Exclusive or promiscuous? Role(s) of the moonlighting auxiliary subunit PORCN in AMPA receptor physiology
Final Report Abstract
AMPA-type glutamate receptors (AMPARs) are the primary excitatory neurotransmitter receptors in the mammalian central nervous system, playing critical roles in synaptic signaling, development, and plasticity. The functional diversity of AMPARs is enhanced by a plethora of associated proteins, including porcupine protein (PORCN), which stabilizes AMPAR complexes in hippocampal neurons while also performing its canonical function as a palmitoyltransferase for Wnt proteins. However, it remains unclear how these two functions are coordinated within the single PORCN protein and whether they can operate in parallel or must switch between roles. The goal of this project was to further investigate the moonlighting role of PORCN in AMPAR physiology and to explore the regulatory mechanisms underlying its multifunctionality. To address this, we employed a multidisciplinary approach combining molecular biology, cell biology, and electrophysiological techniques. Our findings indicate that under basal conditions PORCN can simultaneously perform both of its functions - Wnt secretion and stabilization of AMPARs. However, phosphorylation of serin 297 in the PORCN protein may serve as a regulatory mechanism for this multifunctionality. Overexpression of the phospho-mimetic mutant PORCN S297D led to reduced Wnt secretion and increased stabilization of GluA1 expression in HeLa cells, as well as limited dendritic growth and synaptic transmission in hippocampal neurons. Interestingly, Wnt5a was found to reduce GluA1 expression in HeLa cells completely independent of PORCN. Co-immunoprecipitation experiments confirmed a direct interaction of Wnt5a and GluA1 as well as the presence of ternary complexes involving Wnt5a, PORCN and GluA1. While the molecular mechanisms and physiological relevance of these findings need to be fully explored, they already suggest a significant interplay between Wnt signaling and AMPAR physiology.
Publications
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Mutation in Porcupine changes morphology of hippocampal neurons. Poster presentation at the Symposium of the Medical Research School (medRSD), Heinrich-Heine University Düsseldorf
Mölders N., Anstötz M. & Erlenhardt N.
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Phospho-mimetic mutant of AMPAR-associated protein Porcupine reduces Wnt5a secretion and neuronal outgrowth. Abstract/poster presentation at the annual meeting of the German Physiological Society (DPG), Vienna, Switzerland
Mölders N., Tofan K. M., Strasdeit T., Klöcker N., Anstötz M. & Erlenhardt N.
