Identification and characterization of an A-kinase anchoring domain in Chromodomain Helicase Binding Protein 8.

Abstract

A-kinase anchoring proteins (AKAPs) localize protein kinase A (PKA) to discrete microdomains in the cell, and act as scaffolds for the phosphorylation targets and regulatory proteins of the PKA signaling pathway. Reduced phosphorylation of PKA substrates and reduced anchoring of PKA by AKAPs has been observed in heart failure. The upregulation of developmental genes is also characteristic of failing hearts. Chromodomain helicase binding protein 8 (Chd8) is a chromatin remodeling protein that is expressed at high levels in embryogenesis, and regulates transcription of apoptotic genes in the context of large protein complexes. A screen for novel AKAPs in the human heart identified Chd8 as a PKA-binding protein. Here we show that Chd8 contains an AKAP domain in its amino terminus, and that phosphorylation of the PKA regulatory subunit modulates anchoring of PKA by Chd8. We have also identified Chd8 in nuclear and perinuclear domains in three cell types. Chd8 was found to be expressed in high levels in embryonic and post-natal heart, and bound to the p53-responsive P2 promoter of the MDM2 gene. These results demonstrate a novel function for Chd8 as an AKAP and characterize Chd8 in the context of cardiac development. We therefore conclude that Chd8 is a novel AKAP and propose that Chd8 plays a role in the regulation of MDM2, a key regulator of p53.