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1.
Oligomerization state-dependent hyperlipidemic effect of angiopoietin-like protein 4 总被引:4,自引:0,他引:4
Angiopoietin-like protein 4 (Angptl4) is the second member of the angiopoietin-like family of proteins previously shown to increase plasma triglyceride (TG) levels in vivo. We recently reported that Angptl4 is a variable-sized oligomer formed by intermolecular disulfide bonds and undergoes regulated proteolytic processing upon secretion. We now show that adenoviral overexpression of Angptl4 potently increases plasma TG levels by a mechanism independent of food intake or hepatic VLDL secretion. We determined that cysteine residues at positions 76 and 80 of Angptl4, conserved among mouse, rat, and human, are required to form higher order structures. By generating adenoviral expression vectors of Angptl4 containing different epitope tags at both N and C termini, we show that loss of oligomerization results in decreased stability of the N-terminal coiled-coil domain of Angptl4 as well as decreased ability to increase plasma TG levels, suggesting that intermolecular disulfide bond formation plays important roles in determining the magnitude of the hyperlipidemic effect of Angptl4. Because Angptl4 is more potent than Angptl3 in increasing plasma TG levels in mice, inappropriate oligomerization of Angptl4 could be associated with disorders of lipid metabolism in vivo. 相似文献
2.
Successful ex vivo expansion of hematopoietic stem cells (HSCs) would greatly benefit the treatment of disease and the understanding of crucial questions of stem cell biology. Here we show, using microarray studies, that the HSC-supportive mouse fetal liver CD3(+) cells specifically express the proteins angiopoietin-like 2 (Angptl2) and angiopoietin-like 3 (Angptl3). We observed a 24- or 30-fold net expansion of long-term HSCs by reconstitution analysis when we cultured highly enriched HSCs for 10 days in the presence of Angptl2 or Angptl3 together with saturating levels of other growth factors. The coiled-coil domain of Angptl2 was capable of stimulating expansion of HSCs. Furthermore, angiopoietin-like 5, angiopoietin-like 7 and microfibril-associated glycoprotein 4 also supported expansion of HSCs in culture. 相似文献
3.
Angiopoietin-like protein 3 and 4 (Angptl3 and Angptl4) are two members of the angiopoietin-like family of proteins. These two closely related proteins have been reported to similarly affect lipid metabolism through their capacity to inhibit lipoprotein lipase. We undertook a series of studies to compare the structure, function, and regulation of Angptl3 and Angptl4. Previously, we reported that Angptl4 exists as variable-sized oligomers that contain intermolecular disulfide bonds. We now have evidence that although there are no intermolecular disulfide bonds evident in Angptl3, higher molecular weight forms do exist. In addition, Angptl4 exhibits a widespread distribution of tissue expression, while Angptl3 is exclusively expressed in the liver. Treatments with various ligands of nuclear receptors reveal that Angptl3 is a target gene of liver X receptor, while Angptl4 expression is activated by ligands of all peroxisome proliferator-activated receptors. Expression of Angptl4 in adipose tissue and liver is induced by fasting, while Angptl3 expression is not appreciably affected by nutritional status. We suggest that the differential regulation of Angptl3 and Angptl4 by sites of expression, nutritional status, and ligands of nuclear receptors may confer unique roles of each in lipoprotein metabolism. 相似文献
4.
Li C 《Current opinion in lipidology》2006,17(2):152-156
PURPOSE OF REVIEW: Lipoprotein lipase activity in a given tissue is the rate limiting step for the uptake of triglyceride-derived fatty acids. Imbalances in the partitioning of fatty acids have major metabolic consequences. Given the central role of lipoprotein lipase in energy metabolism, the discovery of new molecules that affect the activity of lipoprotein lipase holds great potential for novel therapeutic targets. RECENT FINDINGS: Angiopoietin-like proteins 3 and 4 are two members of the angiopoietin-like family of proteins (Angptl). Unique within this family, Angptl3 and 4 inhibit lipoprotein metabolism via their ability to inhibit the activity of lipoprotein lipase. This review highlights recent studies on the biochemistry of Angptl3 and 4 as well as mouse models with selective overexpression of Angptl4 or global knockout of Angptl3, 4, or both. SUMMARY: Both angiopoietins and angiopoietin-like proteins share similar domain structures. Angptl3 and 4 are the only two members of this superfamily that inhibit lipoprotein lipase activity. However, Angptl3 and 4 are differentially regulated at multiple levels, suggesting non-redundant functions in vivo. Angptl3 and 4 are proteolytically processed into two halves and are differentially regulated by nuclear receptors. Transgenic overexpression of Angptl4 as well as knockout of Angptl3 or 4 demonstrate that these two proteins play essential roles in lipoprotein metabolism: liver-derived Angptl3 inhibits lipoprotein lipase activity primarily in the fed state, while Angptl4 plays important roles in both fed and fasted states. In addition, Angptl4 regulates the tissue-specific delivery of lipoprotein-derived fatty acids. Angptl4 is thus an endocrine or autocrine/paracarine inhibitor of lipoprotein lipase depending on its sites of expression. 相似文献
5.
Qiaoling Yao Mi-Kyung Shin Jonathan C. Jun Karen L. Hernandez Neil R. Aggarwal Jason R. Mock Jason Gay Luciano F. Drager Vsevolod Y. Polotsky 《Journal of lipid research》2013,54(4):1058-1065
Chronic intermittent hypoxia (CIH) inhibits plasma lipoprotein clearance and adipose lipoprotein lipase (LPL) activity in association with upregulation of an LPL inhibitor angiopoietin-like protein 4 (Angptl4). We hypothesize that CIH inhibits triglyceride (TG) uptake via Angptl4 and that an anti-Angptl4-neutralizing antibody would abolish the effects of CIH. Male C57BL/6J mice were exposed to four weeks of CIH or intermittent air (IA) while treated with Ab (30 mg/kg ip once a week). TG clearance was assessed by [H3]triolein administration retroorbitally. CIH delayed TG clearance and suppressed TG uptake and LPL activity in all white adipose tissue depots, brown adipose tissue, and lungs, whereas heart, liver, and spleen were not affected. CD146+ CD11b− pulmonary microvascular endothelial cells were responsible for TG uptake in the lungs and its inhibition by CIH. Antibody to Angptl4 decreased plasma TG levels and increased TG clearance and uptake into adipose tissue and lungs in both control and CIH mice to a similar extent, but did not reverse the effects of CIH. The antibody reversed the effects of CIH on LPL in adipose tissue and lungs. In conclusion, CIH inactivates LPL by upregulating Angptl4, but inhibition of TG uptake occurs predominantly via an Angptl4/LPL-independent mechanism. 相似文献
6.
Mandard S Zandbergen F van Straten E Wahli W Kuipers F Müller M Kersten S 《The Journal of biological chemistry》2006,281(2):934-944
Proteins secreted from adipose tissue are increasingly recognized to play an important role in the regulation of glucose metabolism. However, much less is known about their effect on lipid metabolism. The fasting-induced adipose factor (FIAF/angiopoietin-like protein 4/peroxisome proliferator-activated receptor gamma angiopoietin-related protein) was previously identified as a target of hypolipidemic fibrate drugs and insulin-sensitizing thiazolidinediones. Using transgenic mice that mildly overexpress FIAF in peripheral tissues we show that FIAF is an extremely powerful regulator of lipid metabolism and adiposity. FIAF overexpression caused a 50% reduction in adipose tissue weight, partly by stimulating fatty acid oxidation and uncoupling in fat. In addition, FIAF overexpression increased plasma levels of triglycerides, free fatty acids, glycerol, total cholesterol, and high density lipoprotein (HDL)-cholesterol. Functional tests indicated that FIAF overexpression severely impaired plasma triglyceride clearance but had no effect on very low density lipoprotein production. The effects of FIAF overexpression were amplified by a high fat diet, resulting in markedly elevated plasma and liver triglycerides, plasma free fatty acids, and plasma glycerol levels, and impaired glucose tolerance in FIAF transgenic mice fed a high fat diet. Remarkably, in mice the full-length form of FIAF was physically associated with HDL, whereas truncated FIAF was associated with low density lipoprotein. In human both full-length and truncated FIAF were associated with HDL. The composite data suggest that via physical association with plasma lipoproteins, FIAF acts as a powerful signal from fat and other tissues to prevent fat storage and stimulate fat mobilization. Our data indicate that disturbances in FIAF signaling might be involved in dyslipidemia. 相似文献
7.
8.
9.
Gray NE Lam LN Yang K Zhou AY Koliwad S Wang JC 《The Journal of biological chemistry》2012,287(11):8444-8456
Intracellular triacylglycerol (TG) hydrolysis and fatty acid release by the white adipose tissue (WAT) during a fast is stimulated by counter-regulatory factors acting in concert, although how adipocytes integrate these lipolytic inputs is unknown. We tested the role of angiopoietin-like 4 (Angptl4), a secreted protein induced by fasting or glucocorticoid treatment, in modulating intracellular adipocyte lipolysis. Glucocorticoid receptor blockade prevented fasting-induced tissue Angptl4 expression and WAT TG hydrolysis in mice, and TG hydrolysis induced by fasts of 6 or 24 h was greatly reduced in mice lacking Angptl4 (Angptl4(-/-)). Glucocorticoid treatment mimicked the lipolytic effects of fasting, although with slower kinetics, and this too required Angptl4. Thus, fasting-induced WAT TG hydrolysis requires glucocorticoid action and Angptl4. Both fasting and glucocorticoid treatment also increased WAT cAMP levels and downstream phosphorylation of lipolytic enzymes. Angptl4 deficiency markedly reduced these effects, suggesting that Angptl4 may stimulate lipolysis by modulating cAMP-dependent signaling. In support of this, cAMP levels and TG hydrolysis were reduced in primary Angptl4(-/-) murine adipocytes treated with catecholamines, which stimulate cAMP-dependent signaling to promote lipolysis, and was restored by treatment with purified human ANGPTL4. Remarkably, human ANGPTL4 treatment alone increased cAMP levels and induced lipolysis in these cells. Pharmacologic agents revealed that Angptl4 modulation of cAMP-dependent signaling occurs upstream of adenylate cyclase and downstream of receptor activation. We show that Angptl4 is a glucocorticoid-responsive mediator of fasting-induced intracellular lipolysis and stimulates cAMP signaling in adipocytes. Such a role is relevant to diseases of aberrant lipolysis, such as insulin resistance. 相似文献
10.
T Robal M Larsson M Martin G Olivecrona A Lookene 《The Journal of biological chemistry》2012,287(35):29739-29752
Angiopoietin-like protein 4 (Angptl4), a potent regulator of plasma triglyceride metabolism, binds to lipoprotein lipase (LPL) through its N-terminal coiled-coil domain (ccd-Angptl4) inducing dissociation of the dimeric enzyme to inactive monomers. In this study, we demonstrate that fatty acids reduce the inactivation of LPL by Angptl4. This was the case both with ccd-Angptl4 and full-length Angptl4, and the effect was seen in human plasma or in the presence of albumin. The effect decreased in the sequence oleic acid > palmitic acid > myristic acid > linoleic acid > linolenic acid. Surface plasmon resonance, isothermal titration calorimetry, fluorescence, and chromatography measurements revealed that fatty acids bind with high affinity to ccd-Angptl4. The interactions were characterized by fast association and slow dissociation rates, indicating formation of stable complexes. The highest affinity for ccd-Angptl4 was detected for oleic acid with a subnanomolar equilibrium dissociation constant (K(d)). The K(d) values for palmitic and myristic acid were in the nanomolar range. Linoleic and linolenic acid bound with much lower affinity. On binding of fatty acids, ccd-Angptl4 underwent conformational changes resulting in a decreased helical content, weakened structural stability, dissociation of oligomers, and altered fluorescence properties of the Trp-38 residue that is located close to the putative LPL-binding region. Based on these results, we propose that fatty acids play an important role in modulating the effects of Angptl4. 相似文献
11.
E-Chiang Lee Urvi Desai Gennady Gololobov Seokjoo Hong Xiao Feng Xuan-Chuan Yu Jason Gay Nat Wilganowski Cuihua Gao Ling-Ling Du Joan Chen Yi Hu Sharon Zhao Laura Kirkpatrick Matthias Schneider Brian P. Zambrowicz Greg Landes David R. Powell William K. Sonnenburg 《The Journal of biological chemistry》2009,284(20):13735-13745
Angiopoietin-like 3 (ANGPTL3) and angiopoietin-like 4 (ANGPTL4) are
secreted proteins that regulate triglyceride (TG) metabolism in part by
inhibiting lipoprotein lipase (LPL). Recently, we showed that treatment of
wild-type mice with monoclonal antibody (mAb) 14D12, specific for ANGPTL4,
recapitulated the Angptl4 knock-out (-/-) mouse phenotype of reduced
serum TG levels. In the present study, we mapped the region of mouse ANGPTL4
recognized by mAb 14D12 to amino acids
Gln29–His53, which we designate as specific
epitope 1 (SE1). The 14D12 mAb prevented binding of ANGPTL4 with LPL,
consistent with its ability to neutralize the LPL-inhibitory activity of
ANGPTL4. Alignment of all angiopoietin family members revealed that a sequence
similar to ANGPTL4 SE1 was present only in ANGPTL3, corresponding to amino
acids Glu32–His55. We produced a mouse mAb against
this SE1-like region in ANGPTL3. This mAb, designated 5.50.3, inhibited the
binding of ANGPTL3 to LPL and neutralized ANGPTL3-mediated inhibition of LPL
activity in vitro. Treatment of wild-type as well as hyperlipidemic
mice with mAb 5.50.3 resulted in reduced serum TG levels, recapitulating the
lipid phenotype found in Angptl3-/- mice. These results
show that the SE1 region of ANGPTL3 and ANGPTL4 functions as a domain
important for binding LPL and inhibiting its activity in vitro and
in vivo. Moreover, these results demonstrate that therapeutic
antibodies that neutralize ANGPTL4 and ANGPTL3 may be useful for treatment of
some forms of hyperlipidemia.Lipoprotein lipase
(LPL)5 plays a pivotal
role in lipid metabolism by catalyzing the hydrolysis of plasma triglycerides
(TGs). LPL is likely to be regulated by mechanisms that depend on nutritional
status and on the tissue in which it is expressed
(1–3).
Two secreted proteins, angiopoietin-like 3 (ANGPTL3) and angiopoietin-like 4
(ANGPTL4), play important roles in the regulation of LPL activity
(4,
5). ANGPTL3 and ANGPTL4 consist
of a signal peptide, an N-terminal segment containing coiled-coil domains, and
a C-terminal fibrinogen-like domain. The N-terminal segment as well as
full-length ANGPTL3 and ANGPTL4 have been shown to inhibit LPL activity, and
deletion of the N-terminal segment of ANGPTL3 and ANGPTL4 resulted in total
loss of LPL-inhibiting activity
(6,
7). These observations clearly
indicate that the N-terminal region of ANGPTL4 contains the functional domain
that inhibits LPL and affects plasma lipid levels. The coiled-coil domains
have been proposed to be responsible for oligomerization
(8); however, it is not known
whether the coiled-coil domains directly mediate the inhibition of LPL
activity.To define the physiological role of ANGPTL4 more clearly, we characterized
the pharmacological consequences of ANGPTL4 inhibition in mice treated with
the ANGPTL4-neutralizing monoclonal antibody (mAb) 14D12
(9). Injection of mAb 14D12
significantly lowered fasting TG levels in C57BL/6J mice relative to levels in
C57BL/6J mice treated with an isotype-matched anti-KLH control (KLH) mAb
(9). These reduced TG values
were similar to decreases in fasting plasma TG levels measured in
Angptl4 knock-out (-/-) mice. This study demonstrated that mAb 14D12
is a potent ANGPTL4-neutralizing antibody that is able to inhibit systemic
ANGPTL4 activity and thereby recapitulate the reduced lipid phenotype found in
Angptl4-/- mice. The readily apparent pharmacological
effect of mAb 14D12 prompted new questions about the epitope recognized by mAb
14D12 and how this antibody-antigen binding event affected ANGPTL4 function as
an LPL inhibitor.Although ANGPTL4 is able to interact directly with LPL
(10), it is not clear which
amino acids within ANGPTL4 mediate this interaction. Here we show that amino
acids Gln29–His53 of mANGPTL4 contain the epitope
for mAb 14D12. This region, hereby designated specific epitope 1 (SE1), also
defines a domain that mediates the interaction between ANGPTL4 and LPL and the
subsequent inactivation of LPL. With this information we present evidence that
ANGPTL3 also contains an SE1 region, and with antibodies specifically reactive
with ANGPTL3 SE1 we examine whether the ANGPTL3 SE1 region is involved in LPL
binding and inhibition. We also determined whether treatment of C57BL/6 mice
with an anti-ANGPTL3 SE1 mAb can recapitulate the phenotype of lower serum TG
and cholesterol levels found in Angptl3-/- mice. Finally
we tested the therapeutic potential of an anti-ANGPTL3 SE1 mAb for treatment
of hyperlipidemia in apolipoprotein E-/-
(ApoE-/-) or low density lipoprotein
receptor-/- (LDLr-/-) mice. 相似文献
12.
Coiled coils: a highly versatile protein folding motif 总被引:31,自引:0,他引:31
The alpha-helical coiled coil is one of the principal subunit oligomerization motifs in proteins. Its most characteristic feature is a heptad repeat pattern of primarily apolar residues that constitute the oligomer interface. Despite its simplicity, it is a highly versatile folding motif: coiled-coil-containing proteins exhibit a broad range of different functions related to the specific 'design' of their coiled-coil domains. The architecture of a particular coiled-coil domain determines its oligomerization state, rigidity and ability to function as a molecular recognition system. Much progress has been made towards understanding the factors that determine coiled-coil formation and stability. Here we discuss this highly versatile protein folding and oligomerization motif with regard to its structural architecture and how this is related to its biological functions. 相似文献
13.
Baranowski T Kralisch S Bachmann A Lössner U Kratzsch J Blüher M Stumvoll M Fasshauer M 《Hormones et métabolisme》2011,43(2):117-120
Fasting-induced adipose factor/angiopoietin-like protein 4 (FIAF/Angptl4) was recently introduced as a novel adipokine influencing glucose and lipid homeostasis. In the current study, we quantified circulating FIAF/Angtl4 levels in patients on chronic hemodialysis (CD) as compared to controls with a glomerular filtration rate above 50 ml/min. FIAF/Angptl4 was determined by ELISA in control (n=60) and CD (n=60) patients and correlated to clinical and biochemical measures of renal function, glucose and lipid metabolism, as well as inflammation, in both groups. Median serum FIAF/Angptl4 levels were more than 5-fold higher in CD patients (48.3 μg/l) as compared to control subjects (8.4 μg/l) (p<0.001). Furthermore, serum creatinine independently predicted FIAF/Angptl4 concentrations in multiple regression analyses in control subjects (p<0.01). In CD patients, C-reactive protein was independently and positively associated with circulating FIAF/Angptl4 (p<0.01). Taken together, we show that serum FIAF/Angptl4 levels are significantly increased in end-stage renal disease and independently associated with markers of renal function in control subjects. 相似文献
14.
Li S Nagothu K Ranganathan G Ali SM Shank B Gokden N Ayyadevara S Megyesi J Olivecrona G Chugh SS Kersten S Portilla D 《American journal of physiology. Renal physiology》2012,303(3):F437-F448
Peroxisome proliferator-activated receptor-α (PPARα) activation attenuates cisplatin (CP)-mediated acute kidney injury by increasing fatty acid oxidation, but mechanisms leading to reduced renal triglyceride (TG) accumulation could also contribute. Here, we investigated the effects of PPARα and CP on expression and enzyme activity of kidney lipoprotein lipase (LPL) as well as on expression of angiopoietin protein-like 4 (Angptl4), glycosylphosphatidylinositol-anchored-HDL-binding protein (GPIHBP1), and lipase maturation factor 1 (Lmf1), which are recognized as important proteins that modulate LPL activity. CP caused a 40% reduction in epididymal white adipose tissue (WAT) mass, with a reduction of LPL expression and activity. CP also reduced kidney LPL expression and activity. Angptl4 mRNA levels were increased by ninefold in liver and kidney tissue and by twofold in adipose tissue of CP-treated mice. Western blots of two-dimensional gel electrophoresis identified increased expression of a neutral pI Angptl4 protein in kidney tissue of CP-treated mice. Immunolocalization studies showed reduced staining of LPL and increased staining of Angptl4 primarily in proximal tubules of CP-treated mice. CP also increased TG accumulation in kidney tissue, which was ameliorated by PPARα ligand. In summary, a PPARα ligand ameliorates CP-mediated nephrotoxicity by increasing LPL activity via increased expression of GPHBP1 and Lmf1 and by reducing expression of Angptl4 protein in the proximal tubule. 相似文献
15.
Richard A. Kammerer 《Matrix biology》1997,15(8-9)
Subunit oligomerization of many proteins is mediated by α-helical coiled-coil domains. 3,4-Hydrophobic heptad repeat sequences, the characteristic feature of the coiled-coil protein folding motif, have been found in a wide variety of gene products including cytoskeletal, nuclear, muscle, cell surface, extracellular, plasma, bacterial, and viral proteins. Whereas the majority of coiled-coil structures is represented by intracellular α-helical bundles that contain two polypeptide chains, examples of extracellular coiled-coil proteins are fewer in number. Most proteins located in the extracellular space form three-stranded α-helical assemblies. Recently, five-stranded coiled coils have been identified in thrombospondins 3 and 4 in cartilage oligomeric matrix protein, and the formation of a heterotetramer has been observed in in vitro studies with the recombinant asialoglycoprotein receptor oligomerization domain. Coiled-coil domains in laminins and probably also in tenascins and thrombospondins are responsible for the formation of tissue-specific isoforms by selective oligomerization of different polypeptide chains. 相似文献
16.
Plasma triglyceride concentrations are determined by the balance between production of the triglyceride-rich lipoproteins VLDL and chylomicrons in liver and intestine, and their lipoprotein lipase-mediated clearance in peripheral tissues. In the last decade, the group of Angiopoietin-like proteins has emerged as important regulators of circulating triglyceride (TG) levels. Specifically, ANGPTL3 and ANGPTL4 impair TG clearance by inhibiting lipoprotein lipase (LPL). Whereas ANGPTL4 irreversibly inactivates LPL by promoting conversion of active LPL dimers into inactive monomers, ANGPTL3 reversibly inhibits LPL activity. Studies using transgenic or knockout mice have clearly demonstrated the stimulatory effect of Angptl3 and Angptl4 on plasma TG, which is further supported by human genetic data including genome wide association studies. Whereas ANGPTL3 is mainly active in the fed state, ANGPTL4 is elevated by fasting and mediates fasting-induced changes in plasma TG and free fatty acid metabolism. Both proteins undergo oligomerization and are subject to proteolytic cleavage to generate N- and C-terminal fragments with highly divergent biological activities. Expression of ANGPTL3 is exclusive to liver and governed by the liver X receptor (LXR). In contrast, ANGPTL4 is expressed ubiquitously and under sensitive control of the Peroxisome proliferator-activated receptor (PPAR) family and fatty acids. Induction of ANGPTL4 gene expression by fatty acids and via PPARs is part of a feedback mechanism aimed at protecting cells against lipotoxicity. So far there is very little evidence that other ANGPTLs directly impact plasma lipoprotein metabolism. This article is part of a Special Issue entitled Triglyceride Metabolism and Disease. 相似文献
17.
Ming-hon Yau Yu Wang Karen S. L. Lam Jialiang Zhang Donghai Wu Aimin Xu 《The Journal of biological chemistry》2009,284(18):11942-11952
Lipoprotein lipase (LPL) is a principal enzyme responsible for the
clearance of chylomicrons and very low density lipoproteins from the
bloodstream. Two members of the Angptl (angiopoietin-like protein) family,
namely Angptl3 and Angptl4, have been shown to inhibit LPL activity in
vitro and in vivo. Here, we further investigated the structural
basis underlying the LPL inhibition by Angptl3 and Angptl4. By multiple
sequence alignment analysis, we have identified a highly conserved 12-amino
acid consensus motif that is present within the coiled-coil domain (CCD) of
both Angptl3 and Angptl4, but not other members of the Angptl family.
Substitution of the three polar amino acid residues (His46,
Gln50, and Gln53) within this motif with alanine
abolishes the inhibitory effect of Angptl4 on LPL in vitro and also
abrogates the ability of Angptl4 to elevate plasma triglyceride levels in
mice. The CCD of Angptl4 interacts with LPL and converts the catalytically
active dimers of LPL to its inactive monomers, whereas the mutant protein with
the three polar amino acids being replaced by alanine loses such a property.
Furthermore, a synthetic peptide consisting of the 12-amino acid consensus
motif is sufficient to inhibit LPL activity, although the potency is
much lower than the recombinant CCD of Angptl4. In summary, our data suggest
that the 12-amino acid consensus motif within the CCD of Angptl4, especially
the three polar residues within this motif, is responsible for its interaction
with and inhibition of LPL by blocking the enzyme dimerization.Lipoprotein lipase
(LPL)3 is an
endothelium-bound enzyme that catalyzes the hydrolysis of plasma triglyceride
(TG) associated with chylomicrons and very low density lipoproteins
(1,
2). This enzyme plays a major
role in maintaining lipid homeostasis by promoting the clearance of TG-rich
lipoproteins from the bloodstream. Abnormality in LPL functions has been
associated with a number of pathological conditions, including
atherosclerosis, dyslipidemia associated with diabetes, and Alzheimer disease
(1).LPL is expressed in a wide variety of cell types, particularly in
adipocytes and myocytes (2). As
a rate-limiting enzyme for clearance of TG-rich lipoproteins, the activity of
LPL is tightly modulated by multiple mechanisms in a tissue-specific manner in
response to nutritional changes
(3,
4). The enzymatic activity of
LPL in adipose tissue is enhanced after feeding to facilitate the storage of
TG, whereas it is down-regulated during fasting to increase the utilization of
TG by other tissues (5). The
active form of LPL is a noncovalent homodimer with the subunits associated in
a head-to-tail manner, and the dissociation of its dimeric form leads to the
formation of a stable inactive monomeric conformation and irreversible enzyme
inactivation (6). At the
post-translational level, the LPL activity is regulated by numerous
apolipoprotein co-factors. For instance, apoCII, a small apolipoprotein
consisting of 79 amino acid residues in human, activates LPL by directly
binding to the enzyme (7,
8). By contrast, several other
apolipoproteins such as apoCI, apo-CIII, and apoE have been shown to inhibit
the LPL activity in vitro
(3).Angiopoietin-like proteins (Angptl) are a family of secreted proteins
consisting of seven members, Angptl1 to Angptl7
(9,
10). All the members of the
Angptl family share a similar domain organization to those of angiopoietins,
with an NH2-terminal coiled-coil domain (CCD) and a COOH-terminal
fibrinogen-like domain. Among the seven family members, only Angptl3 and
Angptl4 have been shown to be involved in regulating triglyceride metabolism
(10,
11). The biological functions
of Angptl3 in lipid metabolism were first discovered by Koishi et al.
(12) in their positional
cloning of the recessive mutation gene responsible for the hypolipidemia
phenotype in a strain of obese mouse KK/snk. Subsequent studies have
demonstrated that Angptl3 increases plasma TG levels by inhibiting the LPL
enzymatic activity
(13–15).
Angptl4, also known as fasting-induced adipocyte factor, hepatic
fibrinogen/angiopoietin-related protein, or peroxisome proliferator-activated
receptor-γ angiopoietin-related, is a secreted glycoprotein abundantly
expressed in adipocyte, liver, and placenta
(16–18).
In addition to its role in regulating angiogenesis, a growing body of evidence
demonstrated that Angptl4 is an important player of lipid metabolism
(10,
11). Elevation of circulating
Angptl4 by transgenic or adenoviral overexpression, or by direct
supplementation of recombinant protein, leads to a marked elevation in the
levels of plasma TG and low density lipoprotein cholesterol in mice
(19–22).
By contrast, Angptl4 knock-out mice exhibit much lower plasma TG and
cholesterol levels compared with the wild type littermates
(19,
20). Notably, treatment of
several mouse models (such as C57BL/6J, ApoE–/–,
LDLR–/–, and db/db obese/diabetic mice) with a
neutralizing antibody against Angptl4 recapitulate the lipid phenotype found
in Angptl4 knock-out mice
(19). The role of Angptl4 as a
physiological inhibitor of LPL is also supported by the finding that its
expression levels in adipose tissue change rapidly during the fed-to-fasting
transitions and correlate inversely with LPL activity
(23). In humans, a genetic
variant of the ANGPTL4 gene (E40K) has been found to be associated
with significantly lower plasma TG levels and higher high density lipoprotein
cholesterol concentrations in several ethnic groups
(24–26).Angptl3 and Angptl4 share many common biochemical and functional properties
(10). In both humans and
rodents, Angptl3 and Angptl4 are proteolytically cleaved at the linker region
and circulate in plasma as two truncated fragments, including
NH2-terminal CCD and COOH-terminal fibrinogen-like domain
(14,
27–29).
The effects of both Angptl3 and Angptl4 on elevating plasma TG levels are
mediated exclusively by their NH2-terminal CCDs
(15,
22,
23,
27,
30). The CCDs of Angptl3 and
Angptl4 have been shown to inhibit the LPL activity in vitro as well
as in mice
(23,30,31).
Angptl4 inhibits LPL by promoting the conversion of the catalytically active
LPL dimers into catalytically inactive LPL monomers, thereby leading to the
inactivation of LPL (23,
31). However, the detailed
structural and molecular basis underlying the LPL inhibition by Angptl3 and
Angptl4 remain poorly characterized at this stage.In this study, we analyzed all known amino acid sequences of Angptl3 and
Angptl4 from various species and found a short motif,
LAXGLLXLGXGL (where X represents polar
amino acid residues), which corresponds to amino acid residues 46–57 and
44–55 of human Angptl3 and Angptl4, respectively, is highly conserved
despite the low degree of their overall homology (∼30%). Using both in
vitro and in vivo approaches, we demonstrated that this 12-amino
acid sequence motif, in particular the three polar amino acid residue within
this motif, is essential for mediating the interactions between LPL and
Angpt4, which in turn disrupts the dimerization of the enzyme. 相似文献
18.
Wu Yin Stefano Romeo Shurong Chang Nick V. Grishin Helen H. Hobbs Jonathan C. Cohen 《The Journal of biological chemistry》2009,284(19):13213-13222
Angiopoietin-like protein 4 (ANGPTL4) is a secreted protein that modulates
the disposition of circulating triglycerides (TG) by inhibiting lipoprotein
lipase (LPL). Here we examine the steps involved in the synthesis and
post-translational processing of ANGPTL4, and the effects of a naturally
occurring sequence variant (E40K) that is associated with lower plasma TG
levels in humans. Expression of the wild-type and mutant proteins in HEK-293A
cells indicated that ANGPTL4 formed dimers and tetramers in cells prior to
secretion and cleavage of the protein. After cleavage at a canonical
proprotein convertase cleavage site (161RRKR164), the
oligomeric structure of the N-terminal domain was retained whereas the
C-terminal fibrinogen-like domain dissociated into monomers. Inhibition of
cleavage did not interfere with oligomerization of ANGPTL4 or with its ability
to inhibit LPL, whereas mutations that prevented oligomerization severely
compromised the capacity of the protein to inhibit LPL. ANGPTL4 containing the
E40K substitution was synthesized and processed normally, but no monomers or
oligomers of the N-terminal fragments accumulated in the medium; medium from
these cells failed to inhibit LPL activity. Parallel experiments performed in
mice recapitulated these results. Our findings indicate that oligomerization,
but not cleavage, of ANGPTL4 is required for LPL inhibition, and that the E40K
substitution destabilizes the protein after secretion, preventing the
extracellular accumulation of oligomers and abolishing the ability of the
protein to inhibit LPL activity.Angiopoietin-like protein 4
(ANGPTL4)4 is a 50-kDa
protein that is synthesized and secreted from several metabolically active
tissues and has been implicated in the trafficking of circulating TG
(1,
2). Triglycerides, either
acquired from the diet or synthesized endogenously, circulate in blood as
constituents of chylomicrons and very low density lipoproteins (VLDL). As
these lipoproteins circulate in tissues they encounter lipoprotein lipase
(LPL) at the vascular endothelial surfaces. LPL hydrolyzes the TG, producing
free fatty acids that are taken up by the surrounding tissues. ANGPTL4
inhibits the activity of LPL, thereby limiting the uptake of TG-derived fatty
acids by the underlying cells
(3,
4). Overexpression of ANGPTL4
in mice causes severe hypertriglyceridemia, whereas mice lacking ANGPTL4 have
increased LPL activity and low plasma levels of TG
(5,
6). In mice, ANGPTL4 is
predominantly expressed in adipose tissue and is strongly induced by fasting
(2). Accordingly it has been
proposed that ANGPTL4 inhibits LPL activity in adipose tissue to reroute fatty
acids away from fat to muscle and other tissues when food intake is low
(3,
4).ANGPTL4 belongs to a family of seven structurally similar secreted proteins
(ANGPTL1-ANGPTL7) that contain a signal sequence followed by an
α-helical region predicted to form a coiled-coil, and a globular
fibrinogen-like domain at the C terminus
(1). Gel filtration studies of
recombinant ANGPTL4 indicate that the protein assembles into oligomers that
are stabilized by disulfide bonds
(7). Substitution of two highly
conserved cysteine residues at positions 76 and 80 in the α-helical
domain prevents oligomerization of ANGPTL4 and impairs the ability of the
recombinant protein to increase plasma TG levels when overexpressed in the
livers of rats (7).Upon secretion into the circulation, ANGPTL4 is cleaved into an N-terminal
domain and a C-terminal fibrinogen-like domain
(8). The N-terminal peptide
circulates as an oligomer, and the fibrinogen-like domain circulates as a
monomer (8). The N-terminal
helical region of ANGPTL4 is necessary and sufficient for inhibition of LPL
(9). A peptide corresponding to
amino acids 1-187 of the protein binds LPL with high affinity and converts the
enzyme from catalytically active dimers to inactive monomers, thereby
inhibiting LPL activity (10).
After disrupting the LPL dimer, ANGPTL4 is released. The LPL monomers remain
folded and stable but fail to re-form active dimers. These data suggest that
the N-terminal domain of ANGPTL4 interacts directly but transiently with LPL,
triggering a stable conformational switch in LPL that irreversibly inactivates
the enzyme.Recently, we used a population-based resequencing strategy to examine the
metabolic role of ANGPTL4 in humans
(11). Resequencing the coding
region of ANGPTL4 in a large (n = 3,501), multiethnic sample
revealed multiple rare sequence variations that alter an amino acid in the
protein and are associated with low plasma TG levels. In addition, we
identified a more common variant (E40K), that was present in ∼3% of
European-Americans and was associated with significantly lower plasma levels
of TG and low density lipoprotein-cholesterol (LDL-C), and higher levels of
high density lipoprotein (HDL)-C in two large epidemiological studies
(11). These association
studies confirmed that ANGPTL4 is involved in TG metabolism in humans, and
also revealed additional roles in humans in the metabolism of HDL and LDL,
which were not apparent from studies in genetically modified mice.Here we examined the synthesis, secretion, and processing of ANGPTL4 and
determine the mechanism by which substitution of a basic (lysine) for an
acidic (glutamate) residue at residue 40 affects the function of the
protein. 相似文献
19.
Angiopoietin-like protein 3, a hepatic secretory factor,activates lipolysis in adipocytes 总被引:19,自引:0,他引:19
Shimamura M Matsuda M Kobayashi S Ando Y Ono M Koishi R Furukawa H Makishima M Shimomura I 《Biochemical and biophysical research communications》2003,301(2):604-609
Our previous work identified a genetic mutation in the gene encoding angiopoietin-like protein 3 (Angptl3) in KK/Snk mice (previously KK/San), a mutant strain of KK obese mice. KK/Snk had significantly lower plasma triglyceride and free fatty acid (FFA) than KK mice. Human ANGPTL3 treatment increased both plasma triglyceride and FFA. ANGPTL3 inhibited the activity of lipoprotein lipase, which accounted for the increase of plasma triglyceride. The mechanism how ANGPTL3 affects plasma FFA has not been known. The current study reveals that ANGPTL3 targets on adipose cells and induces lipolysis. Both plasma FFA and glycerol decreased in KK/Snk and increased by the treatment of human ANGPTL3. Specific bindings of ANGPTL3 to adipose cells were shown using fluorescence-labeled protein visually and 125I-labeled protein by the binding analysis. Furthermore, ANGPTL3 activated the lipolysis to stimulate the release of FFA and glycerol from adipocytes. We conclude that ANGPTL3 is a liver-derived lipolytic factor targeting on adipocyte. 相似文献
20.
Smyth CP Lundbäck T Renzoni D Siligardi G Beavil R Layton M Sidebotham JM Hinton JC Driscoll PC Higgins CF Ladbury JE 《Molecular microbiology》2000,36(4):962-972
H-NS is a major component of the bacterial nucleoid, involved in condensing and packaging DNA and modulating gene expression. The mechanism by which this is achieved remains unclear. Genetic data show that the biological properties of H-NS are influenced by its oligomerization properties. We have applied a variety of biophysical techniques to study the structural basis of oligomerization of the H-NS protein from Salmonella typhimurium. The N-terminal 89 amino acids are responsible for oligomerization. The first 64 residues form a trimer dominated by an alpha-helix, likely to be in coiled-coil conformation. Extending this polypeptide to 89 amino acids generated higher order, heterodisperse oligomers. Similarly, in the full-length protein no single, defined oligomeric state is adopted. The C-terminal 48 residues do not participate in oligomerization and form a monomeric, DNA-binding domain. These N- and C-terminal domains are joined via a flexible linker which enables them to function independently within the context of the full-length protein. This novel mode of oligomerization may account for the unusual binding properties of H-NS. 相似文献