Negatively regulates long-term potentiation and modulates adult synaptic plasticity. Stabilizes the interaction of RTN4 isoform A/Nogo-A with its receptors, inhibiting clustering of postsynaptic AMPA receptors at synaptic sites. Upon neuronal stimulation, degraded at synapses, reducing RTN4 signaling and allowing AMPA receptor clustering at individual synapses. . This is the function of C22orf39 (chromosome 22 open reading frame 39, ENSG00000242259).