Advertisement
J. Lipid Res.
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

Originally published In Press as doi:10.1194/jlr.M600437-JLR200 on February 28, 2007 Originally published In Press as doi:10.1194/jlr.M600437-JLR200 on February 26, 2007

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
M600437-JLR200v1
M600437-JLR200v2
48/5/1062    most recent
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowRequest Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Wang, Y.
Right arrow Articles by Oram, J. F.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Wang, Y.
Right arrow Articles by Oram, J. F.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati  
What's this?

Journal of Lipid Research, Vol. 48, 1062-1068, May 2007
Copyright © 2007 by American Society for Biochemistry and Molecular Biology

Unsaturated fatty acids phosphorylate and destabilize ABCA1 through a protein kinase C {delta} pathway

Yutong Wang and John F. Oram1

Department of Medicine, University of Washington, Seattle, WA 98195

Published, JLR Papers in Press, February 28, 2007.

1 To whom correspondence should be addressed. e-mail: joram{at}u.washington.edu


   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 EXPERIMENTAL PROCEDURES
 RESULTS
 DISCUSSION
 REFERENCES
 
Abnormal HDL metabolism among patients with diabetes and insulin resistance may contribute to their increased risk of atherosclerosis. ABCA1 mediates the transport of cholesterol and phospholipids from cells to HDL apolipoproteins and thus modulates HDL levels and atherogenesis. Unsaturated fatty acids, which are increased in diabetes, impair the ABCA1 pathway in cultured cells by destabilizing ABCA1 protein. We previously reported that unsaturated fatty acids destabilize ABCA1 in murine macrophages and ABCA1-transfected baby hamster kidney cells by increasing its serine phosphorylation through a phospholipase D (PLD) pathway. Here, we examined the cellular pathway downstream of PLD that mediates the ABCA1-destabilizing effects of unsaturated fatty acids. The protein kinase C {delta} (PKC{delta})-specific inhibitor rottlerin and PKC{delta} small interfering RNA completely abolished the ability of unsaturated fatty acids to inhibit lipid transport activity, to reduce protein levels, and to increase serine phosphorylation of ABCA1, implicating a role for PKC{delta} in the ABCA1-destabilizing effects of fatty acids. These data indicate that unsaturated fatty acids destabilize ABCA1 by activating a PKC{delta} pathway that phosphorylates ABCA1 serines.

Supplementary key words ATP binding cassette transporter A1 • high density lipoproteins • cardiovascular disease • diabetes


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
EXPERIMENTAL PROCEDURES
 RESULTS
 DISCUSSION
 REFERENCES
 
Population studies have revealed that HDL is a major cardioprotective factor. Lipidation of apolipoprotein A-I (apoA-I) by ABCA1 is the rate-limiting step in generating plasma HDL (1–3). ABCA1 is an integral membrane protein that mediates the transport of cellular cholesterol and phospholipids to lipid-deficient HDL apolipoproteins (4, 5). ABCA1 is a member of a large family of ABC transporters and contains two ATP binding domains and two six helix transmembrane domains (6). Mutations in ABCA1 cause Tangier disease (7–10), a severe HDL deficiency syndrome characterized by the deposition of sterols in tissue macrophages and prevalent atherosclerosis (11, 12).

ABCA1 expression by macrophages is highly regulated. Cholesterol loading of macrophages markedly increases ABCA1 mRNA and protein levels (10, 13), consistent with a transporter that functions to export excess cholesterol. The transcription of this gene is regulated by nuclear liver X receptors (LXR{alpha} and LXRß) and retinoid X receptor (14–17). Analogs of cAMP are also known to activate murine ABCA1 gene transcription (18–20). The ABCA1 protein degradation rate is also regulated. ApoA-I increases ABCA1 protein stability by decreasing the phosphorylation of a sequence in ABCA1 that directs calpain proteolysis (21) and by activating protein kinase C (22). Protein kinases A, protein kinase 2, and Janus kinase 2 have also been shown to affect ABCA1 activity (23–25).

Patients with diabetes have an increased risk of cardiovascular disease. It is possible that diabetes-associated metabolic factors impair ABCA1 expression or activity and contribute to the higher mortality rate among these patients. Our previous studies showed that the long-chain unsaturated fatty acids palmitoleate, oleate, linoleate, and arachidonate but not the saturated fatty acids palmitate and stearate decrease ABCA1 expression in cells by increasing its protein degradation rate (26). Furthermore, we also showed that these unsaturated fatty acids accelerate ABCA1 protein turnover through a signaling pathway involving the activation of phospholipase D2 (PLD2) and the phosphorylation of ABCA1 serine residues (27). We also found that diacylglycerol (DAG) containing unsaturated but not saturated fatty acyl groups reduced ABCA1 protein levels.

In this study, we examined the mechanism by which unsaturated fatty acids destabilize ABCA1 protein. We found that linoleate-induced ABCA1 degradation was associated with increased protein kinase C {delta} (PKC{delta}) activity and the phosphorylation of ABCA1 serines. Inhibiting PKC{delta} with rottlerin or depleting PKC{delta} with small interfering RNA (siRNA) reduced or abolished the ability of linoleate to promote ABCA1 phosphorylation and degradation. Thus, unsaturated fatty acids activate a PKC{delta} signaling pathway that phosphorylates ABCA1 serine residues, which destabilizes the protein.


   EXPERIMENTAL PROCEDURES
TOP
 ABSTRACT
 INTRODUCTION
 EXPERIMENTAL PROCEDURES
RESULTS
 DISCUSSION
 REFERENCES
 
Lipoproteins and apoA-I
LDL and HDL were prepared by sequential ultracentrifugation in the density ranges 1.019–1.063 and 1.125–1.21 g/ml, respectively, and HDL was depleted of apoE and apoB by heparin-agarose chromatography (28). ApoA-I was purified from HDL and delipidated as described previously (28). LDL was acetylated by the method of Goldstein et al. (29).

Cell culture and lipid efflux
Baby hamster kidney (BHK) cells expressing mifepristone-inducible human ABCA1 were generated as described previously (30). Murine RAW 264.7 macrophages and ABCA1-expressing BHK cells were maintained in DMEM (Invitrogen) containing 10% fetal bovine serum or incubated in serum-free DMEM plus 1 mg/ml fatty acid-free BSA (DMEM/BSA). To radiolabel cellular cholesterol, 1 µCi/ml [3H]cholesterol (NEN Life Science Products) was added to the growth medium (BHK cells) or to DMEM/BSA containing 50 µg/ml acetylated LDL (RAW 264.7 macrophages) at 24 h immediately preceding the treatments (26, 30). Washed cells were then incubated for 6–16 h with medium containing 5 mg/ml BSA in the presence or absence of 125 µM fatty acids (molar ratios to BSA of 0:1.8). Fatty acids were added from a stock solution bound to BSA at a 3.5 molar ratio and were adjusted to lower ratios by adding fatty acid-free BSA. To induce ABCA1, 0.5 mM 8-Br-cAMP was added to the medium for RAW 264.7 and 10 nM mifepristone was added to the medium for ABCA1-expressing BHK cells.

To measure cholesterol efflux, cells were incubated with DMEM/BSA with or without 10 µg/ml apoA-I for 2 h at 37°C and chilled on ice, and the medium was collected and centrifuged to remove detached cells. The medium was counted for 3H, and the cells were assayed for free and esterified [3H]cholesterol after isolation by thin-layer chromatography (31). ApoA-I-mediated cholesterol efflux is expressed as the fraction of total free [3H]cholesterol released into the medium after subtraction of values obtained in the absence of apoA-I.

Immunoblots
Cells were washed and dislodged from the dish at 0°C in buffer containing protease inhibitors. To isolate PKC{delta} or ABCA1, cell proteins were solubilized in PBS containing 1% Triton X-100 plus protease inhibitors, and the extract was incubated overnight at 4°C with antibody against PKC{delta} (Upstate) or ABCA1 (Novus Biologicals). The antibody-antigen complex was isolated by protein A-coated magnetic beads (Dynal) and electrophoresed in SDS using a 6% polyacrylamide gel. Each gel lane received immunoprecipitated protein corresponding to equal amounts of cells. For immunoblots of PKC{delta}, PKCß1, and PKC{theta} from RAW 264.7 cells or BHK cells, PKC proteins were isolated by immunoprecipitation with PKC-specific antibodies (Santa Cruz Biotechnology) and resolved by SDS-PAGE. For immunoblots of whole membrane ABCA1 from RAW 264.7 cells, microsomal membranes were isolated from homogenized cells by ultracentrifugation, membrane proteins were solubilized in SDS buffer and resolved by SDS-PAGE, and ABCA1 was identified by immunoblot analysis (19). Equal amounts of membrane protein were added per gel lane. For immunoblots of ABCA1 from ABCA1-expressing BHK cells, cell proteins were solubilized in PBS containing 1% Triton X-100 plus protease inhibitors, and equal amounts of protein were added per gel lane. For immunoblots of phospho-PKC{delta}, PKC{delta} was isolated by immunoprecipitation with PKC{delta} antibody and SDS-PAGE, and blots were probed with phospho-PKC{delta} [threonine-505 (Thr505)] antibody (Cell Signaling Technology).

ABCA1 serine phosphorylation
ABCA1 phosphoserines were assayed by immunoprecipitation with ABCA1 antibody followed by immunoblot analysis using phosphoserine antibody (Biomol). ABCA1 serine phosphorylation was quantitated using OptiQuant software (Packard Instrument).

siRNA transfections
PKC{delta} siRNA expressing plasmid pKD-PKC{delta}-v6 (Millipore) targets the 678–699 nucleotide region of mouse PKC{delta} mRNA, which is not homologous to other PKC isoforms. pKD-PKC{delta}-v6 and control plasmid pKD-NegCon-v1 (Millipore) were transfected into RAW 264.7 macrophages using FuGene 6 (Roche) as described in the manufacturer's protocol. Briefly, 2 µl of 0.1 mg/ml siRNA plasmid was mixed with 37.7 µl of DMEM/BSA and 0.3 µl of FuGene 6 and incubated at room temperature for 20 min. Plasmid-FuGene 6 complex was applied to 360 µl of DMEM/BSA with 10% fetal bovine serum in each well of a 24-well plate containing cultured RAW 264.7 macrophages at ~70% confluence. PKCß1 and PKC{theta} (Santa Cruz Biotechnology) and scrambled negative control (Ambion) siRNAs were transfected into RAW 264.7 macrophages using siPORTTM Lipid (Ambion) as described in the manufacturer's protocol. Briefly, 1 µl of 20 µM siRNA was mixed with 41.5 µl of DMEM/BSA, and 2 µl of siPORTTM Lipid was diluted in 5.5 µl of DMEM/BSA and incubated at room temperature for 20 min. After the incubation, the diluted siPORTTM Lipid was combined with the diluted siRNA and incubated for an additional 20 min at room temperature. A total of 50 µl of siRNA-siPORTTM Lipid complex was applied to 200 µl of DMEM/BSA in each well of a 24-well plate containing cultured RAW 264.7 macrophages at ~70% confluence.


   RESULTS
TOP
 ABSTRACT
 INTRODUCTION
 EXPERIMENTAL PROCEDURES
 RESULTS
DISCUSSION
 REFERENCES
 
PKC{delta} is required for fatty acid inhibition of ABCA1
We previously demonstrated that the long-chain unsaturated fatty acids palmitoleate, oleate, linoleate, and arachidonate decreased apoA-I-mediated lipid efflux from murine macrophages and ABCA1-transfected BHK cells (27) by increasing ABCA1 degradation through a PLD2-DAG pathway that increased ABCA1 serine phosphorylation. Because this implicated a PKC pathway, we screened PKC isoform-specific inhibitors for their abilities to reverse the destabilizing effects of unsaturated fatty acids. Inhibitors of PKC{alpha}/ß1 (Gö 6976; EMD Biosciences), PKC{zeta} (myristoylated PKC{zeta} pseudosubstrate inhibitor), or PKC{theta} (myristoylated PKC{theta} pseudosubstrate inhibitor) had no effect on linoleate-inhibited apoA-I-mediated cholesterol efflux from ABCA1-expressing BHK cells when they were incubated for 6 h with or without fatty acid or inhibitor (data not shown). The PKC{delta}-specific inhibitor rottlerin, however, completely abolished the ability of linoleate to inhibit apoA-I-mediated cholesterol efflux (Fig. 1A ), reduce ABCA1 protein levels (Fig. 1B), and increase ABCA1 serine phosphorylation (Fig. 1C). Rottlerin also blocked the inhibitory effects of linoleate on apoA-I-mediated cholesterol efflux from J774 macrophages (data not shown). The maximum inhibitory effects of rottlerin were <5 µM with both ABCA1-transfected BHK cells and J774 macrophages. These results suggest that PKC{delta} mediates the ABCA1-destabilizing effects of fatty acids.


Figure 1
View larger version (13K):
[in this window]
[in a new window]

  		Fig. 1. The protein kinase C {delta} (PKC{delta}) inhibitor rottlerin prevents ABCA1 impairment by unsaturated fatty acids. A: ABCA1-expressing baby hamster kidney (BHK) cells were incubated for 16 h in DMEM with 10 nM mifepristone and 1 mg/ml BSA, then incubated for 6 h in DMEM with 10 nM mifepristone and either 5 mg/ml BSA alone or BSA plus 125 µM linoleate (BSA molar ratio of 1.8) in the presence or absence of 5 µM rottlerin, and apolipoprotein A-I (apoA-I)-mediated [3H]cholesterol efflux was measured during subsequent 2 h incubations as described in Experimental Procedures. Each value represents the mean ± SD of three incubations. B: ABCA1 protein levels were assayed by immunoblot analysis. C: ABCA1-expressing BHK cells were incubated for 40 min in DMEM with either 5 mg/ml BSA alone or BSA plus linoleate (BSA molar ratio of 1.8) in the presence or absence of 5 µM rottlerin. ABCA1 was isolated by immunoprecipitation and SDS-PAGE, and blots were probed with phosphoserine antibody. All results are representative of three similar experiments. Ctrl, control.

 
To confirm that PKC{delta} activation is important for the ABCA1-destabilizing effects of unsaturated fatty acids, we knocked down PKC{delta} expression with a specific siRNA and measured the effects of linoleate on ABCA1 activity and levels. We used siRNAs for PKCß1 and PKC{theta} as positive controls. Because of their higher transfection efficiency, we used murine RAW 264.7 macrophages for these studies. Transfections with PKC siRNAs decreased PKC{delta}, PKCß1, and PKC{theta} levels by >80%, and linoleate treatment had no effect on PKC protein levels (Fig. 2A ). PKC{delta} siRNA abolished the ability of linoleate to inhibit apoA-I-mediated cholesterol efflux (Fig. 2B), to reduce ABCA1 protein levels (Fig. 2C), and to increase the phosphorylation of ABCA1 serines (Fig. 2D). In contrast, knocking down either PKCß1 or PKC{theta} had no effect on the ability of linoleate to inhibit ABCA1 cholesterol efflux activity (Fig. 2B), reduce ABCA1 protein (Fig. 2C), or increase ABCA1 serine phosphorylation (Fig. 2D). Thus, ablating PKC{delta} expression completely blocks the ABCA1-inhibitory and -phosphorylating effects of linoleate, indicating that PKC{delta} is required for these fatty acid effects.


Figure 2
View larger version (25K):
[in this window]
[in a new window]

  		Fig. 2. PKC{delta} small interfering RNA (siRNA) blocks linoleate-mediated effects on ABCA1. A: RAW 264.7 macrophages were transfected with mouse PKC{delta} siRNA expression plasmid or control plasmid (Ctrl), or cells were transfected with PKCß1, PKC{theta}, or their scrambled (Ctrl) siRNAs as described in Experimental Procedures. PKC{delta}, PKCß1, and PKC{theta} protein levels were assayed by immunoblot analysis. Results are representative of three similar experiments. B: Cholesterol-loaded siRNA-transfected cells were incubated for 16 h with 0.5 mM 8-Br-cAMP and either 5 mg/ml BSA alone or BSA plus 125 µM linoleate (BSA molar ratio of 1.8). ApoA-I-mediated [3H]cholesterol efflux was measured during subsequent 2 h incubations. Each value is the mean ± SD of triplicate determinations. Results are representative of three similar experiments. C: Membrane ABCA1 protein levels were assayed by immunoblot analysis. Results are representative of three similar experiments. D: Cells transfected with siRNA were incubated for 40 min with either 5 mg/ml BSA alone or BSA plus linoleate (BSA molar ratio of 1.8). ABCA1 was isolated by immunoprecipitation and SDS-PAGE, and blots were probed with phosphoserine antibody. Results are representative of three similar experiments.

 
Unsaturated fatty acids impair ABCA1 via PKC{delta} activation
It was demonstrated that PKC{delta} activation is linked to phosphorylation at Thr505 (32). To test whether unsaturated fatty acids activate PKC{delta}, we incubated ABCA1-expressing BHK cells for 30 min with stearate, linoleate, dioctanoylglycerol, or oleoylacetylglycerol and measured PKC{delta} phosphorylation. In the absence of inducers of stearoyl-CoA desaturase 1, the saturated fatty acid stearate has no effect on ABCA1 stability (26, 27). We also showed previously that dioctanoylglycerol had no affect on ABCA1 activity, levels, or phosphorylation, whereas oleoylacetylglycerol, which contains an unsaturated fatty acyl side chain, mimicked the effects of unsaturated fatty acids on these parameters (27). Phospho-Thr505 immunoblot analyses of immunoprecipitated PKC{delta} revealed that linoleate and oleoylacetylglycerol markedly increased PKC{delta} phosphorylation at Thr505, whereas the saturated fatty acid stearate and dioctanoylglycerol failed to increase phospho-Thr505 (Fig. 3 ). These data indicate that unsaturated fatty acids and a DAG containing an unsaturated fatty acyl side chain induce PKC{delta} activity.


Figure 3
View larger version (24K):
[in this window]
[in a new window]

  		Fig. 3. Linoleate and an oleoyl-containing diacylglycerol (DAG) activate PKC{delta}. ABCA1-expressing BHK cells were incubated for 30 min in DMEM with 5 mg/ml BSA alone or BSA plus 125 µM stearic acid (SA), 125 µM linoleate (LA), 100 µM 1,2-dioctanoyl-sn-glycerol (DOG), or 100 µM 1-oleoyl-2-acetyl-sn-glycerol (OAG). PKC{delta} was isolated by immunoprecipitation with a PKC{delta} antibody and SDS-PAGE, and blots were probed with anti-PKC{delta} (threonine-505) antibody. Results are representative of three similar experiments. Ctrl, control.

 

   DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 EXPERIMENTAL PROCEDURES
 RESULTS
 DISCUSSION
REFERENCES
 
Metabolic factors that modulate ABCA1 activity could have a profound impact on cholesterol transport and atherosclerosis. Our previous studies revealed that unsaturated fatty acids impair ABCA1 expression by enhancing its degradation rate through a PLD2 pathway. Here, we provide evidence that this occurs by increasing the phosphorylation of ABCA1 serines through a PKC{delta} signaling pathway.

Unsaturated fatty acids reduced ABCA1 protein levels in both murine macrophages and ABCA1-transfected BHK cells. Inhibition of PKC{delta} with the PKC{delta}-specific inhibitor rottlerin or reducing PKC{delta} levels with siRNA reversed the ability of linoleate to increase ABCA1 serine phosphorylation and reduce ABCA1 protein levels. Linoleate increased the phosphorylation of PKC{delta} Thr505, which is associated with enzyme activity. These observations strongly suggest that phosphorylation of ABCA1 serines through a PKC{delta} pathway is responsible for the fatty acid-induced destabilization of this transporter. We are in the process of preparing ABCA1 serine mutants to identify the residues that are the targets of PKC{delta}.

Our previous results implied that the fatty acid-stimulated PLD2 pathway activates a protein kinase that targets ABCA1 for proteolysis. PLD generates several important signaling molecules that activate protein kinases, including phosphatidic acid, lysophosphatidic acid, and DAG. We had obtained results suggesting that DAG containing unsaturated fatty acyl groups mediates the ABCA1-destabilizing effects of PLD2 (27). Here, we further demonstrate that a DAG containing an unsaturated fatty acyl group activates PKC{delta}. These findings suggest that the PLD2 pathway serves to generate DAG subspecies enriched in unsaturated fatty acids that function as signaling molecules to activate PKC{delta}, thus increasing serine phosphorylation and the degradation of ABCA1.

Previous studies have shown that oleate stimulates PKC{delta} translocation in RAW 264.7 macrophages (33). PKC{delta} belongs to a novel PKC subfamily of serine/threonine kinases that includes PKC{delta}, {varepsilon}, {eta}, and {theta}. They are maximally activated by DAG without requiring calcium (34). It has been shown that in murine macrophages, the glucocorticoid-induced tumor necrosis factor receptor stimulated the secretion of matrix metalloproteinase 9 via the activation of PKC{delta} and PLD (35), linking these two pathways together. Here, our results demonstrated that linoleate can activate PLD2 and PKC{delta} to phosphorylate its downstream target ABCA1.

Our current and previous studies suggest the following model for the ABCA1-destabilizing effects of fatty acids (Fig. 4 ). Unsaturated fatty acids are transported into the cell by fatty acid transfer protein and converted to their acyl-CoA derivatives, some of which are incorporated into pools of phosphatidylcholine containing unsaturated acyl side chains. These acyl-CoAs also activate PLD2, which acts as a feed-forward mechanism to generate phosphatidic acid and DAG enriched in unsaturated acyl groups. These DAG subspecies activate PKC{delta}, which phosphorylates serine residues in ABCA1 that target ABCA1 for proteolysis. PKC{delta} can further activate PLD2 to form a positive feedback loop (35).


Figure 4
View larger version (12K):
[in this window]
[in a new window]

  		Fig. 4. A model for the inhibition of ABCA1 by unsaturated fatty acids. PA, phosphatidic acid; PC, phosphatidylcholine; PL, phospholipid; PLD, phospholipase D; SCD, stearoyl-CoA desaturase; Ser, serine; sFA, saturated fatty acid; uFA, unsaturated fatty acid.

 
This model implies that the fatty acid-induced downregulation of ABCA1 has a biological function. Fatty acids acutely destabilize ABCA1 over a fatty acid-to-albumin molar ratio in the high physiologic range (26). Multiple unsaturated fatty acids have the same effects, including the most abundant one, oleate. In the presence of LXR ligands, which are generated when cells overaccumulate cholesterol, the saturated fatty acids palmitate and stearate also become ABCA1 destabilizers because they are converted to unsaturated fatty acids by the LXR-induced enzyme stearoyl-CoA desaturase 1 (36). Thus, the activity of the ABCA1 pathway in cholesterol-loaded cells, such as atherogenic macrophages, is likely to become rapidly suppressed when they are exposed to moderately high levels of the most common fatty acids, oleate and palmitate.

Although the physiologic reason for this suppression is unknown, it is consistent with other studies showing cross-regulation of the fatty acid and sterol metabolic pathways (37–39). There are several possible reasons why unsaturated fatty acids would inhibit ABCA1. The incorporation of unsaturated fatty acids into phospholipids may promote membrane synthesis, which would require an increased supply of cholesterol. Membrane ABCA1 might also play a direct role in the formation of membrane lipid rafts. Recent studies have shown that overexpressing ABCA1 in cells disrupts membrane lipid rafts (40), whereas ablating ABCA1 expression increases the lipid raft content (41). Reducing ABCA1 levels could be one of the mechanisms by which unsaturated fatty acids modulate membrane lipid rafts. It is also possible that inhibiting ABCA1 serves to suppress some other as yet unidentified ABCA1 function that plays a role in fatty acid metabolism.

The current study has important therapeutic implications for treating cardiovascular disease. A mouse study showed that ABCA1 mRNA and protein levels in tissues were highly discordant (42), consistent with the importance of posttranscriptional events in regulating ABCA1 levels. Thus, an understanding of the mechanisms by which fatty acids increase ABCA1 degradation will be helpful for designing therapeutic interventions that enhance the activity of this cholesterol-removal pathway and prevent atherosclerosis.


   ACKNOWLEDGMENTS
 
This work was supported by National Institutes of Health Grants HL-55362 and DK-02456.

Submitted on October 3, 2006
Revised on January 17, 2007


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 EXPERIMENTAL PROCEDURES
 RESULTS
 DISCUSSION
 REFERENCES
 
  1. Joyce, C., L. Freeman, H. B. Brewer, Jr., and S. Santamarina-Fojo. 2003. Study of ABCA1 function in transgenic mice. Arterioscler. Thromb. Vasc. Biol. 23: 965–971.[Abstract/Free Full Text]

  2. Aiello, R. J., D. Brees, and O. L. Francone. 2003. ABCA1-deficient mice: insights into the role of monocyte lipid efflux in HDL formation and inflammation. Arterioscler. Thromb. Vasc. Biol. 23: 972–980.[Abstract/Free Full Text]

  3. Basso, F., L. Freeman, C. L. Knapper, A. Remaley, J. Stonik, E. B. Neufeld, T. Tansey, M. J. Amar, J. Fruchart-Najib, N. Duverger, et al. 2003. Role of the hepatic ABCA1 transporter in modulating intrahepatic cholesterol and plasma HDL cholesterol concentrations. J. Lipid Res. 44: 296–302.[Abstract/Free Full Text]

  4. Oram, J. F., and J. W. Heinecke. 2005. ATP-binding cassette transporter A1: a cell cholesterol exporter that protects against cardiovascular disease. Physiol. Rev. 85: 1343–1372.[Abstract/Free Full Text]

  5. Wang, N., and A. R. Tall. 2003. Regulation and mechanisms of ATP-binding cassette transporter A1-mediated cellular cholesterol efflux. Arterioscler. Thromb. Vasc. Biol. 23: 1178–1184.[Abstract/Free Full Text]

  6. Luciani, M. F., F. Denizot, S. Savary, M. G. Mattei, and G. Chimini. 1994. Cloning of two novel ABC transporters mapping on human chromosome 9. Genomics. 21: 150–159.[CrossRef][Medline]

  7. Brooks-Wilson, A., M. Marcil, S. M. Clee, L. H. Zhang, K. Roomp, M. van Dam, L. Yu, C. Brewer, J. A. Collins, H. O. Molhuizen, et al. 1999. Mutations in ABC1 in Tangier disease and familial high-density lipoprotein deficiency. Nat. Genet. 22: 336–345.[CrossRef][Medline]

  8. Bodzioch, M., E. Orso, J. Klucken, T. Langmann, A. Bottcher, W. Diederich, W. Drobnik, S. Barlage, C. Buchler, M. Porsch-Ozcurumez, et al. 1999. The gene encoding ATP-binding cassette transporter 1 is mutated in Tangier disease. Nat. Genet. 22: 347–351.[CrossRef][Medline]

  9. Rust, S., M. Rosier, H. Funke, J. Real, Z. Amoura, J. C. Piette, J. F. Deleuze, H. B. Brewer, N. Duverger, P. Denefle, et al. 1999. Tangier disease is caused by mutations in the gene encoding ATP-binding cassette transporter 1. Nat. Genet. 22: 352–355.[CrossRef][Medline]

  10. Lawn, R. M., D. P. Wade, M. R. Garvin, X. Wang, K. Schwartz, J. G. Porter, J. J. Seilhamer, A. M. Vaughan, and J. F. Oram. 1999. The Tangier disease gene product ABC1 controls the cellular apolipoprotein-mediated lipid removal pathway. J. Clin. Invest. 104: R25–R31.[Medline]

  11. Assman, G., A. von Eckardstein, and H. B. Brewer. 1995. Familial high lipoprotein deficiency: Tangier disease. In The Metabolic and Molecular Bases of Inherited Disease, C. R. Scriver, et al., editors. McGraw-Hill, New York. 2053–2072.

  12. Serfaty-Lacrosniere, C., F. Civeira, A. Lanzberg, P. Isaia, J. Berg, E. D. Janus, M. P. Smith, Jr., P. H. Pritchard, J. Frohlich, R. S. Lees, et al. 1994. Homozygous Tangier disease and cardiovascular disease. Atherosclerosis. 107: 85–98.[CrossRef][Medline]

  13. Langmann, T., J. Klucken, M. Reil, G. Liebisch, M. F. Luciani, G. Chimini, W. E. Kaminski, and G. Schmitz. 1999. Molecular cloning of the human ATP-binding cassette transporter 1 (hABC1): evidence for sterol-dependent regulation in macrophages. Biochem. Biophys. Res. Commun. 257: 29–33.[CrossRef][Medline]

  14. Schwartz, K., R. M. Lawn, and D. P. Wade. 2000. ABC1 gene expression and apoA-I-mediated cholesterol efflux are regulated by LXR. Biochem. Biophys. Res. Commun. 274: 794–802.[CrossRef][Medline]

  15. Costet, P., Y. Luo, N. Wang, and A. R. Tall. 2000. Sterol-dependent transactivation of the ABC1 promoter by the liver X receptor/retinoid X receptor. J. Biol. Chem. 275: 28240–28245.[Abstract/Free Full Text]

  16. Venkateswaran, A., B. A. Laffitte, S. B. Joseph, P. A. Mak, D. C. Wilpitz, P. A. Edwards, and P. Tontonoz. 2000. Control of cellular cholesterol efflux by the nuclear oxysterol receptor LXR alpha. Proc. Natl. Acad. Sci. USA. 97: 12097–12102.[Abstract/Free Full Text]

  17. Cavelier, L. B., Y. Qiu, J. K. Bielicki, V. Afzal, J. F. Cheng, and E. M. Rubin. 2001. Regulation and activity of the human ABCA1 gene in transgenic mice. J. Biol. Chem. 276: 18046–18051.[Abstract/Free Full Text]

  18. Smith, J. D., M. Miyata, M. Ginsberg, C. Grigaux, E. Shmookler, and A. S. Plump. 1996. Cyclic AMP induces apolipoprotein E binding activity and promotes cholesterol efflux from a macrophage cell line to apolipoprotein acceptors. J. Biol. Chem. 271: 30647–30655.[Abstract/Free Full Text]

  19. Oram, J. F., R. M. Lawn, M. R. Garvin, and D. P. Wade. 2000. ABCA1 is the cAMP-inducible apolipoprotein receptor that mediates cholesterol secretion from macrophages. J. Biol. Chem. 275: 34508–34511.[Abstract/Free Full Text]

  20. Bortnick, A. E., G. H. Rothblat, G. Stoudt, K. L. Hoppe, L. J. Royer, J. McNeish, and O. L. Francone. 2000. The correlation of ATP-binding cassette 1 mRNA levels with cholesterol efflux from various cell lines. J. Biol. Chem. 275: 28634–28640.[Abstract/Free Full Text]

  21. Martinez, L. O., B. Agerholm-Larsen, N. Wang, W. Chen, and A. R. Tall. 2003. Phosphorylation of a pest sequence in ABCA1 promotes calpain degradation and is reversed by ApoA-I. J. Biol. Chem. 278: 37368–37374.[Abstract/Free Full Text]

  22. Yamauchi, Y., M. Hayashi, S. Abe-Dohmae, and S. Yokoyama. 2003. Apolipoprotein A-I activates protein kinase C alpha signaling to phosphorylate and stabilize ATP binding cassette transporter A1 for the high density lipoprotein assembly. J. Biol. Chem. 278: 47890–47897.[Abstract/Free Full Text]

  23. See, R. H., R. A. Candy-Malcolm, R. R. Singaraja, S. Zhou, A. Silverston, M. T. Huber, J. Moran, E. R. James, R. Janoo, J. M. Savill, et al. 2002. Protein kinase A site-specific phosphorylation regulates ATP-binding cassette A1 (ABCA1)-mediated phospholipid efflux. J. Biol. Chem. 277: 41835–41842.[Abstract/Free Full Text]

  24. Roosbeek, S., F. Peelman, A. Verhee, C. Labeur, H. Caster, M. F. Lensink, C. Cirulli, J. Grooten, C. Cochet, J. Vandekerckhove, et al. 2004. Phosphorylation by protein kinase CK2 modulates the activity of the ATP binding cassette A1 transporter. J. Biol. Chem. 279: 37779–37788.[Abstract/Free Full Text]

  25. Tang, C., A. M. Vaughan, and J. F. Oram. 2004. Janus kinase 2 modulates the apolipoprotein interactions with ABCA1 required for removing cellular cholesterol. J. Biol. Chem. 279: 7622–7628.[Abstract/Free Full Text]

  26. Wang, Y., and J. F. Oram. 2002. Unsaturated fatty acids inhibit cholesterol efflux from macrophages by increasing degradation of ATP-binding cassette transporter A1. J. Biol. Chem. 277: 5692–5697.[Abstract/Free Full Text]

  27. Wang, Y., and J. F. Oram. 2005. Unsaturated fatty acids phosphorylate and destabilize ABCA1 through a phospholipase D2 pathway. J. Biol. Chem. 280: 35896–35903.[Abstract/Free Full Text]

  28. Mendez, A. J., J. F. Oram, and E. L. Bierman. 1991. Protein kinase C as a mediator of high density lipoprotein receptor-dependent efflux of intracellular cholesterol. J. Biol. Chem. 266: 10104–10111.[Abstract/Free Full Text]

  29. Goldstein, J. L., Y. K. Ho, S. K. Basu, and M. S. Brown. 1979. Binding site on macrophages that mediates uptake and degradation of acetylated low density lipoprotein, producing massive cholesterol deposition. Proc. Natl. Acad. Sci. USA. 76: 333–337.[Abstract/Free Full Text]

  30. Vaughan, A. M., and J. F. Oram. 2003. ABCA1 redistributes membrane cholesterol independent of apolipoprotein interactions. J. Lipid Res. 44: 1373–1380.[Abstract/Free Full Text]

  31. Mendez, A. J., G. M. Anantharamaiah, J. P. Segrest, and J. F. Oram. 1994. Synthetic amphipathic helical peptides that mimic apolipoprotein A-I in clearing cellular cholesterol. J. Clin. Invest. 94: 1698–1705.[Medline]

  32. Ringshausen, I., F. Schneller, C. Bogner, S. Hipp, J. Duyster, C. Peschel, and T. Decker. 2002. Constitutively activated phosphatidylinositol-3 kinase (PI-3K) is involved in the defect of apoptosis in B-CLL: association with protein kinase Cdelta. Blood. 100: 3741–3748.[Abstract/Free Full Text]

  33. Chen, J. S., A. S. Greenberg, and S. M. Wang. 2002. Oleic acid-induced PKC isozyme translocation in RAW 264.7 macrophages. J. Cell. Biochem. 86: 784–791.[CrossRef][Medline]

  34. Steinberg, S. 2004. Distinctive activation mechanisms and functions for protein kinase Cdelta. Biochem. J. 384: 449–459.[CrossRef][Medline]

  35. Lee, H. S., S. Y. Park, H. W. Lee, and H. S. Choi. 2004. Secretions of MMP-9 by soluble glucocorticoid-induced tumor necrosis factor receptor (sGITR) mediated by protein kinase C (PKC)delta and phospholipase D (PLD) in murine macrophage. J. Cell. Biochem. 92: 481–490.[CrossRef][Medline]

  36. Wang, Y., B. Kurdi-Haidar, and J. F. Oram. 2004. LXR-mediated activation of macrophage stearoyl-CoA desaturase generates unsaturated fatty acids that destabilize ABCA1. J. Lipid Res. 45: 972–980.[Abstract/Free Full Text]

  37. Brown, M. S., and J. L. Goldstein. 1999. A proteolytic pathway that controls the cholesterol content of membranes, cells, and blood. Proc. Natl. Acad. Sci. USA. 96: 11041–11048.[Abstract/Free Full Text]

  38. Osborne, T. F. 2000. Sterol regulatory element-binding proteins (SREBPs): key regulators of nutritional homeostasis and insulin action. J. Biol. Chem. 275: 32379–32382.[Free Full Text]

  39. Repa, J. J., G. Liang, J. Ou, Y. Bashmakov, J. M. Lobaccaro, I. Shimomura, B. Shan, M. S. Brown, J. L. Goldstein, and D. J. Mangelsdorf. 2000. Regulation of mouse sterol regulatory element-binding protein-1c gene (SREBP-1c) by oxysterol receptors, LXRalpha and LXRbeta. Genes Dev. 14: 2819–2830.[Abstract/Free Full Text]

  40. Landry, Y. D., D. Nandi, S. Bell, A. M. Vaughan, and X. Zha. 2006. ATP-binding cassette transporter A1 expression disrupts raft membrane microdomains through its ATPase-related functions. J. Biol. Chem. 281: 36091–36101.[Abstract/Free Full Text]

  41. Koseki, M., K-I. Hirano, D. Masuda, C. Ikegami, M. Tanaka, A. Ota, J. C. Sandoval, N. Nakagawa-Toyama, S. B. Sato, T. Kobayashi, et al. 2007. Increased lipid rafts and accelerated lipopolysaccaride-induced tumor necrosis factor-alpha secretion in ABCA1-deficient macrophages. J. Lipid Res. 48: 299–306.[Abstract/Free Full Text]

  42. Wellington, C. L., E. K. Walker, A. Suarez, A. Kwok, N. Bissada, R. Singaraja, Y. Z. Yang, L. H. Zhang, E. James, J. E. Wilson, et al. 2002. ABCA1 mRNA and protein distribution patterns predict multiple different roles and levels of regulation. Lab. Invest. 82: 273–283.[Medline]


Add to CiteULike CiteULike   Add to Complore Complore   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati    What's this?


This article has been cited by other articles:


Home page
 J. Biol. Chem.Home page
M. H. Nagelin, S. Srinivasan, J. L. Nadler, and C. C. Hedrick
Murine 12/15-Lipoxygenase Regulates ATP-binding Cassette Transporter G1 Protein Degradation through p38- and JNK2-dependent Pathways
J. Biol. Chem., November 6, 2009; 284(45): 31303 - 31314.
[Abstract] [Full Text] [PDF]

Home page
 Eur Heart JHome page
S. Rashid, M. Marcil, I. Ruel, and J. Genest
Identification of a novel human cellular HDL biosynthesis defect
Eur. Heart J., September 2, 2009; 30(18): 2204 - 2212.
[Abstract] [Full Text] [PDF]

Home page
 Arterioscler. Thromb. Vasc. Bio.Home page
G. L. Weibel, M. R. Joshi, E. T. Alexander, P. Zhu, I. A. Blair, and G. H. Rothblat
Overexpression of Human 15(S)-Lipoxygenase-1 in RAW Macrophages Leads to Increased Cholesterol Mobilization and Reverse Cholesterol Transport
Arterioscler Thromb Vasc Biol, June 1, 2009; 29(6): 837 - 842.
[Abstract] [Full Text] [PDF]

Home page
 J. Lipid Res.Home page
V. Paul, H. H. D. Meyer, K. Leidl, S. Soumian, and C. Albrecht
A novel enzyme immunoassay specific for ABCA1 protein quantification in human tissues and cells
J. Lipid Res., October 1, 2008; 49(10): 2259 - 2267.
[Abstract] [Full Text] [PDF]

Home page
 Am. J. Physiol. Endocrinol. Metab.Home page
C. Fernandez, M. Lindholm, M. Krogh, S. Lucas, S. Larsson, P. Osmark, K. Berger, J. Boren, B. Fielding, K. Frayn, et al.
Disturbed cholesterol homeostasis in hormone-sensitive lipase-null mice
Am J Physiol Endocrinol Metab, October 1, 2008; 295(4): E820 - E831.
[Abstract] [Full Text] [PDF]

Home page
 J. Biol. Chem.Home page
R. L. Jacobs, S. Lingrell, Y. Zhao, G. A. Francis, and D. E. Vance
Hepatic CTP:Phosphocholine Cytidylyltransferase-{alpha} Is a Critical Predictor of Plasma High Density Lipoprotein and Very Low Density Lipoprotein
J. Biol. Chem., January 25, 2008; 283(4): 2147 - 2155.
[Abstract] [Full Text] [PDF]

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
M600437-JLR200v1
M600437-JLR200v2
48/5/1062    most recent
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowRequest Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Wang, Y.
Right arrow Articles by Oram, J. F.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Wang, Y.
Right arrow Articles by Oram, J. F.
Social Bookmarking
Add to CiteULike   Add to Complore   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati  
What's this?

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
 All ASBMB Journals   Journal of Biological Chemistry 
 Molecular and Cellular Proteomics   ASBMB Today 
Advertisement
spacer
Advertisement
Advertisement