Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

In normal and obese humans, lipid mobilization and systemic nonesterified fatty acid levels are thought to be acutely controlled by catecholamines (ie, epinephrine and norepinephrine) and insulin. Natriuretic peptides (NPs) are known to play a key role in the regulation of salt and water balance and blood pressure homeostasis. They are involved in the pathophysiology of hypertension and heart failure. NPs have recently been found to exert potent lipolytic effects (ie, activating the breakdown of stored triacylglycerols) in isolated human fat cells and to promote lipid mobilization in vivo. Atrial natriuretic peptide increases the intracellular 3', 5'-cyclic guanosine monophosphate (cGMP) concentration which activates cGMP-dependent protein kinase leading to perilipin and hormone-sensitive lipase phosphorylation and lipolysis. NPs promote lipid mobilization when administered intravenously. NPs are also responsible for the residual lipid-mobilizing action observed under oral beta-blockade in subjects performing physical exercise. NPs are therefore novel factors which may open promising research pathways to explain the control of lipid mobilization in physiological and pathological conditions. The metabolic impact of altered production and circulation of NPs remains to be established. The potential influence of NPs on the development of lipid disorders, obesity-related cardiovascular events, and cardiac cachexia will be discussed in this review.
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PMID:An unsuspected metabolic role for atrial natriuretic peptides: the control of lipolysis, lipid mobilization, and systemic nonesterified fatty acids levels in humans. 1612 23

Hormones mobilize intracellular second messengers and initiate signalling cascades involving protein kinases and phosphatases, which are often spatially compartmentalized by anchoring proteins to increase signalling specificity. These scaffold proteins may themselves be modulated by hormones. In adipocytes, stimulation of beta-adrenergic receptors increases cyclic AMP levels and activates protein kinase A (PKA), which stimulates lipolysis by phosphorylating hormone-sensitive lipase and perilipin. Acute insulin treatment activates phosphodiesterase 3B, reduces cAMP levels and quenches beta-adrenergic receptor signalling. In contrast, chronic hyperinsulinaemic conditions (typical of type 2 diabetes) enhance beta-adrenergic receptor-mediated cAMP production. This amplification of cAMP signalling is paradoxical because it should enhance lipolysis, the opposite of the known short-term effect of hyperinsulinaemia. Here we show that in adipocytes, chronically high insulin levels inhibit beta-adrenergic receptors (but not other cAMP-elevating stimuli) from activating PKA. We measured this using an improved fluorescent reporter and by phosphorylation of endogenous cAMP-response-element binding protein (CREB). Disruption of PKA scaffolding mimics the interference of insulin with beta-adrenergic receptor signalling. Chronically high insulin levels may disrupt the close apposition of beta-adrenergic receptors and PKA, identifying a new mechanism for crosstalk between heterologous signal transduction pathways.
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PMID:Insulin disrupts beta-adrenergic signalling to protein kinase A in adipocytes. 1617 93

In mature adipocytes, triglyceride is stored within lipid droplets, which are coated with the protein perilipin, which functions to regulate lipolysis by controlling lipase access to the droplet in a hormone-regulatable fashion. Adipocyte differentiation-related protein (ADRP) is a widely expressed lipid droplet binding protein that is coexpressed with perilipin in differentiating fat cells but is minimally present in fully differentiated cultured adipocytes. We find that fibroblasts ectopically expressing C/EBPalpha (NIH-C/EBPalpha cells) differentiate into mature adipocytes that simultaneously express perilipin and ADRP. In response to isoproterenol, perilipin is hyperphosphorylated, lipolysis is enhanced, and subsequently, ADRP expression increases coincident with it surrounding intracellular lipid droplets. In the absence of lipolytic stimulation, inhibition of proteasomal activity with MG-132 increased ADRP levels to those of cells treated with 10 mum isoproterenol, but ADRP does not surround the lipid droplet in the absence of lipolytic stimulation. We overexpressed a perilipin A construct in NIH-C/EBPalpha cells where the six serine residues known to be phosphorylated by protein kinase A were changed to alanine (Peri A Delta1-6). These cells show no increase in ADRP expression in response to isoproterenol. We propose that ADRP can replace perilipin on existing lipid droplets or those newly formed as a result of fatty acid reesterification, under dynamic conditions of hormonally stimulated lipolysis, thus preserving lipid droplet morphology/structure.
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PMID:Dynamics of lipid droplet-associated proteins during hormonally stimulated lipolysis in engineered adipocytes: stabilization and lipid droplet binding of adipocyte differentiation-related protein/adipophilin. 1623 56

Perilipin A is a key regulator of triacylglycerol storage and hydrolysis in adipocytes; phosphorylation of perilipin A by protein kinase A facilitates maximal lipolysis. Chronic stimulation of lipolysis in 3T3-L1 adipocytes causes large perinuclear lipid droplets to fragment into myriad dispersed perilipin A-covered microlipid droplets. In cultured fibroblasts stably expressing ectopic perilipin A, clustered lipid droplets disperse throughout the cytoplasm upon incubation of the cells with forskolin and isobutylmethylxanthine (IBMX) to elevate levels of cAMP and activate protein kinase A, mirroring events observed in adipocytes. Furthermore, diethylum-belliferyl phosphate inhibits stimulated lipolysis but not the dispersion of lipid droplets, suggesting that products of lipolysis are not required for this remodeling process. We hypothesized that protein kinase A-mediated phosphorylation of perilipin A triggers the remodeling of lipid droplets. The mutation of serine 492 of perilipin A to alanine prevented the dispersion of clustered lipid droplets in fibroblasts stably expressing the mutated perilipin upon incubation with forskolin and IBMX. In contrast, the substitution of serines 81, 222, 276, or 433 with alanine, either singly or in combinations, did not affect the protein kinase A-mediated remodeling of lipid droplets. Interestingly, substitution of serines 433, 492, and 517 of perilipin A with glutamic acid residues blocked the dispersion of clustered lipid droplets in cells incubated with forskolin and IBMX, indicating that the addition of a negative charge does not mimic a phosphate group. We conclude that protein kinase A-mediated phosphorylation of serine 492 of perilipin A drives the fragmentation and dispersion of lipid droplets.
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PMID:The phosphorylation of serine 492 of perilipin a directs lipid droplet fragmentation and dispersion. 1648 86

Lipolysis is primarily regulated by protein kinase A (PKA), which phosphorylates perilipin and hormone-sensitive lipase (HSL), and causes translocation of HSL from cytosol to lipid droplets in adipocytes. Perilipin coats lipid droplet surface and assumes to prevent lipase access to triacylglycerols, thus inhibiting basal lipolysis; phosphorylated perilipin facilitates lipolysis on PKA activation. Here, we induced lipolysis in primary rat adipocytes by inhibiting protein serine/threonine phosphatase with specific inhibitors, okadaic acid and calyculin. The incubation with calyculin promotes incorporation of 32Pi into perilipins, thus, confirming that perilipin is hyperphosphorylated. The lipolysis response to calyculin is gradually accompanied by increased accumulation of phosphorylated perilipin A in a concentration- and time-responsive manner. When perilipin phosphorylation is abrogated by the addition of N-ethylmaleimide, lipolysis ceases. Different from a considerable translocation of HSL upon PKA activation with isoproterenol, calyculin does not alter HSL redistribution in primary or differentiated adipocytes, as confirmed by both immunostaining and immunoblotting. Thus, we suggest that inhibition of the phosphatase by calyculin activates lipolysis via promoting perilipin phosphorylation rather than eliciting HSL translocation in adipocytes. Further, we show that when the endogenous phosphatase is inhibited by calyculin, simultaneous PKA activation with isoproterenol converts most of the perilipin to the hyperphosphorylated species, and induces enhanced lipolysis. Apparently, as PKA phosphorylates perilipin and stimulates lipolysis, the phosphatase acts to dephosphorylate perilipin and attenuate lipolysis. This suggests a two-step strategy governed by a kinase and a phosphatase to modulate the steady state of perilipin phosphorylation and hence the lipolysis response to hormonal stimulation.
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PMID:Calyculin and okadaic acid promote perilipin phosphorylation and increase lipolysis in primary rat adipocytes. 1654 98

Hormone-sensitive lipase (HSL) is the predominant lipase effector of catecholamine-stimulated lipolysis in adipocytes. HSL-dependent lipolysis in response to catecholamines is mediated by protein kinase A (PKA)-dependent phosphorylation of perilipin A (Peri A), an essential lipid droplet (LD)-associated protein. It is believed that perilipin phosphorylation is essential for the translocation of HSL from the cytosol to the LD, a key event in stimulated lipolysis. Using adipocytes retrovirally engineered from murine embryonic fibroblasts of perilipin null mice (Peri-/- MEF), we demonstrate by cell fractionation and confocal microscopy that up to 50% of cellular HSL is LD-associated in the basal state and that PKA-stimulated HSL translocation is fully supported by adenoviral expression of a mutant perilipin lacking all six PKA sites (Peri Adelta1-6). PKA-stimulated HSL translocation was confirmed in differentiated brown adipocytes from perilipin null mice expressing an adipose-specific Peri Adelta1-6 transgene. Thus, PKA-induced HSL translocation was independent of perilipin phosphorylation. However, Peri Adelta1-6 failed to enhance PKA-stimulated lipolysis in either MEF adipocytes or differentiated brown adipocytes. Thus, the lipolytic action(s) of HSL at the LD surface requires PKA-dependent perilipin phosphorylation. In Peri-/- MEF adipocytes, PKA activation significantly enhanced the amount of HSL that could be cross-linked to and co-immunoprecipitated with ectopic Peri A. Notably, this enhanced cross-linking was blunted in Peri-/- MEF adipocytes expressing Peri Adelta1-6. This suggests that PKA-dependent perilipin phosphorylation facilitates (either direct or indirect) perilipin interaction with LD-associated HSL. These results redefine and expand our understanding of how perilipin regulates HSL-mediated lipolysis in adipocytes.
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PMID:Perilipin promotes hormone-sensitive lipase-mediated adipocyte lipolysis via phosphorylation-dependent and -independent mechanisms. 1659 69

Human fat cell lipolysis was considered until recently to be an exclusive cAMP/protein-kinase A (PKA)-regulated metabolic pathway under the control of catecholamines and insulin. Moreover, exercise-induced lipid mobilization in humans was considered to mainly depend on catecholamine action and interplay between fat cell beta- and alpha2-adrenergic receptors controlling adenylyl cyclase activity and cAMP production. We have recently demonstrated that natriuretic peptides stimulate lipolysis and contribute to the regulation of lipid mobilization in humans. Atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP) stimulate lipolysis in human isolated fat cells. Activation of the adipocyte plasma membrane type A guanylyl cyclase receptor (NPR-A), increase in intracellular guanosine 3',5'-cyclic monophosphate (cyclic GMP) levels and activation of hormone-sensitive lipase mediate the action of ANP. ANP does not modulate cAMP production and PKA activity. Increment of cGMP induces the phosphorylation of hormone-sensitive lipase and perilipin A via the activation of a cGMP dependent protein kinase-I (cGK-I). Plasma concentrations of glycerol and nonesterified fatty acids are increased by i.v. infusion of ANP in humans. Physiological relevance of the ANP-dependent pathway was demonstrated in young subjects performing physical exercise. ANP plays a role in conjunction with catecholamines in the control of exercise-induced lipid mobilization. This pathway becomes of major importance when subjects are submitted to chronic treatment with a beta-blocker. Oral beta-adrenoceptor blockade suppresses the beta-adrenergic component of catecholamine action in fat cells and potentiates exercise-induced ANP release by the heart. These findings may have several implications whenever natriuretic peptide secretion is altered such as in subjects with left ventricular dysfunction, congestive heart failure and obesity.
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PMID:[Natriuretic peptides: a new lipolytic pathway in human fat cells]. 1659 2

Chronic ethanol consumption disrupts G protein-dependent signaling pathways in rat adipocytes. Because lipolysis in adipocytes is regulated by G protein-mediated cAMP signal transduction, we hypothesized that cAMP-regulated lipolysis may be vulnerable to long-term ethanol exposure. Male Wistar rats were fed a liquid diet containing ethanol as 35% of total calories or pair-fed a control diet that isocalorically substituted maltose dextrins for ethanol for 4 wk. Lipolysis was measured by glycerol release over 1 h with or without agonists in adipocytes isolated from epididymal fat. Chronic ethanol feeding decreased beta-adrenergic receptor-stimulated lipolysis, but had no effect on basal lipolysis. In response to beta-adrenergic activation, the early peak of cAMP accumulation was suppressed after ethanol feeding, although the basal cAMP concentration in adipocytes did not differ between pair- and ethanol-fed rats. The suppression in cAMP accumulation caused by ethanol feeding was associated with increased activity of phosphodiesterase 4. Chronic ethanol feeding also decreased beta-adrenergic receptor-stimulated protein kinase A activation and phosphorylation of its downstream proteins, perilipin A and hormone-sensitive lipase, the primary lipase-mediating lipolysis. In conclusion, these data suggest that chronic ethanol feeding increased phosphodiesterase 4 activity in adipocytes, resulting in decreased accumulation of cAMP in response to beta-adrenergic activation and a suppression of beta-adrenergic stimulation of lipolysis.
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PMID:Chronic ethanol feeding suppresses beta-adrenergic receptor-stimulated lipolysis in adipocytes isolated from epididymal fat. 1679 14

Perilipins are the proteins associating with the lipid droplets in adipocytes and steroidogenic cells. Unphosphorylated perilipins coat the surface of intracellular lipid droplets to form a barrier that prevents lipase from accessing to triacylglycerol core, thus suppressing lipolysis. Upon activation of protein kinase A (PKA), two proteins, hormone-sensitive lipase (HSL) and perilipins, are phosphorylated. The phosphorylated perilipin is required for inducing the translocation of HSL from the cytosol to the lipid droplets of adipocytes and is essential for the initiation of lipolytic reaction. It is proposed that phosphorylation of perilipin is a key step for the activation of lipolytic cascade via PKA and ERK signaling pathways. Dysregulation of perilipin involves in the pathogenesis of obesity, diabetes and atherosclerosis.
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PMID:[Perilipin associated with lipid droplets regulates lipolysis]. 1700 29

Phosphorylation of the lipid droplet-associated protein perilipin A (Peri A) mediates the actions of cyclic AMP-dependent protein kinase A (PKA) to stimulate triglyceride hydrolysis (lipolysis) in adipocytes. Studies addressing how Peri A PKA sites regulate adipocyte lipolysis have relied on non-adipocyte cell models, which express neither adipose triglyceride lipase (ATGL), the rate-limiting enzyme for triglyceride catabolism in mice, nor the "downstream" lipase, hormone-sensitive lipase (HSL). ATGL and HSL are robustly expressed by adipocytes that we generated from murine embryonic fibroblasts of perilipin knock-out mice. Adenoviral expression of Peri A PKA site mutants in these cells reveals that mutation of serine 517 alone is sufficient to abrogate 95% of PKA (forskolin)-stimulated fatty acid (FA) and glycerol release. Moreover, a "phosphomimetic" (aspartic acid) substitution at serine 517 enhances PKA-stimulated FA release over levels obtained with wild type Peri A. Studies with ATGL-and HSL-directed small hairpin RNAs demonstrate that 1) ATGL activity is required for all PKA-stimulated FA and glycerol release in murine embryonic fibroblast adipocytes and 2) all PKA-stimulated FA release in the absence of HSL activity requires serine 517 phosphorylation. These results provide the first demonstration that Peri A regulates ATGL-dependent lipolysis and identify serine 517 as the Peri A PKA site essential for this regulation. The contributions of other PKA sites to PKA-stimulated lipolysis are manifested only in the presence of phosphorylated or phosphomimetic serine 517. Thus, serine 517 is a novel "master regulator" of PKA-stimulated adipocyte lipolysis.
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PMID:Control of adipose triglyceride lipase action by serine 517 of perilipin A globally regulates protein kinase A-stimulated lipolysis in adipocytes. 1711 92


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