title: Novel role for cyclin-dependent kinase 2 in neuregulin-induced acetylcholine receptor epsilon subunit expression in differentiated myotubes.
abstract: Cyclin-dependent kinases (CDKs) are a family of evolutionarily conserved serine/threonine kinases. CDK2 acts as a checkpoint for the G(1)/S transition in the cell cycle. Despite a down-regulation of CDK2 activity in postmitotic cells, many cell types, including muscle cells, maintain abundant levels of CDK2 protein. This led us to hypothesize that CDK2 may have a function in postmitotic cells. We show here for the first time that CDK2 can be activated by neuregulin (NRG) in differentiated C2C12 myotubes. In addition, this activity is required for expression of the acetylcholine receptor (AChR) epsilon subunit. The switch from the fetal AChRgamma subunit to the adult-type AChRepsilon is required for synapse maturation and the neuromuscular junction. Inhibition of CDK2 activity with either the specific CDK2 inhibitory peptide Tat-LFG or by RNA interference abolished neuregulin-induced AChRepsilon expression. Neuregulin-induced activation of CDK2 also depended on the ErbB receptor, MAPK, and PI3K, all of which have previously been shown to be required for AChRepsilon expression. Neuregulin regulated CDK2 activity through coordinating phosphorylation of CDK2 on Thr-160, accumulation of CDK2 in the nucleus, and down-regulation of the CDK2 inhibitory protein p27 in the nucleus. In addition, we also observed a novel mechanism of regulation of CDK2 activity by a low molecular weight variant of cyclin E in response to NRG. These findings establish CDK2 as an intermediate molecule that integrates NRG-activated signals from both the MAPK and PI3K pathways to AChRepsilon expression and reveal an undiscovered physiological role for CDK2 in postmitotic cells.
authors.affiliation: Department of Genome Science, Genome Research Institute, University of Cincinnati, 2180 E. Galbraith Road, Cincinnati, OH 45237, USA.
authors.forename: Gang
authors.initials: G
authors.lastname: Lu
authors.forename: Karen A
authors.initials: KA
authors.lastname: Seta
authors.forename: David E
authors.initials: DE
authors.lastname: Millhorn
mesh_terms: D000818:Animals; D015153:Blotting, Western; D042846:CDC2-CDC28 Kinases / Q000378:metabolism / Q000502:physiology*; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism; D002454:Cell Differentiation; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D019927:Cyclin E / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017931:DNA Primers / Q000737:chemistry; D015536:Down-Regulation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation; D047468:Immunoprecipitation; D020935:MAP Kinase Signaling System; D051379:Mice; D008938:Mitosis; D018485:Muscle Fibers, Skeletal / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism; D020890:Neuregulin-1 / Q000378:metabolism*; D018739:Oncogene Proteins v-erbB / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D012313:RNA / Q000378:metabolism; D034622:RNA Interference; D011950:Receptors, Cholinergic / Q000378:metabolism*; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000502:physiology*; D011994:Recombinant Proteins / Q000737:chemistry; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D013347:Subcellular Fractions; D013569:Synapses / Q000378:metabolism; D014158:Transcription, Genetic; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; C502449:Chrne protein, mouse; D019927:Cyclin E; D017931:DNA Primers; D004791:Enzyme Inhibitors; D020890:Neuregulin-1; D018739:Oncogene Proteins v-erbB; D011950:Receptors, Cholinergic; D011978:Receptors, Nicotinic; D011994:Recombinant Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D012313:RNA; D019869:Phosphatidylinositol 3-Kinases; D042846:CDC2-CDC28 Kinases; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2