cAMP-stimulated protein phosphatase 2A activity associated with muscle A kinase-anchoring protein (mAKAP) signaling complexes inhibits the phosphorylation and activity of the cAMP-specific phosphodiesterase PDE4D3.
The concentration of the second messenger cAMP is tightly controlled in cells by the activity of phosphodiesterases. We have previously described how the protein kinase A-anchoring protein mAKAP serves as a scaffold for the cAMP-dependent protein kinase PKA and the cAMP-specific phosphodiesterase PDE4D3 in cardiac myocytes. PKA and PDE4D3 constitute a negative feedback loop whereby PKA-catalyzed phosphorylation and activation of PDE4D3 attenuate local cAMP levels. We now show that protein phosphatase 2A (PP2A) associated with mAKAP complexes is responsible for reversing the activation of PDE4D3 by catalyzing the dephosphorylation of PDE4D3 serine residue 54. Mapping studies reveal that a C-terminal mAKAP domain (residues 2085-2319) binds PP2A. Binding to mAKAP is required for PP2A function, such that deletion of the C-terminal domain enhances both base-line and forskolin-stimulated PDE4D3 activity. Interestingly, PP2A holoenzyme associated with mAKAP complexes in the heart contains the PP2A targeting subunit B56delta. Like PDE4D3, B56delta is a PKA substrate, and PKA phosphorylation of mAKAP-bound B56delta enhances phosphatase activity 2-fold in the complex. Accordingly, expression of a B56delta mutant that cannot be phosphorylated by PKA results in increased PDE4D3 phosphorylation. Taken together, our findings demonstrate that PP2A associated with mAKAP complexes promotes PDE4D3 dephosphorylation, serving both to inhibit PDE4D3 in unstimulated cells and also to mediate a cAMP-induced positive feedback loop following adenylyl cyclase activation and B56delta phosphorylation. In general, PKA.PP2A.mAKAP complexes exemplify how protein kinases and phosphatases may participate in molecular signaling complexes to dynamically regulate localized intracellular signaling.
Dodge-Kafka
Kimberly L
KL
Pat and Jim Calhoun Center for Cardiology, University of Connecticut Health Center, Farmington, Connecticut 06030, USA. dodge@uchc.edu
Bauman
Andrea
A
Mayer
Nicole
N
Henson
Edward
E
Heredia
Lorena
L
Ahn
Jung
J
McAvoy
Thomas
T
Nairn
Angus C
AC
Kapiloff
Michael S
MS
D054758:A Kinase Anchor Proteins / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4 / Q000378:metabolism*; D025461:Feedback, Physiological; D015971:Gene Expression Regulation, Enzymologic; D006801:Humans; D010766:Phosphorylation; D011485:Protein Binding; D025941:Protein Interaction Mapping; D054648:Protein Phosphatase 2 / Q000737:chemistry* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D015398:Signal Transduction
D054758:A Kinase Anchor Proteins; C093173:AKAP6 protein, human; C484293:Akap6 protein, rat; D000242:Cyclic AMP; D054648:Protein Phosphatase 2; D054703:Cyclic Nucleotide Phosphodiesterases, Type 4