Cyclin A levels, the duration of S phase and sensitivity to a chemotherapeutic agent are altered in fibroblasts cultured on a fibronectin matrix.
Culture of murine embryonic fibroblasts, but not vascular smooth muscle cells, on a fibronectin matrix significantly shortens their transit time through the S phase of the cell cycle. This shortening corresponds to an increase in both cyclin A protein levels and active cyclin A/cdk2 complex. The increase in cyclin A protein appears due to a translational/post-translational mechanism since there is no increase in cyclin A mRNA following culture of the cells on fibronectin. Treatment of cells cultured on fibronectin with a short pulse of the S phase chemotherapeutic agent camptothecin, resulted in a relative protection from cell death when compared to cells cultured on tissue culture plastic. Thus, while the cells have increased rate of transit through S phase fibronectin-mediated signaling protects the cells from S phase mediated apoptosis. In addition, fibroblasts constitutively expressing a mutant E2F1 transcription factor (E2F1d87) have a lengthened S phase, due to a truncation of the cyclin A/cdk2 binding domain. Culture of these mutant- expressing cells on fibronectin did not shorten their S phase duration in spite of the fact that cyclin A levels and active cyclin A/cdk2 complex were significantly elevated. Thus, although the fibronectin signaling mechanisms culminating in elevated cyclin A were intact in these mutant E2F1 expressing cells, they were insensitive to the effects of this elevated cyclin A. The effect of the mutant E2F1d87 on slowing transit through S phase appears dominant over the effect of elevated cyclin A.
Department of Biochemistry and Molecular Pharmacology, Thomas Jefferson University, Philadelphia, PA 19107, USA.
I
I
Min
M C
MC
Stubbs
G D
GD
Strachan
D J
DJ
Hall
D016475:3T3 Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D042846:CDC2-CDC28 Kinases; D002166:Camptothecin / Q000494:pharmacology*; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D019925:Cyclin A / Q000096:biosynthesis / Q000378:metabolism*; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D005109:Extracellular Matrix / Q000502:physiology; D005353:Fibronectins / Q000494:pharmacology*; D051379:Mice; D009154:Mutation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D056465:Retinoblastoma-Binding Protein 1; D016196:S Phase / Q000187:drug effects* / Q000502:physiology; D012680:Sensitivity and Specificity; D050680:Transcription Factor DP1; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology
D000972:Antineoplastic Agents, Phytogenic; C533431:Arid4a protein, mouse; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D019925:Cyclin A; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493754:E2f1 protein, mouse; D005353:Fibronectins; D056465:Retinoblastoma-Binding Protein 1; D050680:Transcription Factor DP1; D014157:Transcription Factors; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D002166:Camptothecin