Stimulus-evoked ERK-dependent phosphorylation of activity-regulated cytoskeleton-associated protein (Arc) regulates its neuronal subcellular localization

- ERK binds a non-canonical docking motif in the Arc C-terminal domain.
- In vitro kinase assays identify five ERK phosphorylation sites on Arc.
- Stimulus-evoked phosphorylation occurs on Ser206 in the central hinge region of Arc.
- Phosphorylation regulates Arc subcellular localization in hippocampal neurons.
- Endogenous Arc is Ser206 phosphorylated during LTP in live rats.

Activity-regulated cytoskeletal-associated protein (Arc) is implicated as a master regulator of long-term synaptic plasticity and memory formation in mammalian brain. Arc acts at synapses and within the nucleus, but the mechanisms controlling Arc localization and function are little known. As Arc transcription and translation are regulated by extracellularsignal-regulated kinase (ERK) signaling, we asked whether Arc protein itself is phosphorylated by ERK. GST-fused Arc of rat origin was able to pull down endogenous ERK2 from rat hippocampal lysates. Using a peptide array, we show that ERK binds a non-canonical docking (D) motif in the C-terminal domain of Arc, and this interaction is abolished by phosphorylation of Tyr309. Activated ERK2 phosphorylated bacterially expressed Arc in vitro at all five predicted sites, as confirmed by phospho-specific protein staining and LC-MS/MS analysis. In neuroblastoma cells expressing epitope tagged-Arc, we demonstrate ERK-dependent phosphorylation of Arc in response to activation of muscarinic cholinergic receptors with carbachol. Using phosphosite-specific antibodies, this stimulus-evoked phosphorylation was shown to occur on Ser206 located within the central hinge region of Arc. In cultured hippocampal neurons expressing phosphomutant Arc under control of the activity-dependent promoter, we show that Ser206 phosphorylation regulates the nuclear:cytosolic localization of Arc. Thus, the neuronal activity-induced phosphomimic exhibits enhanced cytosolic localization relative to phosphodeficient and wild-type Arc. Furthermore, enhanced Ser206 phosphorylation of endogenous Arc was detected in the dentate gyrus cytoskeletal fraction after induction of long-term potentiation (LTP) in live rats. Taken together, this work demonstrates stimulus-evoked ERK-dependent phosphorylation and regulation of Arc protein.