Involvement of Protein Kinase D in Phosphorylation and Increase of DNA Binding of Activator Protein 2α to Downregulate ATP-Binding Cassette Transporter A1

Background— Activator protein (AP) 2α negatively regulates expression of ABCA1 gene through Ser-phosphorylation of AP2α (Circ Res . 2007;101:156–165). Potential specific Ser-phosphorylation sites for this reaction were investigated in human AP2α.Methods and Results— The phosphorylation was shown mediated by PKD, and Ser258 and Ser326 were found in its specific phosphorylation sequence segment in AP2α. PKD phosphorylated Ser258 more than Ser326 and induced its binding to the ABCA1 promoter. These reactions and AP2α-induced suppression of the ABCA1 promoter activity were reversed by mutation of Ser258 more than Ser326 mutation. Knockdown of PKD by siRNA reduced the AP2α Ser-phosphorylation, and increased ABCA1 expression and HDL biogenesis. Gö6983 inhibited PKD more selectively than PKC in THP-1 and HEK 293 cells and in mice, and increased ABCA1 expression, HDL biogenesis, and plasma HDL level.Conclusion— PKD phosphorylates AP2α to negatively regulate expression of ABCA1 gene to increase HDL biogenesis. The major functional phosphorylation of AP2α was identified at Ser258 by PKD, in the AP2α basic domain highly conserved among species and all 5 subtypes of AP2. PKD/AP2 system can be a potent pharmacological target for prevention of atherosclerosis.