title: AP-1 family members act with Sox9 to promote chondrocyte hypertrophy.
abstract: An analysis of Sox9 binding profiles in developing chondrocytes identified marked enrichment of an AP-1-like motif. Here, we have explored the functional interplay between Sox9 and AP-1 in mammalian chondrocyte development. Among AP-1 family members, Jun and Fosl2 were highly expressed within prehypertrophic and early hypertrophic chondrocytes. Chromatin immunoprecipitation followed by DNA sequencing (ChIP-seq) showed a striking overlap in Jun- and Sox9-bound regions throughout the chondrocyte genome, reflecting direct binding of each factor to the same enhancers and a potential for protein-protein interactions within AP-1- and Sox9-containing complexes. In vitro reporter analysis indicated that direct co-binding of Sox9 and AP-1 at target motifs promoted gene activity. By contrast, where only one factor can engage its DNA target, the presence of the other factor suppresses target activation consistent with protein-protein interactions attenuating transcription. Analysis of prehypertrophic chondrocyte removal of Sox9 confirmed the requirement of Sox9 for hypertrophic chondrocyte development, and in vitro and ex vivo analyses showed that AP-1 promotes chondrocyte hypertrophy. Sox9 and Jun co-bound and co-activated a Col10a1 enhancer in Sox9 and AP-1 motif-dependent manners consistent with their combined action promoting hypertrophic gene expression. Together, the data support a model in which AP-1 family members contribute to Sox9 action in the transition of chondrocytes to the hypertrophic program.
authors.affiliation: Department of Stem Cell Biology and Regenerative Medicine, Eli and Edythe Broad CIRM Center for Regenerative Medicine and Stem Cell Research, W.M. Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
authors.forename: Xinjun
authors.initials: X
authors.lastname: He
authors.affiliation: Department of Bioengineering, the University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Shinsuke
authors.initials: S
authors.lastname: Ohba
authors.affiliation: Department of Stem Cell Biology and Regenerative Medicine, Eli and Edythe Broad CIRM Center for Regenerative Medicine and Stem Cell Research, W.M. Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA.
authors.forename: Hironori
authors.initials: H
authors.lastname: Hojo
authors.affiliation: Department of Stem Cell Biology and Regenerative Medicine, Eli and Edythe Broad CIRM Center for Regenerative Medicine and Stem Cell Research, W.M. Keck School of Medicine, University of Southern California, Los Angeles, CA 90033, USA amcmahon@med.usc.edu.
authors.forename: Andrew P
authors.identifier: 0000-0002-3779-1729
authors.initials: AP
authors.lastname: McMahon
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000235:genetics / Q000502:physiology; D002478:Cells, Cultured; D019902:Chondrocytes / Q000166:cytology* / Q000378:metabolism*; D020219:Chondrogenesis / Q000235:genetics / Q000502:physiology; D047369:Chromatin Immunoprecipitation; D004742:Enhancer Elements, Genetic / Q000235:genetics / Q000502:physiology; D006801:Humans; D055758:SOX9 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D055758:SOX9 Transcription Factor; D018808:Transcription Factor AP-1; D014157:Transcription Factors
keywords: Chondrocyte development; Hypertrophy; Mouse; Sox9; Transcriptional program