title: E3 Ubiquitin Ligase Fbw7 Negatively Regulates Osteoblast Differentiation by Targeting Runx2 for Degradation.
abstract: Runx2, a master regulator of osteoblast differentiation, is tightly regulated at both transcriptional and post-translational levels. Post-translational modifications such as phosphorylation and ubiquitination have differential effects on Runx2 functions. Here, we show that the reduced expression and functions of Runx2 upon its phosphorylation by GSK3β are mediated by its ubiquitin-mediated degradation through E3 ubiquitin ligase Fbw7α. Fbw7α through its WD domain interacts with Runx2 both in a heterologous (HEK293T cells) system as well as in osteoblasts. GSK3β was also present in the same complex as determined by co-immunoprecipitation. Furthermore, overexpression of either Fbw7α or GSK3β was sufficient to down-regulate endogenous Runx2 expression and function; however, both failed to inhibit endogenous Runx2 when either of them was depleted in osteoblasts. Fbw7α-mediated inhibition of Runx2 expression also led to reduced Runx2 transactivation and osteoblast differentiation. In contrast, inhibition of Fbw7α restored Runx2 levels and promoted osteoblast differentiation. We also observed reciprocal expression levels of Runx2 and Fbw7α in models of bone loss such as lactating (physiological bone loss condition) and ovariectomized (induction of surgical menopause) animals that show reduced Runx2 and enhanced Fbw7α, whereas this was reversed in the estrogen-treated ovariectomized animals. In addition, methylprednisolone (a synthetic glucocorticoid) treatment to neonatal rats showed a temporal decrease in Runx2 with a reciprocal increase in Fbw7 in their calvarium. Taken together, these data demonstrate that Fbw7α negatively regulates osteogenesis by targeting Runx2 for ubiquitin-mediated degradation in a GSK3β-dependent manner and thus provides a plausible explanation for GSK3β-mediated bone loss as described before.
authors.affiliation: From the Biochemistry Division, CSIR-Central Drug Research Institute (CSIR-CDRI), Sector-10, Jankipuram Extension, Lucknow, 226031 Uttar Pradesh and.
authors.forename: Yogesh
authors.initials: Y
authors.lastname: Kumar
authors.affiliation: From the Biochemistry Division, CSIR-Central Drug Research Institute (CSIR-CDRI), Sector-10, Jankipuram Extension, Lucknow, 226031 Uttar Pradesh and.
authors.forename: Isha
authors.initials: I
authors.lastname: Kapoor
authors.affiliation: the Division of Endocrinology and Center for Research in Anabolic Skeletal Targets in Health and Illness (ASTHI), CSIR-Central Drug Research Institute (CSIR-CDRI), Sector-10, Jankipuram Extension, Lucknow, 226031 Uttar Pradesh, India.
authors.forename: Kainat
authors.initials: K
authors.lastname: Khan
authors.affiliation: From the Biochemistry Division, CSIR-Central Drug Research Institute (CSIR-CDRI), Sector-10, Jankipuram Extension, Lucknow, 226031 Uttar Pradesh and.
authors.forename: Gatha
authors.initials: G
authors.lastname: Thacker
authors.affiliation: the Division of Endocrinology and Center for Research in Anabolic Skeletal Targets in Health and Illness (ASTHI), CSIR-Central Drug Research Institute (CSIR-CDRI), Sector-10, Jankipuram Extension, Lucknow, 226031 Uttar Pradesh, India.
authors.forename: Mohd Parvez
authors.initials: MP
authors.lastname: Khan
authors.affiliation: From the Biochemistry Division, CSIR-Central Drug Research Institute (CSIR-CDRI), Sector-10, Jankipuram Extension, Lucknow, 226031 Uttar Pradesh and.
authors.forename: Nidhi
authors.initials: N
authors.lastname: Shukla
authors.affiliation: From the Biochemistry Division, CSIR-Central Drug Research Institute (CSIR-CDRI), Sector-10, Jankipuram Extension, Lucknow, 226031 Uttar Pradesh and.
authors.forename: Jitendra Kumar
authors.initials: JK
authors.lastname: Kanaujiya
authors.affiliation: From the Biochemistry Division, CSIR-Central Drug Research Institute (CSIR-CDRI), Sector-10, Jankipuram Extension, Lucknow, 226031 Uttar Pradesh and.
authors.forename: Sabyasachi
authors.initials: S
authors.lastname: Sanyal
authors.affiliation: the Division of Endocrinology and Center for Research in Anabolic Skeletal Targets in Health and Illness (ASTHI), CSIR-Central Drug Research Institute (CSIR-CDRI), Sector-10, Jankipuram Extension, Lucknow, 226031 Uttar Pradesh, India.
authors.forename: Naibedya
authors.initials: N
authors.lastname: Chattopadhyay
authors.affiliation: From the Biochemistry Division, CSIR-Central Drug Research Institute (CSIR-CDRI), Sector-10, Jankipuram Extension, Lucknow, 226031 Uttar Pradesh and arun3vedi@cdri.res.in.
authors.forename: Arun Kumar
authors.initials: AK
authors.lastname: Trivedi
mesh_terms: D000818:Animals; D001862:Bone Resorption / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation; D050659:Core Binding Factor Alpha 1 Subunit / Q000235:genetics / Q000378:metabolism*; D044783:F-Box Proteins / Q000235:genetics / Q000378:metabolism*; D000073979:F-Box-WD Repeat-Containing Protein 7; D005260:Female; D038362:Glycogen Synthase Kinase 3 / Q000096:biosynthesis; D000071679:Glycogen Synthase Kinase 3 beta; D057809:HEK293 Cells; D006801:Humans; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism*; D010012:Osteogenesis / Q000235:genetics; D059748:Proteolysis; D051381:Rats; D017207:Rats, Sprague-Dawley; D015533:Transcriptional Activation; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D050659:Core Binding Factor Alpha 1 Subunit; D044783:F-Box Proteins; D000073979:F-Box-WD Repeat-Containing Protein 7; C513272:Fbxw7 protein, mouse; C493716:Runx2 protein, mouse; C493717:Runx2 protein, rat; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; C000605508:Gsk3b protein, rat; D038362:Glycogen Synthase Kinase 3
keywords: Fbw7; GSK3-beta; Runx2; osteoblast; proteasome; protein degradation; ubiquitin ligase; ubiquitylation (ubiquitination)