Effects of insulin and phorbol esters on subcellular distribution of protein kinase C isoforms in rat adipocytes

Farese, Robert V.; Standaert, Mary L.; François, Alan; Ways, Kirk; Arnold, Thomas Paul; Hernandez, Hector H.; Cooper, Denise R.

doi:10.1042/bj2880319

Cited by 67 publications

(59 citation statements)

References 13 publications

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“…In previous studies, we examined the effect of phorbol ester (TPA), which can mimic in part the effect of DAG, the natural ligand for PKC (31). Phorbol esters activate conventional and novel PKCs immediately (32,33), but long term treatment with TPA results in a decrease in PKC in several cell types (34), mainly because of an increased rate of degradation of PKC protein (35,36). Because activation of PKC did not stimulate LPL, our data suggested that PKC plays a constitutive role in maintaining LPL synthesis.…”

Section: Pkc Isoformsmentioning

confidence: 67%

Regulation of Lipoprotein Lipase by Protein Kinase Cα in 3T3-F442A Adipocytes

Ranganathan¹,

Song²,

Dean³

et al. 2002

Journal of Biological Chemistry

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Lipoprotein lipase (LPL) is an important enzyme in adipocyte and lipid metabolism with complex cellular regulation. Previous studies demonstrated an inhibition of LPL activity and synthesis following depletion of protein kinase C (PKC) isoforms with long term treatment of 3T3-F442A adipocytes with 12-O-tetradecanoylphorbol-13-acetate. To identify the specific PKC isoforms involved, we treated cells with antisense oligonucleotides that block expression of specific PKC isoforms. An antisense oligonucleotide to PKC␣ inhibited LPL activity by 78 ؎ 8%, whereas antisense oligonucleotides directed against PKC␦ or PKC⑀ had no effect on LPL activity. The change in LPL activity was maximal at 72 h and was accompanied by a decrease in LPL protein and LPL synthetic rate but no change in LPL mRNA, suggesting regulation at the level of translation. However, PKC depletion resulted in no change in the polysome profile, indicating that translation initiation was not affected. However, the addition of cytoplasmic extracts from adipocytes treated with 12-O-tetradecanoylphorbol-13-acetate or PKC␣ antisense oligomers inhibited LPL translation in vitro. This inhibition of LPL translation in vitro was lost when the LPL mRNA transcript did not contain nucleotides 1599 -3200, thus implicating the 3-untranslated region of LPL in the regulation of translation by PKC depletion. Both LPL activity and Raf1 activity were decreased in parallel following depletion of either total PKC or specific inhibition of PKC␣. An antisense oligonucleotide to RAF1, which inhibited RAF1 activity, also inhibited LPL activity by 48 ؎ 10%, and this decrease in LPL activity was not accompanied by a change in LPL mRNA. Cells were treated with U0126, a specific inhibitor of the ERK-activating kinases MEK1 and MEK2. Although U0126 inhibited ERK1 and ERK2 phosphorylation, U0126 had no effect on LPL activity, indicating that MEK/ERK pathways were not involved in this mechanism of LPL regulation. Together, these data indicate that PKC␣ and RAF1 are important in the translational regulation of LPL in adipocytes and that the mechanism of regulation is probably through an ERK-independent pathway.

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Section: Pkc Isoformsmentioning

confidence: 67%

Regulation of Lipoprotein Lipase by Protein Kinase Cα in 3T3-F442A Adipocytes

Ranganathan¹,

Song²,

Dean³

et al. 2002

Journal of Biological Chemistry

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“…The adipocyte differentiation of 3T3L1 cells is known to be mediated through various signal transduction pathways by hormones, growth factors, and cytokines (Ailhaud, 1997;Kim et al, 2001;Koutnikova and Auwerx, 2001). Transcription factors, such as CCAAT/enhancer binding proteins and peroxisome proliferator-activated receptors were also found to be involved in adipocyte differentiation (Holst and Grimaldi, 2002), through many different signal transduction pathways, involving, phosphatidylinositol 3-kinase (PI3K), MAPKs, cAMP, steroid hormones, and protein kinase C (Farese et al, 1992;Frevert and Kahn, 1996;Engelman et al, 1998;Aubert et al, 1999). Of the inhibitors used to block specific signal transduction pathways, we found that NAC and LY 294002 effectively inhibited lipid droplet formation and MT-II induction during adipocyte differentiation in 3T3L1 cells.…”

Section: Discussionmentioning

confidence: 99%

“…In an attempt to find a critical signaling pathway involved in adipose differentiation in 3T3L1 cells, a variety of inhibitors, namely, PD 98059 (an MEK inhibitor) (Aubert et al, 1999), SB 203580 (a p38 kinase inhibitor) (Engelman et al, 1998), LY 294002 (a phosphatidyinositol 3-kinase inhibitor) (Gregoire et al, 1998), H9 (a protein kinase A and protein kinase C inhibitor) (Farese et al, 1992;Zhang et al, 2002), hydroxyurea (a G1/G0 arrest inhibitor) (Tang et al, 2003), and genistein (a tyrosine kinase inhibitor) (Harmon et al, 2002), and antioxidants (Mahadev et al, 2002), such as NAC, GSH, vitamin C, and retinoic acid, were pretreated and lipid droplet formation was estimated by oil red O staining. Notably, NAC and LY 294002 inhibited lipid droplet formation in 3T3L1 cells (Figure 3).…”

Section: Roles Of Mt-ii In the Adipocyte Differentiation Of 3t3l1 Prementioning

confidence: 99%

Association of anti-obesity activity of N-acetylcysteine with metallothionein-II down-regulation

Kim

Ryu²,

Chung³

et al. 2006

Exp Mol Med

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People with upper body or visceral obesity have a much higher risk of morbidity and mortality from obesity-related metabolic disorders than those with lower body obesity. In an attempt to develop therapeutic strategies targeting visceral obesity, depotspecific differences in the expression of genes in omental and subcutaneous adipose tissues were investigated by DNA array technology, and their roles in adipocyte differentiation were further examined. We found that levels of metallothionein-II (MT-II) mRNA and protein expression were higher in omental than in subcutaneous adipose tissues. The study demonstrates that MT-II may play an important role in adipocyte differentiation of 3T3L1 preadipocytes, and that N-acetylcysteine (NAC) inhibits the adipocyte differentiation of 3T3L1 cells by repressing MT-II in a time-and dose-dependent manner. Furthermore, the intraperitoneal administration of NAC to rats and mice resulted in a reduction of body weights, and a marked reduction in visceral fat tissues. These results suggest that MT-II plays important roles in adipogenesis, and that NAC may be useful as an anti-obesity drug or supplement.

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“…Its activation by insulin was noted early on in rat skeletal muscle tissues and adipocytes, as well as in HIRC-B cells and BC3H-1 myocytes [41,[115][116][117]. Like PKCβII, PKCε is also resistant to phorbol ester-induced down-regulation in HIRC-B fibroblasts, suggesting that PKCε resides in a specialized compartment in cells.…”

Section: Pkcεmentioning

confidence: 99%

Specific protein kinase C isoforms as transducers and modulators of insulin signaling

Sampson

Cooper

2006

Molecular Genetics and Metabolism

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Recent studies implicate specific PKC isoforms in the insulin-signaling cascade. Insulin activates PKCsα, βII, δ and ζ in several cell types. In addition, as will be documented in this review, certain members of the PKC family may also be activated and act upstream of PI3 and MAP kinases. Each of these isoforms has been shown one way or another either to mimic or to modify insulin-stimulated effects in one or all of the insulin-responsive tissues. Moreover, each of the isoforms has been shown to be activated by insulin stimulation or conditions important for effective insulin stimulation. Studies attempting to demonstrate a definitive role for any of the isoforms have been performed on different cells, ranging from appropriate model systems for skeletal muscle, liver and fat, such as primary cultures, and cell lines and even in vivo studies, including transgenic mice with selective deletion of specific PKC isoforms. In addition, studies have been done on certain expression systems such as CHO or HEK293 cells, which are far removed from the tissues themselves and serve mainly as vessels for potential protein-protein interactions. Thus, a clear picture for many of the isoforms remains elusive in spite of over two decades of intensive research. The recent intrusion of transgenic and precise molecular biology technologies into the research armamentarium has opened a wide range of additional possibilities for direct involvement of individual isoforms in the insulin signaling cascade. As we hope to discuss within the context of this review, whereas many of the long soughtafter answers to specific questions are not yet clear, major advances have been made in our understanding of precise roles for individual PKC isoforms in mediation of insulin effects. In this review, in which we shall focus our attention on isoforms in the conventional and novel categories, a clear case will be made to show that these isoforms are not only expressed but are importantly involved in regulation of insulin metabolic effects.

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Effects of insulin and phorbol esters on subcellular distribution of protein kinase C isoforms in rat adipocytes

Cited by 67 publications

References 13 publications

Regulation of Lipoprotein Lipase by Protein Kinase Cα in 3T3-F442A Adipocytes

Regulation of Lipoprotein Lipase by Protein Kinase Cα in 3T3-F442A Adipocytes

Association of anti-obesity activity of N-acetylcysteine with metallothionein-II down-regulation

Specific protein kinase C isoforms as transducers and modulators of insulin signaling

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