A novel mechanism by which thiazolidinediones facilitate the proteasomal degradation of cyclin D1 in cancer cells.
This study identifies a novel mechanism by which thiazolidinediones mediate cyclin D1 repression in prostate cancer cells. Based on the finding that the thiazolidinedione family of peroxisome proliferator-activated receptor gamma (PPARgamma) agonists mediated PPARgamma-independent cyclin D1 degradation, we developed a novel PPARgamma-inactive troglitazone derivative, STG28, with high potency in cyclin D1 ablation. STG28-mediated cyclin D1 degradation was preceded by Thr-286 phosphorylation and nuclear export, which however, were independent of glycogen synthase kinase 3beta. Mutational analysis further confirmed the pivotal role of Thr-286 phosphorylation in STG28-induced nuclear export and proteolysis. Of several kinases examined, inhibition of IkappaB kinase alpha blocked STG28-mediated cytoplasmic sequestration and degradation of cyclin D1. Pulldown of ectopically expressed Cul1, the scaffold protein of the Skp-Cullin-F-box E3 ligase, in STG28-treated cells revealed an increased association of cyclin D1 with beta-TrCP, whereas no specific binding was noted with other F-box proteins examined, including Skp2, Fbw7, Fbx4, and Fbxw8. This finding represents the first evidence that cyclin D1 is targeted by beta-TrCP. Moreover, beta-TrCP expression was up-regulated in response to STG28, and ectopic expression and small interfering RNA-mediated knock-down of beta-TrCP enhanced and protected against STG28-facilitated cyclin D1 degradation, respectively. Because cyclin D1 lacks the DSG destruction motif, mutational and modeling analyses indicate that cyclin D1 was targeted by beta-TrCP through an unconventional recognition site, (279)EEVDLACpT(286), reminiscent to that of Wee1. Moreover, we obtained evidence that this beta-TrCP-dependent degradation takes part in controlling cyclin D1 turnover when cancer cells undergo glucose starvation, which endows physiological relevance to this novel mechanism.
Wei
Shuo
S
Division of Medicinal Chemistry and Pharmacognosy, College of Pharmacy, The Ohio State University, Columbus, Ohio 43210, USA.
Yang
Hsiao-Ching
HC
Chuang
Hsiao-Ching
HC
Yang
Jian
J
Kulp
Samuel K
SK
Lu
Pei-Jung
PJ
Lai
Ming-Derg
MD
Chen
Ching-Shih
CS
D020816:Amino Acid Motifs / Q000235:genetics; D001578:Benzopyrans / Q000494:pharmacology*; D018797:Cell Cycle Proteins / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D044842:Cullin Proteins / Q000235:genetics / Q000378:metabolism; D056741:Cyclin D; D016213:Cyclins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D044783:F-Box Proteins / Q000235:genetics / Q000378:metabolism; D000073979:F-Box-WD Repeat-Containing Protein 7; D038362:Glycogen Synthase Kinase 3 / Q000235:genetics / Q000378:metabolism; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D051550:I-kappa B Kinase / Q000235:genetics / Q000378:metabolism; D008297:Male; D008958:Models, Molecular; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism*; D047495:PPAR gamma / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D011471:Prostatic Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D061988:Proteasome Inhibitors; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism; D045162:Thiazolidinediones / Q000494:pharmacology*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism; D044844:beta-Transducin Repeat-Containing Proteins / Q000235:genetics / Q000378:metabolism
C513003:5-(4-((6-(allyloxy)-2,5,7,8-tetramethylchroman-2-yl)methoxy)-3-methoxybenzylidene)thiazolidine-2,4-dione; D001578:Benzopyrans; D018797:Cell Cycle Proteins; C100318:Cullin 1; D044842:Cullin Proteins; D056741:Cyclin D; D016213:Cyclins; D044783:F-Box Proteins; D000073979:F-Box-WD Repeat-Containing Protein 7; C508146:FBXO4 protein, human; C513273:FBXW7 protein, human; D009363:Neoplasm Proteins; D047495:PPAR gamma; D061988:Proteasome Inhibitors; D044786:S-Phase Kinase-Associated Proteins; D045162:Thiazolidinediones; D044844:beta-Transducin Repeat-Containing Proteins; D044767:Ubiquitin-Protein Ligases; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D051550:I-kappa B Kinase; D038362:Glycogen Synthase Kinase 3; D046988:Proteasome Endopeptidase Complex