Flavopiridol-induced apoptosis during S phase requires E2F-1 and inhibition of cyclin A-dependent kinase activity.
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.
Jiang
Jingrui
J
Department of Medical Oncology and Lowe Center for Thoracic Oncology, Dana-Farber Cancer Institute, Dana 810A, 44 Binney Street, Boston, MA 02115, USA.
Matranga
Christian B
CB
Cai
Dongpo
D
Latham
Vaughan M
VM
Zhang
Xinxin
X
Lowell
April M
AM
Martelli
Fabio
F
Shapiro
Geoffrey I
GI
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*
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