title: Inhibition of ERK1/2 and activation of liver X receptor synergistically induce macrophage ABCA1 expression and cholesterol efflux.
abstract: ATP-binding cassette transporter A1 (ABCA1), a molecule mediating free cholesterol efflux from peripheral tissues to apoAI and high density lipoprotein (HDL), inhibits the formation of lipid-laden macrophage/foam cells and the development of atherosclerosis. ERK1/2 are important signaling molecules regulating cellular growth and differentiation. The ERK1/2 signaling pathway is implicated in cardiac development and hypertrophy. However, the role of ERK1/2 in the development of atherosclerosis, particularly in macrophage cholesterol homeostasis, is unknown. In this study, we investigated the effects of ERK1/2 activity on macrophage ABCA1 expression and cholesterol efflux. Compared with a minor effect by inhibition of other kinases, inhibition of ERK1/2 significantly increased macrophage cholesterol efflux to apoAI and HDL. In contrast, activation of ERK1/2 reduced macrophage cholesterol efflux and ABCA1 expression. The increased cholesterol efflux by ERK1/2 inhibitors was associated with the increased ABCA1 levels and the binding of apoAI to cells. The increased ABCA1 by ERK1/2 inhibitors was due to increased ABCA1 mRNA and protein stability. The induction of ABCA1 expression and cholesterol efflux by ERK1/2 inhibitors was concentration-dependent. The mechanism study indicated that activation of liver X receptor (LXR) had little effect on ERK1/2 expression and activation. ERK1/2 inhibitors had no effect on macrophage LXRalpha/beta expression, whereas they did not influence the activation or the inhibition of the ABCA1 promoter by LXR or sterol regulatory element-binding protein (SREBP). However, inhibition of ERK1/2 and activation of LXR synergistically induced macrophage cholesterol efflux and ABCA1 expression. Our data suggest that ERK1/2 activity can play an important role in macrophage cholesterol trafficking.
authors.affiliation: Colleges of Life Sciences, Nankai University, Tianjin 300071, China.
authors.forename: Xiaoye
authors.initials: X
authors.lastname: Zhou
authors.forename: Zhinan
authors.initials: Z
authors.lastname: Yin
authors.forename: Xianzhi
authors.initials: X
authors.lastname: Guo
authors.forename: David P
authors.initials: DP
authors.lastname: Hajjar
authors.forename: Jihong
authors.initials: J
authors.lastname: Han
mesh_terms: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters / Q000032:analysis / Q000235:genetics*; D000818:Animals; D016632:Apolipoprotein A-I / Q000378:metabolism; D050197:Atherosclerosis / Q000209:etiology; D001692:Biological Transport; D002460:Cell Line; D002784:Cholesterol / Q000378:metabolism*; D005786:Gene Expression Regulation; D008075:Lipoproteins, HDL / Q000378:metabolism; D000071518:Liver X Receptors; D008264:Macrophages / Q000378:metabolism*; D017737:Macrophages, Peritoneal / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D048052:Mitogen-Activated Protein Kinase 3 / Q000037:antagonists & inhibitors*; D057093:Orphan Nuclear Receptors / Q000378:metabolism*; D055550:Protein Stability; D012333:RNA, Messenger / Q000032:analysis
chemical_list: D064286:ATP Binding Cassette Transporter 1; D018528:ATP-Binding Cassette Transporters; D016632:Apolipoprotein A-I; D008075:Lipoproteins, HDL; D000071518:Liver X Receptors; C000605214:Nr1h3 protein, mouse; D057093:Orphan Nuclear Receptors; D012333:RNA, Messenger; D002784:Cholesterol; D048052:Mitogen-Activated Protein Kinase 3