title: c-Fos degradation by the ubiquitin-proteasome proteolytic pathway in osteoclast progenitors.
abstract: c-Fos is an immediate early gene type proto-oncogene that belongs to the AP (activator protein)-1 transcription factor family. Gene knockout experiments have demonstrated that, among the Fos family, only c-Fos is indispensable for osteoclast differentiation but that c-Fos can be substituted for by other Fos family members including FosB/DeltaFosB, Fra-1 and Fra-2, in most other tissues and cells. To further understand a unique role of c-Fos in osteoclastogenesis, we investigated the temporal profile and regulatory mode of expression of c-Fos during the course of osteoclast differentiation. The results indicated that c-Fos protein gradually increased in preosteoclasts during differentiation to a greater extent than that of mRNA induction. We then determined the proteolytic pathway of c-Fos conferring unstable nature on c-Fos protein in a preosteoclastic cell line, RAW264.7. Proteasome inhibitors including MG132 and Z-LLF caused a rapid increase in c-Fos protein expression in these cells within several hours, but other inhibitors of cysteine protease (E-64), lysosome (chloroquine) and calpain (ALLM) did not. Moreover, the proteasome inhibitors caused an extensive accumulation of ubiquitinated c-Fos protein and an approximately three-fold extension of the c-Fos protein half-life. We therefore conclude that the ubiquitin-proteasome system is the major proteolytic pathway conferring instability on c-Fos protein in preosteoclasts. Our results further imply that c-Fos stabilization due to dynamic changes in the ubiquitin-proteasome-dependent degradation may be involved in the accumulation of c-Fos protein in differentiating preosteoclasts.
authors.affiliation: Department of Medicine and Bioregulatory Sciences, University of Tokushima Graduate School, Institute of Health Biosciences, 3-18-15 Kuramoto-cho Tokushima 770-8503, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Ito
authors.forename: Daisuke
authors.initials: D
authors.lastname: Inoue
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Kido
authors.forename: Toshio
authors.initials: T
authors.lastname: Matsumoto
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D051379:Mice; D018345:Mice, Knockout; D010010:Osteoclasts / Q000166:cytology* / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D016760:Proto-Oncogene Proteins c-fos / Q000235:genetics / Q000378:metabolism*; D013234:Stem Cells / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism*
chemical_list: D015853:Cysteine Proteinase Inhibitors; D061988:Proteasome Inhibitors; D016760:Proto-Oncogene Proteins c-fos; D025801:Ubiquitin; D046988:Proteasome Endopeptidase Complex