title: Potassium-induced apoptosis in rat cerebellar granule cells involves cell-cycle blockade at the G1/S transition.
abstract: The role of regulators controlling the G1/S transition of the cell cycle was analyzed during neuronal apoptosis in post-mitotic cerebellar granule cells in an attempt to identify common mechanisms of control with transformed cells. Cyclin D1 and its associated kinase activity CDK4 (cyclin-dependent kinase 4) are major regulators of the G1/S transition. Whereas cyclin D1 is the regulatory subunit of the complex, CDK4 represents the catalytic domain that, once activated, will phosphorylate downstream targets such as the retinoblastoma protein, allowing cell-cycle progression. Apoptosis was induced in rat cerebellar granule cells by depleting potassium in presence of serum. Western-blot analyses were performed and protein kinase activities were measured. As apoptosis proceeded, loss in cell viability was coincident with a significant increase in cyclin D1 protein levels, whereas CDK4 expression remained essentially constant. Synchronized to cyclin D1 accumulation, cyclin-dependent kinase inhibitor p27Kip1 drastically dropped to 20% normal values. Cyclin D1/CDK4-dependent kinase activity increased early during apoptosis, reaching a maximum at 9-12 h and decreasing to very low levels by 48 h. Cyclin E, a major downstream target of cyclin D1, decreased concomitantly to the reduction in cyclin D1/CDK4-dependent kinase activity. We suggest that neuronal apoptosis takes place through functional alteration of proteins involved in the control of the G1/S transition of the cell cycle. Thus, apoptosis in post-mitotic neurons could result from a failed attempt to re-enter cell cycle in response to extracellular conditions affecting cell viability and it could involve mechanisms similar to those that promote proliferation in transformed cells.
authors: Departamento de Bioquímica y Biología Molecular y Genética, Universidad de Extremadura, Badajoz, Spain.
authors: F J
authors: FJ
authors: Martín-Romero
authors: B
authors: B
authors: Santiago-Josefat
authors: J
authors: J
authors: Correa-Bordes
authors: C
authors: C
authors: Gutierrez-Merino
authors: P
authors: P
authors: Fernandez-Salguero
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000378:metabolism; D002461:Cell Line, Transformed / Q000166:cytology / Q000378:metabolism*; D002470:Cell Survival / Q000502:physiology; D002525:Cerebellar Cortex / Q000166:cytology / Q000378:metabolism; D003470:Culture Media / Q000494:pharmacology; D019938:Cyclin D1 / Q000378:metabolism*; D019927:Cyclin E / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism*; D015536:Down-Regulation / Q000502:physiology; D016193:G1 Phase / Q000502:physiology*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D011191:Potassium Deficiency / Q000378:metabolism* / Q000503:physiopathology; D011518:Proto-Oncogene Proteins; D051381:Rats; D017208:Rats, Wistar; D016196:S Phase / Q000502:physiology*; D013997:Time Factors; D025521:Tumor Suppressor Proteins
chemical_list: C493962:Cdkn1b protein, rat; D018797:Cell Cycle Proteins; D003470:Culture Media; D019927:Cyclin E; D011518:Proto-Oncogene Proteins; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; C495903:Cdk4 protein, rat; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases