Insulin-induced Adipocyte Differentiation

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Salt-inducible kinase (SIK), first cloned from the adrenal glands of rats fed a high salt diet, is a serine/threonine protein kinase belonging to an AMP-activated protein kinase family. Induced in Y1 cells at an early stage of ACTH stimulation, it regulated the initial steps of steroidogenesis. Here we report the identification of its isoform SIK2. When a green fluorescent protein-fused SIK2 was expressed in 3T3-L1 preadipocytes, it was mostly present in the cytoplasm. When coexpressed in cAMP-responsive element-reporter assay systems, SIK2 could repress the cAMP-responsive element-dependent transcription, although the degree of repression seemed weaker than that by SIK1. SIK2 was specifically expressed in adipose tissues. When 3T3-L1 cells were treated with the adipose differentiation mixture, SIK2 mRNA was induced within 1 h, the time of induction almost coinciding with that of c/EBP␤ mRNA. Coexpressed with human insulin receptor substrate-1 (IRS-1) in COS cells, SIK2 could phosphorylate Ser 794 of human IRS-1. Adenovirus-mediated overexpression of SIK2 in adipocytes elevated the level of phosphorylation at Ser 789 , the mouse equivalent of human Ser 794 . Moreover, the activity and content of SIK2 were elevated in white adipose tissues of db/db diabetic mice. These results suggest that highly expressed SIK2 in insulin-stimulated adipocytes phosphorylates Ser 794 of IRS-1 and, as a result, might modulate the efficiency of insulin signal transduction, eventually causing the insulin resistance in diabetic animals.The lipid metabolism in adipose tissues is under the control of two hormonal signaling pathways; insulin stimulates glucose uptake and lipogenesis, whereas cAMP, generated by exogenous stimuli like adrenalin and glucagon, stimulates lipolysis. If the balance between the two signaling systems becomes lost and the adipose tissues are exposed to hyperinsulinemia for a prolonged time, they gradually become resistant to insulin stimulation (1, 2). The insulin resistance occurring in tissues involved in biological fuel metabolism, such as adipose tissues, liver, and skeletal muscles, would finally cause disorders in energy metabolism of the whole body, such as obesity and type 2 diabetes (3, 4). Insulin receptor substrate (IRS) 1 proteins are key molecules of the insulin-signaling cascade (5); they are phosphorylated on tyrosine residues by the action of insulindependently activated insulin receptor kinase, and the tyrosine-phosphorylated IRS proteins trigger further intracellular cascades. Several investigators recently reported (6, 7) that IRS proteins, under certain non-physiological conditions, were phosphorylated on serine residues. The serine phosphorylation of IRS proteins would modulate the efficiency of the insulinsignaling cascade (8, 9) and eventually render the animals resistant to insulin stimulation (10, 11). Molecular identification of several protein kinases responsible for the serine phosphorylation of IRS proteins has been reported (12-24).Salt-inducible kinase (SIK) was first cloned from ...

Section: Sik2 Is Activated In White Adipose Tissues Of Diabetic Mice-mentioning

confidence: 88%

Adipose-specific Expression, Phosphorylation of Ser794 in Insulin Receptor Substrate-1, and Activation in Diabetic Animals of Salt-inducible Kinase-2

Horike

Takemori

Katoh

et al. 2003

141

179

“…In previous experiments, we demonstrated that expression of constitutively active forms of CREB in 3T3-L1 cells overcomes the inhibition of adipogenesis due to blockade of Ras/Raf/ERK signaling (17). These data highlighted CREB as a primary target for agents and signaling pathways that stimulate adipogenesis and as a crucial were selected with appropriate antibiotics, and large, rapidly growing colonies were recovered and combined.…”

Section: Depletion Of Creb/atf1 Blocks Adipogenesis Induced By Ectopimentioning

confidence: 94%

“…␣-We previously demonstrated that ectopic expression of constitutively active forms of CREB stimulated adipogenesis in 3T3-L1 cells (16) even when the ERK signaling pathway was repressed (17). In the current studies, we next sought to determine whether increased CREB activity would stimulate adipogenic conversion in cells depleted of C/EBP ␣ or ␤ or PPAR␥2.…”

Section: Activation Of Creb Overcomes Inhibition Of Adipogenesis Due mentioning

confidence: 99%

“…Subsequently we demonstrated that ectopic expression of constitutively active forms of CREB was sufficient to drive adipogenic conversion of 3T3-L1 cells, whereas dominant negative forms of CREB inhibited this process (16). The central role of CREB in adipogenesis is exemplified by the ability of constitutively active forms of CREB to overcome inhibition of adipogenic conversion due to blockade of Ras/ERK signaling (17). In addition, diminished CREB activity in mature adipocytes induces apoptosis, in part, through decreased Akt expression (18).…”

mentioning

confidence: 99%

See 1 more Smart Citation

Depletion of cAMP-response Element-binding Protein/ATF1 Inhibits Adipogenic Conversion of 3T3-L1 Cells Ectopically Expressing CCAAT/Enhancer-binding Protein (C/EBP) α, C/EBP β, or PPARγ2

Fox

Fankell

Erickson

et al. 2006

Self Cite

110

The differentiation of preadipocytes to adipocytes is orchestrated by the expression of the "master adipogenic regulators," CCAAT/enhancer-binding protein (C/EBP) ␤, peroxisome proliferator-activated receptor ␥ (PPAR␥), and C/EBP ␣. In addition, activation of the cAMP-response element-binding protein (CREB) is necessary and sufficient to promote adipogenic conversion and prevent apoptosis of mature adipocytes. In this report we used small interfering RNAto deplete CREB and the closely related factor ATF1 to explore the ability of the master adipogenic regulators to promote adipogenesis in the absence of

“…1). The insulin-induced adipogenesis of 3T3-L1 cells involves a number of disease-linked proteins such as phosphatidylinositol 3-kinase, Ras, peroxisome proliferator-activated receptor ␥, p38, or phosphodiesterases, and known drugs for a range of diseases have been reported to have phenotypic effects on the adipogenesis (7)(8)(9)(10)(11)(12). A morphology-based adipogenesis screen of a chemical library could identify a pool of biologically active compounds with many distinct pharmacological effects.…”

mentioning

confidence: 99%

Identification of Bioactive Molecules by Adipogenesis Profiling of Organic Compounds

Choi

Kawazoe

Murakami

et al. 2003

An important step in the postgenomic drug discovery is the construction of high quality chemical libraries that generate bioactive molecules at high rates. Here we report a cell-based approach to composing a focused library of biologically active compounds. A collection of bioactive non-cytotoxic chemicals was identified from a divergent library through the effects on the insulin-induced adipogenesis of 3T3-L1 cells, one of the most drastic and sensitive morphological alterations in cultured mammalian cells. The resulting focused library amply contained unique compounds with a broad range of pharmacological effects, including glucose-uptake enhancement, cytokine inhibition, osteogenesis stimulation, and selective suppression of cancer cells. Adipogenesis profiling of organic compounds generates a focused chemical library for multiple biological effects that are seemingly unrelated to adipogenesis, just as genetic screens with the morphology of fly eyes identify oncogenes and neurodegenerative genes.