Oligophrenin-1 regulates synaptic activity dependent shuttling between synapses and nucleus of Rev-erbAalpha

Oligophrenin-1 (OPHN1) is a synaptic RhoGTPase-activating protein involved in X-linked mental retardation that regulates dendritic spines shape and outgrowth of axons in brain (Govek et al., 2004). By using the C-terminal fragment of Oligophrenin 1 as bait in a two-hybrid screening of a human fetal brain cDNA library we identified as an interactor, NR1D1 (Rev-erbAalpha). Rev-erbAalpha is an orphan nuclear receptor that constitutively suppresses gene transcription and regulates the circadian clock in the CNS (Preitner et al. 2002). We confirmed the interaction in vitro and in vivo by co-immunoprecipitation and GST-pull down. In COS-7 cells we observed that overexpressed Oligophrenin-1 is able to recruit Rev-erbAalpha (normally localized in the nucleus) to the cytoplasm. Furthermore, overexpression Oligophrenin-1 induces an accumulation of endogenous Rev-erbAalpha in dendritic spines in hippocampal neurons. The Oligophrenin-1deltaC (deleted of C-terminus), a mutant that mimics the mutation present in the XLMR patients, wasn’t able to induce this effect in COS7 and in hippocampal neurons. In HEK cells we observed that Oligophrenin-1 protects Rev-erbAalpha from degradation by GSK3beta We also have found that RNAi knockdown of Oligophrenin-1 inhibited the translocation of Rev-erbAalpha into the dendritic spines. More remarkable, synaptic activity mediated by AMPA receptors induces translocation of Rev-erbAalpha to the dendritic spines. RNAi experiments showed that Oligophrenin-1 is required for the translocation of Rev-erbAalpha in spines induced by synaptic activity. Moreover we observed an alteration of Rev-erbAalpha expression in Oligophrenin-1 KO mouse: there is a reduction of Rev-erbAalpha in hippocampus. Our results demonstrate for the first time the interaction between an orphan receptor (Rev-erbAalpha) and a synaptic protein (Oligophrenin-1). This interaction regulates the localization of Rev-erbAalpha between synapse and nucleus induced by synaptic activation.