Inhibition Of Mitotic Clonal Expansion Research Articles

Spliceostatin A treatment inhibits mitotic clonal expansion and adipogenesis

Adipogenesis is a differentiation process from mesenchymal stem cells to adipocytes. It has been reported that adipogenesis is regulated by a highly orchestrated transcriptional cascade. However, the effects of modulation of mRNA splicing on adipogenesis remain unknown. To investigate these effects, 3T3-L1 preadipocyte were treated with the potent splicing inhibitor spliceostatin A, which revealed that splicing inhibition suppressed adipogenesis. In addition, treatment of 3T3-L1 cells with spliceostatin A during the early phase of adipogenesis was sufficient to inhibit adipogenesis. In the early phase of adipogenesis, the cells re-entered the cell cycle, which is referred to as mitotic clonal expansion. As mitotic clonal expansion is required for adipogenesis, it was assumed that splicing inhibition would suppress mitotic clonal expansion, and consequently inhibit adipogenesis. As expected, spliceostatin A treatment caused G1 phase arrest and inhibited cell proliferation, i.e., inhibition of mitotic clonal expansion. These results suggest that splicing activity is required for mitotic clonal expansion and adipogenesis.

Flavonoids kaempferide and 4,2′-dihydroxy-4′,5′,6′-trimethoxychalcone inhibit mitotic clonal expansion and induce apoptosis during the early phase of adipogenesis in 3T3-L1 cells

ObjectiveKaempferide and 4,2′-dihydroxy-4′,5′,6′-trimethoxychalcone (DTMC) are two major flavonoids found in Chromolaena odorata Linn. leaf extract. The aim of this study was to elucidate the mechanism by which these two flavonoids exerted their effect on adipogenesis. The inhibitory effect of kaempferide and DTMC on adipocyte differentiation and their mechanisms involving mitotic clonal expansion (MCE) and apoptosis during the early stage of adipogenesis were investigated. MethodsConfluent 3T3-L1 preadipocytes were induced to differentiate and exposed to the flavonoids during various phases of differentiation. Intracellular lipid accumulation, cell density and expression of the transcription factors peroxisome proliferator-activated receptor γ and CCAAT/enhancer-binding proteins α were assessed using AdipoRed, Oil red O and Western blot assays. Effects of both flavonoids on cell proliferation and apoptosis were also determined by carboxyfluorescein diacetate succinimidyl ester and annexin V-fluorescein isothiocyanate/propidium iodide-staining assays, respectively. ResultsKaempferide and DTMC showed significant, concentration-dependent anti-adipogenic activity and effect on cell density in the early phase of adipogenesis. The expression of the transcription factors seemed to be reduced when the treatment was prolonged or in the early phase of adipogenesis. These flavonoids interrupted MCE via inhibition of preadipocyte proliferation and induction of apoptosis. DTMC was nearly three times more potent than kaempferide in inducing apoptosis. ConclusionKaempferide and DTMC exerted their anti-adipogenic activity through inhibition of MCE, either by suppressing cell proliferation or by inducing apoptosis during the early phase of differentiation.

Syringic acid (4-hydroxy-3,5-dimethoxybenzoic acid) inhibits adipogenesis and promotes lipolysis in 3T3-L1 adipocytes

Increase in adiposity is associated with obesity and obesity-related complications. Syringic acid (SA), a phenolic acid facilitates oxidation, polymerization, and condensation reactions, may function as an effective anti-adipogenic agent. This study examined whether SA inhibits adipogenesis in 3T3-L1 preadipocytes by inhibiting differentiation and controlling lipid accumulation. Ten days of SA treatment suppressed differentiation of 3T3-L1 preadipocyte to mature adipocytes in a concentration-dependent manner as determined by Oil Red O staining. Suppression of adipogenic differentiation by SA was primarily from inhibition of mitotic clonal expansion during the early stages of differentiation. Treatment of adipocytes with SA reduced triglyceride production (lipogenesis) and increased glycerol release (lipolysis). The addition of SA to the adipocytes attenuated in vitro ROS production. These results indicate that SA inhibits the adipogenesis of 3T3-L1 preadipocytes, reduces lipid accumulation, and attenuates ROS accumulation, suggesting for the first time that SA has an anti-obesity effect in vitro.

Sulforaphane attenuates bisphenol A-induced 3T3-L1 adipocyte differentiation through cell cycle arrest

Bisphenol A (BPA) may be a critical risk factor for metabolic disorders including obesity and diabetes. Sulforaphane is known to inhibit adipocyte differentiation and induce adipocyte lipolysis. This study sought to investigate the possible effects of sulforaphane on BPA-induced adipocyte differentiation in 3T3-L1 cells. During the preadipocytes differentiation process, sulforaphane suppressed the expression of early adipogenic factors, PPARγ and C/EBPα, induced by BPA in 3T3-L1 cells. Based on cell cycle analysis, sulforaphane mediated the inhibition of mitotic clonal expansion via cell cycle arrest at the G0/G1 phase. The compound inhibited cell cycle progression by suppressing cell cycle regulators such as cyclin D1 and pRb and by increasing p21 and p27, cell cycle inhibitors. Moreover, sulforaphane activated phosphorylation of AMPK and ACC and decreased that of ERK1/2 and Akt. Sulforaphane exerts inhibitory effects on BPA-induced adipocyte differentiation in 3T3-L1 cells. Sulforaphane could be adipogenic properties for improving environmental pollutants.

Ligand-dependent corepressor (LCoR) represses the transcription factor C/EBPβ during early adipocyte differentiation

Nuclear receptors (NRs) regulate gene transcription by recruiting coregulators, involved in chromatin remodeling and assembly of the basal transcription machinery. The NR-associated protein ligand-dependent corepressor (LCoR) has previously been shown to suppress hepatic lipogenesis by decreasing the binding of steroid receptor coactivators to thyroid hormone receptor. However, the role of LCoR in adipogenesis has not been established. Here, we show that LCoR expression is reduced in the early stage of adipogenesis in vitro LCoR overexpression inhibited 3T3-L1 adipocyte differentiation, whereas LCoR knockdown promoted it. Using an unbiased affinity purification approach, we identified CCAAT/enhancer-binding protein β (C/EBPβ), a key transcriptional regulator in early adipogenesis, and corepressor C-terminal binding proteins as potential components of an LCoR-containing complex in 3T3-L1 adipocytes. We found that LCoR directly interacts with C/EBPβ through its C-terminal helix-turn-helix domain, required for LCoR's inhibitory effects on adipogenesis. LCoR overexpression also inhibited C/EBPβ transcriptional activity, leading to inhibition of mitotic clonal expansion and transcriptional repression of C/EBPα and peroxisome proliferator-activated receptor γ2 (PPARγ2). However, LCoR overexpression did not affect the recruitment of C/EBPβ to the promoters of C/EBPα and PPARγ2 in 3T3-L1 adipocytes. Of note, restoration of PPARγ2 or C/EBPα expression attenuated the inhibitory effect of LCoR on adipogenesis. Mechanistically, LCoR suppressed C/EBPβ-mediated transcription by recruiting C-terminal binding proteins to the C/EBPα and PPARγ2 promoters and by modulating histone modifications. Taken together, our results indicate that LCoR negatively regulates early adipogenesis by repressing C/EBPβ transcriptional activity and add LCoR to the growing list of transcriptional corepressors of adipogenesis.

Amentoflavone protects against high fat-induced metabolic dysfunction: Possible role of the regulation of adipogenic differentiation.

In the present study, we evaluated the protective effects of amentoflavone (AMF) against high-fat (HF) diet-induced metabolic dysfunction and focused on the influence of AMF on adipogenic differentiation during 3T3-L1 adipocyte differentiation. For this purpose, male Wistar rats were fed a HF diet or a HF diet with AMF (10 or 50 mg/kg). We found that AMF protected against HF diet-induced metabolic dysfunction in a dose-dependent manner, as evidenced by a decrease in the fasting blood glucose levels, fasting insulin levels and the homeostatic model assessment-insulin resistance index (HOMA-IR), as well as by a decrease in the glucose level, as shown by the intraperitoneal glucose tolerance test and intraperitoneal insulin tolerance test. Moreover, the results revealed that AMF significantly inhibited the increase in body weight, the weight of perirenal adipose tissues and the serum triglyceride (TG) content of the rats fed the HF diet in a dose-dependent manner. AMF also inhibited the accumulation of oil droplets in differentiated 3T3-L1 adipocytes in a concentration-dependent manner. The incubation of the cells with AMF for 0–8, 0–2, 2–4, or 4–8 days markedly inhibited adipogenesis. During the early phase of the adipocyte differentiation of 3T3-L1 cells, AMF decreased CCAAT/enhancer-binding protein (C/EBP) β expression in a concentration-dependent manner, leading to the inhibition of mitotic clonal expansion (MCE). Moreover, our results demonstrated that AMF significantly increased reactive oxygen species (ROS) generation in the cells and the antioxidant, N-acetylcysteine (NAC), markedly attenuated the inhibitory effects of AMF on adipogenesis. AMF also inhibited the expression of peroxisome proliferator-activated receptor γ (PPARγ) and C/EBPα and the expression of downstream targets in a concentration-dependent manner. The overexpression of PPARγ and C/EBPα (by transfection with respective overexpression plasmids) attentuated the inhibitory effects of AMF on the formation of oil droplets. The inhibitory effects of AMF on adipocyte differentiation may contribute to its protective effects against HF diet-induced metabolic dysfunction. Overall, the data in our study provide novel insight into the mechanisms responsible for the protective effects of AMF against HF diet-induced metabolic dysfunction and those for its inhibitory effect on adipocyte differentiation.

Seapolynol Extracted from Ecklonia cava Inhibits Adipocyte Differentiation in Vitro and Decreases Fat Accumulation in Vivo.

Seapolynol (SN) is a polyphenol mixture derived from Ecklonia cava. We evaluated the effects of SN on lipid accumulation in adipocytes, zebrafish, and mice. SN effectively inhibited lipid accumulation in three experimental models by suppressing adipogenic factors. Triglyceride synthetic enzymes such as diacylglycerol acyltransferase 1 (DGAT1) and GPAT3 were also downregulated by SN. This SN-induced inhibition of adipogenic factors was shown to be due to the regulatory effect of SN on early adipogenic factors; SN downregulated the expression of Krueppel-like factor 4 (KLF4), KLF5, CCAAT-enhancer-binding protein β (C/EBPβ), C/EBPδ, and Protein C-ets-2 (ETS2), while KLF2, an anti-early adipogenic factor, was upregulated by SN. SN-mediated inhibition in early adipogenesis was closely correlated with the inhibition of mitotic clonal expansion via cell cycle arrest. SN inhibited cell cycle progression by suppressing cell cycle regulators, such as cyclin A, cyclinD, and pRb but increased p27, a cell cycle inhibitor. In a mouse study, SN effectively reduced body weight and plasma lipid increases induced by a high-fat diet; triglycerides, total cholesterol, and low-density lipoprotein (LDL) levels were markedly reduced by SN. Moreover, SN remarkably improved high-fat-diet-induced hepatic lipid accumulation. Furthermore, SN activated AMP-activated protein kinase-α (AMPKα), an energy sensor, to suppress acetyl-coA carboxylase (ACC), inhibiting lipid synthesis. Our study suggests that SN may be an edible agent that can play a positive role in prevention of metabolic disorders.

Ethanol Extract of Alismatis rhizome Inhibits Adipocyte Differentiation of OP9 Cells.

The rhizome of Alisma orientale (Alismatis rhizome) has been used in Asia for promoting diuresis to eliminate dampness from the lower-jiao and to expel heat. In this study, an ethanol extract of the rhizome of Alisma orientale (AOE) was prepared and its effects on adipocyte differentiation of OP9 cells were investigated. Treatment with AOE in a differentiation medium for 5 days resulted in dose-dependent inhibition of lipid droplet formation in OP9 cells. Furthermore, AOE significantly inhibited adipocyte differentiation by downregulating the expression of the master transcription factor of adipogenesis, peroxisome proliferation-activity receptor γ (PPARγ), and related genes, including CCAAT/enhancer binding protein β (C/EBPβ), fatty acid-binding protein (aP2), and fatty acid synthase (FAS). AOE exerted its inhibitory effects primarily during the early adipogenesis stage (days 1-2), at which time it also exerted dose-dependent inhibition of the expression of C/EBPβ, a protein related to the inhibition of mitotic clonal expansion. Additionally, AOE decreased the expression of autophagy-related proteins, including beclin 1, and the autophagy-related genes, (Atg) 7 and Atg12. Our results indicate that AOE's inhibitory effects on adipocyte differentiation of OP9 cells are mediated by reduced C/EBPβ expression, causing inhibition of mitotic clonal expansion and autophagy.

Inhibition of mitotic clonal expansion mediates fisetin-exerted prevention of adipocyte differentiation in 3T3-L1 cells

Adipocytes are the key player in adipose tissue inflammation and subsequent systemic insulin resistance and its development involves complex process of proliferation and differentiation of preadipocytes. Fistein, a polyphenol flavonoid, is known to exert anti-inflammatory, anti-carcinogenic and anti-diabetic effects. In this study, we aimed to investigate the effect of fisetin on adipocyte proliferation and differentiation in 3T3-L1 preadipocyte cell line and its mechanism of action. We found that fisetin inhibits adipocyte differentiation in a concentration dependent manner, which were evidenced by Oil Red O staining and the protein expression of mature adipocyte marker genes fatty acid synthase and peroxisome proliferator-activated receptor γ. Moreover, the proliferation of preadipocytes was also markedly suppressed by treatment of fisetin for 24 and 48 h in the differentiation medium. We also found that fisetin inhibition of adipocyte differentiation was largely due to the effect on mitotic clonal expansion. Fisetin suppression of preadipocyte proliferation at early stage of differentiation was accompanied by the changes of expression of a series of cell cycle regulatory proteins. Altogether, our results suggest that the inhibition of adipocyte differentiation by fisetin may be at least in part mediated by cell cycle arrest during adipogenesis.

Radicicol, a heat shock protein 90 inhibitor, inhibits differentiation and adipogenesis in 3T3-L1 preadipocytes

Heat shock protein 90 (Hsp90) is involved in various cellular processes, such as cell proliferation, differentiation and apoptosis. As adipocyte differentiation plays a critical role in obesity development, the present study investigated the effect of an Hsp90 inhibitor radicicol on the differentiation of 3T3-L1 preadipocytes and potential mechanisms. The cells were treated with different concentrations of radicicol during the first 8days of cell differentiation. Adipogenesis, the expression of adipogenic transcriptional factors, differentiation makers and cell cycle were determined. It was found that radicicol dose-dependently decreased intracellular fat accumulation through down-regulating the expression of peroxisome proliferator-activated receptor γ (PPARγ) and CCAAT element binding protein α (C/EBPα), fatty acid synthase (FAS) and fatty acid-binding protein 4 (FABP4). Flow cytometry analysis revealed that radicicol blocked cell cycle at G1-S phase. Radicicol redcued the phosphorylation of Akt while showing no effect on β-catenin expression. Radicicol decreased the phosphorylation of phosphoinositide-dependent kinase 1 (PDK1). The results suggest that radicicol inhibited 3T3-L1 preadipocyte differentiation through affecting the PDK1/Akt pathway and subsequent inhibition of mitotic clonal expansion and the expression/activity of adipogenic transcriptional factors and their downstream adipogenic proteins.

Seanol® and its major compound, dieckol suppress lipid accumulation during adipogenesis through inhibition of Mitotic Clonal Expansion (MCE) and cell cycle arrest.

Seanol® is a polyphenol extract derived from a brown alga, Ecklonia cava (EC), which is native to the sea off Korea and Japan. It consists of phlorotannins including eckol and dieckol. In this study, we investigated the effect of Seanol® and its major compounds, eckol and dieckol on adipocyte differentiation in 3T3‐ L1 cells. Our data showed that Seanol® and dieckol inhibited lipid accumulation in 3T3‐L1 in a dose dependent manner, while eckol didn't have a significant inhibitory effect on lipid accumulation in Oil red O staining, suggesting that dieckol plays as a major inhibitory compound of Seanol® on lipid accumulation. The inhibition of dieckol was usually occurred in early stage of adipogenesis. Dieckol inhibited mRNA expression of early adipogenic genes such as CCAAT/ enhancer binding protein‐β (C/EBPβ), C/EBPδ, Krueppel‐like factor 4 (KLF4), and KLF5, whereas it enhanced mRNA expression of preadipocyte secreted factor (Pref‐1) in RT‐PCR. These results were reflected in downregulation of late adipogenic factors such as peroxisome proliferator‐activated receptor‐γ (PPARγ), C/EBPα, and adipocyte protein 2 (ap2). Our cell cycle analysis showed that dieckol inhibited MCE stage through the arrest of G1/G0 phase, which is supported by suppression of adipocyte proliferation in trypan blue assay. Our study suggests that dieckol is a potential edible agent in controlling lipid accumulation in metabolic disorder.

C1q/Tumor Necrosis Factor-related Protein 11 (CTRP11), a Novel Adipose Stroma-derived Regulator of Adipogenesis

C1q/TNF-related proteins (CTRPs) are a family of secreted regulators of glucose and lipid metabolism. Here, we describe CTRP11, a novel and phylogenetically conserved member of the C1q family. Our studies revealed that white and brown adipose are major tissues that express CTRP11, and its expression is acutely regulated by changes in metabolic state. Within white adipose tissue, CTRP11 is primarily expressed by stromal vascular cells. As a secreted multimeric protein, CTRP11 forms disulfide-linked oligomers. Although the conserved N-terminal Cys-28 and Cys-32 are dispensable for the assembly of higher-order oligomeric structures, they are unexpectedly involved in modulating protein secretion. When co-expressed, CTRP11 forms heteromeric complexes with closely related CTRP10, CTRP13, and CRF (CTRP14) via the C-terminal globular domains, combinatorial associations that potentially generate functionally distinct complexes. Functional studies revealed a role for CTRP11 in regulating adipogenesis. Ectopic expression of CTRP11 or exposure to recombinant protein inhibited differentiation of 3T3-L1 adipocytes. The expression of peroxisome proliferator-activated receptor-γ and CAAT/enhancer binding protein-α, which drive the adipogenic gene program, was markedly suppressed by CTRP11. Impaired adipogenesis was caused by a CTRP11-mediated decrease in p42/44-MAPK signaling and inhibition of mitotic clonal expansion, a process essential for adipocyte differentiation in culture. These results implicate CTRP11 as a novel secreted regulator of adipogenesis and highlight the potential paracrine cross-talk between adipocytes and cells of the stromal vascular compartment in maintaining adipose tissue homeostasis.

Small-molecule COH-SR4 inhibits adipocyte differentiation via AMPK activation

Obesity is a chronic metabolic disorder caused by an imbalance between energy intake and expenditure. It is one of the principal causative factors involved in the development of metabolic syndrome and cancer. Inhibition of adipocyte differentiation has often been a target of anti-obesity strategies since obesity is caused not only by hypertrophy but also by adipocyte hyperplasia. In this study, we investigated the effects of COH-SR4, a novel compound with anticancer properties, on the adipogenesis in 3T3-L1 cells. Treatment with COH-SR4 significantly inhibited adipocyte differentiation in a dose-dependent manner. This inhibitory effect mainly occurred at the early phase of differentiation through inhibition of mitotic clonal expansion and cell cycle arrest at the G1/S phase transition. In differentiating adipocytes, COH-SR4 significantly reduced intracellular lipid accumulation and downregulated the expression of key adipogenesis-related transcription factors and lipogenic proteins. COH-SR4 exhibited no cytotoxic effects in 3T3-L1 cells, but indirectly activated AMP-activated protein kinase (AMPK). AMPK activation by COH-SR4 also resulted in the phosphorylation of raptor and tuberous sclerosis protein 2 (TSC2), two proteins involved in the mammalian target of rapamycin (mTOR) signaling pathways. Additionally, COH-SR4 decreased the phosphorylation of p70 kDa ribosomal protein S6 kinase (S6K) and initiation factor 4E (eIF4E) binding protein 1 (4EB‑P1), two downstream effectors of mTOR that regulate protein synthesis. Interestingly, knockdown of AMPKα1/α2 prevented the ability of COH-SR4 to inhibit cell cycle arrest and overall adipogenesis and lipid accumulation in the differentiating 3T3-L1 cells. Taken together, these results suggest that COH-SR4 inhibits 3T3-L1 adipogenesis via AMPK activation. COH-SR4 may be a promising compound for the treatment of obesity and related metabolic disorders.

Widdrol Blocks 3T3-L1 Preadipocytes Growth and Differentiation Due to Inhibition of Mitotic Clonal Expansion

Adipocyte differentiation is strongly associated with obesity, which causes metabolic disorders. In this study, we investigated the inhibitory effects of widdrol on 3T3- L1 preadipocyte growth and differentiation. Widdrol decreased lipid droplet accumulation and down-regulated adipogenic transcription factors such as C/EBPalpha, C/EBPbeta, and PPARgamma. Widdrol blocked preadipocyte proliferation and differentiation through the inhibition of mitotic clonal expansion, which was accompanied by the failure of degradation of p21, a cyclin-dependent kinase inhibitor. Cell-cycle analysis clearly indicated that widdrol actively induces cell-cycle arrest at the G1-S phage transition, causing cells to remain in the preadipocyte state. Moreover, widdrol increased p21 expression and inhibited Rb phosphorylation in preadipocyte incubated in a hormone medium. Therefore, these findings clearly suggest that widdrol blocks preadipocyte growth and differentiation through the inhibition of mitotic clonal expansion by p21- and Rb-dependent G1 arrest and can be developed as a potent anti-adipogenic agent for reducing obesity.

Inhibitory Effects of A-769662, a Novel Activator of AMP-Activated Protein Kinase, on 3T3-L1 Adipogenesis

AMP-activated protein kinase (AMPK) is a central player in glucose and lipid metabolism while its role in adipocyte differentiation remains obscure. A-769662, a novel activator of AMPK, has been implicated to reduce body weight gain and decrease liver and plasma triglyceride levels via increasing fatty acid oxidation and reducing fatty acid synthesis in vivo. In this study, we examined the effects of A-769662 on adipocyte differentiation using 3T3-L1 cells. We found that A-769662 significantly inhibited 3T3-L1 differentiation via down-regulation of adipogenesis-related transcription factors and adipogenic markers. The inhibitory effect mainly occurred at the early phase of differentiation through inhibition of mitotic clonal expansion (MCE), which was essential for adipogenesis. A-769662 also decreased cell viability of differentiating and mature 3T3-L1 adipocytes. Moreover, treatment of differentiating 3T3-L1 cells with A-769662 resulted in AMPK over-activation, which led to an increased phosphorylation and inactivation of acetyl-CoA carboxylase (ACC), an important enzyme for the synthesis and usage of fatty acids. Taken together, these results suggest that A-769662 inhibits 3T3-L1 adipogenic differentiation in several ways and therefore may be a promising compound for the treatment of obesity.

Knockdown of Macrophage Migration Inhibitory Factor Disrupts Adipogenesis in 3T3-L1 Cells

Obesity is a condition in which adipose tissue mass is expanded. Increases in both adipocyte size and number contribute to enlargement of adipose tissue. The increase in cell number is thought to be caused by proliferation and differentiation of preadipocytes. Macrophage migration inhibitory factor (MIF) is expressed in adipocytes, and intracellular MIF content is increased during adipogenesis. Therefore, we hypothesized that MIF is associated with adipocyte biology during adipogenesis and focused on the influence of MIF on adipogenesis. To examine the effects of MIF on adipocytes, MIF expression in 3T3-L1 preadipocytes was inhibited by RNA interference, and cell differentiation was induced by standard procedures. The triglyceride content of MIF small interfering RNA (siRNA)-transfected 3T3-L1 cells was smaller than that of nonspecific siRNA-transfected cells. In addition, MIF knockdown apparently abrogated increases in adiponectin mRNA levels during differentiation. Gene expression of peroxisome proliferator-activated receptor (PPAR)gamma, CCAAT/enhancer binding protein (C/EBP)alpha, and C/EBPdelta decreased with MIF siRNA transfection, but C/EBPbeta expression increased. Cell number and incorporation of 5-bromo-2-deoxyuridine into cells decreased from 1-3 d and from 14-20 h, respectively, after induction of differentiation in MIF siRNA-transfected cells, thus suggesting that MIF siRNA inhibits mitotic clonal expansion. Taken together, these results indicated that MIF regulates differentiation of 3T3-L1 preadipocytes, at least partially, through inhibition of mitotic clonal expansion and/or C/EBPdelta expression.

Compound C inhibits clonal expansion of preadipocytes by increasing p21 level irrespectively of AMPK inhibition

AMP-activated protein kinase (AMPK) activation inhibits adipocyte differentiation. This study investigated the effect of compound C (CC), a widely used AMPK inhibitor, on differentiation of 3T3-L1 preadipocytes. CC treatment blocked hormone-induced preadipocyte differentiation due to inhibition of mitotic clonal expansion, which was accompanied by the failure of degradation of p21, a cyclin-dependent kinase inhibitor. CC increased the level of p21 protein, but not its mRNA, in preadipocytes incubated in a hormone-free medium. Cycloheximide decreased the basal p21 level, which was inhibited by CC treatment, supporting the stabilization of p21 by CC. Treatment of AICAR or metformin, AMPK activators, failed to induce p21 or inhibit the ability of CC to increase p21 level. In conclusion, CC inhibits proliferation of preadipocytes as a consequence of an increase in p21 content, which might result from p21 stabilization, and the increase in p21 level by CC might not be associated with AMPK inhibition.