Neuronal ER-plasma membrane junctions couple excitation to Ca2+-activated PKA signaling

Abstract

Junctions between the endoplasmic reticulum (ER) and the plasma membrane (PM) are specialized membrane contacts ubiquitous in eukaryotic cells. Concentration of intracellular signaling machinery near ER-PM junctions allows these domains to serve critical roles in lipid and Ca²⁺ signaling and homeostasis. Subcellular compartmentalization of protein kinase A (PKA) signaling also regulates essential cellular functions, however, no specific association between PKA and ER-PM junctional domains is known. Here, we show that in brain neurons type I PKA is directed to Kv2.1 channel-dependent ER-PM junctional domains via SPHKAP, a type I PKA-specific anchoring protein. SPHKAP association with type I PKA regulatory subunit RI and ER-resident VAP proteins results in the concentration of type I PKA between stacked ER cisternae associated with ER-PM junctions. This ER-associated PKA signalosome enables reciprocal regulation between PKA and Ca²⁺ signaling machinery to support Ca²⁺ influx and excitation-transcription coupling. These data reveal that neuronal ER-PM junctions support a receptor-independent form of PKA signaling driven by membrane depolarization and intracellular Ca²⁺, allowing conversion of information encoded in electrical signals into biochemical changes universally recognized throughout the cell.

A-kinase anchoring proteins (AKAPs) target protein kinase A to specific locations within the cell. Here, the authors identify SPHKAP as an AKAP that enriches protein kinase A near ER-plasma membrane contact sites in brain neurons.