Role of Insulin in Growth Hormone-Stimulated 3T3 Cell Adipogenesis*

Guller, Seth; Corin, Robert E.; Mynarcik, Dennis C.; London, Beverly M.; Sonenberg, Martin

doi:10.1210/endo-122-5-2084

Cited by 58 publications

(41 citation statements)

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“…In addition, these authors also described a weak constitutive transcriptional activity of the isolated PPAR␥1 N terminus, and this was also increased when serine 82 was mutated. Whether or not the activity of insulin to enhance transcription by intact PPAR␥2 (32) or PPAR␥2 N terminus as reported here is mediated by phosphorylation of PPAR␥2, it is clear that signaling by PPAR␥ and insulin produce a number of common effects, including the ability to promote adipocyte differentiation (35,36). Another indication of convergent pathways for these molecules is the fact that the insulin-sensitizing thiazoladinediones are now known to act by binding to and activating PPAR␥ (7,8).…”

Section: Discussionmentioning

confidence: 75%

Ligand-independent Activation Domain in the N Terminus of Peroxisome Proliferator-activated Receptor γ (PPARγ)

Werman

Hollenberg

Solanes

et al. 1997

Journal of Biological Chemistry

260

164

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Peroxisome proliferator-activated receptor ␥ (PPAR␥) is a member of the nuclear hormone receptor superfamily, and is an important regulator of adipogenesis and adipocyte gene expression. PPAR␥ exists as two isoforms, PPAR␥1 and PPAR␥2, that differ only in their N termini. Both isoforms are activated by ligands that include the antidiabetic thiazoladinedione drugs and 15-deoxy-⌬ 12, 14 -prostaglandin J2, and potential differences in their function have yet to be described. We report that, in addition to a ligand-activated transcriptional activity, when studied under conditions of ligand depletion, intact PPAR␥ has a ligand-independent activation domain. To identify the basis for this ligand-independent activation, we used GAL4-PPAR␥ chimeric expression constructs and UAS-TK-LUC in CV1 cells and isolated rat adipocytes. In both cell systems, isolated PPAR␥1 and PPAR␥2 N termini have activation domains, and the activation function of PPAR␥2 is 5-6-fold greater than that of PPAR␥1. Insulin enhances the transcriptional effect mediated by both PPAR␥1 and PPAR␥2 N-terminal domains. These data demonstrate that 1) PPAR␥ has an N-terminal (ligandindependent) activation domain; 2) PPAR␥1 and PPAR␥2 N termini have distinct activation capacities; and 3) insulin can potentiate the activity of the N-terminal domain of PPAR␥.The peroxisome proliferator-activated receptor ␥ (PPAR␥) 1 is a member of the nuclear receptor superfamily that plays a pivotal role in the molecular determination of adipogenesis and the regulation of adipocyte gene expression (1-5). Under appropriate conditions, expression of PPAR␥ through retroviral infection of fibroblastic cell lines is sufficient to cause differentiation along an adipocyte lineage, as assessed by expression of adipocyte-specific genes, accumulation of lipid, and acquisition of adipocyte morphology (6). Recently, it has been shown that 15-deoxy-⌬ 12, 14 -prostaglandin J2 (PG J2) is a high affinity ligand for PPAR␥ (7,8) and that PPAR␥ is also the receptor for the thiazoladinedione class of insulin-sensitizing drugs (7,8). PPAR␥ resembles other members of the nuclear receptor superfamily in that ligand-dependent receptor activation alters the rates of transcription of genes, specifically those that have peroxisome proliferator response elements (PPREs) within their promoters (e.g. aP2, phosphoenolpyruvate carboxykinase, and uncoupling protein) (9 -11).PPAR␥ exists as two isoforms, PPAR␥1 and PPAR␥2, that differ only in their N termini, with PPAR␥2 having an additional 30 amino acids that are encoded by a single exon (9, 12). Expression of mRNA encoding the two isoforms is driven by alternative promoters within a single PPAR␥ gene (12), and their expression is differentially regulated in a tissue-specific manner. PPAR␥2 is most abundantly expressed in adipocytes and is relatively specific for this tissue (9, 13). In contrast, while PPAR␥1 is also expressed at a high level in adipocytes, it is also found at significant but lower levels in a number of other tissues, including muscle (13-15...

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Section: Discussionmentioning

confidence: 75%

Ligand-independent Activation Domain in the N Terminus of Peroxisome Proliferator-activated Receptor γ (PPARγ)

Werman

Hollenberg

Solanes

et al. 1997

Journal of Biological Chemistry

260

164

View full text Add to dashboard Cite

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“…In contrast, glucocorticoids are more adipogenic than insulin in TA1 cell line and primary rabbit preadipose cells [42,182]. In 3T3-F442A cells, insulin is only effective when cells have been previously stimulated with GH [95]. However, an earlier role of insulin is not to be excluded: this hormone is indeed sufficient to enhance adipose conversion of porcine preadipocytes in the absence of other stimulators, and to increase the expression of extracellular matrix proteins, such as laminin and type IV collagen [27,113].…”

Section: Insulin Igf-1 and Ghmentioning

confidence: 96%

The adipose conversion process: regulation by extracellular and intracellular factors

Boone

Mourot

Gregoire³

et al. 2000

Reprod. Nutr. Dev.

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-White adipose tissue regulates lipid metabolism and acts as a secretory organ. Because of its importance for human health and animal production, many studies have attempted to better understand its development at the cellular and molecular levels by culturing preadipose cells in vitro. This synthesis article describes our current knowledge, acquired by this approach, concerning the regulation of the different steps of the adipocyte differentiation program by extracellular (hormones, cytokines, growth factors, retinoids and fatty acids) and intracellular agents (second messengers and transcription factors). The discrepant effects that have been observed for some of these factors are also discussed. This information is very important in the perspective of a better control of fat deposits in human and breeding species.preadipocyte / differentiation / hormonal agent / second messenger / transcription factor Résumé -Le processus d'adipoconversion : sa régulation par des facteurs extracellulaires et intracellulaires. Le tissu adipeux blanc régule le métabolisme lipidique et agit comme un organe de sécrétion. Étant donné son importance pour la santé humaine et la production animale, de nombreuses études ont tenté de mieux comprendre son développement aux niveaux cellulaire et moléculaire en utilisant des cultures de préadipocytes. Cet article de synthèse décrit notre connaissance actuelle, issue de cette approche, concernant la régulation des différentes étapes du programme de la diffé-renciation adipocytaire par des facteurs extracellulaires (hormones, cytokines, facteurs de croissance, rétinoïdes et acides gras) et intracellulaires (seconds messagers et facteurs de transcription). Les effets divergents observés pour certains de ces facteurs sont également discutés. Ces informations sont très importantes dans la perspective d'un meilleur contrôle des dépôts adipeux chez l'humain et les espèces d'élevage.préadipocyte / différenciation / hormone / second messager / facteur de transcription Reprod. Nutr. Dev. 40 (2000) 325-358 325

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Section: Introductionmentioning

confidence: 99%

“…These inducers activate multiple signal transduction pathways, which may be redundant or which may involve crosstalk between pathways, because any one of the three components alone can promote differentiation, albeit weakly. At least three secondmessenger pathways have been implicated in the induction of differentiation of 3T3-L1 preadipocytes, i.e., the cAMPdependent protein kinase-the glucocorticoid-and the insulinlike growth factor-I͞insulin-signaling pathways (2,3,(18)(19)(20).The goal of this research is to identify the intermediaries in the second messenger-signaling pathways that link the pathway(s) to the genes that activate (or derepress) the differentiation program. In this paper, we provide evidence that calpain functions between the cAMP-signaling pathway and the expression of the C͞EBP␣ gene, a critical step in the adipocyte differentiation program.…”

mentioning

confidence: 99%

Role of calpain in adipocyte differentiation

Patel

Lane

1999

Proc. Natl. Acad. Sci. U.S.A.

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Evidence is presented that the calciumactivated protease, calpain, is required for differentiation of 3T3-L1 preadipocytes into adipocytes induced by methylisobutylxanthine (a cAMP phosphodiesterase inhibitor), dexamethasone, and insulin. Calpain is expressed by preadipocytes and its level falls during differentiation. Exposure of preadipocytes to the calpain inhibitor N-acetyl-Leu-Leu-norleucinal or overexpression of calpastatin, a specific endogenous inhibitor of calpain, blocks expression of adipocyte-specific genes, notably the CCAAT͞enhancer-binding protein (C͞EBP)␣ gene, and acquisition of the adipocyte phenotype. The inhibitor disrupts the differentiation-inducing effect of methylisobutylxanthine (by means of the cAMP-signaling pathway), but is without effect on differentiation induced by dexamethasone or insulin. N-acetyl-Leu-Leu-norleucinal, or overexpression of calpastatin, inhibits reporter gene expression mediated by the C͞EBP␣ gene promoter by preventing C͞EBP␤, a transcriptional activator of the C͞EBP␣ gene, from binding to the promoter. These findings implicate calpain in the transcriptional activation of the C͞EBP␣ gene, a process required for terminal adipocyte differentiation.Terminal differentiation involves the coordinate expression of a cell type-specific set of genes that gives rise to a new and unique phenotype. The mouse 3T3-L1 preadipocyte system provides a well-characterized cell culture model for the study of adipocyte-specific terminal differentiation (1-7). During adipocyte differentiation, CCAAT͞enhancer-binding protein (C͞EBP)␣ functions as a plieotropic transcriptional activator of numerous adipocyte genes (2, 3). The promoters of these genes possess C͞EBP regulatory elements that mediate transactivation by C͞EBP␣. Moreover, the proximal promoter of the C͞EBP␣ gene itself contains a C͞EBP regulatory element that mediates transactivation by other members of the C͞EBP family, notably C͞EBP␤, which is expressed before C͞EBP␣ in the differentiation program (8-11). C͞EBP␣ has an essential function in the differentiation process as indicated by the fact that forced expression of C͞EBP␣ is sufficient to trigger differentiation of 3T3-L1 preadipocytes in the absence of the exogenous inducers usually required (11,12). Moreover, blocking expression of C͞EBP with antisense C͞EBP␣ RNA prevents adipocyte differentiation (13).Growth-arrested (confluent) 3T3-L1 preadipocytes can be induced to differentiate by treatment with a combination of inducers including methylisobutylxanthine (MIX), dexamethasone (DEX), insulin, and fetal bovine serum (FBS) (14), hereafter referred to as the MDI protocol. On exposure to these inducers, preadipocytes reenter the cell cycle and undergo several rounds of cell division (15), which mimics differentiation-associated mitotic clonal expansion (2). Clonal expansion is followed by the coordinate expression of a subset of genes that confer the morphological and biochemical adipocyte phenotype (3,16,17). Whereas each component of the MDI protocol is capable of...

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Role of Insulin in Growth Hormone-Stimulated 3T3 Cell Adipogenesis*

Cited by 58 publications

References 0 publications

Ligand-independent Activation Domain in the N Terminus of Peroxisome Proliferator-activated Receptor γ (PPARγ)

Ligand-independent Activation Domain in the N Terminus of Peroxisome Proliferator-activated Receptor γ (PPARγ)

The adipose conversion process: regulation by extracellular and intracellular factors

Role of calpain in adipocyte differentiation

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