MCP-1 impacts RCT by repressing ABCA1, ABCG1, and SR-BI through PI3K/Akt posttranslational regulation in HepG2 cells

J Lipid Res. 2013 May;54(5):1231-40. doi: 10.1194/jlr.M032482. Epub 2013 Feb 12.

Abstract

Monocyte chemoattractant protein-1 (MCP-1) plays crucial roles at multiple stages of atherosclerosis. We hypothesized that MCP-1 might impair the reverse cholesterol transport (RCT) capacity of HepG2 cells by decreasing the cell-surface protein expression of ATP binding cassette A1 (ABCA1), ATP binding cassette G1 (ABCG1), and scavenger receptor class B type I (SR-BI). MCP-1 reduced the total protein and mRNA levels of ABCA1 and SR-BI, but not of ABCG1. MCP-1 decreased the cell-surface protein expression of ABCA1, ABCG1, and SR-BI in dose-dependent and time-dependent manners, as measured using cell-surface biotinylation. We further studied the phosphoinositide 3-kinase (PI3K)/serine/threonine protein kinase Akt pathway in regulating receptor trafficking. Both the translation and transcription of ABCA1, ABCG1, and SR-BI were not found to be regulated by the PI3K/Akt pathway. However, the cell-surface protein expression of ABCA1, ABCG1, and SR-BI could be regulated by PI3K activity, and PI3K activation corrected the MCP-1-induced decreases in the cell-surface protein expression of ABCA1, ABCG1, and SR-BI. Moreover, we found that MCP-1 decreased the lipid uptake by HepG2 cells and the ABCA1-mediated cholesterol efflux to apoA-I, which could be reversed by PI3K activation. Our data suggest that MCP-1 impairs RCT activity in HepG2 cells by a PI3K/Akt-mediated posttranslational regulation of ABCA1, ABCG1, and SR-BI cell-surface expression.

MeSH terms

  • ATP Binding Cassette Transporter 1
  • ATP Binding Cassette Transporter, Subfamily G, Member 1
  • ATP-Binding Cassette Transporters / genetics*
  • ATP-Binding Cassette Transporters / metabolism
  • Atherosclerosis / genetics*
  • Atherosclerosis / pathology
  • Chemokine CCL2 / genetics*
  • Chemokine CCL2 / metabolism
  • Cholesterol / metabolism
  • Elafin / metabolism
  • Gene Expression Regulation
  • Hep G2 Cells
  • Humans
  • Oncogene Protein v-akt / metabolism
  • Protein Processing, Post-Translational
  • Scavenger Receptors, Class B / genetics*
  • Scavenger Receptors, Class B / metabolism
  • Signal Transduction

Substances

  • ABCA1 protein, human
  • ABCG1 protein, human
  • ATP Binding Cassette Transporter 1
  • ATP Binding Cassette Transporter, Subfamily G, Member 1
  • ATP-Binding Cassette Transporters
  • CCL2 protein, human
  • Chemokine CCL2
  • Elafin
  • PI3 protein, human
  • SCARB1 protein, human
  • Scavenger Receptors, Class B
  • Cholesterol
  • Oncogene Protein v-akt