Publications (13)61.55 Total impact
-
Article: The translation regulatory subunit eIF3f controls the kinase-dependent mTOR signaling required for muscle differentiation and hypertrophy in mouse.
[show abstract] [hide abstract]
ABSTRACT: The mTORC1 pathway is required for both the terminal muscle differentiation and hypertrophy by controlling the mammalian translational machinery via phosphorylation of S6K1 and 4E-BP1. mTOR and S6K1 are connected by interacting with the eIF3 initiation complex. The regulatory subunit eIF3f plays a major role in muscle hypertrophy and is a key target that accounts for MAFbx function during atrophy. Here we present evidence that in MAFbx-induced atrophy the degradation of eIF3f suppresses S6K1 activation by mTOR, whereas an eIF3f mutant insensitive to MAFbx polyubiquitination maintained persistent phosphorylation of S6K1 and rpS6. During terminal muscle differentiation a conserved TOS motif in eIF3f connects mTOR/raptor complex, which phosphorylates S6K1 and regulates downstream effectors of mTOR and Cap-dependent translation initiation. Thus eIF3f plays a major role for proper activity of mTORC1 to regulate skeletal muscle size.PLoS ONE 01/2010; 5(2):e8994. · 4.09 Impact Factor -
Article: Inhibition of atrogin-1/MAFbx mediated MyoD proteolysis prevents skeletal muscle atrophy in vivo.
[show abstract] [hide abstract]
ABSTRACT: Ubiquitin ligase Atrogin1/Muscle Atrophy F-box (MAFbx) up-regulation is required for skeletal muscle atrophy but substrates and function during the atrophic process are poorly known. The transcription factor MyoD controls myogenic stem cell function and differentiation, and seems necessary to maintain the differentiated phenotype of adult fast skeletal muscle fibres. We previously showed that MAFbx mediates MyoD proteolysis in vitro. Here we present evidence that MAFbx targets MyoD for degradation in several models of skeletal muscle atrophy. In cultured myotubes undergoing atrophy, MAFbx expression increases, leading to a cytoplasmic-nuclear shuttling of MAFbx and a selective suppression of MyoD. Conversely, transfection of myotubes with sh-RNA-mediated MAFbx gene silencing (shRNAi) inhibited MyoD proteolysis linked to atrophy. Furthermore, overexpression of a mutant MyoDK133R lacking MAFbx-mediated ubiquitination prevents atrophy of mouse primary myotubes and skeletal muscle fibres in vivo. Regarding the complex role of MyoD in adult skeletal muscle plasticity and homeostasis, its rapid suppression by MAFbx seems to be a major event leading to skeletal muscle wasting. Our results point out MyoD as the second MAFbx skeletal muscle target by which powerful therapies could be developed.PLoS ONE 02/2009; 4(3):e4973. · 4.09 Impact Factor -
Article: MAFbx/Atrogin-1 controls the activity of the initiation factor eIF3-f in skeletal muscle atrophy by targeting multiple C-terminal lysines.
[show abstract] [hide abstract]
ABSTRACT: We recently presented evidence that the subunit eIF3-f of the eukaryotic initiation translation factor eIF3 that interacts with the E3-ligase Atrogin-1/muscle atrophy F-box (MAFbx) for polyubiquitination and proteasome-mediated degradation is a key target that accounts for MAFbx function during muscle atrophy. To understand this process, deletion analysis was used to identify the region of eIF3-f that is required for its proteolysis. Here, we report that the highly conserved C-terminal domain of eIF3-f is implicated for MAFbx-directed polyubiquitination and proteasomal degradation. Site-directed mutagenesis of eIF3-f revealed that the six lysine residues within this domain are required for full polyubiquitination and degradation by the proteasome. In addition, mutation of these six lysines (mutant K(5-10)R) displayed hypertrophic activity in cellulo and in vivo and was able to protect against starvation-induced muscle atrophy. Taken together, our data demonstrate that the C-terminal modifications, believed to be critical for proper eIF3-f regulation, are essential and contribute to a fine-tuning mechanism that plays an important role for eIF3-f function in skeletal muscle.Journal of Biological Chemistry 01/2009; 284(7):4413-21. · 4.77 Impact Factor -
Article: eIF3-f function in skeletal muscles: to stand at the crossroads of atrophy and hypertrophy.
[show abstract] [hide abstract]
ABSTRACT: The control of muscle cell size is a physiological process balanced by a fine tuning between protein synthesis and protein degradation. MAFbx/Atrogin-1 is a muscle specific E3 ubiquitin ligase upregulated during disuse, immobilization and fasting or systemic diseases such as diabetes, cancer, AIDS and renal failure. This response is necessary to induce a rapid and functional atrophy. To date, the targets of MAFbx/Atrogin-1 in skeletal muscle remain to be identified. We have recently presented evidence that eIF3-f, a regulatory subunit of the eukaryotic translation factor eIF3 is a key target that accounts for MAFbx/Atrogin-1 function in muscle atrophy. More importantly, we showed that eIF3-f acts as a "translational enhancer" that increases the efficiency of the structural muscle proteins synthesis leading to both in vitro and in vivo muscle hypertrophy. We propose that eIF3-f subunit, a mTOR/S6K1 scaffolding protein in the IGF-1/Akt/mTOR dependent control of protein translation, is a positive actor essential to the translation of specific mRNAs probably implicated in muscle hypertrophy. The central role of eIF3-f in both the atrophic and hypertrophic pathways will be discussed in the light of its promising potential in muscle wasting therapy.Cell cycle (Georgetown, Tex.) 05/2008; 7(12):1698-701. · 5.36 Impact Factor -
Article: MyoD undergoes a distinct G2/M-specific regulation in muscle cells.
[show abstract] [hide abstract]
ABSTRACT: The transcription factors MyoD and Myf5 present distinct patterns of expression during cell cycle progression and development. In contrast to the mitosis-specific disappearance of Myf5, which requires a D-box-like motif overlapping the basic domain, here we describe a stable and inactive mitotic form of MyoD phosphorylated on its serine 5 and serine 200 residues by cyclin B-cdc2. In mitosis, these modifications are required for releasing MyoD from condensed chromosomes and inhibiting its DNA-binding and transcriptional activation ability. Then, nuclear MyoD regains instability in the beginning of G1 phase due to rapid dephosphorylation events. Moreover, a non-phosphorylable MyoD S5A/S200A is not excluded from condensed chromatin and alters mitotic progression with apparent abnormalities. Thus, the drop of MyoD below a threshold level and its displacement from the mitotic chromatin could present another window in the cell cycle for resetting the myogenic transcriptional program and to maintain the myogenic determination of the proliferating cells.Experimental Cell Research 01/2007; 312(20):3999-4010. · 3.58 Impact Factor -
Article: Degradation of MyoD mediated by the SCF (MAFbx) ubiquitin ligase.
[show abstract] [hide abstract]
ABSTRACT: MyoD controls myoblast identity and differentiation and is required for myogenic stem cell function in adult skeletal muscle. MyoD is degraded by the ubiquitin-proteasome pathway mediated by different E3 ubiquitin ligases not identified as yet. Here we report that MyoD interacts with Atrogin-1/MAFbx (MAFbx), a striated muscle-specific E3 ubiquitin ligase dramatically up-regulated in atrophying muscle. A core LXXLL motif sequence in MyoD is necessary for binding to MAFbx. MAFbx associates with MyoD through an inverted LXXLL motif located in a series of helical leucine-charged residue-rich domains. Mutation in the LXXLL core motif represses ubiquitination and degradation of MyoD induced by MAFbx. Overexpression of MAFbx suppresses MyoD-induced differentiation and inhibits myotube formation. Finally the purified recombinant SCF(MAFbx) complex (SCF, Skp1, Cdc53/Cullin 1, F-box protein) mediated MyoD ubiquitination in vitro in a lysine-dependent pathway. Mutation of the lysine 133 in MyoD prevented its ubiquitination by the recombinant SCF(MAFbx) complex. These observations thus demonstrated that MAFbx functions in ubiquitinating MyoD via a sequence found in transcriptional coactivators. These transcriptional coactivators mediate the binding to liganded nuclear receptors. We also identified a novel protein-protein interaction module not yet identified in F-box proteins. MAFbx may play an important role in the course of muscle differentiation by determining the abundance of MyoD.Journal of Biological Chemistry 02/2005; 280(4):2847-56. · 4.77 Impact Factor -
Article: Critical role for lysine 133 in the nuclear ubiquitin-mediated degradation of MyoD.
[show abstract] [hide abstract]
ABSTRACT: The ubiquitin-proteasome system is responsible for the regulation and turnover of the nuclear transcription factor MyoD. The degradation of MyoD can occur via an NH2 terminus-dependent pathway or a lysine-dependent pathway, suggesting that MyoD ubiquitination may be driven by different mechanisms. To understand this process, deletion analysis was used to identify the region of MyoD that is required for rapid proteolysis in the lysine-dependent pathway. Here we report that the basic helix-loop-helix domain is required for ubiquitination and lysine-dependent degradation of MyoD in the nucleus. Site-directed mutagenesis in MyoD revealed that lysine 133 is the major internal lysine of ubiquitination. The half-life of the MyoD K133R mutant protein was longer than that of wild type MyoD, substantiating the implication of lysine 133 in the turnover of MyoD in myoblasts. In addition, the MyoD K133R mutant displayed activity 2-3-fold higher than the wild type in transactivation muscle-specific gene and myogenic conversion of 10T1/2 cells. Taken together, our data demonstrate that lysine 133 is targeted for ubiquitination and rapid degradation of MyoD in the lysine-dependent pathway and plays an integral role in compromising MyoD activity in the nucleus.Journal of Biological Chemistry 03/2004; 279(7):5413-20. · 4.77 Impact Factor -
Article: CD44: a new means to inhibit acute myeloid leukemia cell proliferation via p27Kip1.
[show abstract] [hide abstract]
ABSTRACT: Acute myeloid leukemia (AML) is sustained by the extensive proliferation of leukemic stem and progenitor cells, which give rise to the population of leukemic blasts with defective differentiation and low proliferative capacity. We have recently shown that ligation of CD44, a cell surface molecule present on AML cells, with specific monoclonal antibodies (mAbs) inhibits their proliferation. However, its mechanism has not been investigated yet. Here, using the NB4 cell line as a model of proliferating human AML cells, and the A3D8 mAb to ligate CD44, we show for the first time that CD44 ligation stabilizes the cyclin-dependent kinase inhibitor p27(Kip1) (p27) protein, resulting in increased association with cyclin E/Cdk2 complexes and inhibition of their kinase activity. Moreover, using a p27 antisense vector, we provide direct evidence that p27 is the main mediator of cell growth arrest by CD44. CD44 ligation also leads to p27 accumulation in THP-1, KG1a, and HL60 cell lines and in primary leukemic cells, suggesting that this process is general in AML. Taken together, our present results suggest that CD44 is a new and efficient means to increase the expression of p27 in AML cells. Considering that elevated expression of p27 is a factor of good prognosis in AML, these results provide a new basis for developing CD44-targeted therapy in AML.Blood 03/2004; 103(3):1059-68. · 9.90 Impact Factor -
Article: Mutant MyoD lacking Cdc2 phosphorylation sites delays M-phase entry.
[show abstract] [hide abstract]
ABSTRACT: The transcription factors MyoD and Myf-5 control myoblast identity and differentiation. MyoD and Myf-5 manifest opposite cell cycle-specific expression patterns. Here, we provide evidence that MyoD plays a pivotal role at the G(2)/M transition by controlling the expression of p21(Waf1/Cip1) (p21), which is believed to regulate cyclin B-Cdc2 kinase activity in G(2). In growing myoblasts, MyoD reaccumulates during G(2) concomitantly with p21 before entry into mitosis; MyoD is phosphorylated on Ser5 and Ser200 by cyclin B-Cdc2, resulting in a decrease of its stability and down-regulation of both MyoD and p21. Inducible expression of a nonphosphorylable MyoD A5/A200 enhances the MyoD interaction with the coactivator P/CAF, thereby stimulating the transcriptional activation of a luciferase reporter gene placed under the control of the p21 promoter. MyoD A5/A200 causes sustained p21 expression, which inhibits cyclin B-Cdc2 kinase activity in G(2) and delays M-phase entry. This G(2) arrest is not observed in p21(-/-) cells. These results show that in cycling cells MyoD functions as a transcriptional activator of p21 and that MyoD phosphorylation is required for G(2)/M transition.Molecular and Cellular Biology 03/2004; 24(4):1809-21. · 5.53 Impact Factor -
Article: Muscle regulatory factor MRF4 activates differentiation in rhabdomyosarcoma RD cells through a positive-acting C-terminal protein domain.
[show abstract] [hide abstract]
ABSTRACT: Rhabdomyosarcoma (RMS) has deregulated proliferation and is blocked in the differentiation program despite Myf-5, MyoD and myogenin expression. Here we show that ectopic expression of MRF4, which is not subject to an autoregulatory pathway but regulated by the other MRFs protein family, induces growth arrest and terminal differentiation in RD cells. Deletion mapping identified a positive-acting C-terminal domain in MRF4 as the mediator of transcriptional activity, revealing a conserved motif with helix III in MyoD previously found to initiate expression of endogenous skeletal muscle genes. By using chimeric MyoD/MRF4 proteins, we observe that the C-terminal motif of MRF4 rescues MyoD activity in RD cells. Moreover, comparative induction of muscle-specific genes following activation of MyoD, through the expression of a constitutively activated MKK6 either in the absence or presence of MRF4, shows that MyoD and MRF4 can differently regulate muscle genes expression. Together, these results demonstrate that the MRF4 C-terminus functions as specification as well as activation domain in tumor cells. They provide a basis to identify gene products necessary for b-HLH-mediated differentiation versus tumor progression.Oncogene 09/2003; 22(36):5658-66. · 6.37 Impact Factor -
Article: Signal-induced ubiquitination of p57(Kip2) is independent of the C-terminal consensus Cdk phosphorylation site.
[show abstract] [hide abstract]
ABSTRACT: The cyclin-dependent kinase inhibitor p57(Kip2) is required for normal mouse embryonic development. p57(Kip2) consists of four structurally distinct domains in which the conserved C-terminal nuclear targeting domain contains a putative Cdk phosphorylation site (Thr(342)) that shares a great similitude in the adjacent sequences with p27(Kip1) but not with p21(Cip1). Phosphorylation on Thr(187) has been shown to promote degradation of p27(Kip1). Although there is sequence homology between the C-terminal part of p27(Kip1) and p57(Kip2), we show that the ubiquitination and degradation of p57(Kip2) are independent of Thr(342). In contrast a destabilizing element located in the N-terminal is implicated in p57(Kip2) destabilization.FEBS Letters 06/2003; 543(1-3):125-8. · 3.54 Impact Factor -
Article: Stabilization of MyoD by Direct Binding to p57Kip2
[show abstract] [hide abstract]
ABSTRACT: Recent data have demonstrated the role of Cdk1- and Cdk2-dependent phosphorylation of MyoDSer200 in the regulation of MyoD activity and protein turnover. In the present study, we show that in presence of p57Kip2, MyoDAla200, a MyoD mutant that cannot be phosphorylated by cyclin-Cdk complexes, displayed activity 2–5-fold higher than of MyoDAla200 alone in transactivation of muscle-specific genes myosin heavy chain, creatine kinase, and myosin light chain 1. Furthermore, p57Kip2 increases the levels of MyoDAla200 in cotransfected cells. This result implies that p57Kip2 may regulate MyoD through a process distinct from its function as a cyclin-dependent kinase inhibitors. We report that overexpression of p57Kip2 increased the half-life of MyoDAla200. This increased half-life of MyoD involves a physical interaction between MyoD and p57Kip2but not with p16Ink4a, as shown by cross-immunoprecipitation not only on overexpressed proteins from transfected cells, but also on endogenous MyoD and p57Kip2from C2C12 myogenic cells. Mutational and functional analyses of the two proteins show that the NH2 domain of p57Kip2 associates with basic region in the basic helix-loop-helix domain of MyoD. Competition/association assays and site-directed mutagenesis of the NH2 terminus of p57Kip2 identified the intermediate α-helix domain, located between the Cdk and the cyclin binding sites, as essential for MyoD interaction. These data show that the α-helix domain of p57Kip2, which is conserved in the Cip/Kip proteins, is implicated in protein-protein interaction and confers a specific regulatory mechanism, outside of their Cdk-inhibitory activity, by which the p57Kip2 family members positively act on myogenic differentiation.Journal of Biological Chemistry 06/2000; 275(25):18767-18776. · 4.77 Impact Factor -
Article: Cyclin E–Cdk2 Phosphorylation Promotes Late G1-Phase Degradation of MyoD in Muscle Cells
[show abstract] [hide abstract]
ABSTRACT: Proliferating myoblasts already express MyoD before the induction of differentiation. Overexpression of MyoD in normal and transformed cell lines was shown to block cells from entering S phase, suggesting that the MyoD growth suppressive effect must be tightly controlled in growing myoblasts. Here we show that during G1 phase, but not in G2, MyoD abundance is down-regulated by the ubiquitin–proteasome pathway through phosphorylation of serine 200. Roscovitine, a specific inhibitor of cyclin–Cdk2 complexes, prevents both phosphorylation and degradation of MyoD in G1. Inhibition of the ubiquitin-dependent proteasome pathway by MG132 results in stabilization of MyoD-wt, with little effect on a MyoD mutant where serine 200 is replaced by an alanine. Our results show that MyoD Ser200 is the substrate for phosphorylation by cyclin E–Cdk2 stimulating its degradation by the ubiquitin–proteasome system which controls MyoD levels in G1. Phosphorylation/degradation of MyoD at the end of G1 thus represents the regulatory checkpoint in growing myoblasts allowing progression into S phase in a manner similar to the recently examplified cdk2-phosphorylation/degradation of p27Kip1.Experimental Cell Research.
Top co-authors
Top Journals
- Journal of Biological Chemistry (4)
- PLoS ONE (2)
- Blood (1)
- Experimental Cell Research (1)
- FEBS Letters (1)
Institutions
-
2003–2004
-
French National Centre for Scientific Research
Lyon, Rhone-Alpes, France
-
-
2000–2004
-
Institut de Cancérologie Gustave Roussy
Villejuif, Ile-de-France, France
-
