title: MiR-322/424 and -503 are induced during muscle differentiation and promote cell cycle quiescence and differentiation by down-regulation of Cdc25A.
abstract: Induction of a G1 phase cell cycle arrest, caused primarily by the inhibition of cyclin-dependent-kinase 2 (cdk2), is a critical step in the differentiation of myoblasts into myotubes. Here, we report that two microRNAs, miR-322/424 and miR-503, are induced and promote cdk2 inhibition during myogenesis. These microRNAs down-regulate Cdc25A, the phosphatase responsible for removing inhibitory phosphorylation of cdk2, both in myoblasts differentiating into myotubes and in nonmuscle cells. Cdc25A is down-regulated during muscle differentiation by multiple pathways: action of these two microRNAs, proteasomal degradation of Cdc25A protein and transcriptional repression. Overexpression of Cdc25A or of cdk2 with mutations on T14 and Y15 (cdk2-AF), so that it cannot be inhibited by phosphorylation, decreases differentiation and differentiation-induced cell cycle quiescence. Introduction of miR-322/424 and miR-503 in heterologous cancer cells induces G1 arrest, which is also attenuated by overexpression of the cdk2-AF mutant. Until now Cdc25A and the inhibitory phosphorylation on T14 and Y15 of cdk2 have only been implicated in the intra-S phase checkpoint pathway after DNA damage. Our results reveal an unexpected role of Cdc25A down-regulation and the inhibitory phosphorylation of cdk2 T14 and Y15 in cell cycle quiescence during muscle differentiation and implicate two muscle differentiation-induced microRNAs in the process.
authors.affiliation: Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA.
authors.forename: Sukumar
authors.initials: S
authors.lastname: Sarkar
authors.forename: Bijan K
authors.initials: BK
authors.lastname: Dey
authors.forename: Anindya
authors.initials: A
authors.lastname: Dutta
mesh_terms: D000818:Animals; D001483:Base Sequence; D002453:Cell Cycle / Q000502:physiology*; D002454:Cell Differentiation / Q000502:physiology*; D045744:Cell Line, Tumor; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism; D015536:Down-Regulation; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D051379:Mice; D035683:MicroRNAs / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000502:physiology*; D020687:cdc25 Phosphatases / Q000235:genetics / Q000378:metabolism*
chemical_list: C582672:MIRN322 microRNA, mouse; C554214:MIRN424 microrna, human; D035683:MicroRNAs; D051357:Cyclin-Dependent Kinase 2; C517004:CDC25A protein, human; D020687:cdc25 Phosphatases
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