor; C497235:Mitf protein, mouse; D016328:NF-kappa B; D050778:NFATC Transcription Factors; C494005:Nfatc1 protein, mouse; D016760:Proto-Oncogene Proteins c-fos; D011720:Pyrazoles; D012118:Resorcinols; D016212:Transforming Growth Factor beta; C112765:tanespimycin; D025262:Vacuolar Proton-Translocating ATPases