a3Na+/K+-ATPase is a neuronal receptor for Agrin

Agrin, through its interaction with the receptor tyrosine kinase MuSK, mediates accumulation of acetylcholine receptors (AChR) at the developing neuromuscular junction. Agrin has also been implicated in several functions in brain. However, the mechanism by which agrin exerts its effects in neural tissue is unknown. Here we present biochemical evidence that agrin binds to the alpha 3 subunit of the Na+/K+-ATPase (NKA) in CNS neurons. Colocalization with agrin binding sites at synapses supports the hypothesis that the alpha 3NKA is a neuronal agrin receptor. Agrin inhibition of alpha 3NKA activity results in membrane depolarization and increased action potential frequency in cortical neurons in culture and acute slice. An agrin fragment that acts as a competitive antagonist depresses action potential frequency, showing that endogenous agrin regulates native alpha 3NKA function. These data demonstrate that, through its interaction with the alpha 3NKA, agrin regulates activity-dependent processes in neurons, providing a molecular framework for agrin action in the CNS.