Differential regulation of p27 and cyclin D1 by TGF-beta and EGF in C3H 10T1/2 mouse fibroblasts.
Previously, we found that stimulation of C3H 10T1/2 mouse fibroblasts with TGF-beta leads to the striking and rapid down-regulation of p27kip1 expression during G1 phase. Here, we demonstrate that TGF-beta treatment of C3H 10T1/2 cells does not alter the steady-state level of Kip1 message sufficiently to account for the observed down-regulation of p27. This demonstrates that TGF-beta-induced down regulation of p27kip1 occurs at a post-transcriptional level, consistent with a degradative mechanism of p27kip1 down-regulation. Epidermal growth factor (EGF) does not lead to the rapid down-regulation of p27 observed following treatment of cells with TGF-beta. Also in contrast with TGF-beta, EGF causes a strong upregulation of cyclin D1, while neither growth factor affects cdk4 protein levels. These results imply that in this cell type TGF-beta overcomes an inhibitory threshold to cdk activation by cyclin-dependent kinase inhibitors primarily through down-regulation of p27, while EGF overcomes this threshold predominantly through upregulation of cyclin D1 levels. This divergence in pathways may explain why TGF-beta-induced cell cycle kinetics are slower than those of EGF in these cells, and the ability of TGF-beta to delay EGF-induced cell cycle kinetics to its own, slower kinetics. In support of this hypothesis, TGF-beta prevents EGF-induced upregulation of cyclin D1 levels, while TGF-beta is still able to induce p27 down-regulation even in the presence of EGF. In contrast to the case with p27 degredation, neither TGF-beta nor EGF have an observable effect on the steady-state levels of p21 in this cell type.
Ravitz
M J
MJ
Department of Biochemistry, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
Yan
S
S
Dolce
C
C
Kinniburgh
A J
AJ
Wenner
C E
CE
D000818:Animals; D018797:Cell Cycle Proteins; D002478:Cells, Cultured; D019938:Cyclin D1; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism*; D015536:Down-Regulation; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D051379:Mice; D008809:Mice, Inbred C3H; D008869:Microtubule-Associated Proteins / Q000378:metabolism*; D015513:Oncogene Proteins / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D025521:Tumor Suppressor Proteins
C493957:Cdkn1a protein, mouse; C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D008869:Microtubule-Associated Proteins; D015513:Oncogene Proteins; D011518:Proto-Oncogene Proteins; D016212:Transforming Growth Factor beta; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004815:Epidermal Growth Factor; C495902:Cdk4 protein, mouse; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases