Abstract
Regulator of G protein signaling 2 (RGS2) is a GTPase-activating protein for Gαq, which is involved in regulating various vascular functions. To understand how RGS2 regulates foam cell formation, the present study identified signaling pathways controlled by lipopolysaccharide (LPS) and discovered new mechanisms whereby protein kinase C (PKC)-η and phospholipase D (PLD) 2 regulate RGS2 expression. The toll-like receptor (TLR) 4 agonist LPS caused foam cell formation of Raw264.7 macrophages and dramatically decreased RGS2 mRNA expression. RGS2 down-regulation by LPS was partially recovered by TLR4 small interfering RNA (siRNA). Peritoneal macrophages were separated from wild-type and TLR4 mutant mice, and treatment with LPS showed RGS2 expression decrease in wild-type macrophages but no change in TLR4 mutant macrophages. RGS2 overexpression was suppressed, whereas RGS2 down-regulation accelerated foam cell formation by LPS. Treatment of PKC-η pseudosubstrate weakened foam cell formation and recovered RGS2 down-regulation by LPS. In addition, LPS or phorbol 12-myristate 13-acetate stimulated PLD activity, and the pretreatment of PLD inhibitor weakened foam cell formation and recovered RGS2 down-regulation. Inhibition of PLD2 expression by siRNA also weakened foam cell formation and partially recovered LPS-mediated RGS2 down-regulation. On the other hand, PLD2 overexpression intensified RGS2 down-regulation and foam cell formation by LPS. These results suggest that LPS causes foam cell formation by increasing PKC-η and PLD2 activity by down-regulating RGS2 expression via TLR4 dependently.
Footnotes
This work was supported by the Korean Science and Engineering Foundation, Ministry of Education, and Science, and Technology [Grant 2010-0001243]; and by Mid-Career Research Program, National Research Foundation, Ministry of Education, and Science and Technology [Grant 2009-0083759].
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
doi:10.1124/mol.110.064394.
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ABBREVIATIONS:
- RGS
- regulator of G protein signaling
- PKC
- protein kinase C
- PLD
- phospholipase D
- TLR
- toll-like receptor
- GAP
- GTPase activating protein
- PA
- phosphatidic acid
- DAG
- diacylglycerol
- LDL
- low-density lipoprotein
- PCR
- polymerase chain reaction
- RT-PCR
- reverse transcription-polymerase chain reaction
- siRNA
- small interfering RNA
- DMEM
- Dulbecco's modified Eagle's medium
- PS
- pseudosubstrate
- LPS
- lipopolysaccharide
- PMA
- phorbol 12-myristate 13-acetate
- BuOH
- butanol
- ABCA1
- ATP-binding cassette transporter 1.
- Received February 25, 2010.
- Accepted June 17, 2010.
- Copyright © 2010 The American Society for Pharmacology and Experimental Therapeutics
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