Selective Activation of Mitogen-Activated Protein (MAP) Kinase Kinase 3 and p38α MAP Kinase Is Essential for Cyclic AMP-Dependent UCP1 Expression in Adipocytes

Department of Psychiatry and Behavioral Sciences, Duke University Medical Center, Durham, North Carolina 27710, USA.
Molecular and Cellular Biology (Impact Factor: 4.78). 08/2005; 25(13):5466-79. DOI: 10.1128/MCB.25.13.5466-5479.2005
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The sympathetic nervous system regulates the activity and expression of uncoupling protein 1 (UCP1) through the three beta-adrenergic receptor subtypes and their ability to raise intracellular cyclic AMP (cAMP) levels. Unexpectedly, we recently discovered that the cAMP-dependent regulation of multiple genes in brown adipocytes, including Ucp1, occurred through the p38 mitogen-activated protein kinases (MAPK) (W. Cao, K. W. Daniel, J. Robidoux, P. Puigserver, A. V. Medvedev, X. Bai, L. M. Floering, B. M. Spiegelman, and S. Collins, Mol. Cell. Biol. 24:3057-3067, 2004). However, no well-defined pathway linking cAMP accumulation or cAMP-dependent protein kinase (PKA) to p38 MAPK has been described. Therefore, in the present study using both in vivo and in vitro models, we have initiated a retrograde approach to define the required components, beginning with the p38 MAPK isoforms themselves and the MAP kinase kinase(s) that regulates them. Our strategy included ectopic expression of wild-type and mutant kinases as well as targeted inhibition of gene expression using small interfering RNA. The results indicate that the beta-adrenergic receptors and PKA lead to a highly selective activation of the p38alpha isoform of MAPK, which in turn promotes Ucp1 gene transcription. In addition, this specific activation of p38alpha relies solely on the presence of MAP kinase kinase 3, despite the expression in brown fat of MKK3, -4, and -6. Finally, of the three scaffold proteins of the JIP family expressed in brown adipocytes, only JIP2 co-immunoprecipitates p38alpha MAPK and MKK3. Therefore, in the brown adipocyte the recently described scaffold protein JIP2 assembles the required factors MKK3 and p38alpha MAPK linking PKA to the control of thermogenic gene expression.

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Available from: Jacques Robidoux, Jun 23, 2014
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    • "Glucagon also increases the hepatic activity of p38 MAPK via a PKA-dependent mechanism [46], [47]. To investigate the role of p38 MAPK in mediating the glucagon-induced increase in FGF21 secretion, experiments were performed using the selective and cell-permeable p38 MAPK inhibitor, SB203580 [48]. "
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    ABSTRACT: Previous studies have shown that whole body deletion of the glucagon receptor suppresses the ability of starvation to increase hepatic fibroblast growth factor 21 (FGF21) expression and plasma FGF21 concentration. Here, we investigate the mechanism by which glucagon receptor activation increases hepatic FGF21 production. Incubating primary rat hepatocyte cultures with glucagon, dibutyryl cAMP or forskolin stimulated a 3-4-fold increase in FGF21 secretion. The effect of these agents on FGF21 secretion was not associated with an increase in FGF21 mRNA abundance. Glucagon induction of FGF21 secretion was additive with the stimulatory effect of a PPARα activator (GW7647) on FGF21 secretion. Inhibition of protein kinase A (PKA) and downstream components of the PKA pathway [i.e. AMP-activated protein kinase and p38 MAPK] suppressed glucagon activation of FGF21 secretion. Incubating hepatocytes with an exchange protein directly activated by cAMP (EPAC)-selective cAMP analog [i.e. 8-(4-chlorophenylthio)-2'-O-methyladenosine-3', 5'-cyclic monophosphate (cpTOME)], stimulated a 3.9-fold increase FGF21 secretion, whereas inhibition of the EPAC effector, Rap1, suppressed glucagon activation of FGF21 secretion. Treatment of hepatocytes with insulin also increased FGF21 secretion. In contrast to glucagon, insulin activation of FGF21 secretion was associated with an increase in FGF21 mRNA abundance. Glucagon synergistically interacted with insulin to stimulate a further increase in FGF21 secretion and FGF21 mRNA abundance. These results demonstrate that glucagon increases hepatic FGF21 secretion via a posttranscriptional mechanism and provide evidence that both the PKA branch and EPAC branch of the cAMP pathway play a role in mediating this effect. These results also identify a novel synergistic interaction between glucagon and insulin in the regulation of FGF21 secretion and FGF21 mRNA abundance. We propose that this insulin/glucagon synergism plays a role in mediating the elevation in FGF21 production during starvation and conditions related to metabolic syndrome.
    PLoS ONE 04/2014; 9(4):e94996. DOI:10.1371/journal.pone.0094996 · 3.23 Impact Factor
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    • "Some studies have hinted that UCP1 activity and expression in BAT can be activated by p38/MAPK, AMPK, PI3K, and cAMP-dependent PKA (Robidoux et al., 2005; Tseng et al., 2008). In addition, PGC-1 is induced by cold exposure or adrenergic stimulation in BAT but not in WAT, and ectopic expression of PGC-1a in WAT induces the expression of UCP1 (Tseng et al., 2008). "
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    • "The components of the signaling cascade and the transcription factors beyond cAMP to the UCP1 gene have remained elusive for years. More recently, p38 mitogenactivated protein kinase (MAPK) was demonstrated to play a central role in this response [40] [41]. It was shown that, in brown adipocytes, the cAMP-dependent activation of protein kinase A (PKA) leads to p38 MAPK activation; and two important downstream substrates of p38 MAPK for UCP1 gene expression were identified: activating transcription factor 2 (ATF-2), which, following phosphorylation by p38 MAPK, drives transcription of the UCP1 and the PPAR coactivator-1α (PGC-1α) genes through the cAMP-regulatory elements in their respective promoter; and the PGC-1α protein itself, which, following phosphorylation by p38 MAPK, drives transcription of the UCP1 gene by co-activating the PPARγ bound to the UCP1 gene promoter. "
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    ABSTRACT: The role of brown adipose tissue in the regulation of energy balance and maintenance of body weight is well known in rodents. Recently, interest in this tissue has re-emerged due to the realization of active brown-like adipose tissue in adult humans and inducible brown-like adipocytes in white adipose tissue depots in response to appropriate stimuli ("browning process"). Brown-like adipocytes that appear in white fat depots have been called "brite" (from brown-in-white) or "beige" adipocytes and have characteristics similar to brown adipocytes, in particular the capacity for uncoupled respiration. There is controversy as to the origin of these brite/beige adipocytes, but regardless of this, induction of the browning of white fat represents an attractive potential strategy for the management and treatment of obesity and related complications. Here, the different physiological, pharmacological and dietary determinants that have been linked to white-to-brown fat remodelling and the molecular mechanisms involved are reviewed in detail. In the light of available data, interesting therapeutic perspectives can be expected from the use of specific drugs or food compounds able to induce a program of brown fat differentiation including uncoupling protein 1 expression and enhancing oxidative metabolism in white adipose cells. However, additional research is needed, mainly focused on the physiological relevance of browning and its dietary control, where the use of ferrets and other non-rodent animal models with a more similar adipose tissue organization and metabolism to humans could be of much help. This article is part of a Special Issue entitled Brown and White Fat: From Signaling to Disease.
    Biochimica et Biophysica Acta 12/2012; 1831(5). DOI:10.1016/j.bbalip.2012.12.002 · 4.66 Impact Factor
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