title: Flavopiridol-induced apoptosis during S phase requires E2F-1 and inhibition of cyclin A-dependent kinase activity.
abstract: Transformed cells are selectively sensitized to apoptosis induced by the cyclin-dependent kinase inhibitor flavopiridol after their recruitment to S phase. During S phase, cyclin A-dependent kinase activity neutralizes E2F-1 allowing orderly S phase progression. Inhibition of cyclin A-dependent kinase by flavopiridol could cause inappropriately persistent E2F-1 activity during S phase traversal and exit. Transformed cells, with high baseline levels of E2F-1 activity, may be particularly sensitive to cyclin A-dependent kinase inhibition, as the residual level of E2F-1 activity that persists may be sufficient to induce apoptosis. Here, we demonstrate that flavopiridol treatment during S phase traversal results in persistent expression of E2F-1. The phosphorylation of E2F-1 is markedly diminished, whereas that of the retinoblastoma protein is minimally affected, so that E2F-1/DP-1 heterodimers remain bound to DNA. In addition, manipulation of E2F-1 levels leads to predictable outcomes when cells are exposed to flavopiridol during S phase. Tumor cells expressing high levels of ectopic E2F-1 are more sensitive to flavopiridol-induced apoptosis during S phase compared with parental counterparts, and high levels of ectopic E2F-1 expression are sufficient to sensitize nontransformed cells to flavopiridol. Furthermore, E2F-1 activity is required for flavopiridol-induced apoptosis during S phase, which is severely compromised in cells homozygous for a nonfunctional E2F-1 allele. Finally, the response to flavopiridol during S phase is blunted in cells expressing a nonphosphorylatable E2F-1 mutant incapable of binding cyclin A, suggesting that the modulation of E2F-1 activity produced by flavopiridol-mediated cyclin-dependent kinase inhibition is critical for the apoptotic response of S phase cells.
authors: Department of Medical Oncology and Lowe Center for Thoracic Oncology, Dana-Farber Cancer Institute, Dana 810A, 44 Binney Street, Boston, MA 02115, USA.
authors: Jingrui
authors: J
authors: Jiang
authors: Christian B
authors: CB
authors: Matranga
authors: Dongpo
authors: D
authors: Cai
authors: Vaughan M
authors: VM
authors: Latham
authors: Xinxin
authors: X
authors: Zhang
authors: April M
authors: AM
authors: Lowell
authors: Fabio
authors: F
authors: Martelli
authors: Geoffrey I
authors: GI
authors: Shapiro
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001859:Bone Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D002289:Carcinoma, Non-Small-Cell Lung / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins; D002461:Cell Line, Transformed; D045744:Cell Line, Tumor; D004273:DNA, Neoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins; D004357:Drug Synergism; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology*; D006801:Humans; D008175:Lung Neoplasms / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D012516:Osteosarcoma / Q000188:drug therapy / Q000201:enzymology / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D010880:Piperidines / Q000494:pharmacology*; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases; D016196:S Phase / Q000502:physiology; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism / Q000502:physiology*
chemical_list: D000970:Antineoplastic Agents; D018797:Cell Cycle Proteins; D004273:DNA, Neoplasm; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D004791:Enzyme Inhibitors; D005419:Flavonoids; D010880:Piperidines; D047428:Protein Kinase Inhibitors; D050680:Transcription Factor DP1; D014157:Transcription Factors; C077990:alvocidib; D011494:Protein Kinases; C102333:histone H1 kinase