Contribution of D4-F to ABCA1 Expression and Cholesterol Efflux in THP-1 Macrophage-derived Foam Cells

Adenosine triphosphate-binding cassette transporter A1 (ABCA1) plays a crucial role in apolipoprotein A-I (apoA-I) binding activity and promotes cellular cholesterol efflux. ApoA-I mimetic peptide D4-F has reported to have the similar ability as apoA-I. However, the detailed mechanisms of ABCA1 regulation by D4-F are not understood. In the present study, we investigated the effects of D4-F on ABCA1 expression and ABCA1-dependent cholesterol efflux and examined the role of Cdc42/cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) pathway on the regulation of ABCA1 by D4-F in THP-1 macrophage-derived foam cells. Results showed that D4-F stabilized ABCA1 protein and enhanced ABCA1-dependent cholesterol efflux but had no effect on ABCA1 messenger RNA expression. We also revealed that D4-F enhanced cAMP level and PKA activity and ABCA1 serine phosphorylation. Short interfering RNA of PKA led to reduction of ABCA1 serine phosphorylation and ABCA1-mediated cholesterol efflux compensated by D4-F. PKA-specific activation by PKA agonist enhanced the upregulation of ABCA1 serine phosphorylation and ABCA1-mediated cholesterol efflux by D4-F. However, ABCA1 expression did not change by treatment with PKA agonist or PKA-short interfering RNA. We found that secramine B of Cdc42 inhibitor reduced the cAMP level compensated by D4-F. These results provide evidence that D4-F enhances ABCA1 serine phosphorylation and ABCA1-dependent cholesterol efflux through Cdc42/cAMP/PKA pathway in THP-1 macrophage-derived foam cells.