title: E2F-1 accumulation bypasses a G1 arrest resulting from the inhibition of G1 cyclin-dependent kinase activity.
abstract: Numerous experiments have defined a critical role for the G1 cyclins and associated kinases in allowing a normal progression of cells from a quiescent state, through G1, and into S phase. We now demonstrate that G1 cyclin-dependent kinase activity is critical for the accumulation of E2F activity late in G1. Moreover, E2F-1 overexpression can overcome a G1 arrest caused by the inhibition of G1 cyclin-dependent kinase activity, consistent with E2F activation being an important consequence of the action of G1 cyclins. E2F-1 also overcomes a G1 block caused by gamma irradiation and leads to an apparent complete replication of the cellular genome and entry into mitosis. This E2F-1-mediated induction of S phase and mitosis is not accompanied by the rise in either cyclin D-associated kinase activity or cdk2 activity that is normally observed during the G1 phase of the cell cycle. We conclude that one key function for G1 cyclin-dependent kinase activity is the activation of E2F-1, that the accumulation of E2F activity may be sufficient to allow initiation and completion of S phase, but that additional events, including G1 cyclin kinase activity, are likely necessary for a normal proliferative event.
mesh_terms: D015153:Blotting, Western; D042846:CDC2-CDC28 Kinases; D002352:Carrier Proteins / Q000235:genetics / Q000494:pharmacology; D018797:Cell Cycle Proteins; D051357:Cyclin-Dependent Kinase 2; D019941:Cyclin-Dependent Kinase Inhibitor p16; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors* / Q000235:genetics; D004247:DNA / Q000528:radiation effects; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D016193:G1 Phase / Q000528:radiation effects; D016195:G2 Phase; D005720:Gamma Rays; D005786:Gene Expression Regulation; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000494:pharmacology; D008938:Mitosis; D010957:Plasmids; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases / Q000235:genetics; D016160:Retinoblastoma Protein / Q000096:biosynthesis / Q000235:genetics; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects; D025521:Tumor Suppressor Proteins
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019941:Cyclin-Dependent Kinase Inhibitor p16; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D008869:Microtubule-Associated Proteins; D016160:Retinoblastoma Protein; D056465:Retinoblastoma-Binding Protein 1; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004247:DNA; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases