TGFbeta prevents proteasomal degradation of the cyclin-dependent kinase inhibitor p27kip1 for cell cycle arrest.
TGFbeta mediates cell cycle arrest in late G(1) phase of the cell cycle with a simultaneous peak in the levels of the cyclin-dependent kinase inhibitor, p27(kip1) (p27). In this report, we show that whereas p27 resides in the cytoplasm in the endometrial carcinoma (ECA) cell line HEC-1A, TGFbeta increases the total levels and translocation of p27 into the nucleus. Concomitantly, TGFbeta activates the transcription factors Smad2 and Smad3, inhibits proliferation, and blocks Cdk2 activity; all these events are blocked by an inhibitor of TbetaRI serine kinase activity (SD208). In addition, we show that inhibiting p27 transcription with a specific siRNA completely blocks TGFbeta-mediated growth inhibition in these cells. These data suggest that TGFbeta inhibits cellular proliferation by increasing p27 levels through Smad2/3 signaling in HEC-1A cells. We further show that TGFbeta decreases the levels of components of the SCF(Skp2) targeting complex for ubiquitin-mediated degradation of p27 in proteasomes, at the protein but not the mRNA level. Therefore, TGFbeta accumulates nuclear p27 by preventing its degradation to enable G(1) arrest in HEC-1A cells. Importantly, these data suggest a novel mechanism for TGFbeta/Smad mediated growth inhibition that might be inoperable in the numerous human cancers demonstrating early dysregulated TGFbeta signaling and loss of growth inhibition. The TGFbeta/p27 axis might provide novel therapeutic targets for cancer.
Lecanda
Jon
J
Department of Medicine and New York University Cancer Institute, New York University School of Medicine, New York, New York 10016, USA.
Ganapathy
Vidya
V
D'Aquino-Ardalan
Christine
C
Evans
Brad
B
Cadacio
Caprice
C
Ayala
Aidee
A
Gold
Leslie I
LI
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D002453:Cell Cycle; D045744:Cell Line, Tumor; D051357:Cyclin-Dependent Kinase 2 / Q000235:genetics / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000235:genetics / Q000378:metabolism*; D016193:G1 Phase; D006801:Humans; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000378:metabolism; D051899:Smad2 Protein / Q000235:genetics / Q000378:metabolism; D051900:Smad3 Protein / Q000235:genetics / Q000378:metabolism; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000378:metabolism*
D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; C497782:SMAD2 protein, human; D051899:Smad2 Protein; D051900:Smad3 Protein; D016212:Transforming Growth Factor beta; C067713:lactacystin; D050760:Cyclin-Dependent Kinase Inhibitor p27; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2; D046988:Proteasome Endopeptidase Complex; D000111:Acetylcysteine