Functional Interactions of Phosphatidylinositol 3-Kinase with GTPase-Activating Protein in 3T3-L1 Adipocytes

Depaolo, D.; Reusch, Jane E.B.; Carel, Kirstin; Bhuripanyo, Penpun; Leitner, J. Wayne; Draznin, Boris

doi:10.1128/mcb.16.4.1450

Cited by 29 publications

(24 citation statements)

References 68 publications

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“…This controversial finding might be explained by tissue-specific differences in interactions of signalling molecules (6). In 3T3-L1 adipocytes, the PI3K inhibitor LY294002 blocks activation of p21 ras and decreases MAP kinase activation by insulin (6). However, we do not see MAP kinase activation by increased PI3K activity alone, suggesting that other signalling events need to be stimulated in parallel.…”

Section: Discussionmentioning

confidence: 62%

“…Similarly, activated PI3K was found not to affect MAP kinase activation in COS-7 cells (21). Indeed, the activation of PI3K might have a more permissive role for p21 ras activation by functional interaction with the GTPase-activating protein in 3T3-L1 adipocytes (6).…”

Section: Discussionmentioning

confidence: 92%

Section: Discussionmentioning

confidence: 99%

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Differential Effects of Constitutively Active Phosphatidylinositol 3-Kinase on Glucose Transport, Glycogen Synthase Activity, and DNA Synthesis in 3T3-L1 Adipocytes

Frevert

Kahn

1997

Molecular and Cellular Biology

165

122

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Phosphatidylinositol 3-kinase (PI3K) activation is necessary for many insulin-induced metabolic and mitogenic responses. However, it is unclear whether PI3K activation is sufficient for any of these effects. To address this question we increased PI3K activity in differentiated 3T3-L1 adipocytes by adenovirus-mediated expression of both the inter-SH2 region of the regulatory p85 subunit of PI3K (iSH2) and the catalytic p110␣ subunit (p110). Coexpression resulted in PI3K activity that exceeded insulin-stimulated activity by two-to fivefold in cytosol, total membranes, and the low density microsome (LDM) fraction, the site of greatest insulin stimulation. While insulin increased glucose transport 15-fold, coexpression of iSH2-p110 increased transport 5.2-؎ 0.7-fold with a parallel increase in GLUT4 translocation to the plasma membrane. Constitutive activation of PI3K had no effect on maximally insulin-stimulated glucose transport. Neither basal nor insulinstimulated activity of glycogen synthase or mitogen-activated protein kinase was altered by iSH2-p110 coexpression. DNA synthesis was increased twofold by insulin in control 3T3-L1 adipocytes transduced with ␤-galactosidase-encoding recombinant adenovirus, while iSH2-p110 coexpression increased DNA synthesis fivefold. These data indicate that (i) increased PI3K activity is sufficient to activate some but not all metabolic responses to insulin, (ii) activation of PI3K to levels exceeding the effect of insulin in adipocyte LDM results in only a partial stimulation of glucose transport, and (iii) increased PI3K activity in the absence of growth factor or oncoprotein stimulation is a potent stimulus of DNA synthesis.Insulin is pivotal in the regulation of glucose homeostasis. One of the primary actions of insulin is the stimulation of glucose transport into insulin-sensitive tissues by eliciting translocation of the major insulin-responsive glucose transporter, GLUT4, from an intracellular pool to the plasma membrane. Resistance to this stimulatory effect of insulin is a major pathologic feature of both type I and type II diabetes (5, 43). In most insulin-resistant states the expression of GLUT4 in skeletal muscle, the major site of insulin-stimulated glucose disposal, is not reduced (16), suggesting a defect in the signalling cascade or the cellular elements linking the insulin receptor to GLUT4 translocation, fusion with the plasma membrane, and/or activation (15). Although the number of molecules known to be involved in insulin signalling is increasing rapidly (2), the exact signalling pathways responsible for glucose transporter translocation remain to be defined. Ultimately these pathways could be attractive targets for novel therapeutic strategies to reduce or prevent insulin resistance.Insulin stimulation of phosphatidylinositol 3-kinase (PI3K) was first observed by Ruderman et al. (31). Subsequently, several studies using either the PI3K inhibitors wortmannin and LY 294002 (3, 27) or dominant negative approaches (22) demonstrated that stimulation of PI3K activ...

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Section: Discussionmentioning

confidence: 62%

Section: Discussionmentioning

confidence: 92%

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Differential Effects of Constitutively Active Phosphatidylinositol 3-Kinase on Glucose Transport, Glycogen Synthase Activity, and DNA Synthesis in 3T3-L1 Adipocytes

Frevert

Kahn

1997

Molecular and Cellular Biology

165

122

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“…Studies have in fact shown that p85 can be recruited to tyrosine-phosphorylated proteins independent of p110 (41). Other studies have demonstrated that p85 is able to couple to p120 Gap and Grb2 (42,43), proteins involved in the regulation of Ras activation. As carbachol has been shown to activate Ras in other cell systems (44), it is possible that calcium agonists activate the Ras pathway via coupling to p85.…”

Section: Effect Of Wortmannin On Calcium-dependent Chloride Secretionmentioning

confidence: 98%

Phosphatidylinositol 3-Kinase Mediates the Inhibitory Effect of Epidermal Growth Factor on Calcium-dependent Chloride Secretion

Uribe¹,

Keely

Traynor‐Kaplan³

et al. 1996

Journal of Biological Chemistry

107

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Epidermal growth factor (EGF) and carbachol both inhibit calcium-activated chloride secretion by the human colonic epithelial cell line, T 84 . Although the inhibitory mechanism for the carbachol effect involves the 3,4,5,6-isomer of inositol tetrakisphosphate, the mechanisms responsible for the EGF effect have not yet been fully elucidated. Here, we studied the role of phosphatidylinositol 3-kinase (PI 3-kinase) in the inhibitory effect of EGF. The PI 3-kinase inhibitor, wortmannin, slightly increased basal chloride secretion and potentiated the secretory response to thapsigargin. Wortmannin also partially reversed EGF-induced, but not carbachol-induced, inhibition of thapsigargin-stimulated chloride secretion. Wortmannin alone had no effect on carbacholor histamine-induced chloride secretion and completely reversed EGF-induced inhibition of the secretory response to these agonists. EGF, carbachol, histamine, and thapsigargin all increased levels of the 85-kDa regulatory subunit of PI 3-kinase in antiphosphotyrosine immunoprecipitates. However, only EGF significantly increased levels of the 110-kDa catalytic subunit. Furthermore, only EGF increased PI 3-kinase activity in an in vitro kinase assay. High levels of phosphatidylinositol (3)-monophosphate were present in unstimulated cells and significantly reduced by wortmannin. EGF, but not carbachol, rapidly increased levels of phosphatidylinositol (3,4)-bisphosphate and phosphatidylinositol (3,4,5)-trisphosphate. Production of these lipids was also sensitive to wortmannin. Our data suggest that EGF activates PI 3-kinase and that its lipid products may mediate the inhibitory effect of EGF on calcium-dependent chloride secretion. Our data also suggest that a phosphatidylinositol-specific 3-kinase activity is present in unstimulated T 84 cells and may regulate production of phosphatidylinositol (3)-monophosphate and basal secretory tone.The regulation of intestinal epithelial chloride transport is under the control of neural, humoral, and immune-related mechanisms (1). As the active transepithelial movement of chloride into the gastrointestinal lumen is an important mechanism governing the passive movement of water, breakdown in the regulation of this process can lead to excessive secretory responses, resulting in diarrhea. Our laboratory has focused on understanding the intracellular mechanisms responsible for the regulation of chloride secretion.Chloride secretion is positively regulated via two predominant pathways, utilizing cyclic nucleotides or calcium as second messengers, respectively (1). Calcium-dependent secretion can be evoked experimentally by agents such as the muscarinic agonist, carbachol, histamine, or the calcium ATPase inhibitor, thapsigargin. All of these stimuli elevate cytoplasmic calcium concentrations, which in turn evokes secretion. Moreover, we have shown that calcium-dependent chloride secretion is also subject to a number of negative regulatory influences. Thus carbachol, while itself serving as an initial agonist of chloride secretion, ...

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“…RasGAP also binds the Src-related family of kinases, including Src, Hck, Fyn, and Lck, through its Nterminal proline-rich region, serving as a substrate for these kinases (17). It binds Rab5 and stimulates its activity (18), whereas, it co-precipitates with p85 phosphatidylinositol 3-kinase, which inhibits its activity (19). It binds annexin VI through its C2, Ca 2ϩ -dependent, lipid-binding domain (20), the significance of which is still unknown.…”

mentioning

confidence: 99%

An Alliance between Ras GTPase-activating Protein, Filamin C, and RasGTPase-activating Protein SH3 Domain-binding Protein Regulates MyocyteGrowth

Lypowy¹,

Chen²,

Abdellatif³

2005

Journal of Biological Chemistry

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We have previously reported that Ras GTPase-activating protein (RasGAP) is involved in a pathway that regulates total cellular mRNA and protein synthesis in cardiac myocytes. A yeast two-hybrid screen resulted in identification of filamin C (FLN-C) as one of its targets. Knockdown of RasGAP or FLN-C, or severing their interaction, resulted in down-regulation of the RNA polymerase II kinase, cyclin-dependent kinase 7 (Cdk7). This appeared to be provoked by the release of cdk7 mRNA from RasGAP SH3 domain-binding protein, G3BP, and its subsequent degradation. In parallel, myocyte growth was also inhibited. On the other hand, overexpression of RasGAP induced a Cdk7-and FLN-C-dependent growth. Thus, we propose that the physical interaction between RasGAP and FLN-C facilitates an interaction between G3BP and cdk7 mRNA. This results in stabilization of cdk7 mRNA, an increase in its protein, which is required for cell growth.

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Functional Interactions of Phosphatidylinositol 3-Kinase with GTPase-Activating Protein in 3T3-L1 Adipocytes

Cited by 29 publications

References 68 publications

Differential Effects of Constitutively Active Phosphatidylinositol 3-Kinase on Glucose Transport, Glycogen Synthase Activity, and DNA Synthesis in 3T3-L1 Adipocytes

Differential Effects of Constitutively Active Phosphatidylinositol 3-Kinase on Glucose Transport, Glycogen Synthase Activity, and DNA Synthesis in 3T3-L1 Adipocytes

Phosphatidylinositol 3-Kinase Mediates the Inhibitory Effect of Epidermal Growth Factor on Calcium-dependent Chloride Secretion

An Alliance between Ras GTPase-activating Protein, Filamin C, and RasGTPase-activating Protein SH3 Domain-binding Protein Regulates MyocyteGrowth

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