Postsynaptic Signaling Pathways

University Of Iowa, Iowa City IA

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Abstract

DESCRIPTION (provided by applicant): Synapses are central players in neuronal signal transmission and prime targets for drug treatments of various neurological disorders. The long-term goal of this application is to characterize the assembly and function of signaling pathways at postsynaptic sites. This proposal focuses on molecular mechanisms that target PKA together with its regulator (B2 adrenergic receptor, b2 AR) and its antagonist (phosphatase PP2A) to postsynaptic effector proteins, in particular class C L-type Ca2+ channel, whose activity is upregulated by PKA. This channel is clustered at postsynaptic sites of glutamatergic synapses. We discovered that this channel assembles the b2 AR, the trimeric Gs protein, adenylyl cyclase, AKAP75/150, PKA, and the counterbalancing phosphatase PP2A into a macromolecular signaling complex. We also found that upregulation of channel activity upon stimulation of b2 AR is highly localized in neurons. This is the very first example of a complex that links a cAMP-coupled receptor to one of its ultimate targets. The localized signaling explains how the diffusible cAMP can mediate specific effects. The interaction sites of the channel with b2 AR, AKAP75/15O, and PP2A will be defined and mutated for functional studies in heterologous expression systems (HEK293 cells). Peptides and fusion proteins will be developed and used to disrupt these interactions in neurons for subsequent biochemical and electrophysiological evaluation of regulation of class C channel activity by phosphorylation. The hypothesized impairment of class C channel phosphorylation by PKA and dephosphorylation by PP2A will be tested in these systems and in AKAP 150 KO mice, which are already available. Overstimulation of glutamatergic synapses has been implicated in neuropathologies due to stroke, status epilepticus, and brain trauma. A chronic increase in L-type channels activity contributes to the etiology of Alzheimer's disease. The activity of glutamate receptors and class C channels is upregulated by PKA. The postsynaptic assembly of specific signaling components that control PKA-mediated phosphorylation of class C channels and AMPA receptors provides, therefore, a potentially very effective and specific target for drugs which may act by disrupting some of these interactions.