AKAP79 enables calcineurin to directly suppress protein kinase A activity.

Timothy W Church,João Antunes,Trevor G Smart,Jeanette Hellgren Kotaleski,Olivia Eriksson,Parul Tewatia,Saad Hannan,Matthew G Gold

doi:10.7554/elife.68164

Abstract

Interplay between the second messengers cAMP and Ca2+ is a hallmark of dynamic cellular processes. A common motif is the opposition of the Ca2+-sensitive phosphatase calcineurin and the major cAMP receptor, protein kinase A (PKA). Calcineurin dephosphorylates sites primed by PKA to bring about changes including synaptic long-term depression (LTD). AKAP79 supports signaling of this type by anchoring PKA and calcineurin in tandem. In this study, we discovered that AKAP79 increases the rate of calcineurin dephosphorylation of type II PKA regulatory subunits by an order of magnitude. Fluorescent PKA activity reporter assays, supported by kinetic modeling, show how AKAP79-enhanced calcineurin activity enables suppression of PKA without altering cAMP levels by increasing PKA catalytic subunit capture rate. Experiments with hippocampal neurons indicate that this mechanism contributes toward LTD. This non-canonical mode of PKA regulation may underlie many other cellular processes.

Highlights

Cyclic adenosine monophosphate and Ca2+ are ancient second messengers that are fundamental to the regulation of many dynamic cellular processes including synaptic plasticity (Huang et al, 1994), heart contraction (Bers et al, 2019), and glycogen metabolism (Roach et al, 2012)
A-kinase anchoring protein 79 (AKAP79)/150 contains a 346 ‘PIAIIIT’ CN anchoring motif that is necessary for long-term depression (LTD) (Jurado et al, 2010; Sanderson et al, 2012)
We show that the key substrate for CN is likely to be full-length pRII subunits, and that in 361 fact AKAP79 enhances the activity towards pRII at physiological concentrations by more than ten-fold

Summary

Introduction

Cyclic adenosine monophosphate (cAMP) and Ca2+ are ancient second messengers that are fundamental to the regulation of many dynamic cellular processes including synaptic plasticity (Huang et al, 1994), heart contraction (Bers et al, 2019), and glycogen metabolism (Roach et al, 2012). The anchoring protein is necessary for both induction of long-term depression (LTD) of CA3-CA1 hippocampal synapses (Lu et al, 2008; Tunquist et al, 2008; Weisenhaus et al, 2010), and for CN89 mediated dephosphorylation of NFAT (Kar et al, 2014; Murphy et al, 2014) – both processes that are driven by CN dephosphorylation of sites primed by PKA Despite these characteristics, the possibility that AKAP79 could support pRII dephosphorylation by CN has been disregarded perhaps because paradoxically AKAP79 acts as a weak inhibitor for CN dephosphorylation of 20-mer peptides corresponding to the phosphorylated RII IS (Coghlan et al, 1995; Kashishian et al, 1998). We went on to determine if AKAP79 can reduce the fraction of dissociated C subunits in concert with CN using fluorescence-based assays supported by kinetic modeling, before substantiating our observations in hippocampal neurons

Results

Discussion

Methods & Materials