Thiazolidinediones mimic glucose starvation in facilitating Sp1 degradation through the up-regulation of beta-transducin repeat-containing protein.
This study investigated the mechanism by which the transcription factor Sp1 is degraded in prostate cancer cells. We recently developed a thiazolidinedione derivative, (Z)-5-(4-hydroxy-3-trifluoromethylbenzylidene)-3-(1-methylcyclohexyl)-thiazolidine-2,4-dione (OSU-CG12), that induces Sp1 degradation in a manner paralleling that of glucose starvation. Based on our finding that thiazolidinediones suppress beta-catenin and cyclin D1 by up-regulating the E3 ligase SCF(beta-TrCP), we hypothesized that beta-transducin repeat-containing protein (beta-TrCP) targets Sp1 for proteasomal degradation in response to glucose starvation or OSU-CG12. Here we show that either treatment of LNCaP cells increased specific binding of Sp1 with beta-TrCP. This direct binding was confirmed by in vitro pull-down analysis with bacterially expressed beta-TrCP. Although ectopic expression of beta-TrCP enhanced the ability of OSU-CG12 to facilitate Sp1 degradation, suppression of endogenous beta-TrCP function by a dominant-negative mutant or small interfering RNA-mediated knockdown blocked OSU-CG12-facilitated Sp1 ubiquitination and/or degradation. Sp1 contains a C-terminal conventional DSG destruction box ((727)DSGAGS(732)) that mediates beta-TrCP recognition and encompasses a glycogen synthase kinase 3beta (GSK3beta) phosphorylation motif (SXXXS). Pharmacological and molecular genetic approaches and mutational analyses indicate that extracellular signal-regulated kinase-mediated phosphorylation of Thr739 and GSK3beta-mediated phosphorylation of Ser728 and Ser732 were critical for Sp1 degradation. The ability of OSU-CG12 to mimic glucose starvation to activate beta-TrCP-mediated Sp1 degradation has translational potential to foster novel strategies for cancer therapy.
Wei
Shuo
S
Division of Medicinal Chemistry, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA.
Chuang
Hsiao-Ching
HC
Tsai
Wan-Chi
WC
Yang
Hsiao-Ching
HC
Ho
Shiuh-Rong
SR
Paterson
Andrew J
AJ
Kulp
Samuel K
SK
Chen
Ching-Shih
CS
D045744:Cell Line, Tumor; D005260:Female; D005947:Glucose / Q000172:deficiency*; D038362:Glycogen Synthase Kinase 3 / Q000502:physiology; D000071679:Glycogen Synthase Kinase 3 beta; D006801:Humans; D048369:MAP Kinase Kinase 1 / Q000502:physiology; D008297:Male; D010766:Phosphorylation; D011471:Prostatic Neoplasms / Q000378:metabolism; D011944:Receptors, Androgen / Q000235:genetics; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D045162:Thiazolidinediones / Q000494:pharmacology*; D015854:Up-Regulation; D044844:beta-Transducin Repeat-Containing Proteins / Q000096:biosynthesis*
C542107:5-(4-hydroxy-3-trifluoromethylbenzylidene)-3-(1-methylcyclohexyl)thiazolidine-2,4-dione; C410798:AR protein, human; D011944:Receptors, Androgen; D016329:Sp1 Transcription Factor; D045162:Thiazolidinediones; D044844:beta-Transducin Repeat-Containing Proteins; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; D038362:Glycogen Synthase Kinase 3; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human; D005947:Glucose